B
i

April 2011 

NOAA technical memorandum # F/SPO - 116

Environmental Effects 

of Tidal Energy 

Development

Proceedings of a Scientific Workshop 

March 22-25, 2010

U.S. Department of Commerce 

Gary Locke, Secretary of Commerce 

National Oceanic and Atmospheric 

Administration 

Jane Lubchenco, Ph.D., Administrator of NOAA

National Marine Fisheries Service

Eric C. Schwaab, Assistant Administrator 

for Fisheries

Editors: Brian Polagye1, Brie Van Cleve2, Andrea Copping2, and Keith Kirkendall3

1

University of Washington, Northwest National Marine Renewable Energy Center, 

Box 352600, Seattle, Washington 98195

2

Pacific Northwest National Laboratory, Marine Sciences Laboratory, 

1100 Dexter Ave. N, Seattle, Washington 98109

3

NOAA Fisheries, Northwest Region, Hydropower Division, 1201 NE Lloyd Blvd., Portland, Oregon 97232
ii

Suggested citation:

Polagye, B., B. Van Cleve, A. Copping, and K. Kirkendall (editors). 2011. Environmental effects of tidal energy 

development. U.S. Dept. Commerce, NOAA Tech. Memo. F/SPO-116, 170 p.

A copy of this report may be obtained from:

Northwest Fisheries Science Center

NMFS, NOAA

2725 Montlake Boulevard East

Seattle, Washington 98112

Online at: http://spo.nmfs.noaa.gov/tm/
iii

Table of Contents

Executive Summary..................................................................................................................vii

Acknowledgements...................................................................................................................ix

1. Introduction.............................................................................................................................1

1.1 Workshop Overview............................................................................................................................................................ 2

1.2 Report Structure and Content............................................................................................................................................. 3

1.3 Planning and Regulatory Context....................................................................................................................................... 4

1.4 Tidal Power Technology Overview...................................................................................................................................... 5

1.5 Tidal Power Siting ............................................................................................................................................................... 7

1.6 Tidal Energy Devices .......................................................................................................................................................... 8

1.7 References....................................................................................................................................................................... 17

2. Environmental Effects of Tidal Power..............................................................................18

2.1 Conceptual Approach: Stressors and Receptors ............................................................................................................. 18

2.2 Environmental Effects....................................................................................................................................................... 19

2.3 Installation Effects............................................................................................................................................................. 19

2.4 Operational Effects............................................................................................................................................................ 19

2.5 Decommissioning Effects ................................................................................................................................................. 20

2.6 Accidents .......................................................................................................................................................................... 20

2.7 Scale of Development....................................................................................................................................................... 20

2.8 References........................................................................................................................................................................ 21

3. Environmental Stressors....................................................................................................23

3.1 Presence of Devices: Static Effects.................................................................................................................................. 24

3.2 Presence of Devices: Dynamic Effects............................................................................................................................ 30

3.3 Chemical Effects .............................................................................................................................................................. 35

3.4 Acoustic Effects ............................................................................................................................................................... 41

3.5 Electromagnetic Effects ................................................................................................................................................... 48

3.6 Energy Removal .............................................................................................................................................................. 55

3.7 Cumulative Effects ........................................................................................................................................................... 62

4. Environmental Receptors...................................................................................................69

4.1 Physical Environment: Near-field ..................................................................................................................................... 71

4.2 Physical Environment: Far-field........................................................................................................................................ 75

4.3 Habitat and Invertebrates ................................................................................................................................................. 82

4.4 Fish: Migratory .................................................................................................................................................................. 87

4.5 Fish: Resident ................................................................................................................................................................... 94

4.6 Marine Mammals and Seabirds...................................................................................................................................... 103

4.7 Ecosystem Interactions....................................................................................................................................................110

5. Workshop Outcomes: Challenges..................................................................................115

6. Workshop Outcomes: Recommendations ....................................................................122

6.1 Approaches to Reducing Critical Uncertainties .............................................................................................................. 122

6.2 Approaches to Mitigating Environmental Stressors........................................................................................................ 126

6.3 Development of Strategic and Coordinated Technologies and Capabilities .................................................................. 128

7. Concluding Remarks.........................................................................................................130
iv

List of Figures 

Figure 1 – Workshop participant affiliations.............................................................................................................................3

Figure 2 – Workshop participant geographic distributions. .....................................................................................................3

Figure 3 – Clean Current Turbine, Clean Current Power........................................................................................................9

Figure 4 – Tidal Stream Turbine, Hammerfest Strom UK........................................................................................................9

Figure 5 – SeaGen, Marine Current Turbines .......................................................................................................................11

Figure 6 – ORPC Beta TGU ..................................................................................................................................................12

Figure 7 – ORPC TidGen.......................................................................................................................................................12

Figure 8 – OpenHydro 10m (1 MW peak power) Bay of Fund Turbine ................................................................................14

Figure 9 – Free Flow Kinetic Hydropower System................................................................................................................15

Figure 10 – Sample stressor matrix components..................................................................................................................23

Figure 11 – Stressor matrix: Presence of devices: Static effects – pilot-scale deployment..................................................25

Figure 12– Stressor matrix: Presence of devices: Static effects – commercial-scale deployment.......................................25

Figure 13 – Stressor matrix: Presence of devices: dynamic effects – pilot-scale deployments ...........................................32

Figure 14 – Stressor matrix: Presence of devices: dynamic effects – commercial-scale deployments ...............................32

Figure 15 – Stressor matrix: Chemical effects – pilot-scale deployment ..............................................................................36

Figure 16 – Stressor matrix: Chemical effects – commercial-scale deployment ..................................................................36

Figure 17 – Stressor matrix: Acoustic effects – pilot-and commercial-scale deployments ...................................................43

Figure 18 – Stressor matrix: Electromagnetic effects – pilot-scale deployments..................................................................50

Figure 19 – Stressor matrix: Electromagnetic effects – commercial-scale deployments......................................................50

Figure 20 – Stressor matrix: Energy removal –commercial-scale deployments...................................................................56

Figure 21 – Far-field environment detail for energy removal stressor...................................................................................57

Figure 22 – Stressor matrix: Cumulative effects – pilot-scale deployment ...........................................................................63

Figure 23 – Stressor matrix: Cumulative effects – commercial-scale deployment ...............................................................63

Figure 24 – Sample receptor matrix components .................................................................................................................70

Figure 25 – Receptor matrix: Physical environment: Near-field – pilot-scale deployment ...................................................72

Figure 26 – Receptor matrix: Physical environment: Near-field – commercial-scale deployment .......................................72

Figure 27 – Receptor matrix: Physical environment: Far-field – commercial-scale deployment..........................................76

Figure 28 – Relative changes to far-field flow quantities in an embayment as a consequence of 

 kinetic power extraction for an embayment connected to the ocean by a narrow channel. ............................ 78

Figure 29 – Receptor matrix: Habitat and Invertebrates – pilot-scale deployment.............................................................. 83

Figure 30 – Receptor matrix: Habitat and Invertebrates – commercial-scale deployment.................................................. 83

Figure 31 – Receptor matrix: Fish: Migratory – pilot-scale deployment............................................................................... 88

Figure 32 – Receptor matrix: Fish: Migratory – commercial-scale deployment................................................................... 88

Figure 33 – Receptor matrix: Fish: resident – pilot-scale deployment ................................................................................. 95

Appendix A — Glossary.........................................................................................................131

Appendix B — Plenary Session Extended Abstracts .......................................................136

B.1 – Tidal Technologies, Industry Overview, and the U.S. Department of Energy Water Power Team............................ 136

B.2 – Ecological Effects of Tidal Energy: Experience from the Bay of Fundy..................................................................... 140

B.3 – Physical Habitat and Natural Resources: Maine ....................................................................................................... 145

B.4 – Physical Habitat and Natural Resources: Puget Sound, Washington....................................................................... 151

B.5 – Physical Habitat and Natural Resources: Alaska, with a Focus on Cook Inlet.......................................................... 156

Appendix C — Workshop Participant List..........................................................................165

Appendix D — Workshop Agenda .......................................................................................168

Appendix E — Workshop Evaluation Results....................................................................169
v

Figure 34 – Receptor matrix: Fish: resident – commercial-scale deployment ..................................................................... 95

Figure 35 – Receptor matrix: Marine mammals and seabirds – pilot-scale deployment................................................... 104

Figure 36 – Receptor matrix: Marine mammals and seabirds – commercial-scale deployment....................................... 105

Figure 37 – Receptor matrix: Ecosystem interactions – pilot-scale deployments...............................................................111

Figure 38 – Receptor matrix: Ecosystem interactions – commercial-scale deployment ....................................................111

Figure 39 – Pilot-scale deployment generalized stressor/receptor significance . .............................................................. 123

Figure 40 – Commercial-scale deployment generalized stressor/receptor significance ................................................... 124

Figure 41 – The Puget Sound-Georgia Basin is bisected by the U.S.-Canadian border................................................... 154

Figure 42 – Sites of Puget Sound pilot tidal projects.......................................................................................................... 155

Figure 43 – Areas of significant hydrokinetic energy potential in Alaska............................................................................ 163

Figure 44 – Cook Inlet bathymetry and satellite image showing suspended sediment plumes ........................................ 163

List of Tables

Table 1 – Marine Current Turbines device specifications (Strangford Lough demonstration)..............................................11

Table 2 – ORPC device specifications.................................................................................................................................. 13

Table 3 – OpenHydro device specifications (Bay of Fundy demonstration) ........................................................................ 14

Table 4 – Verdant Power KHPS device specifications ......................................................................................................... 16

Table 5 – Environmental stressors and receptors associated with tidal energy development............................................. 18

Table 6 – Information needs to close critical gaps in understanding (stressor groups). .....................................................117

Table 7 – Information needs to close critical gaps in understanding (receptor groups)......................................................119

Table 8 – Potential mitigation strategies for environmental stressors. ............................................................................... 127

Table 9 – Differences and similarities of Cobscook and Passamaquoddy Bays ............................................................... 146

Table 10 – Primary producers and production on Cobscook Bay ...................................................................................... 147

Table 11 – Examples of Puget Sound plant and animal life ............................................................................................... 152

Table 12 – Pending and Issued FERC permits for hydrokinetic energy projects in Alaska. .............................................. 162
vi
vii

Tidal hydrokinetic energy has the potential to 

provide clean, reliable power, and emerging turbine 

designs are making production of electricity from ocean 

energy technologically and economically feasible. Tidal 

energy projects could be a viable renewable energy 

source, displacing fossil fuel-based energy resources, 

providing benefits to the marine environment through 

the mitigation of carbon dioxide production (which 

can lead to ocean acidification and climate change) and 

a reduction in the risk of catastrophic spills associated 

with fossil fuel extraction and transportation. However, 

the risk to the marine environment and marine organisms 

from tidal energy generation is not well known. 

In order to appropriately site and operate tidal 

power installations and explore the potential contribution tidal power can make to a renewable energy 

portfolio, the environmental risks of the technology 

must be better understood. In doing so, it is important 

to distinguish between environmental effects and environmental impacts. Environmental effects are the broad 

range of potential measurable interactions between 

tidal energy devices and the marine environment. Environmental impacts are effects that, with high certainty, 

rise to the level of deleterious ecological significance. 

This report summarizes the outcomes of a 

March 22-25, 2010, workshop in Seattle, Washington, 

on the environmental effects of tidal energy development. The workshop focused on building capabilities 

to evaluate the environmental effects of tidal energy 

from turbines placed in the water column throughout 

the United States. However, it did not address policy 

issues, details of technology engineering, or the socioeconomic impacts of tidal energy development. The 

goals of the two-day meeting were to:

• Develop an initial assessment of the environmental 

effects of installation, operation, decommissioning, 

and maintenance of tidal power generating devices; 

• Determine the specific marine organisms and 

system components that may be affected; and 

• Develop a general framework of interactions 

against which specific tidal generation projects 

might plan their environmental assessments and 

monitoring programs. 

Workshop participants were chosen from a representative cross-section of academia, research groups, 

regulatory agencies, and industry. These participants 

discussed the environmental effects of tidal energy 

development in the context of stressors (e.g., noise 

generated by device operation) and receptors (e.g., 

marine mammals in a project area). Stressor groups 

focused on attributes of one of the following stressors:

• Presence of devices: static effects;

• Presence of devices: dynamic effects; 

• Chemical effects;

• Acoustic effects;

• Electromagnetic effects;

• Energy removal; and

• Cumulative effects.

Receptor groups focused on attributes of one of 

the following receptors:

• Physical environment: near-field;

• Physical environment: far-field; 

• Habitat;

• Invertebrates;

• Migratory fish;

• Resident fish;

• Marine mammals;

• Seabirds; and

• Ecosystem interactions.

For both stressors and receptors, breakout groups 

evaluated the potential significance of stressor/

receptor interactions and the uncertainty around each 

interaction. This evaluation was performed for pilotscale deployments to identify critical gaps that should 

be resolved in the near-term, as well as for commercial-scale deployments to identify areas of long-term 

concern. In addition, each group called out a few high 

priority interactions and recommended approaches 

to monitoring stressor/receptor interactions and to 

mitigating environmental impacts.

Executive Summary
viii

Workshop participants identified a number of 

common challenges:

• Critical knowledge gaps hinder evaluation of 

environmental impacts. 

 • A lack of clearly identified research priorities 

leaves researchers and developers with little guidance about the most pressing stressor/receptor 

interactions.

• Technologies required to monitor high priority 

stressor/receptor interactions are underdeveloped 

and costly.

• Appropriate mitigation strategies for unavoidable 

environmental impacts are not well developed.

Workshop participants also made a number of 

recommendations to reduce critical uncertainties, 

mitigate for environmental effects, or develop strategic and coordinated technologies and capabilities:

• Understanding of many environmental impacts 

can be achieved only through careful monitoring 

of pilot-scale deployments.

• Priority research areas should be established for 

stressor/receptor interactions.

• The public sector must play a role in funding the 

study of high-priority stressor/receptor interactions, particularly for baseline assessments.

• The effort to share relevant marine energy information through the International Energy Agency’s 

Ocean Energy System Implementing Agreement 

Annex IV should be continued, and other strategies to share data, while protecting intellectual 

property and proprietary information, should be 

developed.

• Analogous and existing data should be compiled 

and reviewed to avoid duplication of data collection and monitoring efforts, particularly for 

baseline monitoring.

• Project and device developers should work with 

oceanographers and other researchers to share 

and discuss monitoring data collection, modeling 

methodologies, and study results.

• Mitigation strategies may be used to reduce 

impacts to an acceptable level.

• Consistent, clear monitoring protocols should be 

developed and used by those conducting environmental research.

• Innovative approaches to monitoring instrumentation should be developed by partnerships among 

research institutions, industry, and funding 

agencies.

• Validated and calibrated ocean and hydrodynamic models can effectively address some 

critical uncertainties. Models are needed, both at 

the scale of a few turbines to address potential 

near-field effects and at regional scales to address 

potential far-field effects.

• Expanded opportunities for interdisciplinary 

collaboration are needed to promote improved 

experimental design and data collection.

Two overarching conclusions were identified. 

First, given the number of potential stressor/receptor 

interactions, research efforts must be prioritized 

and leveraged in order to effectively direct limited 

research dollars and resolve key uncertainties in a 

timely manner. Second, the next step to reducing 

critical uncertainties is careful monitoring of pilotscale device deployments.

Participants found the structure of this workshop useful for eliciting and organizing potential 

environmental effects of tidal energy development 

and associated uncertainties. Future workshops on 

specific stressor or receptor topics were suggested, as 

the industry moves forward and the need to understand and mitigate environmental impacts becomes 

more important. Participants also suggested that 

additional workshops focused on policy and management issues associated with tidal energy development 

may be useful. Nearly 80% of participants agreed to a 

moderate or great degree that the workshop increased 

their understanding of the potential environmental 

effects of tidal energy.

This report contains recommendations relevant 

to tidal energy device and project developers, monitoring instrumentation developers, scientists, and 

regulatory agencies. 
ix

These proceedings describe the discussions and 

outcomes of a workshop modeled after a similarworkshop entitled Wave Energy Ecological Effects, 

held in Newport, Oregon, in 2007, and led by George 

Boehlert of Oregon State University. During that 

workshop, participants developed an initial assessment of the potential environmental effects of wave 

energy development off Oregon’s coast. 

The 2010 tidal energy workshop was organized 

by a steering committee of seven people: Brian 

Polagye, Research Assistant Professor, Department of 

Mechanical Engineering, Northwest National Marine 

Renewable Energy Center, University of Washington; 

Andrea Copping, Senior Program Manager, Marine 

Sciences Laboratory, Pacific Northwest National 

Laboratory; Keith Kirkendall, Chief of the FERC and 

Water Diversions Branch, NOAA Fisheries Northwest 

Region; George Boehlert, Director of the Hatfield 

Marine Science Center, Oregon State University; 

Sue Walker, Hydropower Coordinator, Alaska Region, 

NOAA Fisheries; Michelle Wainstein, Senior Program 

Coordinator, Washington Sea Grant, University of 

Washington; and Brie Van Cleve, Science and Marine 

Policy Analyst, Marine Sciences Laboratory, Pacific 

Northwest National Laboratory. George Boehlert 

participated in both the Oregon wave energy workshop and tidal energy workshop as a member of the 

steering committee. Keith Kirkendall also served 

on the steering committee and as a facilitator at the 

Oregon wave energy workshop. 

Acknowledgements

The steering committee is grateful for the time 

and effort contributed by participants and, in particular, the workshop’s 14 session chairs. Many thanks 

are also extended to the student note takers, who 

captured the details of free-flowing discussions in the 

breakout groups.

Thanks also to technical editor David G. Gordon 

of Washington Sea Grant, who applied the final polish 

to the report’s text, and to graphic designer Robyn 

Ricks, also with Washington Sea Grant, who helped 

shape the report’s design.

This workshop was made possible by generous 

support by NOAA Fisheries and the U.S. Department 

of Energy. 

The conclusions and views expressed in this technical report are a synthesis of discussions that took 

place during the tidal energy workshop. The steering 

committee members summarized these discussions for 

the purpose of this report. The conclusions and views 

do not necessarily reflect those of the sponsoring 

agencies or the individual members of the steering 

committee. No endorsement of any tidal turbine or 

other technology is implied.
1

The generation of power from the rise and fall 

of the tides dates back to at least the Middle Ages 

and, possibly, to the early Roman period (Charlier 

and Finkl 2009). A tide mill consisted of a storage 

pond, filled by the incoming tide through a sluice 

and emptied by the outgoing tide through a water 

wheel. The modern version of this technology is a 

tidal barrage, in which the waters of an estuary are 

impounded behind a dam in a manner analogous to 

conventional hydropower. Tidal barrages enjoyed 

substantial interest in the middle of the 20th century 

although, globally, only three sites are operational, 

because of the environmental impacts and high capital 

costs associated with this technology. More recently, 

development interest has focused on harnessing the 

kinetic energy in swift-moving tidal currents. This 

approach has the potential to generate power from the 

tides with fewer environmental impacts or economic 

challenges. Tidal power is the only form of energy 

that is derived directly from the gravitational interaction between the moon and sun and the earth’s 

oceans. Because the gravitational forces depend on 

the predictable alignments of the celestial bodies, tidal 

power is also predictable to the first order (Polagye et 

al. 2010).

Currently, nearly 70% of the U.S. demand for 

electricity is met by burning fossil fuels, which are 

widely known for contributing to environmental 

impacts including degraded air quality, acid rain, 

ocean acidification, and global climate change. 

Over the past half-decade, the federal government 

has moved to align taxes, markets, incentives, and 

research funding to support development and use 

of renewable energy technologies. States have also 

played key roles in advancing policy to shift towards 

renewable energy. Twenty-nine states plus the District 

of Columbia have enacted renewable portfolio standards or renewable electricity standards requiring 

utilities to obtain a minimum percentage of their 

power from renewable sources by a given date. To 

satisfy this growing demand for renewable energy, 

utilities are pursuing a broad range of technologies. 

Over the past 10 years, land-based wind power has 

been the dominant technology, but utilities, regulators, 

and entrepreneurs are increasingly looking towards 

emerging technologies. These include attempts to 

harvest the power of the ocean. 

Renewable ocean energy, which includes tidal 

current, ocean current, wave, ocean thermal energy 

conversion (OTEC), osmotic pressure, and offshore 

wind power, represents a significant resource for 

clean renewable electricity generation. The worldwide 

natural tidal dissipation is 3.7 terrawatts (TW), which 

is small in comparison to the 15 TW of global power 

consumption (Arbic and Garrett 2010). Because 

harnessing more than a fraction of this natural dissipation for electricity production would have profound 

consequences for regional tides, tidal energy should 

not be viewed as a “silver bullet” for global power 

generation needs. However, in comparison to the 0.3 

TW of power produced by worldwide hydroelectric 

installations, the tidal resource potential is significant, particularly on a regional basis. Estimates of the 

practically recoverable tidal resource are limited to a 

few sites (e.g., Karsten et al. 2008 for Minas Passage, 

NS, Canada), and assessing the globally recoverable 

resource is an active area of academic research.

Hydrokinetic tidal power generation is geographically limited to those areas where tidal currents flow 

fast enough for generation. For semidiurnal tidal 

regimes, peak currents of 2 m/s may be sufficient for 

economic power generation. However, for mixed, 

mainly semidiurnal tidal regimes, peak currents of 

3 m/s or greater are required to compensate for the 

diurnal inequality. In the U.S., some potential sites 

occur close to urban centers – in Washington’s Puget 

Sound, the Gulf of Maine, especially near the Bay of 

Fundy, and Alaska’s Cook Inlet near Anchorage. This 

proximity may enable tidal power to be the first of the 

new ocean energy technologies to be commercialized. 

Tidal energy can provide clean, reliable power, 

and emerging turbine designs are making production 

of electricity from ocean energy technologically and 

economically feasible Tidal energy projects could be 

a viable renewable energy source, displacing fossil 

fuel-based energy resources, providing benefits to 

1. Introduction
2

The workshop followed the successful model 

used to address the environmental effects of wave 

energy development, held in 2007 in Newport, 

Oregon (described in Boehlert et al. 2008). It focused 

on building capabilities to evaluate the environmental 

effects of tidal energy from turbines placed in the 

water column throughout the U.S. The workshop did 

not address policy issues, details of technology engineering, or the socioeconomic impacts of tidal energy 

development; however separate meetings to address 

these topics were among the recommended next steps 

to come out of the workshop. 

The goals of the two-day meeting were to:

• Develop an initial assessment of the environmental effects of installation, operation, maintenance, and decommissioning of tidal power 

generating devices; 

• Determine the specific marine organisms and 

system components that may be affected; and 

• Develop a general framework of interactions 

against which specific tidal generation projects 

might plan their environmental assessments and 

monitoring programs. 

Workshop participants shared their understanding 

of tidal system effects, discussed the latest research 

in their areas of expertise, and contributed to a broad 

discussion of the environmental effects of tidal 

energy. The workshop format combined plenary talks 

and breakout groups targeting specific stressors (i.e., 

those factors that may occur as hydrokinetic tidal 

energy systems are installed, operated, or decommissioned) and marine receptors (i.e., those elements 

of the marine environment that may be affected by 

stressors). From their discussions, breakout groups 

generated summary papers for compilation into this 

report. These discussions incorporated knowledge 

acquired from better-understood analogues, such 

as ocean wind and undersea cable projects. These 

existing ocean technologies have established bodies 

of literature on environmental impacts that may be 

applicable to tidal generation installations. 

the marine environment through the mitigation of 

carbon dioxide production (which can lead to ocean 

acidification, climate change) and a reduction in the 

risk of catastrophic spills associated with fossil fuel 

extraction and transportation. However, the risk to 

the marine environment and marine organisms from 

tidal energy generation is not well known. In order to 

appropriately site and operate tidal power installations 

and explore the potential contribution tidal power can 

make to a renewable energy portfolio, a better understand of the risks of the technology will be required. 

Despite a positive policy environment and modest 

government investment in tidal power research and 

development, permitting of tidal device deployment 

remains a considerable barrier to advancement. The 

tidal power industry and regulators have identified 

poorly understood environmental effects as one of 

three top barriers to getting tidal devices in the water 

(Bedard 2008). 

1.1 Workshop Overview

This report summarizes the outcomes of a 

March 22-25, 2010, workshop in Seattle, Washington, 

about the environmental effects of tidal energy 

development. 

As tidal energy development is still in its early 

stages, there have not been sufficient data collected 

to predict the effects that pilot- and commercial-scale 

tidal projects will have on the marine environment. 

Until such data exist, the most promising method to 

address priorities for regulatory and research attention 

is to rely on the expertise and judgment of scientists 

and engineers with experience in various aspects of 

the technology, biota and habitats, and appropriate 

analogue industries. This workshop was designed to 

bring together that expertise from several nations and 

to address environmental effects through a structured 

process. As data become available to describe these 

effects in the future, the judgments and uncertainties 

recorded in this report can be replaced with better 

predictions and lower uncertainty. 
3

Building on the workshop outcomes, this report 

provides an assessment of environmental effects 

on the marine systems in which tidal power may be 

generated, estimates risks to marine organisms and 

communities, estimates the uncertainties associated 

with our knowledge base, and provides recommendations for future research and monitoring needs. The 

workshop took a first step to systematically address the 

issues of concern and will help frame future discussions about the impact that tidal energy may have on the 

marine environment and marine organisms.

Workshop participants were drawn from a 

representative cross-section of universities, regulatory agencies, research laboratories, and industry. As 

shown in Figure 1, all groups were well-represented. 

Figure 1 – Workshop participant affiliations.

As the outcomes of this workshop are intended to 

be broadly representative of tidal energy development 

in the U.S., it was important to have participants from 

a variety of regions with experience with or interest 

in tidal energy. As shown in Figure 2, a variety of 

regions were represented, although the majority of 

the participants were drawn from the U.S. West Coast 

(California, Oregon, Washington, and Alaska). This 

was a consequence of travel logistics, rather than an 

intentional geographic emphasis.

Figure 2 – Workshop participant geographic distributions.

The workshop was well-received by participants, 

as indicated by the results of a survey distributed 

to all participants. Complete results are included in 

Appendix E. Highlights include:

• 85% of participants rated the overall quality of 

the workshop as “very good” or “excellent”;

• 75% of participants indicated the workshop 

increased their understanding of the environmental effects of tidal energy to a moderate or 

great degree; and

• 90% of participants indicated they were “somewhat likely” or “very likely” to apply the 

information learned at the workshop to tidal 

energy-related projects.

A complete list of participants and affiliations is 

included as Appendix C, and details of the workshop 

agenda are included as Appendix D.

1.2 Report Structure and Content

The report structure and content reflects input 

from a number of sources before, during, and after the 

workshop. 

Section 1 provides background information on 

the regulatory framework for tidal energy projects and 

the technical aspects of tidal energy power generation, 

including engineering details on devices, site requirements, and summaries of device tests conducted to 

date. This section was written by the editors, with key 

narrative and device specifications provided by the 

profiled device developers. 

Section 2 lays out the framework for evaluating 

environmental effects, including the distinction 

between impacts and effects and stressor/receptor 

organization. An overview of the type of environmental effects associated with tidal energy projects is 

given. Qualitative definitions of pilot and commercial 

deployments are also provided. This section was 

included in the original workshop briefing document 

but further modified by the editors after the workshop 

and, consequently, the narratives in Sections 3 and 4 

do not universally adopt the described framework.
4

Sections 3 and 4 are the reports from each of the 

workshop’s stressor and receptor breakout groups. Each 

subsection includes matrices describing the significance 

of and uncertainty around stressor/receptor interactions 

at the pilot and commercial scale. These matrices are 

augmented by narrative discussion and a more detailed 

consideration of high-priority stressor/receptor interactions. These sections were drafted by the session 

chairs with input from group participants. In places, the 

editors have inserted additional, clarifying narrative but 

deferred, whenever possible, to the original text. Because 

the breakout group discussions varied with participant 

expertise, allocated time, and the discretion of the group 

chair, the reported content also varies by subsection.

Section 5 describes common challenges for closing 

information gaps for environmental effects, and Section 

6 presents recommendations for addressing these 

challenges and mitigating potential environmental 

impacts. These sections were written by the editors, 

based on the breakout group reports and further 

discussion with group chairs.

Section 7 concludes by providing a few final 

thoughts from the editors on the workshop and 

possible next steps.

1.3 Planning and Regulatory Context

The regulatory context for tidal power is 

complex and evolving. The Federal Energy Regulatory Commission (FERC) has the authority to issue 

licenses (both commercial and pilot) for all wave 

and tidal projects located on the outer continental 

shelf (OCS) and in state waters, while the Bureau of 

Ocean Energy Management Regulation and Enforcement (BOEMRE, formerly the Minerals Management 

Service) has the authority to issue leases, easements, 

and right-of-ways for wave and tidal projects located 

on the OCS. Because most tidal energy installations 

are likely to occur in state waters (within 3 miles of 

shore), FERC is the federal permitting agency. State 

resource management agencies and local governments 

play important roles through Coastal Zone Management 

Act consistency review, Clean Water Act consistency 

review, review under state codes, and leasing of stateowned bottom lands. 

As part of the federal licensing process, the 

National Oceanic and Atmospheric Administration’s 

National Marine Fisheries Service (NOAA Fisheries), 

the U.S. Fish and Wildlife Service (USFWS), and the 

U.S. Army Corps of Engineers (USACE) consult with 

FERC under the authority of the Federal Power Act, 

Endangered Species Act, Magnuson-Stevens Fishery 

Conservation and Management Act, Migratory Bird 

Treaty Act, Fish and Wildlife Conservation Act, 

Marine Mammal Protection Act, National Environmental Policy Act, and Coastal Zone Management 

Act. The fact that multiple federal and state agencies 

are involved in permitting and regulating tidal power 

make for a complex leasing and licensing process. 

Uncertainty regarding potential environmental 

impacts of tidal energy development and impacts to 

other ocean uses further complicates the permitting 

process and may hamper expansion of the ocean 

energy industry. 

There is a very strong need for integrated 

management at federal and state levels, as sectoral 

management continually fails to address the broad 

perspective needed for ecosystem-based management. Strategic Environmental Assessments (SEAs) 

have been used to good effect in Europe (e.g., SEA 

for marine renewables in Scotland) and Canada (e.g., 

SEA for development of tidal test facilities in the 

Bay of Fundy) to facilitate the siting and development of pilot and commercial-scale marine energy 

projects. The SEA provides a mechanism by which 

all environmental considerations for particular uses/

programs (e.g., marine renewables) are integrated 

into policies at a regional or national level and directs 

public funding to regional scale baseline assessments. While no direct analogue exists in the U.S., 

the goal of ecosystem-based management is being 

pursued through a combination of marine spatial 

planning and adaptive management. 
5

In response to concerns about environmental and 

competing ocean uses, in 2009 the Obama Administration initiated the development of a comprehensive ocean planning framework, Coastal and Marine 

Spatial Planning (CMSP). CMSP is seen by many 

in academia, the policy world, and stakeholders as a 

roadmap towards careful consideration of the tradeoffs among emerging ocean uses, existing uses, 

ecosystem protection, and a mechanism to provide 

regulatory certainty for ocean energy development. 

Spatial planning consists of two distinct phases: 

analysis of spatially referenced ocean data including 

resources and human uses, and a planning process to 

determine placement of various ocean uses (energy 

exploration, fishing, shipping, etc.). Several states, 

in coordination with federal agencies, have already 

developed marine spatial plans for state waters and, 

in some cases, beyond. A Presidential task force 

composed of the heads of multiple federal agencies 

released its Interim Framework for Effective Coastal 

and Marine Spatial Planning in December 2009. This 

framework, if expanded nationally, may help address 

management uncertainties and will provide a mechanism to resolve competing or incompatible ocean uses 

transparently and systematically. 

Adaptive management may also be an effective 

tool for facilitating responsible project development. 

In the context of tidal energy generation, adaptive 

management should be a process that allows stakeholders to set goals and thresholds, and oversee and 

transparently evaluate results of pre-installation and 

monitoring studies. The results could be used in 

combination with information from other relevant 

sources to make adjustments to pre- and post-installation monitoring methods, as appropriate, and to 

manage or change aspects of the project operation, 

siting, scale-up, and goods and services trade-offs. 

This is intended to avoid or minimize unexpected 

or undesirable impacts on resources. The adaptive 

management process could allow for immediate 

action, if necessary to address critical environmental 

impacts of a project, should they occur. Environmental 

studies should focus on very explicit questions about 

the potential impacts and support addressing management issues within the adaptive management realm.

1.4 Tidal Power Technology 

Overview

Hydrokinetic tidal power is derived from the 

conversion of the kinetic power in moving water to 

electricity and depends on the area of water intercepted by the device (a circular area for a horizontal 

axis rotor, rectangular area for a vertical axis rotor), 

the cube of the water velocity, and the efficiency 

at which the device extracts the power in the water 

and converts it to electricity. Mathematically this is 

described as 

 

where P is the power generated by the turbine, ρ is 

the density of seawater (nominally 1,024 kg/m3), U is 

the current velocity, A is the area of water intercepted 

by the device, and η is the water-to-wire efficiency 

of the device. Values for these parameters for a few 

devices installed to date are described in the following 

sections.

1.4.1 Device Components

Although there are a multitude of tidal energy 

devices under development, all hydrokinetic turbines 

include a set of common components: rotors, power 

train, mooring, and foundation. Additionally, all 

devices or arrays require electrical transmission to 

shore and protection against biological fouling. In 

most cases, devices are assembled on land to the 

extent possible (to minimize at-sea operations) and 

transported to the site by boat or barge (in some cases, 

purpose-built for device installation).

The following sections summarize information 

from a recent report to the U.S. Department of Energy 

(DOE) (Polagye and Previsic 2010). 

1.4.2 Rotor

As with wind turbines, the rotor extracts the 

energy in tidal currents and converts it to rotating, 

mechanical energy. The axis of rotation may either be 

parallel to the flow direction (horizontal axis turbine) 

or perpendicular to the flow direction (cross-flow or 

vertical axis turbine). In both instances, the rotors 

typically have aerofoil cross-sections and operate 

on the principle of hydrodynamic lift. Drag-style 

devices are also possible but inherently less efficient. 
6

There are a number of rotor variations that generally 

trade-off efficiency against simplicity and capital cost, 

including variable fixed pitch, asymmetric fixed pitch, 

and symmetric fixed pitch. Depending on the site 

characteristics, a horizontal axis turbine may incorporate a yaw control mechanism (active or passive) to 

keep the rotor aligned with the flow direction. Crossflow turbines do not require yaw control.

For both horizontal axis and cross-flow turbines, 

it is theoretically possible to increase device efficiency by incorporating a diffusing duct downstream 

of the rotor. However, there are two potential complications. First, in practice, it is very difficult to design a 

functional diffusing duct, as evidenced by the fact that 

no commercial wind turbines incorporate diffusers. 

Second, because of the technical challenge of rotating 

the diffuser during slack water, separate diffusers are 

required both upstream and downstream of the rotor.

The rotational speeds of turbine rotors are limited 

by efficiency and cavitation considerations. Ideally, 

a rotation rate is achieved that allows an optimal tip 

speed ratio (the ratio of rotor tip velocity to current 

velocity). Depending on the rotor design, the optimal 

tip speed ratio may vary from 4 to 8. However, if the 

rotor tip speed is too fast, cavitation bubbles may form. 

Strong cavitation is undesirable because it reduces 

hydrodynamic performance, erodes the blade surfaces, 

and generates additional noise. While depth dependent, 

one rule of thumb is that tip speeds should be limited 

to 12 m/s (27 mph). For a 10 m-diameter turbine, this 

corresponds to approximately 20 rpm. Most devices 

proposed to date rotate at between 10 and 40 RPM.

1.4.3 Power train

Once the rotor has converted the kinetic power 

in the currents into mechanical rotation, a power train 

is required to further convert rotation to electrical 

energy. At a high level, power trains can be separated 

into those incorporating a gearbox speed increaser 

between the rotor shaft and electrical generator, those 

in which the rotor shaft is directly coupled to a generator, and those in which the connection between rotor 

shaft and generator is hydraulic. When gearboxes are 

used, the tonal frequency of the high-speed shaft may 

present a distinctive acoustic signature. The drive 

train configuration selected by a device developer 

must balance cost against reliability and efficiency. 

In nearly all cases, power electronics are required 

to condition the power output before interconnection with the grid. For example, the voltage may be 

stepped up from a few hundred volts at the device to 

11-35 kV for transmission to shore.

1.4.4 Mooring

The rotor and power train must be moored to a 

foundation that resists the forces generated by the 

rotor. This mooring will either be rigid or flexible. 

Examples of rigid connections include piles similar 

to those used in the offshore wind industry or tubular 

truss structures. Because the amount of material 

required for a rigid mooring increases as the turbine 

moves up in the water column, the maximum hub 

height for a rigid mooring is limited by economic 

considerations (Kawase et al. 2010). Flexible moorings, consisting of cable or chain, have much lower 

material costs and do not limit hub height. However, 

a device with a flexible mooring must incorporate 

buoyancy control to offset the downward force generated by the device mass and variable tension on the 

mooring line during periods of device operation. 

1.4.5 Foundation

Whether flexible or rigid, the mooring must be 

anchored to the seabed in a way that secures both the 

turbine and mooring against movement. One option 

is a penetrating anchor, such as a driven or drilled 

pile, that is secured in the seabed. For consolidated 

sediments or rocky seabeds, a penetrating anchor 

provides the most holding power for the smallest area 

disturbed. However, because the anchor is generally driven or drilled from the surface, installation in 

water deeper than 50-60 m may be uneconomical for 

a large-diameter pile. In contrast, a gravity foundation does not significantly penetrate the seabed but 

is held in place by its friction alone. Gravity foundations are lowered into position by a surface vessel and 

have a greater range of feasible deployment depths. 

However, for an equivalent resistive load, the footprint 

of a gravity foundation on the seabed is greater than a 

penetrating foundation. For either foundation variant, 

some seabed types may be susceptible to scour. This 

can be mitigated, for example by scour mats, but may 

increase the seabed area disturbed by installation.
7

Depending on the number of devices installed and 

the type of foundation, installation may require anywhere 

from a few hours (single device, gravity foundation) to 

longer than a year (large array, pile foundation).

1.4.6 Electrical Transmission

Electrical transmission from devices to shore is an 

integral aspect of any tidal energy project. The nearshore area adjacent to a tidal energy project may contain 

particularly sensitive ecology that could be disturbed 

by trenching a cable into the seabed. For example, in 

unconsolidated sediments, trenching involves burying 

cables to a depth of 1 to 3 m beneath the seabed, using 

a jet-plow technique. For tidal energy projects, the 

preferred option is to utilize horizontal directional 

drilling (HDD) from the on-shore cable termination 

point (i.e., substation) seaward beyond the nearshore 

region (i.e., the cable will exit onto seabed at the 15 

to 20 m isobath). The feasibility of directional drilling 

is site-dependent, not appropriate in all sediment 

types, and requires a careful geotechnical evaluation. 

Currently, maximum conduit length is limited to a few 

hundred meters.

The portion of the subsea cable crossing the seabed 

may be trenched, weighted, or bolted down (depending 

on the type of substrate) to prevent movement. In some 

cases, the weight of the cable alone may be sufficient to 

accomplish this. A similar approach is used to secure the 

cable between devices. The umbilical cables required to 

connect turbines to shore are comparable to those used 

in the offshore oil and gas industry and for the interconnection of different locations or islands.

1.4.7 Fouling and Corrosion Protection

Fouling from biological growth on devices is a 

significant performance risk (Orme et al. 2001) and 

structural risk. Turbines operating below the photic zone 

may be at lesser risk; however, fouling by barnacles, 

algae, and other organisms remains an issue for any 

deployment with a long maintenance interval. Working 

surfaces are generally treated with an anti-fouling or 

foul-release coating. Possible coatings include conventional biocide paints and inert, low-friction coatings. For 

economic or environmental reasons, other components 

of the foundation and support may remain uncoated, 

with sacrificial anodes providing corrosion protection.

1.5 Tidal Power Siting

Although each tidal energy site is unique, there 

are a number of common features that will affect 

deployment. New approaches to power extraction and 

device anchoring may expand the range of operationally feasible sites.

1.5.1 Tidal Resource

The tidal current speed that will support economically viable development depends on site and devicespecific characteristics, but, generally, current 

velocities should be greater than 2.5 m/s (5 knots) on 

ebb and flood. Devices generally begin to generate 

power around 0.8 m/s (1.5 knots), but, because 

kinetic power depends on the cube of velocity, most 

power generation occurs closer to peak currents. 

Although faster currents are desirable, high-speed 

flows in very narrow channels (e.g., < 100 m width) 

are often accompanied by high levels of turbulence. 

Wind energy analogues indicate that power production will decrease under strongly turbulent conditions 

and device lifetimes will be shortened by increased 

fatigue. Because of irregularities in topography and 

bathymetry, high-speed flows tend to be localized 

and occur with significant spatial variability (e.g., 0.5 

km). This is in sharp contrast to wave energy, where 

more uniform, energetic resources occur over a broad 

geographic extent. Other aspects of tidal resource 

characteristics of significance for siting are discussed 

in Gooch et al. (2009).

1.5.2 Deployment Depth

Because the tidal current boundary layer adjacent 

to the seabed is less energetic than the surrounding 

current, devices should be positioned far enough 

above the seabed to avoid this layer. The boundary 

layer profile is site dependent, but, generally, the 

device should not be placed in the bottom quarter of 

the water column. Devices deployed higher in the 

water column are able to generate more power, but 

foundation costs are also higher (Kawase et al. 2010). 

Deployment depths for pile-anchored foundations are 

currently limited by economic considerations to 50 

m (164 ft) water depth. In theory, gravity-anchored 

foundations have no maximum deployment depth, 

but, to date, device developers have not recommended 
8

deployments deeper than 80 m (263 ft) for operational 

reasons. Turbine hub height is also limited for gravity 

foundations because of the difficulty in resisting 

overturning moments for devices high in the water 

column. The shallowest sites that have been considered for development are approximately 10 m (33 ft) 

in depth, which can accommodate turbines up to 5 m 

(16 ft) in diameter. Shallower sites simplify installation and maintenance activities but increase the risk of 

biological fouling of the device due to proximity to the 

photic zone and may pose a hazard to vessel traffic. If 

devices are to be sited below a commercial shipping 

lane, overhead clearance of 15 to 25 m (49-82 ft) will 

be required, at a minimum.

1.5.3 Commercial Arrays

To date, most tidal energy installations have been 

single devices, used to prove the technical readiness 

and assess environmental effects of a particular design 

concept. The sole exception, to date, is the Verdant 

Power RITE project, which involved an array of six 

devices arranged in three rows of two (Note: because 

of the size and short duration of this project it is still 

considered a pilot deployment, rather than a commercial deployment). Without experimental data, optimum 

array layouts at commercial scale are speculative and 

derived primarily from wind energy analogues. As a 

consequence of kinetic power extraction, a low-speed 

wake will occur downstream of each device. At some 

distance downstream of the device, the wake will mix 

with the bulk flow, restoring homogeneous conditions. 

The distance depends on the rotor size, device efficiency, 

and background turbulence. A tidal energy device 

deployed directly in the wake of another device will 

suffer significant performance loss, and, consequently, 

wake persistence is a significant factor in device spacing 

for commercial arrays. Downstream device spacing of 

5-10 rotor diameters has been suggested as the minimum 

required to prevent wake interactions. The minimum 

lateral spacing is shorter, perhaps as little as half the 

rotor diameter. It is theoretically possible to reduce the 

downstream spacing by staggering successive rows of 

devices, but this has not been demonstrated in practice 

for either wind turbines or tidal turbines. Colby and 

Adonizio (2009) provide an overview of numerical and 

experimental efforts by Verdant Power to characterize the 

hydrodynamic disturbance from turbines in an array and 

highlight the challenges of both methods.

Commercial feasibility studies (e.g., Polagye and 

Previsic 2010) have proposed array layouts consisting of 

regular rows of turbines with uniform lateral and longitudinal spacing. Devices are assumed to be spread across 

a channel to the extent permitted by the tidal current 

resource, bathymetry, rotor diameter, and allowances 

for navigation. From a resource extraction standpoint, 

arrangements that maximize the blockage ratio of an 

array (the ratio of device swept area to channel crosssectional area) are desirable, as high blockage ratios 

enhance turbine performance (Garrett and Cummins 

2007). However, this arrangement may not be desirable 

from the standpoint of environmental risk due to both 

a greater risk of strike to fish and marine mammals and 

elevated energy removal effects due to higher losses 

when the wake mixes with the free stream (Garrett and 

Cummins 2007). Conversely, isolated clusters of turbines 

may be desirable environmentally, but, at commercial 

scale, would reduce the power-generation potential as 

high-speed flows are diverted around the cluster. Similarly, increasing the lateral and longitudinal separation 

between devices could reduce environmental risks but 

lead to inefficient resource utilization.

Without further studies to understand these environmental and performance trade-offs, these issues 

cannot be definitively resolved and are presented here as 

examples of the challenges associated with commercial 

array siting. Of particular concern are environmental 

risks that may not be significant at the pilot scale but 

could be substantial for a commercial installation. For 

example, the effects of noise generated from tidal energy 

devices may have minimal, site-specific impacts at the 

pilot-scale, but noise produced from a 100-trubine tidal 

energy park may be loud enough over a large enough 

area to alter migration patterns of marine fish, invertebrates, and mammals (DOE 2009).

1.6 Tidal Energy Devices

As of March 2010, there are over 60 distinct 

technologies included in DOE’s Energy Efficiency 

and Renewable Energy (EERE) hydrokinetics database. However, only a handful of these have been 

deployed at sea for extended durations. These devices 

are discussed in more detail in the following sections. 

They remain under active development, and the 

specifications for these demonstrations should not be 
9

inferred to be applicable to all possible site developments. In addition to technical enhancements, sitespecific factors are likely to be incorporated into device 

designs. In order to simplify the comparisons between 

different installations, the approximate power output 

of each device is given at a reference speed (2.5 m/s). 

Not included is the Marine Current Turbines SeaFlow 

device, which has been superseded by the larger 

SeaGen project.

1.6.1 Clean Current – Race Rocks (Race Rocks, 

British Columbia)

The Clean Current turbine is a horizontal axis rotor 

enclosed by a diffusing duct (Figure 3). The power train 

is a direct-drive permanent magnet generator around 

the open-center rotor hub. A 6 m diameter prototype 

unit has been intermittently operated at Race Rocks, 

British Columbia, in cooperation with Pearson College. 

This prototype is secured to the seabed by a rigid, 

penetrating monopile. A larger commercial prototype 

planned for installation in the Bay of Fundy in 2012 

will utilize a gravity foundation. Environmental studies 

associated with this project have focused on disturbances associated with device installation (e.g., seabed 

disturbance associated with foundation and cabling, 

noise from drilling) are available through the project 

Web site. Clean Current is based in Canada.

1.6.2 Hammerfest-Strom – Tidal Stream Turbine 

(Hammerfest, Norway)

The Hammerfest-Strom Tidal Stream Turbine is 

a three-bladed horizontal axis rotor with pitch control 

(Figure 4). The alignment of the rotor to the flow is 

fixed (no yaw control), but the rotor pitch is changed 

by 180 degrees during slack water to accommodate 

bi-directional tidal flows. The device was installed 

in 2003 at a depth of 50 m in Kvalsundet, Norway, 

off Hammerfest and has been operational since 2003. 

Virtually no information (device specifications or 

environmental monitoring) regarding this project is in 

the public domain. Hammerfest-Strom is based in the 

United Kingdom.

Figure 3 – Clean Current Turbine, Clean Current Power 

(Source: EERE 2010)

Figure 4 – Tidal Stream Turbine, Hammerfest Strom UK 

(Source: EERE 2010)
10

1.6.3 Marine Current Turbines – SeaGen 

(Stranford Lough, Northern Ireland)

The Marine Current Turbines’ SeaGen is a 

two-bladed horizontal axis rotor with pitch control 

(Figure 5). The alignment of the rotor to the flow is 

fixed (no yaw control), but the rotor pitch is changed 

by 180 degrees during slack water to accommodate 

bi-directional tidal flows. The power train is a variable speed gearbox coupled to an induction generator. 

Each device consists of two rotors connected to a 

monopile foundation by a wing-shaped crossbeam. 

The monopile is surface-piercing and the above-water 

structure houses power electronics and an integrated 

lift mechanism to raise the rotors out of the water for 

routine inspection and maintenance. Marine Current 

Turbines Ltd. is based in the United Kingdom.

For the Strangford Lough project, the monopile 

is secured to the seabed by a pin-piled quadrapod. 

Specifications for the device deployed in Strangford 

Lough are given in Table 1. Per the requirements of 

its operating permit, Marine Current Turbines Ltd. 

and its partners are carrying out environmental monitoring of project effects, including: porpoise behavioral changes, using passive acoustics (echolocation 

hydrophones); seal behavioral changes, using telemetry tags; changes in marine mammal and bird presence, using shore-based observers; noise generated by 

turbine operation and installation; and disturbances to 

the benthos from the physical presence of the device. 

Some of the information being collected is proprietary 

to Marine Current Turbines Ltd., but some is also in 

the public domain. 

Because of the potential for a protected population of harbor seals to be affected by turbine operation, a mitigation plan was enacted within an adaptive 

management framework by MCT and Irish regulators. 

This has proceeded through three phases. 

During the first phase, from June 2008 to August 

2009, turbine operation was restricted to daylight 

hours. A marine mammal observer stationed atop the 

monopole identified seals approaching the turbine and 

initiated device shutdown when a seal was within a 

specified distance. Initially, this shutdown distance 

was set at 200 m, but once the capability for rapid 

shutdown was well-established (e.g., from full power 

to full stop within several seconds), the shutdown 

distance decreased to 100 m in December 2008 and 

to 50 m in April 2009. During this period, a scanning 

active sonar (Tritech Super SeaKing DST) was validated as an alternative tool for detecting harbor seals 

in the vicinity of the turbine. 

During the second phase, from August 2009 to 

April 2010, the marine mammal observer on the pile 

was replaced by an active sonar operator on shore (the 

effectiveness of the active sonar having been evaluated during the first phase of operation). Although 

operation continued to be restricted to daylight hours, 

the sonar was used to assess differences in harbor seal 

activity between day and night, with approximately 

200 hours of nighttime activity analyzed. In January 

2010, the operational window increased from the 

five-day work week to seven days per week and an 

additional hour of operation allowed before sunrise 

and after sunset.

The third phase began in April 2010 and is the 

current operational state, as of late 2010. During 

this phase, operation 24 hours a day, 7 days a week 

is permitted. Shutdown distance, as informed by 

the active sonar, also decreased from 50 m to 30 m. 

Because of the mitigation requirement for temporary 

shutdown when seals may be at risk, this approach 

does not monitor for blade strike.

MCT is currently working with regulators to 

remove the sonar requirement, using statistical 

analyses of data collected to date. 
11

Figure 5 – SeaGen, Marine Current Turbines (Source: Marine Current Turbines)

Table 1 – Marine Current Turbines device specifications (Strangford Lough demonstration)
12

1.6.4 Ocean Renewable Power Company – 

OCGen TGU (Eastport, Maine)

The Ocean Renewable Power Company (ORPC) 

Turbine Generator Unit (TGU) is a cross-flow turbine 

(Figure 6). Power generation is accomplished by 

a variable speed, direct-drive generator. ORPC’s 

TidGen device consists of a single TGU anchored 

Figure 6 – ORPC Beta TGU (Source: Ocean Renewable Power Company)

Figure 7 – ORPC TidGen (Source: Ocean Renewable Power 

Company)

to the seabed by a gravity support frame (Figure 7). 

ORPC is also developing a larger OCGen module in 

which individual TGUs are attached together and float 

in the water column secured to a seafloor foundation 

by compliant mooring cables. Specifications for the 

TidGen device are given in Table 2. ORPC is based in 

the United States and is developing projects in Maine 

and Alaska.
13

1.6.5 OpenHydro – 

Fundy Demonstration 

(Minas Passage, Nova Scotia)

The OpenHydro turbine is a high-solidity horizontal axis rotor with symmetric, fixed-pitch blades. 

The alignment of the rotor to the flow is fixed (no yaw 

control). Power generation is accomplished by a variable speed, direct-drive permanent-magnet generator 

incorporated into the enclosing shroud. The center 

section of the rotor is open. The turbine is secured 

to the seabed by a tripod gravity base. Specifications 

for the 10 m (1 MW peak power) device recently 

Table 2 – ORPC device specifications

deployed in the Bay of Fundy (Figure 8) are given 

in Table 3. Environmental monitoring of this device 

is being conducted as an independent activity by the 

Fundy Ocean Research Centre for Energy (FORCE), 

a non-profit institute that owns and operates a facility 

where tidal turbines are tested and demonstrated. 

OpenHydro also operates a grid-connected test facility 

at the European Marine Energy Centre (EMEC) in 

Orkney, Scotland, where it tests its turbine technology 

at 6 m (250 kW) scale for performance and environmental effects. Environmental monitoring results are 

proprietary to OpenHydro, which is based in Ireland.
14

Figure 8 – OpenHydro 10 m (1 MW peak power) Bay of Fund Turbine (Source: OpenHydro)

Table 3 – OpenHydro device specifications (Bay of Fundy demonstration)
15

Figure 9 – Free Flow Kinetic Hydropower System (Source: Verdant Power)

1.6.6 Verdant Power – RITE 

(East River, New York)

The Verdant Power Kinetic Hydropower System 

(KHPS) is a three-bladed horizontal axis rotor that 

passively yaws to keep the rotor aligned with the 

mean flow direction on ebb and flood (Figure 9). For 

the Roosevelt Island Tidal Experiment (RITE), six 

turbines were supported by streamlined monopile 

foundations that were drilled into the seabed. For 

economic reasons and depending on water depth and 

seabed composition, future deployments will likely be 

anchored by gravity foundations; either in a single or 

triframe (three turbines per foundation) configuration. 

The six-turbine array installed for the RITE project is 

the only demonstration of a tidal turbine array in the 

world. Specifications for the RITE devices (Gen4), as 

well as specifications for the next generation (Gen5) 

machines, which are undergoing final design, are 

given in Table 4. The Gen5 machines will be installed 

as part of the next phase of the RITE project (30 

KHPS for 1 MW-rated capacity; estimated in 2012) 

and other sites. The RITE project included extensive environmental monitoring, such as the use of 

hydroacoustic arrays to monitor fish presence, abundance, behavior, and potential interaction with KHPS 

turbines. Data from this monitoring effort is presented 

in regulatory documents filed for the next phase of the 

RITE project (available at www.theriteproject.com). 

Verdant Power is based in the United States.

The permitting requirements for the RITE project 

included an extensive effort to characterize the risk 

of strike, aggregation, and avoidance posed to fish by 

an array of turbines. To this end, Verdant Power and 

its consultants deployed four types of hydroacoustic 

instrumentation:

• A fixed array of 24 split-beam transducers 

providing coverage of the turbines and near-field 

(out to 12 rotor diameters). Significant postprocessing was required and this technique could 

not distinguish between species, only target size.
16

• A ship-mounted split-beam transducer running 

mobile surveys over the turbine near-field and 

beyond. As with the fixed array, this could not 

distinguish between species.

• A fixed near-video hydroacoustic sonar 

(DIDSON) providing coverage of the turbine 

and immediate vicinity (less coverage than the 

split beam array). Significant post-processing 

was required and instrumentation deployments longer than 2-3 weeks were not feasible. 

Species-specific identification was possible.

• A ship-mounted hybrid system consisting of 

a split-beam and DIDSON sonar deployed in 

a targeted manner to monitor for strike on a 

species-specific basis.

As this was the first study investigating the 

potential for fish strike, aggregation, or avoidance 

associated with the operation of a hydrokinetic 

turbine, several important lessons were learned:

• The fixed array of split-beam transducers 

indicated that fish behavior is influenced 

predominantly by natural tidal currents, with 

the presence of rotating KHPS units acting as 

a secondary effect. Fish were observed to be 

active at slack water, when the machines are not 

operating, and relatively inactive during ebb and 

Table 4 – Verdant Power KHPS device specifications

flood, when the machines are operating.

• Although ship-mounted split-beam hydroacoustics provides abundance and distribution of fish 

over a wide area, it does not provide enough 

temporal or species resolution, in proportion 

to the cost of the surveys, to be used to assess 

behavioral changes and was mutually abandoned 

by Verdant Power and regulatory agencies.

• DIDSON sonars are effective for short-term, 

species-specific monitoring and did observe one 

fish passing around an operating turbine, along 

hydrodynamic streamlines. However, the cost of 

marine operations and instrumentation precludes 

anything other than short-term, targeted deployments.

Verdant Power also conducted a number of 

before and after controlled impact (BACI) studies 

related to hydrodynamics, fish presence/abundance, 

underwater noise, water quality, and benthic habitat. 

These were generally inconclusive due to the scale of 

the pilot project in comparison to existing variability 

(from both natural and other anthropogenic sources). 

Observations that contrasted periods in which the 

turbine array was in operation versus not operating 

were considered to be more productive for assessing 

key stressor/receptor relationships.
17

1.7 References

Arbic, B. and Garrett, C. 2010. A coupled oscillator 

model of shelf and ocean tides. Continental Shelf 

Research, 30(6): 564-574.

Bedard, R. 2008. Prioritized Research, Development, Deployment and Demonstration (RDD&D) 

Needs: Marine and Other Hydrokinetic Renewable Energy. Electric Power Research Institute. 

December 2008. 

Boehlert, G.W., McMurray, G.R. and Tortorici, C.E. 

(Eds.). 2008. Ecological Effects of Wave Energy 

Development in the Pacific Northwest. U.S. 

Department of Commerce, NOAA Technical 

Memorandum NMFS-F/SPO-92. 

Charlier, R.H. and Finkl, C.W. 2009. Section 2: Medieval Engineering that Lasted. In Ocean Energy: 

Tide and Tidal Power. New York, NY: Springer. 

29-64. 

DOE (U.S. Department of Energy Energy). 2010. 

Marine and Hydrokinetic Technology Database. 

Wind & Water Power Program, Energy Efficiency 

and Renewable Energy, U.S. Department of 

Energy. Available from http://www1.eere.energy.

gov/windandhydro/hydrokinetic/default.aspx.

DOE (U.S. Department of Energy Energy). 2009. 

Report to Congress on the Potential Environmental Effects of Marine and Hydrokinetic 

Energy Technologies: Prepared in Response to 

the Energy Independence and Security Act of 

2007, Section 633(B). Wind and Water Power 

Program, Energy Efficiency & Renewable 

Energy, U.S. Department of Energy. December 

2009.

Garrett, C. and Cummins, P. 2007. The efficiency of 

a turbine in a tidal channel. J. Fluid Mechanics, 

588: 243-251.

Gooch, S. Thomson, J., Polagye, B. and Meggitt, D. 

Site characterization for tidal power. MTS/IEEE 

Oceans 2009. Biloxi, MI, October 26-29, 2009.

Karsten, R., McMillan, M., Lickley, M. and Haynes 

R. 2008. Assessment of tidal current energy in 

the Minas Passage, Bay of Fundy. Proceedings 

of the IMechE, Part A: J. Power Energy, 222(5): 

493-507.

Kawase, M., Beba, P. and Fabien, B. 2010. Depth 

dependence of harvestable power in an energetic, 

baroclinic tidal channel. Renewable Energy. 

Article under review. 

Orme, J., Masters, I. and Griffiths, R. 2001. Investigation of the effect of biofouling on the efficiency 

of marine current turbines. In C. French (Ed.) 

Proceedings of MAREC 2001 (Institution of 

Marine Engineers, 2001). 91-99.

Polagye, B., Epler, J. and Thomson, J. Limits to the 

predictability of tidal current energy. MTS/IEEE 

Oceans 2010. Seattle, WA, September 20-23, 

2010.

Polagye, B. and Previsic, M. 2010. Scenario Based 

Analysis of Environmental and Navigation 

Impacts: Tidal Power Scenario Descriptions. 

Technical Report to the U.S. Department of 

Energy by RE Vision Consulting, LLC, Sacramento, CA.
18

It is important to distinguish between environmental 

effects and environmental impacts. Environmental 

effects are the broad range of potential measurable 

interactions between tidal energy devices and the 

marine environment. Environmental impacts are effects 

that, with high certainty, rise to the level of deleterious 

ecological significance (Boehlert and Gill 2010). A 

further distinction is made with respect to potential 

effects or impacts with potential denoting a moderate 

to high level of uncertainty. For effects, this uncertainty 

describes the fundamental nature of whether such interactions can occur. For impacts, the uncertainty describes 

the details of the interaction (e.g., frequency, speciesspecific response) that would elevate the effect to the 

level of environmental significance.

Little is known about the potential environmental 

impacts from ocean energy devices and systems 

(DOE 2009). Tidal power technology is building on 

lessons learned from conventional hydropower and 

the wind industry. However, only a limited number of 

devices have been tested at sea, and the industry has 

yet to settle on a clear preferred technology. 

Research into device performance, environmental 

effects, and siting considerations for tidal power has 

been largely concentrated in the European Union. 

To date, most research has been industry-driven and 

concerned with technological innovation, but recent 

peer-reviewed literature has investigated strategies 

to assess environmental effects as well (Shields et 

al. 2009). There are some similarities between tidal 

power and more mature technologies such as offshore 

wind, and, thus, an investigation of the offshore wind 

2. Environmental Effects of Tidal Power

environmental impact and monitoring literature (e.g., 

Carstensen et al. 2006, Nunneri et al. 2008) is useful 

to anticipate research needed for tidal power environmental effects assessment and siting. 

Recent reviews of the potential environmental 

impacts of tidal power technologies have been 

conducted (e.g., Michel et al. 2007, Wilson et al. 

2007, DOE 2009, Kramer et al. 2010), but these 

assessments are not based on in situ monitoring of 

environmental impacts and only are able to describe 

potential impacts. Furthermore, uncertainties 

associated with scaling up observed effects from 

pilot- to commercial-scale are undocumented. 

2.1 Conceptual Approach: 

Stressors and Receptors

For the purpose of this document, environmental effects are described in terms of stressor/

receptor interactions. Stressors are those factors that 

may occur as hydrokinetic tidal energy systems are 

installed, operated, or decommissioned. Receptors are 

those elements of the marine environment that may 

be affected by stressors. With a few exceptions, the 

approach is very similar to the framework proposed 

by Boehlert and Gill (2010) and, in that language, 

evaluates environmental effects to identify potential environmental impacts. Stressors and receptors 

discussed at the scientific workshop in March 2010 

are summarized in Table 5 – Environmental stressors 

and receptors associated with tidal energy development.Table 5.

Table 5 – Environmental stressors and receptors associated with tidal energy development.
19

2.2 Environmental Effects

Environmental effects of tidal power generation 

are similar in many ways to those of wave power 

and offshore wind power generation. Assessments 

have identified a number of potential environmental 

impacts from tidal energy development. Gill (2005) 

describes a number of indirect ecological effects that 

would result from extensive installation of offshore 

renewable energy developments. These include:

• Alteration of currents and waves;

• Alteration of substrates, sediment transport and 

deposition;

• Alteration of habitats for benthic organisms;

• Noise during construction and operation;

• Emission of electromagnetic fields;

• Toxicity of paints, lubricants, and antifouling 

coatings;

• Interference with animal movements and 

migrations; and

• Strike by rotor blades or other moving parts.

Effects on biological resources could include 

alteration of the behavior of animals, damage and 

mortality to individual plants and animals, and potentially larger, longer-term changes to plant and animal 

populations and communities (Gill 2005, DOE 2009). 

Development of tidal energy involves technology 

testing, site characterization, device installation, 

operation and maintenance, and decommissioning. 

Many installation and decommissioning effects have 

close analogues to existing industries (e.g., offshore 

wind) and are short-term. Consequently, this report 

places an emphasis on operational effects experienced 

over the long term and installation/decommissioning 

effects unique to tidal energy.

2.3 Installation Effects

Installation of tidal power generation devices 

may cause significant disturbance to the local environment. However, other than the actual placement 

of persistent structures (i.e., the device and power 

cables), most installation effects are likely to be 

temporary (weeks to months, with some effects 

lasting longer). Stressors present during deployment 

are similar to those from other construction activities 

in the marine environment (DOE 2009) and include 

construction noise (i.e., air compressors), increased 

vessel activity, and habitat disturbance associated with 

installation of anchors and power cables. The area of 

disturbed habitat depends on the number of devices to 

be installed and type of foundation. If project installation involves pile driving, nearby noise levels are 

likely to exceed damage threshold values for fish and 

marine mammals (MMS 2007), potentially causing 

temporary or lasting harm to affected individuals or 

populations. Deployment timing may help to mitigate 

the effects of these stressors on marine organisms, 

especially migratory fish, marine mammals, and 

seabirds (Gill 2005).

2.4 Operational Effects

Operation of a tidal power generation installation includes movement of turbine blades in the tidal 

current and the conversion of mechanical energy into 

electricity for transmission to shore. Most tidal energy 

generation devices will be controlled and monitored 

remotely. Post-installation monitoring will address 

device performance, structural integrity, and environmental indicators (e.g., noise, currents, marine 

mammal activity).

Rotating machinery, underwater noise, chemicals, 

and electromagnetic fields (EMFs) are frequently 

cited as stressors associated with device operation, 

although the potential for interaction with receptors is 

not well understood. Other important stressors, even 

less well understood, are those associated with energy 

removal and cumulative effects from interaction of 

multiple stressors or multiple devices. 
20

Operational stressors vary temporally with the 

stage of the tide and status of the device. For example, 

when the device is not operating (i.e., currents are 

below cut-in speed), acoustic, electromagnetic, energy 

removal, and dynamic device (i.e., blade rotation) 

stressors are reduced. Depending on the tidal regime 

and device specifics, a turbine can operate nearly 

continuously or for less than half the time. 

Receptors in the marine environment may vary 

temporally (e.g., seasonal trends, migratory behavior) 

and may be exposed to other anthropogenic stressors. 

As a consequence, the interaction between operational 

stressors and receptors may have higher temporal 

variability than either the underlying stressor or 

receptor. Similar considerations apply to the spatial 

variability of stressors (e.g., received acoustic levels 

will vary with proximity to an operating device), 

receptors (e.g., species are not uniformly distributed 

within a project area), and their interactions.

Normal operations also involve maintenance 

activities, which may involve the recovery of the 

device or device components to the surface. Some of 

the environmental stressors associated with maintenance are similar to installation (e.g., increased vessel 

traffic).

2.5 Decommissioning Effects

At the end of its operational life, a device will 

be decommissioned. Environmental stressors will 

be very similar to device installation (e.g., increased 

noise, surface traffic, disruption of habitat). If the 

entire project has reached the end of its operational 

life, all anchors and subsea cables may also be 

removed.

2.6 Accidents 

During installation, operation, maintenance, or 

decommissioning, accidents may occur. Accidents 

involving tidal energy devices are to be expected at 

the pilot stage since many device deployments will 

involve relatively untested designs. An example of 

an acute accident is blade damage. Blade failures 

(also common in the early days of wind energy) 

have occurred during several device tests for a 

variety of reasons (e.g., Marine Current Turbines’ 

SeaGen experienced blade failure due to a software 

error that incorrectly adjusted the blade pitch angle 

during peak current; loads on first-generation Verdant 

Power turbine rotors exceeded design specifications). 

However, the ecological significance of a blade failure 

is uncertain. The most ecologically significant accident would be the release of petrochemicals, which 

could be caused by a vessel collision. The significance of such an event could be mitigated by scheduling vessel operations during conditions (tidal stage, 

weather) when there is less likelihood of oil spills 

occurring and spill response procedures are known to 

be most effective. While most devices currently under 

development do not include ecologically significant 

quantities of lubricants, similar concerns exist for 

devices with hydraulic drive trains.

2.7 Scale of Development

The significance and uncertainty associated 

with a particular stressor/receptor interaction may 

vary with the scale of development. For example, 

the acoustic effects of a single pilot turbine may be 

insignificant in the context of existing ambient noise 

sources but could be significant for a commercial 

array consisting of a hundred turbines. To account for 

this, breakout group discussions during the workshop differentiated between pilot-scale deployments 

(to indicate high-priority areas in the near-term) and 

commercial-scale deployments (to indicate highpriority areas in the long-term). 
21

Pilot projects were considered to have the 

following characteristics:

• Single devices or small device arrays;

• Deployment durations of less than a decade;

• Provisions for project shutdown and early 

removal if unacceptably large environmental 

impacts are observed;

• Power extracted by a pilot project is much less 

than natural tidal dissipation in the project area;

• The rotor swept area (sum of the cross-sectional 

area swept by all turbines) for a pilot project is 

much less than the cross-sectional area of the 

channel in which it is deployed; and

• The primary goal of pilot projects is research and 

development (i.e., revenues generated by electricity sales are relatively incidental compared to 

the implementation cost).

This working definition is qualitatively similar 

to that adopted by the Federal Energy Regulatory 

Commission (FERC) for pilot licensing (FERC 2008), 

but does not adhere to the same quantitative standards 

(e.g., FERC defines pilot projects as having a rated 

capacity of less than 5 MW). 

For the purposes of breakout group discussions, 

commercial projects were considered to have the 

following characteristics:

• Large device arrays (e.g., > 100 devices);

• Service lives of 20-30 years and licensing periods 

of up to 50 years;

• Power extracted by a commercial project may be 

on the same order as natural tidal dissipation in 

the project area;

• The rotor-swept area for a commercial project 

may be on the same order as the cross-sectional 

area of the channel in which it is deployed; and

• The primary goal of commercial projects is 

utility-scale power generation that is costcompetitive with other forms of electricity.

As the tidal energy industry evolves worldwide, 

the scale of pilot projects will likely increase, and the 

line between late-stage pilot projects and early-stage 

commercial projects may be blurred.

2.8 References

Boehlert, G. and Gill, A. 2010. Environmental and 

ecological effects of ocean renewable energy 

development: A current synthesis. Oceanography, 

23(2): 68-81.

Carstensen, J., Henrikson, O.D. and Teimann, J. 2006. 

Impacts of offshore wind farm construction on 

harbor porpoises: acoustic monitoring of echolocation activity using propose detectors (T-PODs). 

Marine Ecology Progress Series, 321: 295-308. 

DOE (U.S. Department of Energy). 2009. Report to 

Congress on the Potential Environmental Effects 

of Marine and Hydrokinetic Energy Technologies: Prepared in Response to the Energy Independence and Security Act of 2007, Section 

633(B). Wind & Power Program, Energy Efficiency & Renewable Energy, U.S. Department 

of Energy. December 2009.

FERC (Federal Energy Regulatory Commission). 

2008. Licensing hydrokinetic pilot projects. 

Available from: http://www.ferc.gov/industries/

hydropower/indus-act/hydrokinetics/pdf/white_

paper.pdf.

Gill, A. 2005. Offshore renewable energy: Ecological 

implications of generating electricity in the 

coastal zone. Journal of Applied Ecology, 42: 

605-615. 

Kramer, S., Previsic, M., Nelson, P. and Woo, S. 2010. 

Deployment Effects of Marine Renewable Energy 

Technologies - Framework for Identifying Key 

Environmental Concerns in Marine Renewable 

Energy Projects. Prepared for the U.S. Department of Energy by RE Vision Consulting, LLC, 

Sacramento, CA. DE-003.

Michel, J., Dunagan, H., Boring, C., Healy, E., Evans, 

W., Dean, J.M., McGillis, A. and Hain, J. 2007. 

Worldwide Synthesis and Analysis of Existing 

Information Regarding Environmental Effects 

of Alternative Energy Uses on the Outer Continental Shelf. Minerals Management Service, U.S. 

Department of the Interior, MMS OCS Report 

2007-038.
22

MMS (Minerals Management Service). 2007. 

Programmatic Environmental Impact Statement 

for Alternative Energy Development and Production and Alternate Use of Facilities on the Outer 

Continental Shelf. U.S. Department of the Interior. OCS EIS/EA MMS 2007-046. October 2007. 

Nunneri, C., Lenhart, H.J., Burkhard, B. and Windhorst, W. 2008. Ecological risk as a tool for 

evaluating the effects of offshore wind farm 

construction in the North Sea. Regional Environmental Change, 8(1): 31-43. 

Shields, M.A., Dillon, L.J., Wolff, D.K. and Ford, 

A.T. 2009. Strategic priorities for assessing 

ecological impacts of marine renewable energy 

devices in the Pentland Firth (Scotland, UK). 

Marine Policy. 33(4)L: 635-642.

Wilson, B., Batty, R.S., Daunt, F. and Carter, C. 

2007. Collision risks between marine renewable 

energy devices and mammals, fish and diving 

birds. Report to the Scottish Executive. Scottish 

Association for Marine Science. Oban, Scotland, 

PA37 1QA.
23

Figure 10 – Sample stressor matrix components

 3. Environmental Stressors

In this section, seven environmental stressors are 

discussed:

• Presence of devices: static effects – stressors 

caused by the presence of the device and foundation, including new structures in the water 

column and disturbances during installation or 

removal or both.

• Presence of devices: dynamic effects – stressors 

caused by the operation of the device, including 

blade strike, entrainment, impingement, and the 

device wake. 

• Chemical effects –stressors due to contaminants 

from lubricants, paints, or coatings.

• Acoustic effects – stressors from noise due to 

device operation or installation or both.

• Electromagnetic effects – stressors from EMFs 

associated with the generator and power electronics on a device or power cable or both.

• Energy removal – stressors, primarily on the farfield environment, which are a consequence of 

energy removal from tidal systems.

• Cumulative effects – stressors arising from a 

combination of other stressors or multiple sites 

(or both) developed in the same geographically 

connected body of water.

Each stressor is discussed using a common 

framework. First, the significance of each stressor 

element on receptors in the natural environment 

(Table 5) is assessed qualitatively as high, medium, 

low, not applicable, or unknown. Second, the uncertainty around this assessment is qualified as high, 

medium, low, or unknown. These results are presented 

as a matrix of stressor/receptor interactions. A key 

describing these matrices is shown in Figure 10. 

The color of the cell denotes the significance of the 

interaction. The number and color of triangles denotes 

the uncertainty of this significance. This evaluation is 

conducted separately for pilot and commercial scale 

deployments, as broadly described in Section 2.7.

High-priority stressor/receptor interactions (e.g., 

of high significance or high uncertainty or both) are 

then discussed in further detail. Each high-priority 

interaction is described, gaps in understanding are 

identified, approaches for monitoring this interaction 

are identified (with emphasis on the stressor), and 

mitigation measures are recommended.

Each breakout group also identified key literature 

references for their stressor.
24

3.1.1 Introduction

Static stressors are primarily the result of immobile, hard structures including tidal energy power 

trains (rotor and generator), foundations, cables, 

and anchors. Tidal energy devices are secured to 

the seabed using monopile or gravity foundations. 

The power train is connected to the foundation by 

a support structure (rigid or compliant mooring). In 

some circumstances, the support structure may pierce 

the water’s surface (e.g., MCT SeaGen). Although 

all tidal energy devices are secured to the seabed, 

this distinction (foundations and other near-bottom 

structure versus devices that have a greater water 

column profile or are surface-piercing) was used to 

evaluate environmental effects on benthic receptors 

and pelagic/surface receptors.

The main effects of static structure are on nearfield physical environments and are associated with 

changes in hydrodynamics (turbulence, wake, etc.), 

sediment dynamics (scour, deposition, etc.), habitat, 

and ecosystem interactions. For example, foundations and support structures can act as artificial reefs, 

affecting scour and deposition in the near-field, and 

providing habitat for reef-associated species. In turn, 

attraction of reef species is likely to attract predators, 

including marine mammals and seabirds. Devices that 

are surface-piercing can affect water column hydrodynamics, provide structure for seabird roosting, or pose 

a collision hazard (Boehlert et al. 2008).

A matrix of stressor/receptor interactions, their 

significance, and uncertainty is given in Figure 11 for 

pilot-scale deployments and in Figure 12 for commercial-scale deployments. The colors denote significance 

and triangles denote uncertainty, as defined in 

Figure 10. 

3.1 Presence of Devices: Static Effects
25

Figure 11 – Stressor matrix: Presence of devices: Static effects – pilot-scale deployment

3.1.2 Stressor Matrix

Figure 12– Stressor matrix: Presence of devices: Static effects – commercial-scale deployment
26

3.1.3 Discussion

Interactions between static structure and receptors were evaluated generically. As such, the results 

could be generally applicable, although many effects 

will be device- and site-specific. Therefore, structure 

types were considered together rather than addressed 

separately, even though some of the interactions could 

be distinctive; for example, slack mooring lines could 

increase the risk of marine mammal entanglement.

Interactions between receptors and static structure that are considered to have a high probability of 

occurrence include effects on near field physical environment (hydrodynamics, sediment dynamics) and 

on habitat. Both pilot- and commercial-scale developments are considered. With commercial developments, interactions among resident fish, marine 

mammals, seabirds, and ecosystems with static tidal 

devices are considered to have a high probability of 

occurrence. Uncertainty was greatest for effects on 

several receptors including the far-field physical environment, migratory fish, and ecosystem interactions, 

at both the pilot and commercial scales. 

Installations of tidal energy devices and transmission cables are considered to have relatively low 

effects on receptors because of the dynamic nature of 

the habitats likely to be affected and the short duration 

of disturbance. Decommissioning the devices and 

cables is considered to have greater effects because 

decommissioning would involve removal of structure 

that could be used by resident fishes as habitat. 

In general, commercial-scale projects would have 

greater effects than pilot-scale projects.

3.1.4 Priority Area: 

Effects of static structure on benthic ecosystems

Description

New static structures placed on the sea bottom 

will likely affect hydrodynamic processes and sediment movement and will change benthic habitat, thus 

affecting community structure. Numerous studies 

have demonstrated that reef-associated fish are likely 

to be attracted to novel structures (Wilding and Sayer 

2002, Bortone 2006, Wilhelmsson et al. 2006, Hunter 

and Sayer 2009). However, how that attraction 

affects overall community structure, especially marine 

mammals and seabirds, is less well understood. It is 

uncertain whether fish species will be attracted to the 

devices (a phenomenon known as an artificial reef 

effect) and whether the devices will increase resident 

fish populations or be population “sinks,” drawing 

fish away from natural habitat.

Gaps in Understanding

Effects on the magnitude and scale of hydrodynamic and sediment dynamic changes on fish interaction with structure and on changes to community 

structure are not well understood, especially for 

marine mammals and seabirds, in such dynamic and 

difficult-to-study tidal environments. Some understanding of these effects can be gained by evaluating 

analogues such as pier or bridge pilings and offshore 

wind turbines. Development of modeling approaches 

to evaluate effects of static structure on hydrodynamics and sediment dynamics is encouraged.

Approaches to Monitoring

Methods and equipment useful for evaluating 

the hydrodynamic disturbance of static structures 

include use of drifters or drogues (Muller et al. 2009), 

Acoustic Doppler Current Profilers (ADCPs) (Teledyne RDI, 2006), numerical models, and scale models 

in flumes. These techniques and instrumentation are 

well-developed.
27

Effects on sediment dynamics and habitat could 

be evaluated using video and still cameras. Depending 

on ambient conditions, video cameras could be 

deployed to monitor changes to benthic habitat in the 

nearfield. However, the effective range for video is 

relatively short, particularly below the photic zone 

(i.e. 7 m or less with full-spectrum lighting) or if 

natural turbidity is high. Therefore, cameras deployed 

directly on a tidal energy device will be limited to 

near-field observations. Cameras mounted to remotely 

operated vehicles (ROVs) may be able to survey 

broad areas, although the strength of the currents 

presents a challenging operating environment, even 

around slack water. Before-and-after comparisons of 

benthic habitat in the immediate vicinity of a tidal 

energy device installation would help to evaluate 

disruptions during installation and recovery. Similar 

comparisons would help to evaluate the rate of 

colonization on foundations, moorings, and support 

structures.

For monitoring fish communities, drift nets and 

acoustic approaches should be considered. Acoustic 

approaches could include active acoustics (sonar), 

acoustic cameras, and acoustic telemetry (both with 

stationary receivers and mobile hydrophone tracking) 

of tagged fish. However, detection probability for 

small fish using active acoustics may be low at some 

locations because of high sediment loads, turbulent 

mixing of fresh and salt water, and air-bubble entrainment (see also Sections 0, Fish: migratory, and 4.5, 

Fish: resident). 

For evaluating effects on marine mammals, 

passive acoustic hydrophones, visual observations, 

and telemetry are the primary monitoring methods 

(see also Section 0, Marine mammals and seabirds). 

Monitoring pilot deployments will provide information on near-field effects, but a phased approach to 

commercial buildouts using adaptive management is 

recommended, because effects may not be linear and 

it will be necessary to “learn as you go.” 

Mitigation Measures

Hydrodynamic effects may be decreased by 

minimizing anchor sizes, decreasing the number of 

moorings and slack lines, and streamlining support 

structures. 

Multidisciplinary design teams (e.g., biologists 

working with engineers) could develop best management practices and improve structural designs to 

minimize biological impacts.

Mitigation measures to reduce the effects of 

installation on benthic communities should include 

minimizing extraneous lighting and defining “work 

windows” to avoid timing of sensitive species’ migratory or reproductive activities. 

3.1.5 Priority Area: 

Effects of static structure on the water column 

and/or surface

Description

New static structures placed in the water column 

will affect hydrodynamic processes, including 

changing pelagic habitat, which may affect community structure. There is reasonable certainty that 

pelagic fish will use devices as refuges from strong 

currents; however, effects on community structure, 

especially on marine mammals and seabirds, are less 

well understood. Whether migratory fish species 

will be attracted to the devices (the Fish Aggregating 

Device or FAD effect) is uncertain in temperate 

ecosystems (Wilhelmsson et al. 2006). Surfacepiercing structures may attract seabirds that roost and 

marine mammals that haul out. There is reasonable 

certainty that seabirds will use surface-piercing structures to roost and that many bird species are sensitive 

to lighting. Surface structures will require lighting for 

safety and navigation, which will affect seabirds and 

other species.
28

Gaps in Understanding

Effects on the magnitude and scale of hydrodynamic changes, on fish interaction with structure, 

and on changes to community structure, are not well 

understood, especially for marine mammals and 

seabirds. These interactions are difficult to study in 

dynamic tidal environments. For example, hydrodynamic changes may affect fish behavior and distribution and could improve feeding success for pinnipeds. 

Birds are known to be affected by lighting, but 

specific effects on seabirds remain unknown. Knowledge about these effects could be extrapolated from 

analogues. Development of modeling approaches to 

evaluate effects of static structure on hydrodynamics 

is encouraged. 

Approaches to Monitoring

Monitoring approaches will vary with receptor 

and species.

To evaluate effects on fish, acoustic methods 

generally do not work well near the surface because 

of turbulence and wave action; however, acoustic 

tags are an exception and can be used to tag fish and 

their predators. For example, if a predator consumes 

a tagged individual fish, then the two tags will remain 

together. However, the tagging intensity and receiver 

density required for these types of studies may not be 

cost-effective, particularly at the pilot scale.

To evaluate effects on seabird behavior, monitoring approaches include radar (depending on 

distance from shore) and visual observations from 

boats, ferries, and air taxis. 

To evaluate pinniped behavior and feeding 

success, animal-borne video cameras (Moll et al. 

2007) can be used to study predation and interaction 

with devices. Scat samples can be evaluated for coded 

wire tags, PIT tags, or acoustic tags from tagged fish. 

Remote webcams or cameras on devices could also be 

valuable monitoring tools. 

Mitigation Measures

Minimizing or shrouding lights, using strobes 

instead of constant lighting, and careful selection 

of lighting color should be considered on surfacepiercing structures. Structures can be designed to 

be less desirable for pinniped haul-out or seabird 

roosting behaviors. Tidal energy device profiles can 

be streamlined to reduce hydrodynamic effects and 

minimize the area that fish and pinnipeds can use to 

hold or rest against tidal currents. 

3.1.6 Priority Area: 

Frequency and duration of tidal energy device 

maintenance

Description

Maintenance of tidal energy devices will entail 

removing structure (either the power train or entire 

device) and thereby disrupting habitats and species 

attracted to the devices. Reef-associated fish are 

likely to be attracted to novel structures on the bottom 

(Hunter and Sayer 2009); however, removal, cleaning 

and maintenance, and replacement will temporarily 

displace species. Frequency and duration of maintenance activities will be device- and site-specific, with 

devices deployed in shallower water likely requiring 

more maintenance and cleaning.

Gaps in Understanding

The primary gap in understanding is the range 

of maintenance options, especially for addressing 

biofouling. The extent of biofouling on devices is 

unknown and will be very site-specific. Preliminary 

indications are that biofouling may be significant and 

rapid for devices deployed within the photic zone 

(e.g., Clean Current deployment at Race Rocks and 

more gradual for deeper deployments (Polagye and 

Thomson 2010). The frequency of device removal 

for maintenance and cleaning, and whether portions 

of the structure (for example, the foundations) will 

remain in place are device- and site-specific. The 

effects of removal on resident fish attracted to structures are not known.
29

Approaches to Monitoring

Acoustic methods (acoustic surveys, cameras, 

acoustic cameras, telemetry) are recommended for 

monitoring fish and other species, as described above, 

but with an emphasis on evaluating behavior associated with maintenance events. Biofouling organisms 

should be evaluated in pilot deployments, by periodically recovering and examining devices, evaluating 

in-situ with ROVs, or using settlement plates. Information gained from pilot-scale deployments will 

be useful for evaluating the effects associated with 

scaling up to commercial build outs. 

Mitigation Measures

Cleaning of biofouling should be done in a 

manner that contains any biocides present in marine 

coatings, and biofouling organisms should be tested 

for contaminant load. If rapid biofouling is an issue, 

projects should be placed below the photic zone 

or treated with anti-fouling coatings. Maintenance 

should be conducted using work windows to minimize effects on resident fish species, especially during 

mating or spawning and, for migratory fish, during 

peak migration periods.

3.1.7 Recommended References

Borton, S.A. 2006. A perspective of artificial reef 

research: the past, present and future. Bulletin of 

Marine Science, 78(1): 1-8.

Hunter, W.R. and Sayer, M.D.J. 2009. The comparative effects of habitat complexity on faunal 

assemblages of northern temperate artificial and 

natural reefs. ICES Journal of Marine Science, 

66: 691-698.

Moll, R.J., Millspaugh, J.J., Beringe,r J., Sartwell, 

J. and He, Z. 2007. A new ‘view’ of ecology 

and conservation through animal-borne video 

systems. Trends in Ecology and Evolution, 

22(12): 660-668.

Muller, H., Blank, B., Dumas, F., Lekien, F. and Mariette, V. 2009. Estimating the Lagrangian residual 

circulation in the Iroise Sea. Journal of Marine 

Systems, 78 Supplement 1: S17-S36.

Polagye, B. and Thomson, J. 2010. Screening for 

biofouling and corrosion of tidal energy device 

materials: In-situ results for Admiralty Inlet, 

Puget Sound, Washington. Northwest National 

Marine Renewable Energy Center Technical 

Memorandum. Northwest National Marine 

Renewable Energy Center. Seattle, WA. Available 

from http://hdl.handle.net/1957/16203.

Teledyne RDI. 2006. Acoustic Doppler current 

profiler principles of operation: A practical primer. Poway, CA: Teledyne. RDI P/N 

951-6069-00.

Wildling, T.A. and Sayer, M.D.J. 2002. Evaluating 

artificial reef performance: approaches to preand post-deployment research. ICES Journal of 

Marine Science, 59: 222-230.

Wilhelmsson D., Malm, T. and Ohman, M.C. 2006. 

The influence of offshore windpower on demersal 

fish. ICES Journal of Marine Science, 63: 

775-784.
30

3.2.1 Introduction

Dynamic effects of device presence include 

strike, entrainment or impingement against moving 

turbine blades, and pressure and velocity gradients 

around an operating device. The presence of rigid, 

moving structures and possible cavitation near blades 

(from the sudden water pressure change from front 

to back of the blade) could result in animal strikes 

or mortality. Although collisions with any of the 

hard surfaces or cables associated with the device 

are possible, collision with the turbine rotors is the 

most intuitive risk to marine vertebrates (Wilson et 

al. 2007). Strike mortality is a product of the strike 

probability and force. Force is proportional to turbine 

velocity. Different turbine designs offer different 

potentials for strike mortality. For example, the speed 

of a vertical axis turbine rotor is equal along the blade, 

while the speed of a horizontal axis turbine rotor is 

faster towards the blade tip (DOE 2009). Although 

there is no direct evidence of marine animals’ ability 

to avoid spinning tidal turbine rotors, Wilson et al. 

(2007) suggest that marine mammals and fish may 

see or hear the device and either avoid the area or take 

evasive action at close range.

When compared with rates of fish strike in 

conventional hydro dams, it is expected that the 

likelihood of strike is far less for un-ducted tidal 

turbines than for conventional hydropower turbines, 

because animals have little opportunity to avoid 

conventional hydro turbines and the rotational speed 

is much greater than that of tidal turbines. Exposure 

to conventional hydro turbines is a single, highprobability event, while exposure to turbines in a 

tidal energy array has a low likelihood but could be 

repeated for different devices within the array (DOE 

2009). Turbine strike may be compared to collision 

with the bow of a ship (Wilson et al. 2007). However, 

unlike tidal turbines, large ship hulls generate a 

suction that can pull animals towards the ship and 

increase the likelihood of a strike (Fraenkel 2006).

A matrix of stressor/receptor interactions, their 

significance, and uncertainty is given in Figure 13 

for pilot-scale deployments and in Figure 14 for 

commercial-scale deployments. The colors denote 

significance and triangles denote uncertainty, as 

defined in Figure 10.

3.2 Presence of Devices: Dynamic Effects
31

Figure 13 – Stressor matrix: Presence of devices: dynamic effects – pilot-scale deployments

3.2.2 Stressor Matrix

Figure 14 – Stressor matrix: Presence of devices: dynamic effects – commercial-scale deployments
32

3.2.3 Discussion

The presence of singular or multiple tidal turbines 

in the marine environment will create the potential 

for a number of physical interactions with the water, 

seabed, and species or habitats in the surrounding 

area. In order to determine the likely effects arising 

from a moving turbine in the marine environment, the 

group discussed the following stressor elements:

• Direct interactions – blade strike, impingement, 

entrainment;

• Increase/decrease in water velocity;

• Increase/decrease in pressure; and

• Effects of the rotor wake.

The significance and likely occurrence of an 

effect on receptors for each of the stressor elements in 

Figures 13 and 14 was discussed at length. The group 

consisted of device developers, marine mammal and 

fish experts, and those with experience of marine 

mammal interactions with offshore wind turbines. 

It was concluded that changes in velocity, pressure, 

and effects from the wake of rotors were likely to be 

highly localized and, therefore, unlikely to produce 

measurable events, even in the near-field environment for smaller-scale projects. Examples of in-situ 

measurements were given from Verdant Power (Colby 

and Adonizio 2009), OpenHydro, and MCT in relation to the actual changes in pressure, wake effects, 

and physical effects such as cavitation. A number of 

these data, however, are not yet in the public domain, 

therefore data-led evidence on the physical effects is 

yet to be quantified. The conclusion is that velocity 

changes and pressure changes are highly localized to 

the blades themselves, and there is little potential for 

these changes to affect receptors.

The effects of wake from the turbines was 

determined to be aligned to energy extraction and 

the ability to optimally lay out turbines arrays and 

would, therefore, be unlikely to affect the receiving 

environment because of the dynamic nature of tidal 

energy sites. The high density of water, coupled with 

the rapid in-stream changes in hydrodynamics, as 

understood in a tidal stream environment, was thought 

to be so variable as to mask any measurable effect at a 

receptor level.

The key stressor of concern was the ability to 

predict, monitor, and mitigate the likely potential for 

direct interactions between marine receptors and the 

tidal technology devices themselves. This group of 

effects includes direct contact with moving blades or 

rotors, impingement within devices (where possible), 

and entrainment.

3.2.4 Priority Area: 

Potential for direct interactions of marine species

Description 

The key priority identified within the group was 

the potential for direct interactions of marine species, 

including migratory fish, marine mammals, and resident fish (at their various life stages) with the rotating 

blades of a tidal turbine. This issue is of high priority 

where there are endangered or threatened species.

Gaps in Understanding

In general, there is insufficient knowledge to accurately assess the risk posed to fish, marine mammals, 

and seabirds.

Migratory Fish—Migratory fish, such as salmonids, are often endangered or protected under various 

legislative controls. Salmonids and other anadromous and 

marine fishes are known to use tidal currents to navigate 

through areas of interest (Moser and Ross 1994, Levy 

and Cadenhead 1995, Barbin 1998, Lacoste et al. 2001, 

Metcalfe and Hunter 2003). However, it was agreed 

that knowledge of fish behavioral ecology in relation to 

device interactions was limited and not at the level necessary to adequately understand potential effects. 

Marine Mammals—It was agreed that little is 

known on the behavior of marine mammals in a tidal 

energy context, particularly their activity level or usage of 

tidal flows. The group determined that physical interactions between marine mammals and devices are likely to 

depend on site characteristics and the species or population of mammals found in that region. Therefore, any 

interactions would be specific to a project and would 

require adequate monitoring and associated mitigation in 

order to further understand the interactions. Details of the 

marine mammal monitoring and mitigation effort undertaken by Marine Current Turbines Ltd. are described in 

Section 1.6.3 of this report.
33

Levels of uncertainty were thought to be high for 

both the pilot-scale and commercial-scale projects. 

For the case of a Puget Sound, Washington, 

project, it was agreed that there were some studies 

suggesting that Southern Resident Killer Whales 

utilize tidal currents to move in and out of Puget 

Sound, therefore increasing the likelihood of possible 

interactions. The movement of marine mammals 

throughout Puget Sound is not understood at a 

temporal or spatial resolution required to establish 

the potential for “take” under the federal Endangered 

Species Act; the levels of uncertainty and risk remain 

high.

Seabirds —The possibility of the interaction 

between tidal devices and seabirds was agreed to 

be highly unlikely in depths greater than that of the 

maximum diving depth of any resident birds. Because 

the potential effect of tidal devices on the aggregation of target prey species is poorly understood, it 

was agreed that diving birds were not a priority at this 

stage of development but that the levels of uncertainty 

were high. Should projects progress to a commercial 

scale, further studies would be required in order to 

understand interactions.

Approaches to Monitoring and Mitigation

In general, it was agreed that the ability to 

monitor for and mitigate against potential direct interactions of marine mammals, fish species, and seabirds 

with tidal turbines would be extremely complex. 

However, a mechanism for early establishment of 

what types of interaction and at what frequency interactions occur would be required to further understand 

interactions and potential mitigation. 

Migratory Fish—The use of active acoustics 

was discussed to understand near-field interactions 

and activity of fish species around the turbines. 

Active acoustics have been used to study interaction 

with some success at Verdant Power’s RITE project, 

although at high cost and with inconclusive outcomes. 

It was agreed that a further workshop was required 

to review the existing models for analysis of fish and 

modes of measurement such as acoustic telemetry and 

tagging protocols.

The existing models for behavioral ecology of 

fish species were thought to be too large-scale to be 

applied to species-specific interactions (e.g., protected 

or endangered species). However, existing models 

and understanding could be reviewed and possibly 

adapted to meet the survey and monitoring requirements associated with tidal energy projects. 

Marine Mammals—Acoustic monitoring (both 

split- and multi-beam) is one approach to detect 

large cetaceans and pinnipeds in the region of a 

turbine. However, the resolution and range of such 

instrumentation is limited and this class of problem 

is analogous to the yet-unsolved military concern 

of reliable “swimmer detection.” Any monitoring 

approach should allow for the immediate shutdown 

of a turbine in order to reduce the possibility of direct 

marine mammal interaction, particularly for at-risk 

or protected species. Further workshops are recommended to scope:

• Maximum swimming velocities of marine 

mammals;

• Safe stopping distance and risk “envelope”;

• Available instrumentation for marine mammal 

detection; and

• System integration and data analysis.

Mitigation measures could include: using direct 

and low-cost options to increase the visibility of 

rotors to fish; using acoustic avoidance measures; 

and using shock absorbers on the leading edges of the 

blades (Wilson et al. 2007). Because devices require 

a minimum speed to operate, this stressor/receptor 

interaction is present only over a portion of the tidal 

cycle. Depending on the cut-in speed and site characteristics, a turbine may rotate between 40% and 80% 

of the time. 

It was agreed that impacts should be monitored 

at the pilot scale to evaluate potential effects from 

larger-scale development. Adaptive management of 

the monitoring plan should be adopted to ensure all 

effects are correctly mitigated for over the project 

lifetime. In general, a “deploy and monitor” strategy 

should be adopted to reduce uncertainty in this area. 
34

3.2.5 Recommended References

Barbin, G.P. 1998. The role of olfaction in homing 

and estuarine migratory behavior of yellow-phase 

American eels. Canadian Journal of Fisheries 

and Aquatic Sciences, 55(3): 564-575.

Colby, J. and Adonizio, M. 2009. Hydrodynamic 

analysis of kinetic hydropower arrays. Waterpower XVI, Spokane, WA. July 27-30, 2009. 

Fraenkel, P. 2006. Tidal current energy technologies. 

Ibis, 148: 145-151.

Lacoste, K.N., Munro, J., Castonguay, M., Saucier, 

F.J. and Gagne, J.A. 2001. The influence of 

tidal streams on the pre-spawning movements 

of Atlantic herring, Clupea harengus L., in the 

St Lawrence Estuary. ICES Journal of Marine 

Science, 58(6): 1286-1298.

Metcalfe, J. and Hunter, E. 2003. Being there and 

getting there: Balancing the costs of migration 

against the benefits of changing habitat for North 

Sea plaice. Journal of Fish Biology, 63 Supplement 1: 237-238.

Moser, M.L. and Ross, S.W. 1994. Effects of 

changing current regime and river discharge on 

the estuarine phase of anadromous fish migration. In Dyer, K.R. and Orth, R.J. (Eds.). Changes 

in Fluxes in Estuaries. Fredensborg, Denmark: 

Olsen & Olsen. 343-347.

Verdant Power. Roosevelt Island Tidal Energy Pilot 

License Application, FERC No. 12611. Filed 

December 2010. Volumes 1-4 available at http://

www.theriteproject.com/Documents.html.

Wilson, B., Batty, R.S., Daunt, F. and Carter, C. 

2007. Collision risks between marine renewable 

energy devices and mammals, fish and diving 

birds. Report to the Scottish Executive. Scottish 

Association for Marine Science. Oban, Scotland, 

PA37 1QA.
35

3.3 Chemical Effects

3.3.1 Introduction

Depending on the tidal energy technology, several 

types of hazardous chemicals could be present in the 

marine environment during installation, operation, 

and removal. The chemical effects stressor section 

identified two major stressors of equal potential 

concern: (1) acute release (i.e., a spill) of large 

amounts of lubricants, hydraulic fluids, vessel fuel, or 

other petroleum based products associated with installation, operation, maintenance, or removal of tidal 

energy devices; (2) chronic release of toxic contaminants from antifouling coatings used on tidal devices 

that can potentially affect water and sediment quality. 

Further complications could result if the contaminants 

bioaccumulate in the food chain, potentially affecting 

public health if the aquatic organisms are consumed 

by humans. Spills have a higher certainty of impact 

if the spills are large. Impacts from chemicals in 

coatings are more uncertain due to lack of information about their composition and expediency of their 

release mechanisms. Other stressors identified and 

discussed but deemed to be of lesser concern were: 

slow leakage of lubricants associated with the operation of the tidal devices; release of cleaning solvents 

or lubricants associated with maintenance activities; 

release of oil from power conveyance cables (power 

cables may be filled with an organic-based fluid); and 

unintentional release of chemicals that may be utilized 

during installation, maintenance, or device removal 

operations.

A matrix of stressor/receptor interactions, their 

significance, and uncertainty is given in Figure 15 for 

pilot-scale deployments and in Figure 16 for commercial-scale deployments. The colors denote significance 

and triangles denote uncertainty, as defined in 

Figure 10.
36

3.3.2 Stressor Matrix

Figure 16 – Stressor matrix: Chemical effects – commercial-scale deployment

Figure 15 – Stressor matrix: Chemical effects – pilot-scale deployment
37

3.3.3 Discussion

The chemical effects group identified the 

following stressor elements that may have potential 

impacts during the installation, operation, maintenance, or removal of a tidal power device: 

• Diffusion of chemicals from or flaking of the 

marine coating(s) used to prevent corrosion or 

biofouling on the tidal device; 

• Large spills of petroleum-based products (e.g., 

vessel fuel) during installation, operation, maintenance, or removal of tidal power devices; 

• Leakage of lubricants, cleaning fluids, solvents, 

hydraulic fluids, and vessel fuel during installation or removal of the tidal device, normal operation, and maintenance activities; 

• Release of contaminants from power conveyance 

cables (cables may be oil-filled or oil impregnated) 

during installation, operation, or removal; and 

• Resuspension of historical contaminants buried in 

sediments during installation of power conveyance 

lines to shore.

In identifying stressor elements, the group felt that 

it was important to distinguish between the volume 

of fluids that might be released during installation, 

operation, maintenance, or device removal and the 

much larger release that might occur during an accident 

(e.g., sinking of a vessel or barge containing fuel or 

fluids). Chemical stressors, when viewed as potential 

contaminants, were not assumed to have any impact on 

the physical environment (either near- or far-field), but 

rather on the habitat, fish, marine mammals, and seabird 

and ecosystem receptors. 

3.3.4 Priority Area: Anti-fouling coatings

Description

Most of the tidal energy structures will be 

submerged in saltwater where biofouling (growth of 

marine organisms) could occur. Severe biofouling of a 

turbine rotor will degrade device performance (Orme 

et al. 2000). Severe biofouling on the turbine foundation will increase drag, leading to increased stresses 

on foundation for individual devices and, for very 

large arrays, the far-field effects from their deployment 

(Garrett and Cummins 2007). To protect against longterm biofouling and corrosion, most components would 

be treated with antifouling or foul release coatings. 

The outer surfaces of antifouling coatings are designed 

to slowly erode, exposing a fresh layer of the biocide. 

This process releases the biocide into the aquatic 

environment through dissolution or flaking. Historically, major environmental impacts resulted from use of 

tributyltin as an anti-fouling biocide. Currently, copper 

is a common anti-fouling biocide. Anti-fouling coatings on marine tidal devices can have harmful impacts 

on marine organisms if concentrations reach threshold 

toxicity levels in water or sediments.

Gaps in Understanding

A major gap in understanding of this stressor is that 

it is unclear what anti-fouling biocides will be used by 

the tidal power industry. From the limited data available, biofouling rates in shallow water (e.g., within 15 

m of the surface) are generally faster than at greater 

depths (e.g., 50 m below the surface; Polagye and 

Thomson 2010). Since it is unknown what coating(s) 

will be on a tidal device, it is also unclear what toxicological impacts the coating(s) may have or what 

behavior, fate, or bioaccumulative effects the biocide 

might have.

Approaches to Monitoring

Prior to any environmental monitoring, an initial 

assessment of the potential impact of the anti-fouling 

biocide on the environment should be conducted to 

assess whether sophisticated environmental fate and 

effect modeling or monitoring is warranted. One 

assessment approach would be to determine the mass 

of biocide released (from leaching studies) and then use 

this information to predict what the concentration level 

of the biocide would be in a specific sediment area or 

water volume. A range of receptor area sizes/volumes 

should be used for assessment purposes. If the predicted 

concentration of the biocide in a “target” receptor area 

or water volume exceeds toxicity screening criteria, 

then a risk management assessment may be warranted 

that involves more detailed modeling, monitoring, or 

mitigation measures. There are a variety of monitoring 

approaches that could be used to assess the impact of 

the anti-fouling biocide on the ecosystem, including 

caged fish or shellfish studies, biogeochemical behavior 

and fate studies, surface sediment monitoring, and 

water column monitoring.
38

Mitigation Measures

Use of anti-fouling biocides should be avoided, if 

possible. If it is deemed necessary, minimal amounts 

should be used. Where use of anti-fouling biocides 

is necessary, toxicity screening of materials should 

be conducted to inform selection and design. It is 

important to note that anti-fouling biocides are likely 

to be continually released into the environment, 

possibly at toxic levels of chronic exposure for some 

organisms, precluding or making highly problematic 

any mitigation measures. Because of this continual 

release and inability to mitigate, the impact on habitat 

is potentially high and also highly uncertain because 

of the paucity of information on toxicity and biogeochemical behavior of newly developed biocides. Foul 

release coatings, which create an inert, low-adhesion 

surface, may be an effective alternative. However, the 

feasibility of applying these coatings to tidal energy 

devices has not yet been demonstrated. Physical 

removal of surface fouling may be accomplished by 

high-pressure water jets once a device is recovered to 

the surface or transported to shore. Most device developers have proposed service intervals of no greater 

than every four years.

3.3.5 Priority Area: 

Resuspension of pollutant chemicals from sediment

Description

Installation of tidal power devices has the potential to disturb fine sediments and introduce historically deposited contaminants to the water column. 

The most likely place sediment disturbance could 

occur is where power conveyance cables pass through 

fine-grained sediments near shore. Nearshore areas 

are also more likely to be contaminated than offshore 

sediments. Water velocities at most tidal energy 

deployment sites are anticipated to be high enough 

that fine grained sediments containing contaminants 

will not be present in most cases. 

Gaps in Understanding

The major unknowns with respect to resuspension 

of contaminated sediments are the lack of knowledge 

of how the power cable will be laid and the strongly 

site-specific nature of contamination. 

Approaches to Monitoring and Mitigation

Use of directional drilling techniques to install 

the cable would prevent or significantly reduce sediment disturbance. Horizontal directional drilling 

bores beneath the nearshore area. Depending on soil 

composition and shoreline conditions, bores up to 500 

m in length are feasible. If a technique that disturbs 

sediments is used to lay the cable (e.g., trenching 

through the nearshore environment), monitoring 

of the sediments in the area for contaminant levels 

should be conducted prior to installation, to avoid 

areas of concern.

3.3.6 Priority Area: Large oil spills

Description

A variety of petroleum-based products (lubricants, hydraulic fluids, vessel fuel, etc.) will be 

utilized or present during the installation, operation, 

maintenance, and removal of tidal energy devices. 

Although catastrophic release of these materials to the 

aquatic environment is likely to be of low probability 

with safe and effective operational practices, accidents 

should be anticipated. Mitigation options should be 

considered prior to deployment, and rapid and effective spill response procedures need to be developed 

prior to device installation. Unsuccessful containment or response to a large spill can have significant environmental impacts, especially if the spill 

reaches a highly sensitive ecosystem habitat (e.g., a 

wetland area utilized for breeding or spawning). One 

particular challenge is that tidal energy devices will be 

operated in high-energy environments and normal oil 

spill response procedures may not be effective. For 

example, placing a boom around the spill will not be 

effective in a high-velocity turbulent environment. 
39

Gaps in Understanding

Based on the history of large accidents and 

chemical spills in the marine environment, it is clear 

that such an incident will have high impact. Research 

documenting the impacts of large spills is sufficient 

enough to rate the uncertainty associated with the 

nature and severity of the impact as low to moderate. 

Any uncertainty in impact would likely be associated 

with spills involving unusual materials, biotic species 

presence, or specifics of the ecosystem. A large spill 

incident will be equally harmful, whether it occurs 

during installation, operation, maintenance, or device 

removal. Two major gaps exist in the understanding 

of the impact of large spills on the environment: (1) 

the ability to predict where and when the spill will 

impact the shoreline, and (2) for some chemicals, 

information on the behavior, fate, (e.g., volatility, 

solubility, etc.) and bioaccumulation/biomagnification 

in the marine environment. 

Approaches to Monitoring

Many of the sites proposed for tidal energy 

development in the United States already accommodate large-scale vessel traffic or, in the particular case 

of Cook Inlet, Alaska, oil and gas exploration. For 

these sites, the effectiveness of existing spill response 

procedures should be assessed in the context of tidal 

energy development. If existing procedures are not 

sufficient, additional studies and inputs to regional oil 

spill plans may be needed. Specific elements of these 

inputs could include:

1. Develop both predictive and real-time trajectory modeling capability. The goal would be to 

provide spill trajectory information in real time, 

using input from tidal current prediction, wind 

speed and direction, and other sensors, so that 

measures can be taken to minimize impact on 

the environment. Spill response teams can be 

directed to predicted target areas.

2. Identify trajectory conditions that might lead to 

transport of spills to sensitive areas. The specific 

hydrodynamic and atmospheric conditions that 

must exist in order for a spill to reach a particularly sensitive ecosystem area could be identified.

3. Conduct baseline studies of sensitive environments vulnerable to spills. This effort should be 

done in coordination with the previous item in 

order to prioritize and focus on the most sensitive areas that are likely targets of a spill. The 

focus should be to obtain that necessary pre-spill 

characterization information in order to assess the 

impact on the receptor environment. 

4. Avoid or minimize the use of toxic materials. 

Choice of lubricants and fluids should be made 

based on environmental toxicity information. 

5. Identify remote sensing tools. Determine whether 

remote sensing tools can be used to assist in the 

detection and tracking of spills. 

Mitigation Measures

Installation, maintenance, and decommissioning 

activities should be scheduled during periods when 

hydrodynamic and atmospheric conditions would 

not allow a spill to reach a particularly sensitive 

ecosystem. Most of these activities would, by necessity, occur during less energetic periods when traditional spill response measures would be more timely 

and effective than during periods of strong tidal 

currents. 

Designs that minimize the volume of lubricants 

and hydraulic fluids are preferred. A number of tidal 

energy devices require either no lubricants (water 

lubricated bearings) or only small quantities of biodegradable lubricants. The highest lubricant volumes 

are associated with hydraulic drive trains on devices. 

Although relatively common for the wave energy 

devices, this power take-off option is proposed for 

relatively few tidal device concepts.
40

3.3.7 Recommended References

Almeida, E., Diamantino, C. and de Sousa, O. 2007. 

Marine paints: The particular case of antifouling 

paints. Progress in Organic Coatings, 59: 2–20.

Brooks, S.J. and Waldock, M. 2009. Section 9, 

Chapter 24: Copper Biocides in the Marine Environment. In T. Arai et al. (eds.), Ecotoxicology of 

Antifouling Biocides. New York, NY: Springer. 

413-428. 

Karlsson, J., Ytreberg, E. and Eklund. B. 2010. 

Toxicity of anti-fouling paints for use on ships 

and leisure boats to non-target organisms representing three trophic levels. Environmental Pollution, 158: 681-687.

Konstantinou, I.K. and Albanis, T.A. 2004. Worldwide occurrence and effects of antifouling paint 

booster biocides in the aquatic environment: A 

review. Environment International, 30: 235– 248.

NOAA (National Oceanic and Atmospheric Administration). 2010. Office of Response and Restoration. Available at http://response.restoration.

noaa.gov/.

Orme, J., Masters, I. and Griffiths, R. 2001. Investigation of the effect of biofouling on the efficiency 

of marine current turbines. In C. French (ed.) 

Proceedings of MAREC 2001 (Institution of 

Marine Engineers, 2001). 91-99.

Polagye, B. and Thomson, J. 2010. Screening for 

biofouling and corrosion of tidal energy device 

materials: In-situ results for Admiralty Inlet, 

Puget Sound, Washington. Northwest National 

Marine Renewable Energy Center Technical 

Memorandum. Northwest National Marine 

Renewable Energy Center. Seattle, WA. 

Schiff, K., Diehl, D. and Valkirs, A. 2004. Copper 

emissions from antifouling paint on recreational 

vessels. Marine Pollution Bulletin, 48: 371-377.
41

3.4 Acoustic Effects 

3.4.1 Introduction

In this section, the risks of underwater sound to the 

marine environment and marine organisms associated 

with tidal energy devices, including both their construction and operation phases, are discussed and evaluated. Sound can be produced underwater by numerous 

mechanisms all involving some kind of vibration or 

impact feature (such as a bubble collapse). Observed 

effects of underwater sound include changes in responsiveness to other stimuli, masking, temporary threshold 

suppression, and injury, as well as the general effects on 

communication, echolocation, spawning, and shoaling 

behavior (Michel et al. 2007). Various activities and 

processes, both natural and anthropogenic, combine 

to form the sound profile within the ocean, generally 

referred to as ambient ocean noise. Except for sounds 

generated by some marine animals using active acoustics for echolocation, most ambient noise is broadband 

(composed of a spectrum of numerous frequencies 

without a differentiating pitch) representing virtually 

the entire frequency spectrum. Distant shipping is the 

primary source of ambient noise in the 20- to 500-Hz 

range (OMP 2006). Spray and bubbles associated with 

breaking waves are the major contributors to ambient 

noise in the 500- to 100,000-Hz range. Noise from wave 

and tidal action can cause coastal environments to have 

particularly high ambient noise levels. Anthropogenic 

activities that contribute to ambient ocean noise include 

ship traffic (commercial and recreational boating, as well 

as military training exercises), aircraft flying over water, 

dredging, nearshore construction activities, mineral/oil/

gas exploration and extractions, geographical surveys, 

and seismic surveys.

It should be noted that because tidal devices necessarily operate in high-flow environments, it is essential 

that the phenomenon of pseudo-noise, defined as the 

signal recorded by an underwater sound measurement 

device (hydrophone) produced by turbulence being 

advected over the face of the hydrophone be distinguished from a truly propagating sound field associated 

with noise generation from tidal energy production. 

Non-propagating pseudo-sound (Strasberg 1988) should 

not be viewed as a genuine environmental stressor. 

Nonetheless, measurements of sound at proposed tidal 

energy sites can be easily contaminated by this effect. 

Strategies to reduce this effect are discussed in a subsequent section of this document. 

It should also be noted that, as a practical matter, 

the frequency range of underwater noise associated with 

tidal energy devices is limited, and these limits need to 

be understood to properly bound the problem and more 

efficiently allocate measurement and analysis resources 

(e.g., Richard et al. 2007). To best understand this 

frequency range, the noise frequency spectrum can be 

partitioned into the following decades: 1-10 Hz, 10-100 

Hz, 100-1,000 Hz, 1,000-10,000 Hz, and greater than 

10,000 Hz (10 kHz).
42

In regards to the first decade (1-10 Hz), because 

tidal power generation will necessarily occur in 

shallow water (i.e., within depths on the order of 

100 m or less) features of shallow water acoustic 

waveguide propagation must be considered (Frisk 

1994). Specifically, sound does not propagate well 

for frequencies below the mode-1 cutoff frequency 

and, for a depth of 100 m and seabed properties 

representing hard, rocky substrate (expected in highflow areas), the mode-1 cutoff frequency is ~10 Hz, 

increases with decreasing depth. Thus sound pressure in the 1- to 10-Hz range is expected to be of 

little significance in terms of risks and impacts. It is 

noted, however, that sound particle acceleration in this 

infrasonic range may be an issue and, thus, the 1-10 

Hz frequency remains important. The fourth decade, 

1,000-10,000 Hz (1-10 kHz), is expected to have less 

importance because the characteristic frequencies for 

power extraction by the rotor are limited to the 100- to 

1,000-Hz frequency range or less. However, gearboxes and generators spin at higher rates, and noise 

from these may be appreciable in the fourth decade 

(Richards et al. 2007). Little noise is expected from 

turbine operation in the fifth decade. 

In summary, the key frequency range of interest 

for investigations relating risks of underwater noise 

associated with tidal energy production should 

emphasize the first(1-10 Hz), second (10-100 Hz), 

and third (100-1,000 Hz) decades. The fourth decade 

may also be of importance when the turbine drivetrain 

incorporates a speed increasing gearbox. As a corollary, questions that might arise concerning sound 

frequencies far outside this frequency range, such as 

the observed phenomenon of fish avoidance of certain 

sound frequencies in the 100-kHz range, are not 

relevant to this problem unless those frequencies are 

less than 10,000 Hz (10 kHz).

A matrix of stressor/receptor interactions, their 

significance, and uncertainty is given in Figure 17 for 

pilot-and commercial-scale deployments. The colors 

denote significance and triangles denote uncertainty, 

as defined in Figure 17. For the purposes of this 

matrix, impacts on living organisms have been split 

into two levels, nominally consistent with usage by 

NOAA Fisheries:

• Level A – Immediate risk of mortality or physical 

injury (e.g., permanent hearing threshold shifts) – 

180 dB broadband for marine mammals exposed 

to a continuous noise.

• Level B – Disruptions of behavior, including 

temporary shifts in hearing threshold (e.g., often 

resulting in change of swimming path as part 

of avoidance) – 120 dB broadband for marine 

mammals exposed to a continuous noise.

The elements of the stressor matrix differ for 

pilot-scale projects versus full-scale build-outs. In 

general, a pilot-scale project is expected to be of less 

risk than a full-scale build-out. As an approximate 

rule of thumb, a larger array of N devices would result 

in a total noise increase of 10log10(N) in dB. For 

example, two devices would result in an increase 

in noise level of 3 dB, compared to a single device, 

and an array of 10 devices would result in a 10-dB 

increase.
43

Figure 17 – Stressor matrix: Acoustic effects – pilot and commercial-scale deployments

3.4.2 Stressor Matrix

3.4.3 Discussion

Several points relating the risks of underwater 

sound to the marine environment and marine organisms associated with tidal energy devices were 

discussed. The three deemed most relevant are 

summarized here. 

Tonal components associated with tidal energy 

installations 

Operation of tidal energy devices may generate 

tonal sounds. For the purposes of the workshop, 

tones have been defined as increases above ambient 

in the sound pressure level (SPL) in a 1/3-octave 

band. The 1/3-octave band center frequencies have 

standard definitions. For example, the typical lowest 

center frequency for underwater environmental sound 

measurements is 12.5 Hz, followed by 16 Hz, 20 Hz, 

25 Hz, etc., with increasing separation between center 

frequencies, such that the center frequency of 2,000 

Hz is followed by 2,500 Hz. It should be noted that 

SPL is defined in the underwater sound convention 

as decibels referenced to 1 micro Pascal (abbreviated 

dB re 1μPa). Rather than provide a precise definition 

of what constitutes a significant increase in SPL, it 

is noted that SPL can readily vary by 30 dB in the 

natural environment (Tougaard et al. 2009, Bassett et 

al. 2010).

For this element of the acoustic stressor, there is 

uncertainty around the low-frequency tonal components of the spectrum produced by tidal turbines. 

This is driven by both the workgroup participants’ 

unfamiliarity with relevant literature, as well as the 

proprietary nature of turbine noise measurements. As 

a result, there is uncertainty over what effects these 

tonal components might have on different species 

of fish (resident, migratory) or marine mammals 

and at what frequencies these effects would be most 

significant for a particular species. What constitutes 

significance for a tonal-based stressor is to be decided 

by the appropriate agencies. It is noted that auditory 

thresholds for particular marine species may be used 

as a starting reference (Southall et al. 2007).
44

Increases in broadband ambient noise

Ambient noise should be either measured directly 

in, or converted to, 1/3-octave bands. This approach 

is nominally consistent with approaches to assess 

impacts from offshore wind turbines (Tougaard et 

al. 2009). The 1/3-octave bands can also be more 

readily compared to known underwater audiograms 

for selected species of fish and marine mammals, 

from which potential impacts described by “zone of 

audibility” or “zone of masking” can be estimated, if 

need be (Richardson et al. 1995). To the extent that 

tidal energy turbines produce continuous noise for 

long periods, the National Oceanic and Atmospheric 

Administration guideline for level B impacts of 120 

rms dB needs to be assessed (the 120 value being the 

linear, or non-decibel, sum of all the octave bands.)

Ambient noise must not be confused with nonpropagating noise (pseudo-noise) associated with 

advection of turbulence over the face of a hydrophone (Bassett et al. 2010). To avoid this effect, the 

measurement of ambient environmental background 

noise (in absence of a tidal energy device) cannot be 

measured exclusively during periods of slack water, 

because of the presence of ambient noise sources, 

primarily during high currents (e.g., moving cobbles). 

A technical challenge arises as to how ambient 

operational noise is measured, because, by definition, 

the tidal energy device operates during periods of 

high flow. Some promising approaches could involve 

placing flow shields over hydrophones or using 

drifting hydrophones. It is beyond the scope of this 

report to further articulate solutions, other than to note 

that pseudo-noise can be a serious confounding factor.

Baseline ambient noise measurements prior 

to project development need to be established to 

provide insight into the potential risks at a site. For 

example, are noise levels from an installed turbine so 

loud relative to ambient noise that they may interfere with social and predatory acoustic communication or migration patterns? Following construction, 

ambient noise in the vicinity must be studied within 

some standardized framework. This should describe 

received levels at various distances from the installed 

turbine, with attention paid to depth-dependence 

and directionality. Following this characterization, 

measurements at a standardized distance (e.g., 10 

m from the source) may be sufficient to monitor for 

relative changes without resorting to extrapolation to 

a hypothetical 1 m from the source. Noise from flow 

around structures and from the wake of the turbines 

is not important, because the noise source is weak in 

strength or represents pseudo-sound and, therefore, 

should be discounted as a noise stressor. 

Transient sources of high pressure noise such as 

with pile driving

Pile driving during the construction phase 

represents the most probable source of high acoustic 

pressure (in excess of ~1,000 Pa). Mitigation techniques, such as optimized construction timing to 

avoid species seasonally occurring in the area and the 

potential impacts on many marine species are both 

reasonably well understood. Best practices to avoid 

significantly affecting species should be established. 

It should be noted, however, that most device 

concepts do not propose pile driving as a part of 

device installation.

Recommendations

The following recommendations should be 

addressed to reduce the uncertainty with this stressor.

In the short-term, there is a need to investigate technologies to shield transducers from flow/

turbulence-induced noise in order to make accurate 

measurements over the full range of tidal currents. 

Workshop participants recommend applying and, 

perhaps, modifying technologies currently used in 

towed-arrays for naval applications. There is also a 

need to investigate the nature of tonal components 

with respect to shallow acoustic modal propagation. 

This would help to bound investigations by establishing which components are below the waveguide 

cutoff frequency and thus of less importance. A final 

need is to establish standards for reporting noise fields 

associated with tidal energy devices, with specific 

emphasis on determining the appropriate range from 

the device at which measurements should be made. 
45

Over the long-term, there is a need to improve 

on techniques to measure acoustic propagating 

noise fields within highly turbulent environments. 

Also, there is a need to expand the knowledge base 

on marine species concerning their sensitivities to 

anthropogenic noise (e.g., Mueller-Blenkle et al. 

2010). This workshop group cautions, however, that 

this should not be an open-ended endeavor. That is, a 

comprehensive study that includes multiple species is 

not likely to be productive. Also, additional pressure 

density spectra and waveform data on a variety of 

tidal energy devices and operation phases should be 

collected to better bound the potential increase from 

ambient levels.

3.4.4 Priority Area: 

Injury or mortality due to excessive 

transient pressure

Description

Excessive transient pressure is defined as transient acoustic pressures exceeding 1,000 Pa. This may 

result in injury or mortality.

Gaps in Understanding

A large body of literature exists relating mortality 

associated with barotrauma, permanent auditory 

threshold shift (PPT), and temporary threshold shift 

(TTS). This is reviewed in Southall et al. However, 

there are still taxonomic gaps in understanding (e.g., 

baleen whales).

Approaches to Monitoring

If pile driving is part of the construction process 

(and, in many cases, it may not be) then monitoring 

should follow current best practices used in the 

marine construction industry, with ability to temporarily halt operations if significant issues are revealed. 

To quantify high transient pressure the standard sound 

energy level (SEL) definition as proposed by Southall 

et al. is recommended. In practice, a high transient 

pressure would be on the order of 1,000 Pa and 

0.1-second duration. 

Mitigation Measures

As this is expected to be largely associated with 

a short-term construction phase, mitigation should 

include construction timing. Mitigation might also 

include slow ramp-up for operations with intense 

noise (e.g., pile driving), bubble curtains, and the use 

of acoustic deterrents.

3.4.5 Priority Area: 

Behavioral responses to prominent narrow band 

or tonal components

Description

Behavioral responses to prominent narrow band 

or tonal components include a range of responses 

from relatively benign pauses in activity to potentially 

injurious flight from an area. 

Gaps in Understanding

Recent conference proceedings (Noise on Aquatic 

Life 2008) provide some information on tonal disturbance. However, in reference to the comment made 

in the introduction, more information is needed on 

tonal disturbances within the 10- to 100-Hz, 100- to 

1,000-Hz, and 1,000- to 10,000-Hz frequency ranges 

for tidal energy devices.

This workshop group also notes recent work on 

ship avoidance by fish, particularly in the context 

of fishery research vessels conducting surveys of 

fish populations. Quoting from Sund et al. (2008a), 

“it is emphasized that the otolith organs in fish are 

linear acceleration detectors with extreme sensitivity to infrasonic particle acceleration.” What does 

this mean? Audiograms for fish typically show a 

decreased sound-pressure hearing sensitivity with 

frequency for frequencies < 100 Hz (Sund et al. 

2008b). For particle acceleration, however, this 

would translate to a rather flat sensitivity (i.e., not 

decreasing), as discussed in Sund et al. (2008b). This 

issue needs to be understood in the context of the 

possibly very low, or infrasonic, emissions that could 

originate from tidal energy devices.
46

Approaches to Monitoring

Statistically reliable baseline estimates of 

1/3-octave band SPL are needed. This workshop 

group proposes that operation-based measurements 

should be made at a distance 10 m from center of the 

rotor at the hub height of the tidal energy device. The 

reasoning behind this is that the device is large in 

spatial extent (rotor diameters generally greater than 

5 m) and extrapolations to “1 m,” based on spherical 

spreading or some hybrid spreading law, are likely to 

be suspect.

Mitigation Measures

To the degree they exist, tonal disturbances would 

occur during operation, and there are few mitigation measures beyond basic device design (rotational 

speed, number of rotors, etc.).

3.4.6 Priority Area: Behavioral responses to

increases in broad band noise

Description

A significant increase in broad band noise associated with device operation is a concern. Referring 

to the introductory comments on the key frequency 

range of underwater noise associated with tidal 

energy production, the term broad band, therefore, 

necessarily implies the frequency range of 10-1,000 

Hz. This increase may or may not be uniform, but 

it would not be concentrated within a particular 

1/3-octave band (in which case, the noise would 

necessarily be viewed as narrow band). Because 

ordinary variation can result in 30-dB changes in 

broad band SPL (Tougaard et al. 2009), a significant 

increase needs to be at 30 dB, if not more.

Gaps in Understanding

The most significant gaps in understanding relate 

to how long the noise should be averaged and what 

constitutes a significant increase in broad band SPL as 

it relates to effects on animals, which may also differ 

between taxonomic groups. Unlike specific tones or 

very high transient pressure spikes, the impacts of 

an overall increase in broad band noise are less well 

known. To the extent they exist, it is this group’s 

opinion that the impacts will be limited to the Level B 

kind. A major gap in understanding is to what extent 

behavioral modifications due to increased broadband 

noise from tidal energy devices might affect population viability.

Approaches to Monitoring

Statistically reliable baseline estimates of 

1/3-octave band SPL are needed. To address the issue 

of time averaging, it is recommended that the time 

scale over which an average is made is 2 weeks, 

during which continuous averages are made at intervals 1 to 10 min.

Mitigation Measures

To the degree they exist, disturbances associated with broad band increases in noise would occur 

during operation, and there are few known mitigation 

measures beyond basic device design. 
47

3.4.7 Recommended References

Bassett, C. Thomson, J. and Polagye, B. 2010. Characteristics of Underwater Ambient Noise at a 

Proposed Tidal Energy Site. MTS/IEEE Oceans 

2010. September 20-23, 2010. 

Dahl, P.H., Miller, J.H., Cato, D.H. and Andrew, R.K. 

2007. Underwater Ambient Noise, Acoustics 

Today. 3(1): 23-33.

Frisk, G.V. 1994. Ocean and Seabed Acoustics: A 

Theory of Wave Propagation. Englewood Cliffs, 

NJ: Prentice Hall. 

Mueller-Blenkle, C., McGregor, P.K., Gill, A.B., 

Andersson, M.H., Metcalfe, J., Bendall, V., 

Sigray, P., Wood, D.T. and Thomsen F. 2010. 

Effects of Pile-driving Noise on the Behaviour of 

Marine Fish. Technical Report, COWRIE Ref: 

Fish 06-08. March 31 2010.

Richards, S.D., Hardland, E.J. and Jones, S.A.S. 

2007. Underwater Noise Study Supporting 

Scottish Executive Strategic Environmental 

Assessment for Marine Renewables. Technical 

report prepared for the Scottish Executive 

by QinetiQ Ltd., Farnborough, Hampshire. 

QINETIQ/06/02215/2.

Hawkins, A. 2008. Effects of Noise on Aquatic Life: 

the Key Issues. Bioacoustics. 17(1-3): 7-10.

Richardson, W.J., Greene, C.R., Malme, C.I. and 

Thomson, D.H. 1995. Marine Mammals and 

Noise. San Diego, CA: Academic Press.

Southall, B.L., Bowles, A.E, Ellison, W.T., Finneran, 

J.J., Gentry, R.L., Greene, C.R., Kastak, D., 

Ketten, D.R., Miller, J.H., Nachtigall, P.E., Richardson, W.J., Thomas, A. and Tyack, P.L. 2007. 

Marine Mammal Noise Exposure Criteria: Initial 

Scientific Recommendations. Aquatic Mammals, 

33(4): 411-521.

Sund, O., Karlson, H.E. and Knudsen. F.R. 2008. 

Comment on “Silent research vessels are not 

quiet” [2007. J. Acoust. Soc. Am. 121(4): 

EL145-EL150]. J. Acoust. Soc. Am. 123(4): 1831-

1833.

Sund, O., Enger, P.S., Karlson, H.E. and Knudsen, 

F.R. 2001. Detection of Infrasound in Fish and 

Behavioral Responses to Intense Infrasound in 

Juvenile Salmonids and European Silver Eels: A 

Minireview. In Behavioral Technologies for Fish 

Guidance, Coutant, C. (Ed.). American Fisheries 

Society Symposium 26: 183-193.

Strasberg, M. 1988. Dimensional analysis of windscreen noise. J. Acoust. Soc. Am. 83: 544-548.

Tougaard, T., Henriksen, O.D. and Miller, L.A. 2009. 

Underwater noise from three types of offshore 

wind turbines: Estimation of impact zones for 

harbor porpoises and harbor seals. J. Acoust. Soc. 

Am., 125: 3766-3773.
48

3.5 Electromagnetic Effects

3.5.1 Introduction

Tidal current turbines convert the kinetic energy 

associated with the current into rotary motion in order 

to drive a generator. The electricity that is generated 

may be conditioned at sea but, in all cases, will be 

transmitted to shore-based facilities via power cables. 

There are various options for connecting tidal current 

generators to an onshore electrical grid. For example, 

a pilot plant could involve an alternating current 

(AC) generator connected to an AC/DC/AC power 

electronic converter and a step-up transformer to 

the grid voltage, with power transmission via an AC 

cable. For a tidal farm, multiple AC generators could 

be connected to a step-up transformer through one or 

more AC/DC/AC power convertor(s) using AC cables 

and then to the grid at shore using AC cable again. 

There is also a possibility of connecting multiple 

AC turbines to an on-shore step-up transformer via 

alternating current/direct current (AC/DC — with the 

rectifier placed near turbine) and direct current/alternating current (DC/AC — with the inverter placed 

near the on-shore substation) power converters. In 

this scenario, a direct current (DC) cable between 

the power converters would need to be used. Most 

potential sites for pilot and commercial tidal current 

installations are expected to be located relatively close 

to the shore, implying that high-voltage AC power 

transmission (from a step-up transformer to a grid 

on shore) is the most likely scenario. However, some 

device developers have proposed rectification at the 

turbine to DC, transmission by DC cable, and inversion on-shore back to AC for grid connection. Tidal 

installation layout and the size of the power plant will 

vary according to the potential harvestable resource; it 

will be highly site specific.

A conductor carrying AC will produce simultaneous electric and magnetic fields with a frequency 

identical to the source current. However, the field 

induced by DC contains a static magnetic field only. 

The electrical fields are highly attenuated by the metal 

shielding around the cables. Although the magnetic 

fields penetrate most materials, their strength 

decreases with the square of distance from the cable. 

Potential sources of electromagnetic fields (EMFs) 

from the operation of either pilot or commercial 

operation of tidal current power plants are assumed 

to be from the generator and ancillary sub-systems, 

such as converters (power electronics), transformers, 

and power cables. Some generators, consisting of 

permanent magnets, are also thought to be potential 

sources of a magnetic field even when idle. Physical 

damage to the submarine cable of a tidal system, 

such as damage to shielding, could potentially cause 

leakage of an electrical field and this in turn could be 

a potential source for a magnetic field. 
49

The above-mentioned potential EMF contributions from the operation of tidal current power 

systems will add to the earth’s naturally occurring 

static geomagnetic magnetic field (that varies from 20 

to 75 micro Tesla, depending upon the location) and 

low magnitude and frequency (alternating) magnetic 

field generated by tidal motion (for example, on 

the seafloor offshore of Vancouver Island, British 

Columbia, CA, has a natural magnetic field of about 

0.02 micro Tesla with a 50 minute period). The 

marine environment already has many electrical 

cables used for power transmission, communications and other uses. Adding EMF signals from tidal 

devices and associated cabling must be compared 

against the existing fields. 

Electro-reception and magneto-reception have 

been documented in scientific literature for some 

species of fish and other aquatic animals (see recommended references at the end of this section). Almost 

all of these investigations have used fields that simulate those found in nature. A limited number of studies 

have been conducted in the offshore wind energy 

sector to identify the impacts of EMF on marine 

organisms, particularly focusing on the submarine 

power cables (Gill et al. 2005). In most cases, the 

studies focused on animal behavior in mesocosms 

(experimental enclosures designed to approximate 

natural conditions) near conductors. Even though 

various species were found to be sensitive to EMF, 

their specific behavioral and physiological responses 

could not be established. Also, there is lack of sensitivity threshold data for the relevant marine species 

where some of the tidal projects are being planned. 

Certain marine species are electro-sensitive 

while others are magneto-sensitive. For example, 

finfish, eels, sharks, and sea turtles use the earth’s 

DC magnetic field for orientation, navigation, and 

migration (Kirschvink et al. 2001), while weak electric fields can be exploited by certain fishes (rays, 

sharks) for orientation and prey location. Physiological impacts, such as mortality or reproductive 

success, may be dominant for some of these organisms, whereas behavioral responsiveness, like migration or colony formation, may appear more critical 

for others. The duration (short to long-term) and type 

of exposure (e.g., DC/AC, steady-state/transients, 

etc.) may form another layer of complexity.

A matrix of stressor/receptor interactions, their 

significance, and uncertainty is given in Figure 18 

for pilot-scale deployments and in Figure 19 for 

commercial-scale deployments. The colors denote 

significance and triangles denote uncertainty, as 

defined in Figure 10.
50

3.5.2 Stressor Matrix

Figure 19 – Stressor matrix: Electromagnetic effects – commercial-scale deployments

Figure 18 – Stressor matrix: Electromagnetic effects – pilot-scale deployments
51

3.5.3 Discussion

The group discussed the likelihood of effects of 

the above stressor elements on the following receptors: near-field and far field physical environment, 

habitat, migratory fish, resident fish, marine mammals 

and seabirds, and ecosystem/food chain interactions. 

In terms of the likelihood of effects of the EMF 

from the devices and power electronics on the near 

field physical environment, these are unknown. It is 

thought that the stressor elements are likely to have 

no effect on the far-field physical environment. The 

EMFs from the device and power electronics are 

likely to have low effect on habitats; however, EMF 

from AC and DC power cables are likely to have low 

to medium effect with high degree of uncertainty. 

Electric field leakage due to cable shield damage is 

thought to have a low effect. Depending upon the 

spatial layout of the devices and the cables, the EMF 

stressor elements could have low (for pilot-scale) 

to high (for commercial-scale) effects on migratory species. The EMF effects on resident fishes are 

thought to be similar to that of the migratory fish. 

The stressor elements are likely to have a low effect 

on marine mammals and seabirds. The likelihood of 

effect of the EMF from the tidal plant operation on the 

ecosystem interactions is thought to be low for pilot 

plants and low to medium with high uncertainty for 

commercial array operation. 

3.5.4 Priority Area: 

Quantifying EMF from devices (operating and idle)

Description

Knowledge of expected level of EMF from 

pilot and commercial tidal plants will be essential in 

developing any necessary monitoring and mitigation 

strategy.

Gaps in Understanding

From the group discussion, as well as from the 

literature, it is very clear that state of knowledge on 

the EMF contributions from any tidal current power 

generation systems (generator, power electronics) 

is nonexistent in the public literature. There is some 

information in the public domain on EMF contributions for power cables to shore from offshore wind 

energy analogues (e.g., Gill et al. 2005). 

Approaches to Monitoring

In a laboratory environment, it is possible to 

measure both magnetic and electric fields. Laboratory 

studies of magnetic and electric fields around cables 

may be effective at bounding the field strengths for 

different array sizes and configurations. These could 

be correlated against sensitivity thresholds for various 

species to provide a coarse estimate of the potential 

for significant interaction. 

Given the high degree of uncertainty for this 

stressor, magnetic fields around some existing tidal 

current demonstration projects should be measured in 

cooperation with technology and project developers. 

Initially, measurements around the power take-off 

cables are likely to be most tractable. At-sea measurements of the electric and magnetic fields are possible 

but they do require appropriately constructed and 

calibrated instruments. For electric fields, the components need to be low noise and the electronic circuit 

has to have an appropriate 0 V reference, which has 

been calibrated and recorded both before deployment and after recovery from the field. The longer the 

instruments are deployed the more likely the electric 

field measurements will be relative rather than a 

true reflection of the emitted fields. Furthermore, the 

changing tidal water movement and organism movement will induce localized electric fields around the 

tidal device and in relation to the geomagnetic field, 

hence the measurements should be related to the tidal 

regime and the geometry of the measurements should 

be closely considered. Measurements of the magnetic 

field will also be challenging. The magnetic field will 

vary with the power generated by the device and, 

therefore, would need to be profiled over the tidal 

cycle. Given the strength of tidal currents at utilityscale sites, profiling with an ROV is not likely to be 

feasible. Multiple magnetometers would need to be 

deployed on a static frame, or a single magnetometer 

could be actuated along a track by a motor (which 

would require calibration in a magnetically quiet 

laboratory environment to account for the motor’s 

magnetic field). Clearly, this presents a number 

of non-trivial engineering problems, which are 

compounded by a lack of protocols for EMF measurements of device components. 
52

Modeling studies to determine the expected 

level of EMF in the vicinity of tidal current pilot/

commercial project developments must be carried out, 

with necessary inputs from technology and project 

developers familiar with the design and cable layouts. 

Results from modeling and measurements could be 

compared for validation.

Mitigation Measures

Mitigation strategies that reduce the level of EMF 

contributions from the operation of tidal plants to the 

marine environment as well as strategies that reduce 

or avoid exposure of aquatic animals to EMF from 

tidal developments were briefly discussed among 

the group. For an example, peak flux of magnetic 

fields from submarine cables can effectively be 

reduced by burying them. However, burying cables, 

rather than laying them on the seabed, would result 

in greater environment disturbance during installation and may be technically challenging for hard 

substrates (bedrock, cobbles). Some studies have 

shown that core twisting or laying separate AC cables 

in close proximity to each other would decrease the 

induced magnetic fields (Pettersson and Schönborg 

1997). This may also be accomplished by laying two 

DC cables of opposing polarity in close proximity 

(Öhman et al. 2007). 

The mitigation strategies must first use modeling 

to assess various design options at the pre-installation 

stage. This would provide an estimate of the potential 

EMF that a device/system (including cabling) would 

produce. The strategies would also require having a 

knowledge of assessing risk and potential of severity 

of EMF effect (to the extent they are known) on 

relevant aquatic animal for a particular site. 

3.5.5 Priority Area: 

Characterizing the types of electric and magnetic 

thresholds for different sensitive organisms 

relevant to sites

Description

In order to understand how the relevant marine 

life might be affected from the expected EMF levels 

and attributes, it is essential to establish relevant 

threshold values as well as behavioral responses to 

relevant EMF doses.

Gaps in Understanding

From the group discussion, it was very clear that 

the state of knowledge on the detection threshold of 

EMFs by some relevant fish species is very limited, 

including their behavioral responses to relevant EMF 

exposures that tidal development could generate. Due 

to the uncertainty in the significance of the effect, 

studies to monitor behavioral changes in response to 

EMF are not often carried out in the field.

Approaches to Monitoring

Controlled experimental investigations (Underwood 1992, Westerberg and Langenfelt 2008, Gill et 

al. 2009) should be carried out to establish relevant 

knowledge. These could involve catch and release or 

tagging studies (passive and active) for large, mobile 

species and caged organism studies for younger life 

stages or sessile organisms.
53

3.5.6 Recommended References

Bhuyan, G. 2010. World-wide status for harnessing 

ocean renewable resources. IEEE Power and 

Energy Society ES General Meeting. Minneapolis, 

MN, July 25-29, 2010.

Bullock, T.H, Hopkins, C.D., Popper, A.N. and Fay, 

R.R. (Eds.). 2005. Electroreception. New York, 

NY: Springer. 

Charlier, R. and Justus, J. 1993. Ocean Energies: 

Environmental, Economic, and Technological 

Aspects of Alternative Power Sources. New York, 

NY: Elsevier.

Collin, S. and Marshall, N.J. (Eds.). 2003. Sensory 

Processing in Aquatic Environments. New York, 

NY: Springer.

European Wind Energy Association. 2009. Chapter 

5: Environmental Impacts. In Wind Energy - The 

Facts. London, UK: Earthscan. 

Gill, A., Gloyne-Phillips, I., Neal, K. and Kimber, J. 

2005. The potential effects of electromagnetic 

fields generated by sub-sea power cables associated with offshore wind farm developments on 

electrically and magnetically sensitive marine 

organisms – A review. Final report prepared for 

Collaborative Offshore Wind Energy Research 

into the Environment (COWRIE) group. 

COWRIE-EM FIELD 2-06-2004. 

Hara, T. and Zielinski, B. 2007. Sensory Systems 

Neuroscience. New York, NY: Elsevier.

Kajiura, S. and Fitzgerald, T. 2009. Response of 

juvenile scalloped hammerhead sharks to electric 

stimuli. Zoology, 112: 241-250. 

Kajiura, S. 2003. Electroreception in neonatal bonnethead sharks, Sphyrna tiburo. Marine Biology, 143: 

603-611.

Kajiura, S. and Holland, K.N. 2002. Electroreception 

in juvenile scalloped hammerhead and sandbar 

sharks. Journal of Experimental Biology, 205(23): 

3609-3621.

Kajiura, S. 2001. Head morphology and electrosensory 

pore distribution of carcharhinid and sphyrnid 

sharks. Environmental Biology of Fishes, 61(2): 

125-133.

Kalmijn, A.J. 1971. The electric sense of sharks 

and rays. Journal of Experimental Biology, 55: 

371-383.

Kalmijn, A.J. 1984. Theory of electromagnetic orientation: A further analysis. Comparative Physiology 

of Sensory Systems, 525-560.

Kay, J. 1997. Equipment development for the 

measurement of underwater multi influence fields. 

IPENZ Transactions, 24(1/GEN): 48-63.

Khan, M.J. and Bhuyan, G. 2009. Ocean Energy: 

Global Technology Developmental Status. Technical Report for the International Energy Agency 

- Ocean Energy Systems prepared by PowerTech 

Labs Inc., IEA-OES T0104.

Khan, M.J, .G. Bhuyan, Iqbal, M.T. and Quaicoe, J.E. 

2009. Hydro kinetic energy conversion systems 

and assessment of horizontal and vertical axis 

turbines for river and tidal applications: A technology status review. Applied Energy, 86(10): 

1823-1835.

Kirschvink, J.L. 1997. Magnetoreception: homing in 

on vertebrates. Nature, 390: 339-340.

Kobayashi, A. and Kirschvink, J.L. 1995. Magnetoreception and electromagnetic field effects: Sensory 

perception of the geomagnetic field in animals and 

humans. Electromagnetic Fields, 250: 367-394.

Koeller, J., Koeppel, J. and Peters, W. (Eds.). 2006. 

Chapter 14: Effect of Electromagnetic Fields on 

Marine Organisms. In Offshore Wind Energy: 

Research on Environmental Impacts. New York, 

NY: Springer. 223-234.

McGowan, D.W. and Kajiura, S.M. 2009. Electroreception in the euryhaline stingray, Dasyatis 

sabina. Journal of Experimental Biology, 212: 

1544-1552.

Meyer, C.G., Holland, K.N. and Papastamatiou, Y.P. 

2004. Sharks can detect changes in the geomagnetic field. J.R. Soc. Interface, 2005(2): 129-130.

Öhman, M.C., Sigray, P. and Westerberg, H. 2007. 

Offshore Windmills and the Effects of Electromagnetic Fields on Fish. Ambio 36(8): 630-633.
54

Paulin, M.G. 1995. Electroreception and the compass 

sense of sharks. Journal of Theoretical Biology, 

174: 325-339

 Petersen, J.K. and Malm, T. 2006. Offshore Windmill 

Farms: Threats to or Possibilities for the Marine 

Environment. Ambio 35(2): 75-80.

Pettersson, P. and Schönborg, N. 1997. Reduction of 

Power System Magnetic Field by Configuration 

Twist. IEEE Transactions on Power Delivery, 

12(4): 1678–1683.

Tesch, F.W., Wendt, T. and Karlsson, L. 1992. Influence of geomagnetism on the activity and orientation of eel, Anguilla anguilla, as evident from 

laboratory experiment. Ecology of Freshwater 

Fish, 1: 52-60.

Walker, M.M., Dennis, T.E. and Kirschvink, J.L. 2002. 

The magnetic sense and its use in long-distance 

navigation by animals. Current Opinion in Neurobiology, 12: 735-744.

Walker, M.M., Diebel, C.E., Haugh, C.V., Pankhurst, 

P.M., Montgomery, J.C. and Green, C.R. 1997. 

Structure and function of the vertebrate magnetic 

sense. Nature, 390: 371-376.

Westerberg, H. & Langenfelt, I. 2008. Sub-sea power 

cables and the migration behaviour of the European eel. Fisheries Management and Ecology, 15: 

369-375.
55

3.6 Energy Removal

3.6.1 Introduction

Energy removal by hydrokinetic turbines may 

cause regional changes in the tidal regime because the 

existing regime and environment are, in large part, 

established by the natural removal of energy by friction and turbulence. Consequently, energy removal at 

a particular location will affect (augment or reduce) 

tides, currents, and mixing throughout a waterbody. 

These changes are strongly site-specific and depend 

on where power is extracted within a particular 

system. For example, removing the same amount of 

average power from two different sites in the same 

body of water may lead to very different effects on the 

far-field physical environment (Polagye et al. 2009). 

This stressor is common for all hydrokinetic devices, 

although aspects of the device (e.g., foundation and 

support structure) can alter the fraction of energy 

removed that is converted to useful electrical power.

Although energy removal effects are not readily 

generalized, changes to currents are sometimes related 

to the work done by the tide. Blanchfield et al. (2008) 

give an equation for the maximum power extractable 

(Pmax) from a narrow channel linking an enclosed bay 

to the open ocean as 

where ρ is the density of seawater (nominally 1,024 

kg/m3

), g is the acceleration due to gravity (9.81 m/

s2

), a is the tidal amplitude seaward of the narrow 

channel, and Q is the flow rate in the channel without 

extraction. The term γ is a constant that depends on 

the properties of the narrow channel and may be 

estimated by methods described in Blanchfield et al. 

(2008) or Karsten et al. (2008). For the simple case 

described above, the value of γ varies between 0.19 

and 0.26. However, extending this relation to more 

complicated channel networks has been shown to be 

non-trivial (Polagye and Malte, 2010).

 A number of national resource assessments 

attempt to relate far-field effects from energy removal 

to the naturally occurring kinetic power on a channel 

cross section. One assumption, made prior to detailed 

investigation (e.g., Bedard et al. 2006), was that 

extracting 15% of the kinetic power on a cross section 

represented an “environmentally acceptable” level of 

extraction. It has since been rigorously demonstrated 

(Garrett and Cummins, 2008), that the theoretical 

resource and, by extension, environmental effects 

of extracting kinetic power are unrelated to crosssectional kinetic power. However, this misconception 

persists.

Analytical models (e.g., Garrett and Cummins 

2007) and numerical models (e.g., Karsten et al. 

2008) have been applied to study energy removal. 

There have been no attempts at physical modeling to 

date, although such studies are planned under DOEsponsored research programs at the national Labs. 
56

At a large scale, the effects of energy removal 

can be significant. For example, Karsten et al. (2008) 

estimate that extracting the theoretical limit of 7 GW 

of power would result in greater than 30% changes to 

tidal range in the Minas Basin in the Bay of Fundy. 

However, extracting 4 GW of power would change 

the tidal range by less than 10% and 2.5 GW could 

be extracted with less than a 5% change. Changes to 

tides and currents could affect water temperature, the 

behavior of some migratory fish, water quality, and 

sediment transport (DOE 2009). At the pilot scale, 

effects are expected to be immeasurably small. For 

example, a numerical model of a pilot project in 

northern Admiralty Inlet, Puget Sound (Polagye et al. 

2009) suggests a maximum range reduction of 0.2 mm 

(the thickness of two human hairs) in South Sound. 

This is well within the range of modeling uncertainty, 

inconsequential in comparison to natural variability, 

and immeasurably small. 

3.6.2 Stressor Matrix

No significant effects from energy removal 

are expected at the pilot scale (Karsten et al. 2008, 

Polagye et al. 2009). Because the energy removal 

stressor applies, by definition, to regional scales, it is 

not applicable to discuss the effect of this stressor on 

the near-field physical environment. The significance 

and uncertainty associated with stressor/receptor 

interactions at commercial scale are summarized in 

Figure 20. The colors denote significance and triangles denote uncertainty, as defined in Figure 10. 

Figure 20 – Stressor matrix: Energy removal –commercial-scale deployments
57

3.6.3 Discussion

Because energy removal is unlikely to result in 

any detectable changes at the pilot scale, this discussion focuses on commercial-scale deployments. 

Further, there is an emphasis on estuarine sites (e.g., 

Puget Sound) rather than open-ocean sites (e.g., Aleutian Islands, Alaska).

There is high uncertainty regarding the significance of energy removal, because the effects depend 

strongly on the particular stressor element, the natural 

tidal regime, and the estuarine environment. The 

specific elements of the energy removal stressor are 

changes to:

• Tidal range;

• Transport/discharge (residence time or flushing 

rate);

• Turbulent dissipation and boundary layer structure; and

• Wave energy regime – depending on the specific 

wave-current interaction.

Figure 21 – Far-field environment detail for energy removal stressor

The far-field physical environment is expected 

to be most significantly affected by energy removal. 

For the purposes of discussion, the far-field physical 

environment is separated into five areas:

• Sediment transport – significance depends on the 

sediment loading in the natural system;

• Exchange circulation – significance depends on 

the degree of stratification in the natural system;

• Water quality – significance depends on nutrient 

inputs to the natural system and residence time;

• Biological productivity – significance depends 

on nutrient inputs and oxygen availability in the 

natural system; and

• Intertidal area – significance depends on the intertidal area slopes in the natural system. 

The significance and uncertainty for stressor/

receptor combinations amongst these elements varies, 

as shown in Figure 21.
58

Habitat may be affected through changes to 

intertidal areas, changes in nutrient availability for 

kelp and eelgrass, disruption of upwelling, or dispersion of sediment. There is a high degree of uncertainty, because these conditions are site-specific. For 

example, vegetation in intertidal areas can be sensitive 

to small changes in the tidal range, but organisms that 

live on rocky walls are more adaptive to changes.

Direct effects on migratory fish are limited to 

relatively extreme cases in which a reduction in 

tidal range would make a river inaccessible (i.e., 

by creating a waterfall) or if the vertical structure 

of the water column were to change substantially 

(confounding the ability of migratory fish to navigate). The direct effects on resident fish are limited to 

larval dispersion, due to changes in transport. Energy 

removal would not be expected to have significant 

direct effects on marine mammals and seabirds.

Because of the potential changes to the far-field 

physical environment and habitat, ecosystem interactions could be significant but are largely unstudied. 

Better engagement between tidal energy practitioners and physical oceanographers is needed. For 

example, some physical oceanographers are now 

investigating estuarine dynamics from the standpoint of energy input to the system (e.g., Warner and 

MacCready 2009). There may be analogues to energy 

removal by tidal turbines.

3.6.4 Priority Area: 

Changes to the far-field physical environment 

and habitat

Description

The hydrodynamic regime in an estuary is 

established, in large part, by the dissipation of tidal 

energy. Other environmental parameters (temperature, salinity, dissolved oxygen, and nutrients) are a 

function of the hydrodynamic regime and inputs to 

the system. Habitat follows from the hydrodynamic 

regime and environmental parameters. Hydrokinetic 

tidal energy conversion involves local removal of 

energy, thereby altering the hydrodynamic regime 

throughout the system. At the pilot scale, these effects 

will be immeasurable. However, at larger scales 

of development, changes may be environmentally 

significant. Environmental effects, such as changes 

to intertidal areas, are not likely to scale smoothly 

with extraction. “Tipping points” are to be expected, 

whereby a small increase in extraction will result 

in a disproportionately large change to the far-field 

physical environment or habitat. Two examples are 

given here, although others could likely be identified. 

First, incremental reductions in the tidal range that 

may initially have little effect could, beyond a certain 

point, isolate intertidal habitat by permanently inundating or drying out surrounding areas (e.g., reduction 

in range leading to a landlocked tide pool). Second, 

while low levels of extraction would not be expected 

to alter deep saline intrusions into fjord estuaries, 

there may be a point where the resistance posed by 

tidal turbines could prevent these intrusions from 

crossing the sill, with significant consequences for 

dissolved oxygen and water quality in parts of these 

ecosystems.

Gaps in Understanding

There is a growing body of knowledge pertaining 

to the hydrodynamic effects of energy removal (e.g., 

Blanchfield et al. 2008, Karsten et al. 2008, Polagye 

et al. 2009). Results are site-specific, and connecting 

changes in hydrodynamic conditions to other aspects 

of the physical environment is nascent. Neill et al. 

(2009) contains an example pertaining to sediment 

transport. To date, no attempts have been made to 

assess the implications for water quality or biological 

productivity. These are nonlinear processes that are 

difficult to model, even in natural systems.

Approaches to Monitoring and Closing Gaps

A principal challenge is that an understanding 

of the environmental effects of energy removal does 

not scale up from observations at the pilot scale (i.e., 

putting a device in the water will not reduce uncertainties). The available tools to close these gaps are 

also imperfect. Numerical models are an obvious 

choice but, at the estuary scale, tuning for calibration, 

boundary conditions, and an inability to validate a 

predicted change are all problematic. Physical models 

might be used for focused, qualitative investigations, but scale distortions (e.g., vertical exaggeration, Reynolds number) will complicate quantitative 

studies. A third approach is the use of basic physical 

arguments to describe how changes to the natural 
59

system might scale with extraction. However, 

relating these conclusions to real systems may be 

challenging, particularly when scaling is subject to 

large uncertainties. Fourth, an experiment could be 

conducted in a small bay linked to the ocean by a 

narrow channel, where the effects of energy removal 

might be observed from the operation of a small array. 

However, the cost to carry out such an experiment 

would be very high.

Initial research for a particular site should focus 

on establishing order or magnitude hydrodynamic 

changes at different levels of extraction, with the 

effect on particular receptors addressed by smaller, 

focused studies. Not all potential tidal energy sites in 

the United States have well-calibrated models for this 

type of study. Puget Sound, the nation’s East Coast, 

and San Francisco Bay are reasonably well described, 

but Cook Inlet is poorly characterized and is in a 

constant state of flux because of its extremely high 

sediment loads and ice scour of the seabed.

Monitoring for changes to the far-field physical 

environment may be problematic, even for commercial installations. For example, measurements of tidal 

range (easier to obtain than for dissolved oxygen or 

turbulent dissipation) are confounded by long-term 

natural changes such as isostatic release and climatic 

variability. Range changes of less than 10 cm may not 

be statistically significant, compared to natural variations.

Mitigation Measures

A number of mitigation measures may be 

possible with respect to design and operation of tidal 

turbines.

Changes to the far-field environment depend on 

the power dissipated by hydrokinetic turbines. This 

includes the power extracted for electrical generation, 

power lost when the device’s wake mixes with the 

free stream, and power loss due to drag on the device 

support structure. Wake mixing losses are unavoidable, but scale with device efficiency (i.e., the higher 

the efficiency, the slower the wake, and the greater 

the shear between wake and free stream). While 

arrays with high blockage ratios are most efficient/

economic (Garrett and Cummins 2007), they also lead 

to the greatest wake mixing losses. Losses due to drag 

on device support structures can be minimized by 

streamlined designs (Polagye 2009), which should be 

considered a best practice.

The highly variable nature of estuaries means 

these environments may be more sensitive to stressors 

under certain conditions or during certain times of the 

year or both. While specific recommendations cannot 

be made at this point, device operators may consider 

adapting patterns of device operation according to the 

season and prevailing conditions to minimize impact 

on the far-field marine environment (e.g., shutting 

down an array during annual deep saline intrusions 

over sills in fjord estuaries).

Once the development is in place, it may be 

difficult to mitigate negative effects of tidal energy. 

For example, hypoxic conditions in a terminal estuary, 

resulting from diminished flushing due to energy 

extraction, may be ameliorated by bubbling oxygen 

directly through the water (as is sometimes done in 

stagnant ponds); however, such an operation would 

require significant installation costs, additional materials, and increased energy expenditure. This energy 

expenditure could potentially be more than offset by 

reducing the energy removal (e.g., by increasing the 

cut-in speed of the array), if this action alone could 

restore the system’s oxygen balance. Thus, quantifying the effects of energy removal should be thought 

of as an aspect of development feasibility and should 

be taken into consideration early in the process if 

the size of a proposed project is expected to be large 

enough in scale to have environmentally significant 

far-field effects.
60

3.6.5 Priority Area: 

Potential for ecosystem interactions

Description

At large scales of development, energy removal 

may alter the hydrodynamic regime and change 

the far-field physical environment and habitat. In 

turn, migratory and resident fish could be affected. 

Consequently, there are opportunities for significant 

ecosystem interactions.

Gaps in Understanding

The linkages between receptors and aspects 

of their environment are poorly understood. For 

example, although changes to water transport (residence time and flushing rate) might lead to algal 

blooms and anoxic conditions, the factors contributing 

to algal blooms in natural systems are not well-understood. Even when a linkage is clear, effects will be 

site-specific and subject to uncertainty and variability.

Approaches to Monitoring

This is an active area of research in the coastal 

and estuarine community. Monitoring a myriad set of 

parameters to identify interactions is not expected to 

be a productive or economically feasible approach. 

A sensible approach may be to identify key environmental tipping points in advance of array build-out 

and focus a targeted monitoring program on these 

aspects of the marine environment. As an example of 

a tipping point, in San Francisco Bay, California, algal 

blooms are sensitive to small changes to circulation 

and water quality. This could be exacerbated by relatively low levels of energy removal by tidal turbines.

Along these lines, it would be helpful to quantify existing, natural variability in the hydrodynamic 

regime and the ecosystem response to this variability. 

If the changes anticipated from energy removal are 

much smaller, then they are unlikely to have a significant effect.

Mitigation Measures

Mitigation measures are identical to those previously discussed for changes to the physical environment and habitat.
61

3.6.6 Recommended References

Atwater J.F. and Lawrence, G.A. 2010. Power potential of a split tidal channel. Renewable Energy,

35: 329-332.

Bedard, R., Previsic, M., Polagye, B., Hagerman 

G. and Casavant A. 2006. North America Tidal 

In-Stream Energy Conversion Technology 

Feasibility Study. Palo Alto, CA: Electric Power 

Research Institute. EPRI TP-008-NA.

Blanchfield, J., Garrett, C., Wild, P. and Rowe, A. 

2008. The extractable power from a channel 

linking a bay to the open ocean. Proc. IMechE, 

Part A: J. Power and Energy 222(3): 289-297.

DOE (U.S. Department of Energy Energy). 2009. 

Report to Congress on the Potential Environmental Effects of Marine and Hydrokinetic 

Energy Technologies: Prepared in Response to 

the Energy Independence and Security Act of 

2007, Section 633(B). Wind and Water Power 

Program, Energy Efficiency & Renewable 

Energy, U.S. Department of Energy. December 

2009.

Garrett, C. and Cummins, P. 2007. The efficiency of 

a turbine in a tidal channel. J. Fluid Mechanics, 

588: 243-251.

Garrett, C. and Cummins, P. 2008. Limits to tidal 

current power. Renewable Energy, 33(11): 2485-

2490.

Karsten, R.H., McMillian, J.M., Lickley, M.J. and 

Haynes, R.D. 2008. Assessment of tidal current 

energy in Minas Passage, Bay of Fundy. Proc. 

IMechE, Part A: J. Power and Energy 222(5): 

493-507.

Neill, S.P., Litt, E.J., Couch, S.J. and Davies, A.G. 

2009. The impact of tidal stream turbines on 

large-scale sediment dynamics. Renewable 

Energy, 34(12): 2803-2812.

Polagye, B.L. 2009. Hydrodynamic effects of kinetic 

power extraction by in-stream tidal turbines. PhD 

thesis, University of Washington, Seattle, WA.

Polagye, B.L., Kawase, M. and Malte, P.C. 2009 

In-stream tidal energy potential of Puget Sound, 

Washington. Proc. IMechE, Part A: J. Power and 

Energy, 223(5): 571-587.

Polagye, B.L. and Malte, P.C. 2010. Far-field 

dynamics of tidal energy extraction in channel 

networks. Renewable Energy, 36(1): 222-234.

Warner, S.J. and MacCready, P. 2009. Dissecting the 

pressure field in tidal flow past a headland: When 

is form drag “real”?. J. Phys. Ocean. 33(11): 

2971-2984.
62

3.7.1 Introduction

Methods for assessing the potential cumulative 

impacts of tidal devices on elements of the receiving 

environment is nebulous, given the current lack of 

knowledge about the real effects of individual stressors 

on receptors. Assessing cumulative impacts is challenging, even for more mature power generation 

technologies (e.g., terrestrial wind power, conventional 

hydropower). Data that indicate the effects of individual stressor elements on receptors are needed in 

order to inform the assessment of cumulative impact. 

Until such data are available, any models or hypothetical assessments will be limited in usefulness.

There are many uncertainties associated with the 

notion of “cumulative impact” and the boundaries 

that may, in practice, be used to define the extent of 

the receiving environment. Political boundaries are 

rarely relevant from an ecological perspective, and a 

meaningful cumulative impact analysis may sometimes 

need to cross state or national boundaries — and even 

oceans. Adopting a typical project-based approach to a 

cumulative impact analysis is likely to limit the usefulness of its findings, but this will depend on the level of 

existing and planned development within the affected 

area. A high-level, large-scale Strategic Environmental 

Assessment may be the best way to ensure that cumulative effects associated with oceanographic processes 

that operate over much larger systems than the development site and with externalities such as interactions with 

other resource uses and users are identified. In-depth 

ecosystem modeling is needed, but models need to be 

informed by realistic data on patterns of interactions.

It is recognized that the term cumulative impacts

may refer to:

• Scaled-up effects of individual (tidal device 

installation, operation, and decommissioning) 

stressors on receptors. This would occur in scaleup from pilot to commercial installations or from 

multiple devices installed within a geographically 

identifiable subunit (i.e., an estuary).

• Synergies among different combinations of 

stressors (tidal device installation, operation, and 

decommissioning) and receptors; and

• Synergies among the two previously cited definitions, together with other anthropogenic influences and other externalities.

For the purposes of this discussion, cumulative 

impact should be viewed as the potential impact on a 

receptor, caused by synergistic effects of individual 

stressors (i.e., the second definition). Viewed in this 

way, three main areas of concern can be identified. 

The significance and uncertainty associated with 

stressor/receptor interactions are summarized in 

Figure 22 for pilot-scale deployments and in Figure 

23 for commercial-scale deployments. The colors 

denote significance and triangles denote uncertainty, 

as defined in Figure 10.

3.7 Cumulative Effects
63

3.7.2 Stressor Matrix

Figure 23 – Stressor matrix: Cumulative effects – commercial-scale deployment

Figure 22 – Stressor matrix: Cumulative effects – pilot-scale deployment
64

The near field is defined as being within the same 

geographically identifiable subunit, while far-field is 

defined as being outside the subunit.

3.7.3 Discussion

Three top-priority issues have been identified: 

• Effects on large mobile species; 

• Effects caused by energy change in the receiving 

environment; and 

• The difficulty of predicting, detecting and attributing effects and changes to receptors.

3.7.4 Priority Area: 

Effects on large mobile species

Description

Perhaps the primary concern with respect to 

cumulative impacts is the potential for damage to 

large and migratory fish, marine mammals, and 

seabirds. Damage includes collision with underwater 

moving parts and indirect harm, such as deleterious 

behavioral change (e.g., displacement), that may be 

caused by the physical presence of a device or array 

of devices and any outputs from such devices. Such 

potentially harmful outputs may include sound and 

vibrations, electromagnetic field induced along cables, 

or chemical leaching (although this third output seems 

relatively low-risk). 

Although the effects on large mobile species is 

seen as a key concern amongst regulators and some 

expert stakeholders, real data are urgently needed in 

order to assess the extent of these effects.

The potential for collision between large mobile 

species and rotating blades or other moving parts 

is unknown. Until early test devices are monitored, 

speculation will continue on whether or not there is a 

significant risk of direct or indirect damage to these 

species. Large and migratory fish, marine mammals, 

and seabirds are sensitive species that often occur 

in locations where tidal energy development can be 

expected and these species are protected in many 

such areas. Their sensitivity derives partly from the 

areas over which they range (i.e., they have a high 

probability of encountering a device), their body size 

(i.e., that they have a high probability of colliding 

with such a device if encountered), and their slow 

rates of population recovery to compensate for losses 

that could occur as a result of collision. An important feature of many of these species is that even 

very low rates of attrition caused by these devices 

(which may be beyond our capacity to measure with 

current methods) may lead to long-term declines in 

these species. Consequently, declines may be difficult 

to correlate with direct or indirect effects of these 

devices. This means that considerable precaution is 

needed in the form of the design and placement of 

devices that are aimed at total avoidance of effects. 

In order to begin to predict, let alone understand, 

the potential for damage at a cumulative level, the 

tidal energy industry needs to be informed of the 

actual effects of the individual stressor elements on 

these species. For example:

• Do different species actually collide with moving 

underwater blades? 

• Are these species attracted by devices? 

• Is there damage caused to hearing organs attributed to acoustic output from installation (e.g., any 

pile-driving required) or decommissioning?

• Do devices produce any discernible acoustic 

output that might cause displacement and 

possible secondary (i.e., consequential) harm to 

these species?

• What is the potential for large arrays of devices to 

produce a barrier effect with consequent harm to 

key species? 

Gaps in Understanding

Although little data exist from tidal device 

operation, those available provide no evidence of 

harm caused to large mobile species. More data need 

to be collected from different types of devices and 

in varying locations in order to establish confidence 

levels. However, testing is still at a very early stage 

and at small scales of construction. There is a high 

level of certainty that low levels of attrition, which 

may not be measureable, will cause population 

declines.
65

Further, it is unclear whether any effects would 

be non-linear (i.e., not strictly additive) and whether 

there are thresholds (e.g., the threshold between 

laminar and turbulent flow) beyond which the system 

behaves differently.

Adopting a “deploy and monitor” strategy with 

respect to early test developments will allow devices 

to be placed in the water, installed, operated, and 

monitored. Funding will be required to enable these 

deployments to progress and to monitor for stressors 

(e.g., acoustic output, collision events, strandings). 

This will ensure that mitigation methodologies are 

developed alongside device development.

Approaches to Monitoring

Wherever possible, monitoring should be 

conducted according to agreed methodologies, 

ensuring that the purpose of the data gathering is: 

clearly defined and consistent with other deploy-andmonitor schemes. It is also important that monitoring 

protocols not be changed during the program, so that 

variables being monitored can be validly compared 

over time. If new monitoring technologies or protocols become available after the start of monitoring, 

it will be important to assess critically whether the 

original protocols should be continued in parallel with 

the new ones in order to ensure continuity of record.

There are early stage monitoring programs in 

place in some locations (e.g., European Marine 

Energy Center (EMEC), Strangford Lough, Minas 

Basin) that use protocols and standardized protocols 

under development (e.g., Equimar or Scottish Natural 

Heritage Web sites ). Care should be exercised to 

ensure that all relevant work elsewhere with respect to 

monitoring protocols is taken into account. This will 

ensure consistency of approaches, where possible.

Radiotelemetry and sonar or acoustic imaging 

may be useful. There should be careful collection 

of baseline data before installation takes place, in 

order to be able to determine the change in the effects 

monitored.

Mitigation Measures

The adoption of a “deploy and monitor” strategy 

is the main way to gather data on actual device-biota 

interactions and to design future mitigation techniques. However, the high levels of uncertainty make 

it necessary to develop mitigation on the assumption 

that it is required.

Such deploy-and-monitor strategies should begin 

at a small scale and increase incrementally from pilot 

to commercial scale, monitoring carefully at each 

step. Any required design changes would then be 

implemented (e.g., blade design, shrouding, grating to 

avoid or minimize strikes and noise). 

Other methods of mitigation include careful 

site selection or limiting the number of devices in a 

given location until the effect of their operation is 

sufficiently understood. This limit will be site- and 

device-specific.

3.7.5 Priority Area: Effects of energy removal

Description

Long-term, large-scale extraction of energy from 

tidal currents may cause changes to water quality, 

including both physical and biological parameters. 

Any such changes may affect sensitive or susceptible 

habitats, with significant scope for potential secondary 

effects driven by habitat change. These effects are 

likely to have non-linear characteristics and contain 

critical thresholds (also described in 3.6 – Energy 

Removal).

It is thought to be unlikely that cumulative energy 

removal from tidal flow at specific locations will 

cause any detectable change in overall global flow 

strengths and rates; however, local habitat change and 

any cumulative consequences may have significant 

ecological effects.
66

Gaps in Understanding

Without any data on which to base discussions, it 

is impossible to progress any further than conjecture 

on this issue. The effects of energy removal are sitespecific. This is an issue that could potentially benefit 

from more detailed modeling, but such models do 

require actual data as input for validation.

Comparison of energy levels upstream and 

downstream of arrays of tidal devices and analysis 

of energy content of the tidal stream flowing through 

the devices in an array may be useful to establish 

the amount of energy removed from the flow (power 

extraction, wake mixing, drag on support structures, etc.). Industry needs to ground truth models 

that predict energy-extraction levels, for which data 

gathering from real deployments will be required. 

Initiating or supporting large-scale data collection 

upstream and downstream of arrays of tidal devices, 

as the industry progresses into testing arrays, would 

be a potential means of making progress in this area.

Approaches to Monitoring

Wherever possible, monitoring should be 

according to agreed general methodologies, ensuring 

that the purpose of the data gathering is clearly defined 

and consistent with other data-collection schemes.

There are early stage protocols and standards 

for using Doppler profiler data to assess resource 

intensity. However, resource intensity is not directly 

related to the recoverable resource, and there is not yet 

consensus on how national-scale resource assessments 

should be conducted. Care needs to be exercised to 

ensure that all relevant work elsewhere with respect 

to early-stage standards or protocols is taken into 

account. This will ensure consistency of approaches, 

where possible. If far-field effects are anticipated, a 

careful baseline monitoring program will be needed to 

attribute or detect effects from natural variation.

Mitigation Measures

The adoption of a “deploy and monitor” strategy 

is the only real way to gather informative data on 

actual interactions. However, it is difficult to see 

what kind of mitigation strategy could be put in place 

to minimize the unknown effects of energy extraction, when the critical levels of such extraction remain 

unknown.

Projects should begin at the small scale and 

increase incrementally from pilot- to large-scale, 

monitoring carefully at each step.

3.7.6 Priority Area: Difficulty of predicting, 

detecting and attributing changes to the presence/

operation of tidal energy devices 

Description

There is, at present, insufficient understanding of 

the normal behaviors and responses of the different 

receptors to the various stressor synergies in a nonsteady state. Without such understanding, it will be 

difficult to conduct a meaningful cumulative impact 

analysis. If the industry cannot accurately predict 

the extent and severity of cumulative effects, then it 

becomes impossible to perform a complete environmental impact assessment. If methods of detecting 

such effects are not developed, it is impossible to 

predict any such harm with any degree of accuracy.

If there are methods available or developed that 

enable the type and extent of change from cumulative impacts to be detected and measured, then 

determining the extent to which such changes can 

truly be ascribed to the presence of tidal energy 

devices still remains a problem. Although traditional 

before-after-control-impact (BACI) studies may be 

able to detect changes, selection of valid ‘control’ 

sites is challenging because inter-site differences 

create large numbers of variables. Multiple control 

sites are required (Underwood 1991, Underwood 

1994) to distinguish between temporal variations at 

control and impact sites and natural temporal-spatial 

variability. Within an already dynamic system, it 

is difficult to see how changes due to cumulative 

effects might be truly ascribed to the presence of any 

particular development. 
67

Gaps in Understanding

There are high levels of uncertainty about all 

potential environmental impacts of tidal energy 

devices on the range of possible receptors. Until 

adequate monitoring methods to determine the extent 

of such effects have been developed and tested, more 

is known about the effects of individual stressors on 

receptors, and there is a greater understanding of how 

to attribute change within a dynamic environment, 

it is difficult to see how these uncertainties can be 

reduced.

In order to progress, there is a need to support the 

development of the following: 

• Adequate monitoring methods to determine 

the extent of the effects of individual stressor 

elements on receptors; 

• Data collection and analysis according to agreedupon “best practices,” to increase knowledge 

about the effects of individual stressors on receptors; and

• Robust methods for ascribing change seen within 

dynamic environments to a particular stressor.

It may also be helpful to instigate robust Strategic 

Environmental Assessments (SEAs) for key potential 

tidal energy development areas to assess all receptors, highlighting receptors of particularly sensitivity, 

and identify potential cumulative effects that should 

be addressed through monitoring. This may require 

additional data collection at key SEA areas, to ensure 

sufficient baseline datasets. The SEA should incorporate multidisciplinary risk assessment and clear 

decision-making criteria.

Approaches to Monitoring

Once there is some knowledge of the effects of 

individual stressors on receptors, this information 

should be used to inform the development of existing 

ecological models to predict and, possibly, attribute 

change to cumulative effects of tidal devices.

One potentially useful area to develop protocols 

for would be the identification and monitoring of 

specific indicator species. While indicator species 

would be likely to be site-dependent, there may be a 

degree of site-independence in the monitoring methodology (data collection and interpretation). Support 

should be given to studies into the potential for a 

range of indicator species to identify changes from 

cumulative effects of tidal devices. 

Mitigation Measures

It is difficult to envisage what types of mitigation, 

other than “deploy-and-monitor” at the test stages, 

might be possible in respect of these concerns. Highquality, robust, adequate baseline and monitoring data 

need to be acquired.

Projects should begin at the small-scale and 

increase incrementally from pilot- to large-scale, 

monitoring carefully at each step. 

There may need to be some discussion among 

policy makers, regulators, and developers over the 

financial consequences of a particular development 

needing to be removed because of unacceptable environmental impacts. 
68

3.7.7 Recommended References

Gordon, D.C. Jr., Keizer, P.D., Daborn, G.R., 

Schwinghamer, P. and Silvert, W. 1986. Adventures in holistic ecosystem modelling: The 

Cumberland Basin Ecosystem Model. Netherlands Journal of Sea Research, 20(2-3): 325-335.

King, S., Maclean, I.M.D., Norman, T. and Prior, A. 

2009. Developing Guidance on Ornithological 

Cumulative Impact Assessment for Offshore Wind 

Farm Developers. London, UK: COWRIE Ltd. 

Available at http://www.offshorewindfarms.co.uk/

Pages/Publications/Latest_Reports/Birds/Developing_Guidance_onc4f9897d/.

Miller, D., Wherrett, J., Law, A., Birnie, D., Malcolm, 

A., McKeen, M., Hock Tan, B., Baxter, S., Fisher, 

P. Cumulative Impact of Wind Turbines. Report 

prepared for Countryside Commission for Wales. 

Available at http://www.macaulay.ac.uk/ccw/.

Offshore Energy Environmental Research Association. 2008. Fundy Tidal Energy Strategic Environmental Assessment Final Report. Prepared 

by the OEER Association for the Nova Scotia 

Department of Energy. April 2008. Available at 

http://www.offshoreenergyresearch.ca/OEER/

StrategicEnvironmentalAssessment/FinalSEAReport/tabid/312/Default.aspx.

Thomas, G. 1996. An Environmental Assessment 

of Visual and Cumulative Impacts arising from 

Wind farm Developments: A Welsh Planning 

Policy Perspective. MS thesis, University of 

Wales, Aberystwyth. Available at http://users.

aber.ac.uk/zwk/distlearn/virtlib/theses/thomas/

thomas.html.

Whitford, J. 2008. Background Report for the 

Fundy Tidal Energy Strategic Environmental 

Assessment. Prepared by Jacques Whitford for the Offshore Energy Environmental 

Research Association. Available at http://www.

offshoreenergyresearch.ca/OEER/StrategicEnvironmentalAssessment/BackgroundreportfortheFundyTidalEnergySEA/tabid/280/Default.aspx.

Underwood, A.J. 1991. Beyond BACI: Experimental 

designs for detecting human environmental 

impacts on temporal variations in natural populations. Aust. J. Mar. Freshwater Res., 42(5): 

586-587.

Underwood, A.J. 1994. On beyond BACI: Sampling 

designs that might reliably detect environmental 

disturbances. Ecological Applications, 4(1): 3-15.
69

 4. Environmental Receptors

In this section, seven environmental receptors 

are discussed:

• Physical environment: near-field – aspects of the 

physical environment in the region in which the 

specific stressors from tidal energy devices are 

directly observable (e.g., within the device wake)

• Physical environment: far-field – aspects of 

the physical environment beyond the near-field 

region, where specific stressors from tidal energy 

devices may affect the environment 

• Habitat and invertebrates – habitat (including 

benthic and nearshore) and invertebrate species

• Migratory fish – fish that follow predictable 

movements through the environment during their 

lifecycle

• Resident fish – fish that maintain a home range 

or that stay in a relatively stable geographic area 

through most of their lifecycle

• Marine mammals and seabirds

• Ecosystem interactions – interrelations among 

different receptors within an ecosystem

While not ideal, “habitat” is combined with 

“invertebrates” and “marine mammals” is combined 

with “seabirds” for logistical reasons (i.e., maintaining and equal number of stressors and receptors). 

Sea turtles, which are of significant concern for some 

other types of marine renewable energy, were not 

discussed, because they are not present in the marine 

systems currently being considered for tidal energy 

development.

A framework similar to the one applied to 

stressors is used to discuss each receptor. First, the 

significance of each receptor element is assessed 

relative to the environmental stressors associated 

with tidal energy, (Table 5) using “high,” “medium,” 

“low,” “not applicable,” or “unknown ranking.” 

Second, the uncertainty around this assessment is 

qualified as “high,” “medium,” “low,” or “unknown.” 

These results are presented as a matrix of stressor/

receptor interactions. A key describing these matrices 

is shown in Figure 24. The color of the cell denotes 

the significance of the interaction. The number and 

color of triangles denotes the uncertainty of this 

significance. This evaluation is conducted separately 

for pilot- and commercial-scale deployments, as 

described in Section 2.7.

High-priority stressor/receptor interactions (e.g., 

high significance or high uncertainty) are discussed 

in further detail. Each high-priority interaction is 

described, gaps in understanding identified, and 

approaches for monitoring this interaction identified 

(with emphasis on the stressor). 

Each workshop breakout group also identified 

key literature references for their receptor. 
70

Figure 24 – Sample receptor matrix components
71

4.1 Physical Environment: Near-field

4.1.1 Introduction

Workshop participants defined the physical nearfield environment to be comprised of elements in the 

immediate region of a tidal turbine, where direct/

specific effects of a turbine can be detected. These 

elements are water motion, water quality, acoustic 

noise, EMFs, and bottom/sediment properties. These 

basic elements combine to form the biologic suitability/productivity in the near-field region — identified as a key parameter in establishing priority issues. 

Participants also identified, as broad priorities, those changes in water motion, such as wakes 

and acceleration of flow, that may lead to changes 

in pressure, mixing (i.e., water quality, stratification) and settlement of particulates (e.g., sediment, 

larvae). As a cumulative effect, these changes may 

then lead to changes in biological activity/suitability 

(e.g., habitat). In the extreme case, pressure gradients 

across turbine blades may be fatal to small organisms 

drifting with the flow. 

Specific/actionable priorities were also identified, for which more information is needed regarding 

the flow around turbines and regarding the baseline 

hydrodynamics common to tidal energy sites. A 

combination of in situ measurements and computational models was suggested, as was the need for 

more information regarding the acoustic signatures of 

tidal devices during operation.

For many of the elements identified, the significance of effects will be specific to the environment 

and the scale of tidal energy development. For 

example, changes in mixing may only be important if there is strong stratification present (and this 

is unlikely at most high-energy sites). Across the 

various examples postulated, workshop participants 

found it unlikely that pilot-scale projects would have 

significant effects. In addition, it was agreed that 

pilot projects would provide important information to 

estimate the potential for commercial effects. 

The significance and uncertainty associated with 

stressor/receptor interactions are summarized in 

Figure 25 for pilot-scale deployments and in Figure 

26 for commercial-scale deployments. The colors 

denote significance and triangles denote uncertainty, 

as defined in Figure 24.
72

Figure 25 – Receptor matrix: Physical environment: Near-field – pilot-scale deployment

Figure 26 – Receptor matrix: Physical environment: Near-field – commercial-scale deployment

4.1.2 Receptor Matrix
73

4.1.3 Discussion

In identifying water motion as the key element of 

the near-field physical environment, along with water 

quality, the important topics of acoustics and electromagnetic fields (EMFs) have been set aside. Both are 

key elements necessary to describe the local physical 

environment with potential for effects, but these are 

treated elsewhere, as stressors, within the workshop 

proceedings. In a similar manner, habitat/biologic 

condition is used as the cumulative element by which 

factors of the near-field physical environment are 

prioritized; however it is not listed explicitly, because 

it is treated elsewhere in this document as another 

receptor.

4.1.4 Priority Area: Local hydrodynamics

Description

Turbines will alter the flow of water in the form 

of drag and wake features. In addition, large pressure gradients are likely in the immediate vicinity of 

turbine blades. In extreme cases, cavitation may occur. 

The deceleration of flow may enhance settlement 

of particles, such as sediment and plankton, and the 

turbine wake may increase mixing. These impacts are 

dependent on device design and the baseline conditions of a given site. 

Gaps in Understanding

There are no measurements of fluid velocity 

around tidal turbines in the public domain. Thus, it 

is difficult to estimate the potential significance of 

changes in fluid flow. In addition, there is limited 

understanding of the baseline flow conditions at tidal 

energy sites, because these are often oceanographically unique and poorly characterized. Numerical 

modeling is a promising tool to fill these gaps in 

understanding, but models must be properly calibrated 

with data for valid interpretation of results. In addition, implementing high-fidelity turbine models within 

existing oceanographic models is challenging (and 

unproven). 

Approaches to Monitoring

Monitoring for hydrodynamic changes requires 

thorough quantification of baseline conditions, which 

may have many sub-tidal influences (e.g., seasonal 

stratification, wind forcing). The basic oceanographic 

tools use active acoustics (Doppler current profilers, 

and velocimeters), which may not be compatible with 

active acoustics measurements for detection/tracking 

of fish and marine mammals. Acoustic Doppler instruments are quite mature and common in oceanographic 

research, however many limitations remain. Profilers 

are necessarily lower accuracy because of volume 

averaging but are able to make remote measurements over long ranges (order 100 m). Velocimeters, 

in contrast, achieve high accuracy by confining 

measurement to a near-field point. Stable mounting 

is not trivial when using either instrument, and the 

resulting data are sparse compared with the scales of 

tidal energy sites. Monitoring should, at a minimum, 

include upstream and downstream velocity profiles, 

and data analysis should include turbulence statistics, 

boundary layer structure, and sub-tidal exchange flow 

at a project site. 

4.1.5 Priority Area: 

Water quality and sedimentation

Description

Changes in mixing and settlement of particles 

(a result of changes in water flow) may change the 

water quality and sedimentation in the proximity of 

a turbine. In addition, the presence of antifouling 

coatings on the turbine may degrade the local water 

quality. 

Gaps in Understanding

There are no measurements of water quality or 

sedimentation around tidal turbines in the public 

domain. In addition, there is limited understanding 

of the baseline conditions at tidal energy sites; many 

sites are well-mixed and lack settled sediments, 

but there are notable exceptions (e.g., Cook Inlet). 

Numerical modeling is a promising tool to fill these 

gaps in understanding, but models must be properly 

calibrated with data for valid interpretation of results. 
74

Approaches to Monitoring

Monitoring for water quality and sedimentation 

changes requires thorough quantification of baseline conditions, which may be the result of sub-tidal 

processes (e.g., seasonal river discharge, coastal 

upwelling). Common oceanographic measurements 

of temperature, salinity, dissolved oxygen, dissolved 

nutrients, chlorophyll, and turbidity can be used to 

quantify a region, but data tend to be sparse in space 

and time, compared with natural variability. Thus, 

before-and-after comparisons are particularly 

challenging. 

4.1.6 Recommended References

Brumley, B.H., Cabrera, R.G., Deines, K.L. and 

Terray, E.A. 1991. Performance of a broad-band 

acoustic Doppler current profiler. IEEE Journal 

of Oceanic Engineering, 16(4): 402-407.

Chapman, D. 1996. Water Quality Assessments-A 

Guide to Use of Biota, Sediments and Water in 

Environmental Monitoring. (2nd ed). Prepared for 

UNESCO/WHO/UNEP. London, UK: F and FN 

Spon. 

Garrett, C.J.R., Keeley, J.R. and Greenberg, D.A. 

1978. Tidal mixing versus thermal stratification 

in the Bay of Fundy and Gulf of Maine. Atmosphere-Ocean, 16(4): 403-423.

Gooch, S. Thomson, J., Polagye, B. and Meggitt, D. 

Site characterization for tidal power. MTS/IEEE 

Oceans 2009. Biloxi, MI, October 26-29, 2009.

Thomson, J., Polagye, B., Richmond, M. and 

Durgesh, V. 2010. Quantification of turbulence 

for tidal power applications. MTS/IEEE Oceans

2010. Seattle, WA, September 20-23, 2010.

Wiles, P.J., Rippeth, T.P, Simpson, J.H. and 

Hendricks, P.J. 2006. A novel technique for 

measuring the rate of turbulent dissipation in 

the marine environment. Geophysical Research 

Letters, 33(21): 1-5.
75

4.2 Physical Environment: Far-field

4.2.1 Introduction

Tidal energy extraction may affect water quality, 

primary productivity, sediment transport, and the 

nature of the inter-tidal areas within the far-field 

marine environment surrounding a tidal energy 

extraction array. Energy removal and resultant 

changes in tidal range, transport, and mixing would 

be the primary stressor impacting these aspects of 

the marine environment; a secondary stressor would 

be chemical releases from the materials coating 

tidal energy extraction devices or from accidental 

chemical spills during device installation, operation, 

or servicing. A scientific understanding of sensitivities 

of these parameters is needed to determine the impact 

of a given level of energy extraction, but there is a 

large degree of uncertainty due to the nonlinear nature 

of the processes involved, highly site-specific factors, 

and cumulative effects (not to mention significant 

variability from existing natural and anthropogenic 

factors). To reduce uncertainty, it is recommended 

that tidal energy researchers and developers collaborate with the marine science community in order to 

leverage existing knowledge and ongoing research. 

Modeling capabilities should be developed, especially representations of energy extraction and its 

effects on an estuarine-scale hydrodynamic model 

with boundary conditions that can propagate energy 

dissipation throughout the model domain. Before 

modeling can begin in earnest, scientists must 

consolidate existing information to establish baseline 

conditions. Developers should phase the deployment 

of commercial-scale tidal energy arrays up to the full 

capacity. Far-field effects should be negligible for 

pilot-scale installations; for commercial-scale arrays, 

they should be thought of as an aspect of resource 

assessment and must be taken into consideration in 

planning for tidal energy generation.

4.2.2 Receptor Matrix

No significant effect on the far-field physical 

environment is expected for pilot scale deployments. The significance and uncertainty associated 

with stressor/receptor interactions are summarized 

in Figure 27 for commercial-scale deployments. The 

colors denote significance and triangles denote uncertainty, as defined in Figure 24.
76

Figure 27 – Receptor matrix: Physical environment: Far-field – commercial-scale deployment

4.2.3 Discussion

These considerations primarily apply to far-field 

impacts of energy extraction in a coastal embayment 

or an estuary, rather than, for example, areas of fast 

tidal currents in the straits between regional seas. The 

largest tidal energy prospects in the United States are 

of the former types. The far-field is defined as the 

marine area surrounding a tidal array beyond the scale 

over which the specific character of the tidal energy 

device or array is directly discernable. Seen from the 

far-field, the array may be indistinguishable from a 

natural energy-dissipating feature, such as form drag 

over varied topography. While the main concern of 

the scientific workshop was environmental impacts, 

conflicts with other marine uses as potential issues 

in the far-field environment were also discussed. 

Different sets of stressors (from those relevant to 

environmental impacts) may lead to use conflicts.

Aspects of the far-field marine environment that 

may be affected by tidal energy extraction include 

water quality (such as dissolved oxygen and nutrient 

concentration), primary productivity, sediment 

transport, and the nature of the inter-tidal areas. Each 

is a significant element of the regional marine environment and, in a heavily used region, is impacted 

in various ways by human activities. A tidal energy 

developer will be asked by permitting agencies, other 

marine resource users, and the regional community to 

demonstrate that development will not significantly 

and adversely affect the marine environment. For 

pilot-scale installations, such far-field effects should 

be negligible. However, commercial-scale development must anticipate the magnitude of far-field effects 

and how they would scale with the magnitude of 

energy extraction. The eventual scale of a tidal energy 

project will likely be constrained by the magnitude of 

the region-wide impact before the theoretical resource 

limit is reached.
77

It is anticipated that energy removal and resultant changes in tidal range, transport, and mixing 

will be the primary stressor from tidal hydrokinetic 

energy installations impacting the far-field marine 

environment. Changes in tidal range will reduce (or, 

in some cases, increase) the extent of the intertidal 

area that may form significant habitats. Reduction 

in tidal transport could result in reduced flushing of 

embayments, changes in water quality and pollutant 

dispersal (including algal blooms), and altered migration of organisms that use tidal currents. Reduction 

in the kinetic energy of the tidal current could reduce 

turbulence and mixing, which could, in turn, affect 

bottom sediment transport, supply of marine nutrients 

to the photic layer for primary production, and the 

exchange circulation and flushing of estuaries.

Chemical stressors may have far-field impacts 

as well; these include spills during installation, 

servicing, or operation and flaking of coating material containing toxic compounds. Tidal energy arrays 

will be located in areas of strong currents, and this 

could make it challenging to respond to spill incidents 

associated with tidal energy arrays. Uncertainties 

regarding impact of chemical stressors from tidal 

energy devices on the far-field marine environment 

are large at this point. These uncertainties include the 

identity of the chemical(s), their toxicity to biological 

organisms, and their exposure concentrations.

Static and dynamic effects of the presence of a 

device will be considered in the near-field analysis 

of the devices and are not of far-field concern. 

Impacts of electromagnetic and acoustic stresses are 

also likely confined to the near-field of the device/

array or, in the case of the electromagnetic field, are 

primarily associated with the underwater transmission 

cables (although these may run over long distances). 

Although it is possible that, for example, fish aggregation around a tidal energy array could have an 

effect on the overall distribution of fish species and 

species assemblage in the surrounding marine areas 

(and, hence, on the overall marine ecosystem of the 

region), such higher-order, cumulative and ecological 

interaction effects will have correspondingly greater 

uncertainties and cannot be adequately addressed at 

this point.

4.2.4 Priority Area: Effects of energy removal 

Description

The primary stressor of concern for the far-field 

physical environment is energy removal by tidal 

turbines. Although not likely appreciable for pilot 

scale developments, this stressor may be significant 

at the commercial scale. Energy removal may result 

in measurable changes to tides, currents, and mixing 

throughout a region, with attendant effects on water 

quality, habitat, and biological productivity. 

4.2.4.1 Gaps in Understanding

It is agreed that energy removal could have an 

impact on each of the receptor elements, but this 

consensus is tempered by a high degree of uncertainty 

surrounding the important question: How can we 

determine how much energy can actually be removed 

without a significant impact? Different sites would be 

impacted to greater or lesser extents, even within the 

same far-field region surrounding a single tidal 

energy array.

There is a high level of uncertainty surrounding 

the impacts energy removal on the far-field physical 

environment because of the:

• Moderately to highly nonlinear nature of the 

processes involved, which makes it challenging 

to establish scaling relationships between levels 

of energy removal and the quantitative impacts 

on receptor elements. For instance, sedimentary 

processes are highly nonlinear and changes are 

event-dominated; impacts of energy removal may 

occur suddenly once a “tipping point” value of 

extraction is exceeded.

• Highly site-specific factors and combinations of 

factors affecting the degree of impact.

• Significant variability due to natural causes and 

anthropogenic factors other than tidal energy 

extraction (e.g., changes to nutrient concentrations from runoff).
78

Nevertheless, the general relationship between 

energy dissipation by tidal turbines and changes in 

tidal range/transport, at least for simple estuaries, 

is now established (Garrett and Cummins 2004, 

Garrett and Cummins 2007, Polagye et al. 2009) 

as shown in Figure 28. Energy dissipated by tidal 

turbines includes energy extracted for conversion to 

electricity, energy lost when the turbine wake mixes 

with the free stream, and energy lost due to drag 

on the device support structure. The initial scaling 

between energy dissipation by arrays (P) and reduction in tidal transport (Q) is linear (upper left-hand 

portion of Figure 28a). As one moves down the curve 

from left (“no extraction”) to right, additional power 

extraction results in a progressively greater transport 

reduction, until the maximum level of dissipation 

(Pmax) is reached where the transport would be 

40 ~ 50% of the original value. Beyond this point, 

adding more capacity to the array results in decreased 

energy harvesting, although the environment impact 

continues to grow. Comparable relations exist for 

changes to tidal range and average current magnitude 

as a function of dissipation (Figure 28b,c). Such large 

changes to the natural tidal regime would certainly 

be considered an unacceptable environmental impact 

(even setting aside economic limitations from the 

decreasing cost-effectiveness of an array approaching 

Pmax); hence the relevant portion of the range/extraction curve is the linear regime (up to P/Pmax ≈ 0.5). 

Establishing the slope of the curve in this regime, 

either from theoretical considerations or simple 

models, will help quantify changes in the water levels 

in the nearshore environment and in the extent of tidal 

flats. Other environmental processes, such as mixing, 

may depend on the energy density (~Q2) or power 

density (~Q3). Their sensitivity to energy extraction would be correspondingly greater (as shown for 

power density in Figure 28d).

Figure 28 a, b, c, d – Relative changes to far-field flow quantities in an embayment as a consequence of 

kinetic power extraction for an embayment connected to the ocean by a narrow channel (after Polagye 

and Malte 2010).

a c

b d
79

Uncertainties also stem from the lack of data 

needed to characterize the baseline estuarine environment, including variability in the absence of tidal energy 

extraction. Certainly, there are existing data useful for 

such characterization for any given body of water, and 

necessary measurements may have already been made. 

Such studies may not be well-publicized and may only 

be documented in “gray literature”; locating these data 

sources and obtaining access should be a priority. In other 

cases, there is a paucity of available resource data; filling 

those basic gaps may require significant efforts.

Predictive tools (numerical models) for studying 

environmental effects of energy removal are available but 

require significant development. The level of accuracy 

needed to address questions of impacts of tidal energy 

extraction is uncertain, and whether available models 

meet this as-yet-to-be-determined level is also unclear. 

Some potential tidal energy development sites have 

existing models that could be used to investigate far-field 

impacts, given sufficient resources to convert them to 

this application. However, implementing and validating 

a specific model for a specific site is a difficult and 

time-consuming exercise. Moreover, model parameters 

may be highly “tuned” to reproduce existing conditions 

as a result of calibration and validation; they may not 

be appropriate to study conditions far from the current 

regime, including cases with tidal energy extraction.

This tempered view of the usefulness of models 

in addressing questions of far-field impact may be 

countered by the possibility that “imperfect” models 

could still be useful in determining a given estuarine 

system’s sensitivities to change. It is not anticipated 

that the model will exactly replicate the marine environment; rather interest is directed toward relative 

responses to perturbations and investigating whether 

the changes from energy extraction could reach some 

“tipping point” for environmental impact. Such a 

model must still be properly calibrated and used with 

full understanding of the dynamics underlying its 

behavior, its limitations, and the reasonableness of 

the outcomes. The degree of calibration error must be 

translated into a measure of uncertainty surrounding 

the conclusions drawn from any model. If one uses a 

model without basis for evaluating what is a reasonable result, then the model results can easily lead one 

to a wrong conclusion. 

Approaches to Closing Information Gaps

Leverage existing knowledge and ongoing research 

and operations — Questions raised by tidal energy 

development are, in many ways, analogous to those 

raised by management of other marine resource 

uses and are active areas of research in coastal and 

estuarine oceanography. Monitoring and modeling 

programs to enable stewardship of the marine 

environment are in place or being developed for 

many coastal bodies of water, and data on parameters 

relevant to the question of far-field impacts due 

to energy removal are being collected. Baseline 

conditions, including the degree of natural variability, 

might be established from available data. Modeling 

capabilities developed to address general questions of 

variability and sensitivity could be used to test energy 

extraction scenarios and their impacts on the far-field 

environment. Tidal energy researchers and developers 

should actively engage the marine science community 

and seek collaborations.

Improve model confidence — Confidence in 

dynamical models of circulation, biogeochemistry, 

and sediment dynamics in coastal and estuarine 

environments must be gained through model 

development, rigorous verification, validation, and 

calibration. Such models could be used to evaluate 

scenarios for commercial-scale development with 

regard to their effects on the far-field physical 

environment. Two specific technical areas that must 

see development are:

• Representation of energy removal and its nearfield effects in an estuarine-scale hydrodynamic 

model; and

• Boundary conditions that can adjust to additional energy dissipation throughout the model 

domain (i.e., not clamp energy fluxes at the open 

boundary).
80

Laboratory models — Workshop participants 

considered the possibility of laboratory experiments 

to simulate tides and energy extraction and using 

these to verify the performance of numerical models. 

Scaling will be a significant issue because relating 

system parameters at the laboratory scale to those at 

the estuarine scale is not be straightforward. Existing 

laboratory-scale models of marine environments, 

such as the University of Washington’s model of 

Puget Sound, provide intriguing study opportunities; 

however, it is not clear if energy removal experiments 

can be usefully interpreted, beyond qualitative 

comparisons (e.g., direction of a change, such as 

tidal range).

Approaches to Monitoring

Consolidate existing information to establish 

baseline conditions — It is difficult to imagine a 

commercial tidal energy development in a region 

without a well-understood baseline physical 

environment. Physical characteristics of a given 

region can have significant seasonal (and possibly 

interannual) variability and one needs to monitor 

the system under consideration for at least a year 

in order to understand the baseline conditions, and 

how conditions change through the seasons. In many 

cases, important measurements have already been 

made, but finding the study sponsor and obtaining 

the data set can be difficult. Often, it is not that the 

data do not exist, but that nobody knows where the 

data are. Better efforts are required to integrate and 

archive disparate local knowledge. This would be of 

benefit not only to tidal energy developers but to the 

broader oceanographic community. It could also help 

developers identify critical baseline data gaps, and 

develop strategies for gathering needed baseline data 

and ongoing monitoring. As mentioned previously, 

these considerations are restricted to commercialscale deployments and are not expected to be relevant 

at the pilot scale.

Take a phased approach to the development of 

commercial-scale tidal energy arrays — Because 

pilot-scale installations should not have measurable 

impacts on the far-field, monitoring at the pilotscale will not yield useful information regarding 

commercial-scale development. At some point, a 

commercial-scale array that is likely to result in 

measurable far-field effects would have to be installed 

to validate a priori sensitivity studies. Subsequent 

development would then need to be managed 

adaptively as the nature and the magnitude of impacts 

are revealed. It will be a learn-by-doing exercise, 

but the project could be adaptively managed through 

continuing education and refining models through 

experience.
81

4.2.5 Recommended References

Atwater, J.F. and Lawrence, G.A. 2010. Power potential of a split tidal channel. Renewable Energy, 

35: 329-332.

Barltrop, N., Varyani, K.S., Grant, A., Clelland, D. 

and Pham, X.P. 2007. Investigation into wave–

current interactions in marine current turbines. 

Journal of Power and Energy, 221: 233-242.

Blunden, L.S. and Bahaj, A.S. 2007. Tidal energy 

resource assessment for tidal stream generators. 

Journal of Power and Energy, 221: 137-146.

Boehlert, G.W., McMurray, G.R. and Tortorici, C.E. 

(Eds.). 2008. Ecological Effects of Wave Energy 

Development in the Pacific Northwest. U.S. 

Department of Commerce, NOAA Technical 

Memorandum NMFS-F/SPO-92. 

Bryden, I.G., Couch, S.J., Owen, A. and Melville, G. 

2007. Tidal current resource assessment. Journal 

of Power and Energy, 221: 125-135.

Bryden, I.G., Grinstead, T. and Melville, G.T. 2004. 

Assessing the potential of a simple tidal channel 

to deliver useful energy. Applied Ocean Research, 

26: 198-204.

Cada, G., Ahlgrimm, J., Bahleda, M., Bigford, T., 

Stavrakas, S., Hall, D., Moursund, R. and Sale, 

M. 2007. Potential impacts of hydrokinetic and 

wave energy conversion technologies on aquatic 

environments. Fisheries, 32(4): 174-180.

Centre for Marine and Coastal Studies. 2003. A 

baseline assessment of electromagnetic fields 

generated by offshore windfarm cables. Report 

prepared for Collaborative Offshore Wind Energy 

Research into the Environment, COWRIE-EMF – 

01-2002 66. July 2003.

Clarke, J.A., Connor, G., Grant, A.D. and Johnstone, 

C.M. 2007. Design and testing of a contrarotating tidal current turbine. Journal of Power 

and Energy, 221: 171-179.

Dolman, S.J., Green, M. and Simmonds, M.P. 2007. 

Marine Renewable Energy and Cetaceans. SC/59/

E10. Submitted to the Scientific Committee of the 

International Whaling Commission.

Driscoll, F.R., Skemp, S.H., Alsenas, G.M., Coley, 

C.J. and Leland, A. 2010. Florida’s Center for 

Ocean Energy Technology. Available from 

http://www.mitenergyclub.org/assets/2009/3/4/

Florida_s_Center_for_Ocean_Energy_Technology.pdf.

Fraenkel, P.L. 2007. Marine current turbines: 

Pioneering the development of marine kinetic 

energy converters. Journal of Power and Energy, 

221: 159-169.

Garrett, C. and Cummins, P. 2004. Generating power 

from tidal currents. Journal of Waterway, Port, 

Coastal and Ocean Engineering, 130(3): 114-118.

Garrett, C. and Cummins, P. 2007. The efficiency of 

a turbine in a tidal channel. J. Fluid Mechanics, 

588: 243-251.

Gill, A.B. 2005. Offshore renewable energy: Ecological implications of generating electricity in the 

coastal zone. Journal of Applied Ecology, 42: 

605-615.

Myers, L.E. and Bahaj, A.S. 2010. Experimental 

analysis of the flow field around horizontal axis 

tidal turbines by use of scale mesh disk rotor 

simulators. Ocean Engineering, 37: 218-227.

Neill, S.P., Litt, E.J., Couch, S.J. and Davies, A.G. 

2009. The impact of tidal stream turbines on 

large-scale sediment dynamics. Renewable 

Energy, 34(12): 2803-2812.

Polagye, B., Kawase, M. and Malte, P. 2009. 

In-stream tidal energy potential of Puget Sound, 

Washington. Journal of Power and Energy, 223: 

571-587. 

Polagye, B.L. and Malte, P.C. 2010. Far-field 

dynamics of tidal energy extraction in channel 

networks. Renewable Energy, 36(1): 222-234.

Schiff, K., Diehl, D. and Valkirs, A. 2004. Copper 

emissions from antifouling paint on recreational 

vessels. Marine Pollution Bulletin, 48: 371-377.

Spurlock, D.S. 2008. Modeling flows for assessing 

tidal energy generation potential. MS thesis, 

Virginia Polytechnic Institute, Blacksburg, VA. 

Available at http://scholar.lib.vt.edu/theses/available/etd-09212008-134411/unrestricted/D_Spurlock_Thesis.pdf
82

4.3 Habitat and Invertebrates

4.3.1 Introduction

This breakout group discussed the effects of tidal 

energy development on habit and invertebrates. These 

were separated into several categories of potential 

stressor/receptor interactions:

• Benthic substrate: habitat on the seabed;

• Benthic (sessile) invertebrates: invertebrates on 

the seabed unable to move in response to a disturbance (e.g., barnacles and sponges);

• Benthic plants: plants on the seabed, also unable 

to move in response to a disturbance;

• Pelagic habitat: the water column characteristics 

that provide physical, chemical, migratory, and 

feeding functions;

• Nearshore habitat: nearshore areas that could 

experience changes as a consequence of 

increased/decreased tidal rage with energy 

removal;

• Nearshore habitat change in vicinity of cable 

crossing/drilling: nearshore areas that could be 

disturbed by cables or drilling (may be different 

than the benthic habitat disturbed by device 

installation/operation); and

• Beaches: shoreline areas that could experience 

accretion or erosion as a consequence of energy 

removal.

Mobile benthic invertebrates, such as crustaceans, 

were not explicitly discussed. The significance and 

uncertainty associated with stressor/receptor interactions are summarized in Figure 29 for pilot-scale 

deployments and in Figure 30 for commercial-scale 

deployments. The colors denote significance and 

triangles denote uncertainty, as defined in Figure 24.
83

4.3.2 Receptor Matrix

Figure 30 – Receptor matrix: Habitat and Invertebrates – commercial-scale deployment

Figure 29 – Receptor matrix: Habitat and Invertebrates – pilot-scale deployment
84

4.3.3 Discussion

Priority issue areas identified by participants 

in this breakout session included effects on sessile 

(benthic) invertebrates and plants, near- and farfield pelagic habitats, and near- and far-field benthic 

substrate. Outside of those priority issue areas, three 

broad issues were identified. These include: 

• The critical need for modeling far-field effects of

energy removal (mixing and tidal amplitude and 

height),

• Cumulative effects of multiple or commercialscale projects, and

• Availability of data from existing projects.

This breakout discussion does not resolve 

conflicts between generalities and specificity. For 

example, there is a broad range of species within 

each receptor element, with a broad range of potential responses to stressors and impacts. The matrices 

presented in Figure 29 and 30 may reflect the worstcase scenario, best-case scenarios, or the average of 

the two cases; this should be made explicit in subsequent discussion. Species listed under the Endangered 

Species Act (ESA) specifically need close attention. 

In the case of ESA-listed species, loss of individuals 

should be considered as well as population-level 

effects. Also, population-level ESA thresholds are 

much higher than those for community-level effects. 

Although workshop participants spoke of the need 

to establish generalized monitoring protocols, many 

exceptions or unique approaches may have to be 

developed for particular situations. There is also a 

need to examine changes in benthic and pelagic 

food webs.

The general level of knowledge around each of 

the receptor elements is:

• Benthic substrate: moderate in the near-field 

(site-specific) and low in the far-field.

• Sessile species and plants: moderate to high

• Nearshore habitat: high

• Pelagic habitat: moderate to high

Some aspects of acoustic effects, electromagnetic 

effects, and energy removal might be addressed by preinstallation experiments. The presence of devices can 

only be rigorously assessed by pilot projects, and such 

projects would also provide further information 

on acoustic and electromagnetic effects. 

4.3.4 Priority Area: 

Sessile (benthic) species - invertebrates and plants

Description

The impacts of development of multiple arrays 

or multiple sites could potentially have far-reaching 

effects, both spatially and in terms of “ripple effects” 

throughout the ecosystem, from a bottom up perspective. The impacts of energy removal and cumulative 

effects of multiple arrays or multiple sites could be 

significant, resulting in changes in abundance, distribution, and population or community structure of marine 

invertebrates and plants. 

This is a top priority because marine invertebrates 

and marine plants are two groups of organisms not specifically considered in the other sections (marine mammals, 

birds, fish), yet form an important part of the marine 

ecosystem. They respond to many stressors, and because 

at least part of their life history is benthic, cannot move 

away from stressors. Hence they integrate the stressors 

at a particular location. They are particularly sensitive to 

changes in substrate grain size, energy regimes (currents/

waves), and tidal regimes (amplitude and height). 

Changes in abundance, distribution, population, or 

community structure of marine invertebrates (over 3,000 

species) and plants (over 650 species) have major effects 

on the upper trophic levels. Marine plants (seaweeds, 

including kelp species, and seagrasses, including eelgrass) 

also serve as biogenic habitats, providing habitat functions 

such as refuge, migratory paths, substrate for reproduction 

and production of prey items.

Gaps in Understanding

There is a high level of uncertainty about how 

much energy a tidal energy unit, units, or arrays of 

units would remove, and what would be the associated 

effects of energy removal, in particular the effects of 

changes in tidal and energy regimes. However, energy 

removal is unlikely to cause environmental changes at 

the pilot scale.
85

Uncertainty about the effects of acoustic regimes 

on invertebrates was thought to be high. There was 

concern expressed about whether there is information 

available or not, whether it may be considered proprietary, and whether it has been analyzed. 

Approaches to Monitoring

Methods for measuring the types, abundance, and 

distribution of intertidal and subtidal benthic invertebrates and nearshore marine plants are well established (Murray et al. 2002). Accurate identification is 

difficult and expensive because there are few experts 

and the process is time consuming.

4.3.5 Priority Area: 

Changes in pelagic habitat near-field and far-field

Description

These impacts can be very widespread, potentially affecting large proportions of distinct ecosystems that are areas of interest for tidal energy 

development (e.g., Puget Sound and Cook Inlet).

Pelagic habitat is defined here as the water 

column characteristics that provide physical, chemical, migratory, and feeding functions. Although many 

of the workshop discussions focused on large charismatic megafauna, such as marine mammals, adult fish 

and seabirds, the pelagic ecosystem contains phytoplankton and zooplankton and is the means by which 

the spores, eggs, and larval forms of invertebrates and 

many fish are dispersed. Changes in currents, pressure gradients, estuarine stratification and mixing, 

and shear zones alter physical, chemical, and energy 

characteristics of this habitat. Changes could affect 

oxygen levels (hypoxia), nutrient levels, salinity, and 

vertical movement of plankton. These, in turn, affect a 

wide variety of organisms.

Gaps in Understanding

Although modeling indicates negligible far-field 

effects and minimal near-field effects at the pilot 

scale, there is concern about the effects of energy 

removal resulting from commercial-scale tidal energy 

projects. Specifically, effects of energy removal on 

a closed estuarine system are poorly understood, and 

the effect of changes on pelagic organisms is also 

poorly understood. 

The best approach to closing this information 

gap may be modeling, because monitoring of pilotscale deployments is unlikely to provide insight into 

commercial-scale concerns (see Section 4.2, Physical 

Environment: Far-field for a discussion on modeling 

challenges). 

Approaches to Monitoring

Fundamental procedures exist, but, in general, 

studies to collect data about pelagic habitat changes 

as a consequence of energy removal would be very 

difficult and expensive to implement.

4.3.6 Priority Area: 

Changes in benthic substrate both near and far-field

Description

At issue are substrate grain size changes. Grain 

size distribution is affected by the energy regime, as 

well as the movement of sediments and erosion rates. 

The distribution and abundance of benthic organisms 

is almost entirely determined by the type, size distribution, and movement of the substrate. For example, 

because of the glacial origin of Puget Sound, most 

benthic habitats consist of a complex of unconsolidated sediments. Some areas, particularly in the San 

Juan Archipelago of Washington and the Strait of Juan 

De Fuca in Washington and Georgia Strait in British 

Columbia are consolidated but often in a complex 

with unconsolidated sediments. Tidal energy would be 

located in high-energy environments where there are 

several types of substrates. The substrate of Admiralty 

Inlet is a cobble/boulder bottom with few fine-grained 

materials. These comparatively large-sized substrates 

move or roll, resulting in few sessile organisms or 

ones that are resistant to abrasion. Conversely, the 

substrate in Cook Inlet consists of fine-grained sediments deposited by glacial outflow. Other substrates 

include exposed areas of hardpan (Tacoma Narrows, 

Washington) or bedrock (Deception Pass, Washington), scoured of unconsolidated materials and 

having a very different biota compared to sand 

or gravel.
86

This is a top priority because scour, resuspension, deposition, and sediment movement may cause 

changes in biota. These effects can be in the near-field 

(scour and deposition around devices), or far-field 

(large changes in currents, movement of substrate, or 

grain size).

Gaps in Understanding

Substrates in high-energy current areas are poorly 

mapped, and the dynamics are not well understood. 

This is, in part, driven by the difficulties inherent to 

operating in high-current areas and characterizing 

hard substrates. 

Approaches to Monitoring

Grain size characterization is possible for finergrained sediment. For example, optical backscatter 

sensors are capable of monitoring turbidity levels and 

laser in-situ scattering and transmissometry can assess 

grain size up to characteristic dimensions of 500 

microns. However, in scoured environments, direct 

sampling of the seabed is challenging. For example, 

a Washington State Department of Ecology sediment monitoring program excluded all high-energy 

areas because of an inability to collect samples with 

conventional bottom grabs (Long et al. 2003). Monitoring sediment movement in deepwater, high-energy 

environments is not well developed.

4.3.7 Recommended References

Long, E., Dutch, M., Aasen, S., Welch, K. and 

Hameedi, M.J. 2003. Chemical contamination, 

acute toxicity in laboratory tests and benthic 

impacts in sediments of Puget Sound: A summary 

of results of the joint 1997-1999 Ecology/NOAA 

survey. Washington Department of Ecology, 

Report 03-03-049.

Murray, S.N., Ambrose, R.F. and Dethier, M. 2002. 

Methods for Performing Monitoring, Impact, 

and Ecological Studies on Rocky Shores: Final 

Technical Summary. MMS OCS Study 2001-070. 

Coastal Research Center, Marine Science Institute, University of California, Santa Barbara, CA. 

MMS Cooperative Agreement Number 14-35-

0001-3076.
87

4.4 Fish: Migratory

4.4.1 Introduction

Migratory fishes are formally defined as diadromous species. However, some fish species (e.g., 

Atlantic cod) that do not fully enter fresh water follow 

consistent and predictable patterns. Similar concerns 

are likely to exist for the species and, consequently, 

this work group adopted a broader definition of 

migratory fish as “fish that follow predictable movements through the environment during their lifecycle.” Ultimately, for most species, assessing and 

evaluating population-level effects are of primary 

importance. Species that are at low population levels 

will be most at-risk to effects of the devices (e.g., fish 

that are listed as “endangered” under ESA). The risk 

posed by stressor effects on migratory fish depend on: 

• Affected species;

• Life stage;

• Population level of affected species;

• Geomorphology of the area; 

• Large scale site conditions; 

• Local conditions; 

• Type and number of turbines; and 

• Other equipment involved (e.g., power cables). 

For all environmental issues related to migratory fish, workshop participants felt there was a lack 

of information on the physical effects of tidal energy 

devices that hampered the participants’ abilities to 

evaluate stressor/receptor relationships. For some 

issues, information may be available, but it is not 

clear how it can be obtained. A thorough review of 

the physical effects of turbines on the environment is 

needed, and relevant data needs to be made publically 

accessible. 

The most important “actionable” (can be studied 

over the near term) issues pertaining to migratory 

fish are understanding the dynamic effects (spinning movement of the blade) of tidal energy devices 

on migratory fish, assessing the acoustic signatures 

of different devices at varying distances from the 

devices during operation, and evaluating electromagnetic fields associated with energy generation. At 

large scales (assumed to be commercial-scale operations), evaluating cumulative effects of turbines and 

assessing effects of energy removal on migratory 

pathways were considered especially important. It 

is clear, however, that as more is learned about tidal 

energy effects, the prioritization of issues will need 

to be revisited. Some issues may become less of 

a priority for study and research, and others may 

increase in priority. 
88

In order to assess baseline conditions and 

monitor potential turbine effects on migratory fish, a 

full evaluation of available tools and approaches is 

needed. Gaps or deficiencies in approaches to baseline assessments and project effects monitoring and 

evaluation must be identified and actions undertaken 

to address these gaps. 

Figure 32 – Receptor matrix: Fish: Migratory – commercial-scale deployment

Figure 31 – Receptor matrix: Fish: Migratory – pilot-scale deployment

The significance and uncertainty associated with 

stressor/receptor interactions are summarized in 

Figure 31 for pilot-scale deployments and in Figure 

32 for commercial-scale deployments. The colors 

denote significance and triangles denote uncertainty, 

as defined in Figure 24.

4.4.2 Receptor Matrix
89

4.4.3 Discussion

For all environmental issues related to migratory 

fishes, there is a perceived lack of information on the 

physical effects of tidal energy devices that hampered 

the workshop breakout group’s ability to evaluate 

stressor/receptor relationships. For some issues, it is 

likely that more information was available than the 

group was aware of, but how to find and access this 

information was unclear. For example, little data is 

available on the magnitude of electromagnetic fields 

from tidal energy deployments, and there may be 

significant species-specific differences in sensitivity 

to the stressor. A thorough review of physical effects 

of turbines on the environment is needed, and data 

need to be made publically accessible at some point. 

Additional knowledge concerning physical changes 

associated with tidal energy generation may alter what 

are presently considered to be the major knowledge 

gaps.

Ultimately, it is likely that population-level effects 

will be the most important to evaluate. Organisms 

that have low population levels and that interact with 

the devices are most at risk (e.g., fish that are listed as 

“endangered” under ESA). Different approaches to 

monitoring and evaluation may be required, depending 

on the size or level of the population. For example, 

for endangered species (low population levels), “zero 

impact” may be required, such that the presence of 

these fish in the area during turbine operation may 

necessitate shutting down of the equipment. For other 

species, some level of injury, mortality, or behavioral 

change may be acceptable.

The effects of tidal energy devices on migratory fishes are site-specific and depend on species 

and life stage involved, population level of affected 

species, geomorphology of the area, large-scale 

site conditions, local conditions, and the specific 

turbines encountered. For most stressors, there are 

some species and life stages that will be at a greater 

level of risk to that stressor. An example of a life 

stage-specific effect is that some migratory fish make 

use of strong tidal currents to reduce their energy 

expenditure (Gibson 2003). Therefore, the timing of 

migratory movement would coincide with operational 

periods for tidal turbines. These species also avoid 

currents running in opposition to their migratory path 

by moving toward the bottom of the water column or 

into refuge areas where currents are weaker until the 

tide turns. It is possible that the wake in the lee of a 

tidal device support structure could provide this type 

of refuge. An example of a species-specific effect is 

the higher sensitivity of clupeids (e.g., shad) to noise 

at certain frequencies than salmonids. The greatest 

uncertainty with all stressor effects on migratory fish 

is with commercial-scale development. 

To evaluate a number of these effects, devices 

need to be placed in the water and operated. Although 

some assessment and evaluation can come from 

models and baseline data collections, at some point, 

devices must be operated in the water to fully evaluate 

their environmental effects.

Ultimately, the cumulative effects of tidal energy 

stressors on migratory fish at large scales (e.g., 

multiple turbines) must be understood. Migratory fish 

do not necessarily respond to single stressors; rather, 

they respond to the overall environment they are 

experiencing, which includes tidal energy extraction, 

among other issues associated with an area. Understanding cumulative effects is especially complicated 

by a number of factors. One issue is that an effect 

can be produced by a single stressor or by multiple 

stressors associated with turbines. In addition to the 

turbine field, other elements of the environment, such 

as the ambient currents, species present in the area, 

and water quality, can determine how the fish respond. 

Effects on fish will be a product of their experiences 

passing through turbine fields, prior to encountering 

turbine fields, and after encountering turbine fields. 

For example, if fish are already stressed because of 

conditions experienced adjacent to the tidal energy 

devices or because of their life stage (e.g., spawning 

migration for some salmonids), the effects of the 

turbines may be greater. Furthermore, some fish may 

experience disturbances from multiple turbines in 

passing through an array. 
90

To help address uncertainties around effects on 

migratory fish, it is clear that a greater understanding 

of the effects of specific stressor components on the 

fish (e.g., s and sound) is needed. Understanding 

whether these elements have linear (i.e., additive) or 

synergistic (i.e., non-linear or non-additive) effects, 

assessing whether there are effect thresholds, and 

considering the conditions in the surrounding environment and how these affect the fish without turbines 

are additional needs.

A greater understanding of the large scale effects 

(commercial scale operations) of energy removal on 

migratory pathways and behavior of migratory fishes 

is needed. It is recognized that the dominant largescale effect of energy removal will be on habitat (e.g., 

shoreline conditions that are distant from the turbine 

fields). However, it is clear that removal of a sufficient amount of tidal energy could change currents in 

an area that can affect how fish migrate through the 

area. Furthermore, changes to tidal currents could 

also affect how fish are distributed or move through 

an area (Gibson 2003, Lacoste et al. 2001, Levy and 

Cadenhead 1995, Moser and Ross 1994, Metcalfe and 

Hunter 2003). 

4.4.4 Priority Area: 

Dynamic effects of device operation

Description

The dynamic effects of devices (e.g., spinning 

movement of the blade) are fundamental to device 

operation and, arguably, the most direct effect that 

turbines could have on migratory fishes. Specific 

issues include blade strike and pressure changes that 

can cause injury, mortality, and affect behavior of 

migratory fish (DOE 2009). Although lethal affects 

are most dramatic, sub-lethal effects on behavior, 

including alterations in migration routes, changes 

to predator prey interactions, and changes in stress 

levels, are of particular concern. While these types of 

effects are most significant at large commercial scales, 

they still may be observable at pilot scales. 

Gaps in Understanding

Information from tests involving single turbines 

can be used to help develop predictions for the effect 

on migratory fish at larger scales. To address or 

evaluate this issue, assessments will need to be location-specific and consider types of fish (e.g., clupeids, 

sturgeons, juveniles and adult salmonids) and type 

of device. For commercial-scale facilities, baseline 

studies (perhaps integrated into models) should be 

developed that quantify spatial and depth trends 

for migration and enable a pre-operation prediction 

of effects. The level of risk or impact can then be 

assessed, evaluated, and tested. For fish at low population levels, monitoring and operational mitigation 

(e.g., shutdown) may be needed. For other species, 

predicted impacts should be assessed with monitoring 

during operations, as appropriate.

Approaches to Monitoring

Only limited discussion of monitoring and baseline data collection was conducted. Additional workshops are needed to thoroughly evaluate monitoring 

and evaluation approaches. An objective of these 

workshops should be to conduct a full evaluation of 

the tools and approaches that will be needed to answer 

specific questions. Gaps or deficiencies in approaches 

to monitoring and evaluation must be identified and 

actions undertaken to address these gaps.

A diversity of baseline data and monitoring 

approaches will be needed that vary according to 

species of concern, location, device type, methods 

of installation and operation, and project scale. All 

monitoring and baseline work should be driven or 

guided by explicit questions or hypotheses. It is 

recommended that predictions of impacts be first 

developed using the best available information (e.g., 

baseline data, modeling) and the predictions tested 

with monitoring. For example, life history or behavior 

models may provide the best opportunities to develop 

pre-project predictions. Such predictions can then be 

tested using monitoring protocols that may involve 

either active or passive sampling methods.
91

The first step in determining if a tidal energy 

device affects migrating fishes is to determine 

whether migrating fish are present in the area where 

the device is to be installed, prior to device installation. Unfortunately, migratory fish abundance is 

seasonal in nature, and one species or another may 

be in the area at any time of year. At least one year 

of baseline data collection would be required to 

determine if migrating fish use the area where the 

device is to be installed. This monitoring would likely 

involve routine hydroacoustic surveys (density and 

fish size estimates) in combination with net sampling 

(species composition, if endangered species are not of 

concern) and acoustic telemetry. If this information 

can be captured at temporal and spatial scales relevant 

to tidal energy project size, the results of this monitoring could then be used to influence the selection 

of specific sites for devices (i.e., siting them outside 

identified migratory pathways). The importance of 

appropriate array siting with respect to migratory 

pathways is clear from the development of terrestrial 

wind power. One of the earliest commercial wind 

projects developed in the United States is located 

in Altamont Pass, California, and, due to poor site 

selection, causes the death of several thousand birds 

each year, including species protected by the federal 

Migratory Bird Treaty Act. This early mistake contributes to a perception that wind turbines are inherently 

hazardous to birds, despite evidence to the contrary. 

Tidal energy development would be well-served by 

avoiding such costly mistakes.

The second step in determining if tidal energy 

devices affect migratory fish species is to monitor 

operating devices. Even if it were determined (or 

presumed) that no migrating fish use the area, monitoring should be performed, because migrating fish 

might be attracted to the device. This type of monitoring would help to determine new design features 

or operational configurations that have less impact 

on migrating fish species. Depending on the environment, monitoring in the near field of the operating 

device could include active acoustics (split-beam, 

multi-beam, acoustic cameras), optical cameras, 

and, possibly, specialized netting. These would be 

primarily suitable for observation of blade strike or 

near strikes. Acoustic tags would enable detecting 

wider field responses, such as avoidance or attraction, 

or even changes in predation rate. However, it may be 

challenging to determine the root cause of avoidance 

or aggregation in the presence of multiple stressors. 

Fine-scale positioning acoustic tag systems could 

help measure behavioral responses of individuals to 

specific devices. However, obtaining useful knowledge may require a cost-prohibitive tagging intensity 

and receiver density. 

Although modeling work prior to installation can 

help in predicting effects of various stressors, a key 

question is whether migratory fishes can (and do) 

avoid the tidal energy device. This avoidance in itself 

may cause other problems (i.e., increased susceptibility to predation, increased stress).

4.4.5 Priority Area: Acoustic effects

Description

Whether the sounds generated by the turbines 

affect migratory fish behavior or condition must be 

understood. Although high-intensity sound may 

be generated during installation and maintenance 

of turbines (e.g., from pile driving), operational 

effects are more of a concern. Depending on sound 

intensity, frequency, and distance from the turbine, a 

variety of lethal and sub-lethal effects are possible, 

particularly with respect to changes in behavior and 

condition of the fish. Tests could be used (e.g., in 

laboratory settings or field-based cage studies) to 

develop relationships between received sound levels 

and fish response. These results could provide noise 

specifications for developers to bring into their design 

processes. Depending on the specific circumstances, 

fishes could be attracted or repelled by noise from 

operating devices. Migratory species vary in their 

sensitivity to different sound levels, with some species 

and life stages more susceptible to different sounds 

than others.
92

Gaps in Understanding 

It is not clear that acoustic changes caused by 

the devices can be detected by the fish because of 

ambient noise levels. As a first step to understand 

the nature of this issue, received noise levels from 

operating devices need to be characterized. Clearly, 

this requires that devices be placed in the water and 

appropriate sound measurements made. As discussed 

under Section 3.4, Acoustic Effects, obtaining these 

measurements is challenging in high-current environments because of pseudo-noise.

Approaches to Monitoring

Measured sound levels from tidal energy installations need to be related to what is known about effects 

of sound/noises on behavior and stress levels (e.g., on 

reproduction and immune systems) of the fish. This 

information can be used to develop predictions of 

effects on different species/life stages. There is some 

literature on sound effects on fish (e.g., Hastings and 

Popper 2005), but further study on specific species 

or life stages may be needed. Although some in situ 

work may be necessary and feasible, lab studies or 

field cage experiments may help elucidate possible 

effects on selected species. Where appropriate, in situ 

studies could use similar techniques to those previously described in the first priority area.

4.4.6 Priority Area: Electromagnetic effects

Description

A greater understanding of the effects of electromagnetic fields (EMFs) generated by the turbines is 

needed. Some species of fish, such as sturgeon and 

eels, appear to be particularly sensitive to EMF, and 

others, such as salmon, do not appear to be as sensitive. 

Gaps in Understanding

Although turbine generators and power cables 

are expected to create EMFs, the intensity levels of 

the EMFs they generate are not, generally, known. 

Clearly, this gap in understanding of the stressor 

must be addressed before the overall importance of 

this issue can be assessed. This issue is a particular 

concern at full-scale commercial operations when 

large distances of cabling and large numbers of 

turbines are present in relatively small areas. Of 

particular concern are potential behavioral effects on 

species that use EMFs for orientation, navigation, 

foraging, and finding conspecifics. 

This question should first be addressed through 

a thorough review of what is known about fish 

responses to EMFs generated by underwater power 

cables. This type of review could help guide an 

assessment of what species might be at risk and under 

what conditions. However, the present state of knowledge may be insufficient to conduct a meaningful 

risk assessment. More information that is publically 

available on physical changes resulting from different 

devices (e.g., variance in EMFs) is needed. Such 

knowledge may change the questions asked in the 

future about effects of EMFs on different receptor 

elements.

Approaches to Monitoring

As for acoustic effects, measured EMFs from 

tidal energy installations need to be related to what 

we know about effects of these fields on behavior 

and stress levels of fish. This information can then 

be used to develop predictions of effects on different 

species/life stages. Lab or field cage experiments may 

help to elucidate the effects on particular species. 

Where appropriate, in situ studies could use similar 

techniques to those described under dynamic effects. 

However, as noted in Section 3.5, Electromagnetic 

Effects, in situ studies of EMF effects are challenging 

to conduct and, often, inconclusive.
93

4.4.7 Recommended References

Boehlert, G. and Gill, A. 2010. Environmental and 

ecological effects of ocean renewable energy 

development: A current synthesis. Oceanography, 

23(2): 68-81.

Gibson, R.N. 2003. Go with the flow: Tidal migration 

in marine animals. Hydrobiologia, 503: 153-161.

Gill, A., Gloyne-Phillips, I., Neal, K. and Kimber, J. 

2005. The potential effects of electromagnetic 

fields generated by sub-sea power cables associated with offshore wind farm developments on 

electrically and magnetically sensitive marine 

organisms – A review. Final report prepared for 

Collaborative Offshore Wind Energy Research 

into the Environment (COWRIE) group. 

COWRIE-EM FIELD 2-06-2004. 

Hastings, M.C. and Popper, A.N. 2005. Effects 

of Sound on Fish. Report prepared for California Department of Transportation, Contract 

No. 43A0139. Available from http://www.dot.

ca.gov/hq/env/bio/files/Effects_of _Sound_on_

Fish23Aug05.pdf.

Levy, D.A. and Cadenhead, A.D. 1995. Selective 

tidal stream transport of adult sockeye salmon 

(Oncorhynchus nerka) in the Fraser River estuary. 

Canadian Journal of Fisheries and Aquatic 

Sciences, 52(1): 1-12.

Lacoste, K.N., Munro, J., Castonguay, M., Saucier, 

F.J. and Gagne, J.A. 2001. The influence of 

tidal streams on the pre-spawning movements 

of Atlantic herring, Clupea harengus L., in the 

St Lawrence Estuary. ICES Journal of Marine 

Science, 58(6): 1286-1298.

Metcalfe, J. and Hunter, E. 2003. Being there and 

getting there: balancing the costs of migration 

against the benefits of changing habitat for North 

Sea plaice. Journal of Fish Biology, 63 Supplement 1: 237-238.

Moser, M.L. and Ross, S.W. 1994. Effects of 

changing current regime and river discharge on 

the estuarine phase of anadromous fish migration. In Dyer, K.R. and Orth, R.J. (Eds.). Changes 

in Fluxes in Estuaries. Fredensborg, Denmark: 

Olsen & Olsen. 343-347.

Ohman, M.C., Sigray, P. and Westerberg, H. 2007. 

Offshore windmills and the effects of electromagnetic fields on fish. Ambio., 36: 630-633.

Westerberg, H. and I. Lagenfelt. 2008. Sub-sea power 

cables and the migration behaviour of the European eel. Fisheries Management and Ecology, 15: 

369–375
94

4.5 Fish: Resident

4.5.1 Introduction

This work group organized the elements of the 

resident fish receptor in terms of behavioral-, individual-, population-, and community-level effects. 

Resident marine fishes are defined as those saltwater 

fish that do not undergo diadromous migrations. 

Resident fish do undergo daily, tidal, and seasonal 

movements related to foraging, spawning, and energy 

conservation. Because this definition overlaps with the 

broad definition of migratory fish adopted in Section 

4.4, Migratory Fish, some species are included in both 

groups’ discussions. Depending on the locality, resident 

fishes form a broad taxonomic suite including but not 

limited to elasmobranchs (sharks, skates and rays) and 

their relatives, forage fishes (e.g., osmerids, clupeids), 

scorpaeniform fishes (e.g., rockfishes, greenlings, 

sculpins, ling cod), scombrids (e.g., tunas, mackerels) 

and flatfishes. These species can be oriented to the 

bottom or occur as pelagic fishes in the water column. 

The resident fish work group examined and prioritized 

the potential stressor effects that might result from 

pilot- and commercial-scale tidal energy installations. 

It is presumed that these devices would be installed in 

high-current areas with coarse seafloor substrates of 

cobble, boulders, and bedrock. Such environments are 

typical of many potential tidal energy sites in the United 

States, although there are notable exceptions (e.g., fine 

sediments in Cook Inlet).

Because the work group considered biological 

effects, its members identified the levels of biological 

organization as the receptor elements — namely 

behavior, individual, population, and community. In 

terms of behavior, the attraction or avoidance of resident fishes to or from the tidal devices were the main 

factors considered against the stressor effects. Stressor 

effects on individuals consisted of a much more diverse 

suite of factors including sub-lethal effects due to stress, 

disease, reproductive impairment, changes in growth, 

injury, or death. The physical effects of blade strike, 

impingement, or entrainment of eggs, larvae, juveniles, 

and adults were considered to be the most overt effects 

of device deployment. Stressor effects have the greatest 

potential to affect the environment when sublethal 

effects culminate in reducing population fitness or 

directly cause enough mortality to limit population 

growth and stability or compete with other ecosystem 

services provided by the population. Stressors from 

tidal energy devices also have the potential to affect 

resident fish at the community level, bringing about 

changes in species composition, food-web dynamics, 

and intraspecific interactions. The level of concern for 

effects is at the individual level for protected species, 

however, the group decided that population-level effects 

were the most important element to consider, followed 

by individual-level effects, behavioral effects, and 

community level effects.

The significance and uncertainty associated with 

stressor/receptor interactions are summarized in Figure 

33 for pilot-scale deployments and in Figure 34 for 

commercial-scale deployments. The colors denote 

significance and triangles denote uncertainty, as defined 

in Figure 24.
95

4.5.2 Receptor Matrix

Figure 34 – Receptor matrix: Fish: resident – commercial-scale deployment

Figure 33 – Receptor matrix: Fish: resident – pilot-scale deployment
96

The group considered each stressor effect on 

populations and individuals of resident fishes and 

discussed how to rate the potential effects and 

uncertainty. A “high” (red) impact stressor had the 

potential to greatly affect behavior, an individual, a 

population, or fish community. Effects may be either 

detrimental or beneficial. A “medium” (yellow) 

stressor effect was relatively less pervasive but, still 

was detectable at the different levels of biological 

organization. A “low” (green)” stressor effect was 

either not expected or detectable. A “low” level of 

uncertainty was defined as scientists having good 

understanding about the problem; a “medium” level 

of uncertainty meant that scientists have only basic 

knowledge about the problem; and a “high” level 

of uncertainty indicated that scientists barely know 

about the problem. The group also used the term 

“unknown” to emphasize stressor effects and uncertainties that were completely not understood.

4.5.3 Discussion

Energy removal and the cumulative effects of 

stressors had high or medium-high potentials to 

impact individuals and fish populations. Although 

pilot installations were thought to be of low effect 

for many stressors, the occurrence of protected 

species such as federally endangered or threatened 

fish species or fish that are the primary food stock 

of endangered marine mammals may increase the 

potential stressor effects of both pilot and commercial 

installations. The discussion of whether and to what 

extent stressors affected resident fish behavior, individuals, populations, or communities progressed from 

the reductionist to holistic scales of biological organization. Although the group prioritized populationand individual-level elements as the most important 

to consider, this approach provided a logical basis to 

address the level of knowledge and uncertainty about 

the stressors resulting from pilot- and commercialscale installations.

Dynamic effects of commercial installations are 

likely to have the highest potential to change resident 

fish populations. However, this finding was also 

derived with a high level of uncertainty regarding the 

individual- and population-level effects from rotor 

strikes, impingement, and entrainment of fish. 

Chemical effects were identified as a low stressor 

effect, both on the pilot- and commercial-scales. 

Chemical effects were primarily thought to be most 

important during the installation, maintenance, and 

removal of tidal devices because of the enhanced 

chance of oil spills due to collisions at sea. Knowledge exists from studies of chemical contamination 

from industrial and nonpoint sources and oil spills to 

provide the basis to predict chemical effects from tidal 

energy generation.

Acoustic effects include: sound generation during 

energy extraction when a device is rotating; installation process (although this would be just a short 

period of time); noise generation due to the turbulence wake of the turbine; and noise generated by 

supporting cables vibrating in the current. How or if 

these acoustic stressors affect resident fish are of high 

uncertainty, but were rated as medium effect in both 

pilot and commercial installations. 

Electromagnetic fields (EMFs) can be potentially 

sensed by fish and evoke avoidance or attraction 

behaviors (Ohman et al. 2007). Sharks, skates, rays, 

ratfishes, and other elasmobranchs can detect faint 

electric fields (Kalmjin 1982, Kajiura and Holland 

2002, McGowan and Kajiura 2009), and some fish 

have the capacity to sense the Earth’s magnetic field 

for orientation behavior (Lohmann and Johnsen 2000, 

Montgomery and Walker 2001, Hellinger and Hoffmann 2009). How or if tidal devices or cables that 

transmit power to shore affect fish behavior is both 

unknown in terms of effects and uncertainty. 

Energy removal by tidal device operation was 

deemed of low effect and low uncertainty for pilot 

installations but of unknown effect and high uncertainty for commercial installations. 

Cumulative effects on behavior were evaluated 

on the presumed long-term and long-lasting effects of 

all stressors, as well as any interactive compounding 

or cancelling among stressor effects. The cumulative effects on behavior were deemed as medium for 

pilot-scale installations and high for commercial-scale 

installations, and there was low uncertainty for pilotscale installations but high uncertainty for commercial-scale installations.
97

Behavior

Although the behavioral considerations were 

ranked at the third most important element, both pilotand commercial-scale tidal generation installations 

had high potential for affecting resident fish behavior. 

Tidal energy devices would either cause fish to avoid 

or be displaced by the static effect of device deployment or attract benthic and pelagic resident fish to 

the device, in what was termed the “artificial reef 

effect.” Avoidance or displacement could be caused 

if installation or operation of a tidal energy device 

alters habitat to a less favorable type. In many areas, 

artificial habitats consisting of quarried rock, concrete 

rubble, oil rigs, and sunken ships can attract marine 

fishes (Buckley and Hueckel 1985, Love et al. 2005, 

Bortone 2006, Whilhemsson et al. 2006). These 

artificial structures placed over fine or coarse sediments mimic natural rocky habitats for thigmotatic 

species, thus changing one fish community to another. 

Other fishes may be attracted to artificial habitats if 

food resources become newly concentrated near or on 

the structure. Although the artificial reef effect may 

seem beneficial, artificial reefs may serve to increase 

mortality on fish populations, because fishers and 

predators may kill more concentrated individuals on 

artificial structures than under natural conditions, or 

because the physical structure may disrupt the habitat 

for protected or other important resident fishes. This 

effect was rated as a low uncertainty, but the fish 

species and life stages that are attracted to tidal energy 

devices will need to be investigated for specific installations and areas. The artificial reef effect was also 

noted by Wilson et al. (2007) as Fish Aggregating 

Devices (FADs) in their evaluation of collision risks 

to fishes by tidal energy devices. Wilson et al. (2007) 

noted that demersal fishes may not be as affected by 

the static effects of the device as pelagic fishes might, 

but both demersal and pelagic fishes may encounter 

and collide with rotating turbines during feeding or 

other excursions into the water column. Rockfishes in 

the Pacific Northwest and Alaska are good examples 

of species that are attracted to artificial structures, with 

three species currently listed as threatened or endangered in Puget Sound. Given their behavior and sensitivity to overfishing, they may serve as good models to 

investigate behavioral effects by tidal devices.

Because of the anticipated attraction or avoidance 

behavioral effects, the dynamic effects of tidal devices 

were anticipated to have medium effects on resident 

fishes in both pilot- and commercial-scale installations. Open and shrouded blades may have different 

effects and responses by resident fish. 

Video observations of fish schools taken at the 

OpenHydro tidal energy device deployed at the 

European Marine Energy Centre (EMEC) found that 

benthopelagic fish such as pollock moved in close 

to the downstream side of the turbine during slow 

currents (<1.2 m/s) when the turbine was rotating 

slowly or was stationary but were not near the turbine 

during faster currents when the turbine was rotating at 

higher speeds (e.g., 20 rpm). However, because these 

higher rotational speeds are accompanied by stronger 

currents, it was not known whether the change in 

behavior was caused by blade movement or if it was a 

natural response to the tidal currents. 

The body of information developed under the 

Roosevelt Island Tidal Energy (RITE) demonstration 

project showed similar results (FERC Draft License 

application Project 12611, November 2008). Images 

obtained with a concurrent DIDSON camera and 

split-beam transducer showed resident and migrating 

fish present during slack water, when the devices were 

not operating. The images also showed that fish were 

not generally present when the velocity of the water 

increased to greater than 0.8 m/s and the machines 

were operating. On one occasion, images showed fish 

passing by the rotating machine blades along hydrodynamic streamlines. These observations, coupled 

with long-term stationary split-beam transducer arrays 

around the six demonstration units, suggest two types 

of fish behavior in reaction to stationary and rotating 

blades and that fish are not abundant when blades are 

rotating, due to a combination of accelerated currents, 

detection, and passage around machine flow lines. 
98

These results highlight the behavior of fish using 

tidal currents to make directed movements to and 

from basins during flooding or ebbing tides. How 

commercial-scale deployment of tidal generators 

would affect these behavior is still unknown, but 

Wilson et al. (2007) suggest that avoidance behavior 

is one of the most important variables in predicting 

collisions and may be influenced by body size, time of 

day, current speeds, season, and turbidity. A medium 

level of uncertainty surrounds this dynamic stressor 

effect.

Physical Effects on Individuals

The potential effects of tidal power generation on individual fish were considered separately 

from behavior. The physical effects to individuals 

could impair fitness and survival in terms of growth, 

disease, reproductive failure, injuries, and death. 

Although static effects on individuals were considered low in effect and uncertainty for pilot- and 

commercial-scale installations, dynamic effects had 

high potential to affect individuals for commercialscale installations and have medium effect for pilotscale plants. However, blade strikes, entrainment, or 

impingement of resident fish had medium and high 

uncertainty. Wilson et al. (2007) conclude that rotor 

speeds will be at least as powerful as the tail stuns 

with which killer whales stun and kill fish and that 

contact with rotating blades can be fatal. Wilson et 

al. further suggest that demersal fishes may be more 

resistant to blade contact but that dynamic effects 

could include sublethal wounds, direct mortality, 

stress caused by experiencing pressure waves or 

unusual currents, decreased growth, and reproductive 

failure. The scaling up of these effects to the population level has the highest priority in understanding the 

effect of tidal energy development to resident fish. As 

noted in the previous section, post-installation monitoring at EMEC (shrouded rotor, OpenHydro turbine) 

and at RITE (open rotor, Verdant Power turbine) have 

not recorded any incidences of blade strike. 

The chemical effects are likely important in 

the case of accidental spills during the installation, 

removal, or, especially, the maintenance of tidal 

generators. Because of the low amounts of lubricants 

used in tidal generators, these were not anticipated 

to have significant impacts. However, the chemicals used to abate settlement of invertebrates (e.g., 

anti-fouling paints) had an unknown level of effect. 

The installation of a pilot plant was not anticipated 

to have great risk to oil spills or chronic leaching of 

toxic substances, but these potential effects increased 

with commercial installations to a medium effect with 

medium uncertainty. Oil spills due to accidents or 

collisions in high-traffic areas have been documented 

to directly kill fish or contaminate them. Petroleum 

products have been shown to cause higher risk of 

cancers and reproductive impairment in resident 

fishes (U.S. EPA 1999). 

The other stressor effects on individuals, 

including acoustic, EMFs, and energy removal, 

were considered to be of low effect and mostly low 

uncertainty for pilot installations. Acoustic production by tidal energy devices was not considered to 

have a significant physical effect on individual fish in 

either pilot- or commercial-scale installations. EMFs 

had potentially a medium effect in commercial-scale 

installations but, as with behavioral effects, the uncertainty was high because EMFs could have an important role on suitability of the surrounding habitat for 

resident fishes. The potential for energy removal to 

physically affect individuals was unknown, with high 

uncertainty at the commercial scale. This is anticipated to be a far-field effect where waters downstream 

of the facility may suffer from poor water quality due 

to decreased tidal energy flushing the basin. Fish can 

suffer less growth, reproductive failure, and death 

from hypoxia and high water temperatures (Diaz 

2001, Palsson et al. 2008). Because of the potential 

for synergistic interactions, the cumulative stressor 

effects had high potential to affect individual resident 

fish, but the nature of these interactions had high 

uncertainty.
99

Population

Behavioral and physical impacts to individuals 

may accumulate and interact among stressors to affect 

populations. Although diffuse behavioral effects 

or physical impacts on a few individuals may not 

impact populations, if populations are small, any 

loss or behavioral shift may greatly affect population stability. If populations are large, greater effects 

may still impact population health or compete with 

ecosystem services provided by the population to 

predators and humans who harvest or depend upon 

species in other manners. Because of this, stressor 

effects on the populations were considered the most 

important element among behavioral, individual, and 

community elements for resident fish.

Almost all population-level effects were considered to be low for pilot-scale installations of tidal 

energy devices. However, the uncertainty was variable, ranging from low for energy removal and cumulative effects to medium for acoustic, chemical, and 

static stressors and high for dynamic and EMF effects. 

For EMFs, the potential effects were unknown both 

for pilot- and commercial-scale installations. Of all 

potential tidal energy effects, the dynamic stressor 

effects from tidal generators had the highest potential to affect populations. Amplifying the effects and 

uncertainties involving physical effects on individuals, the cumulative impacts of strikes, entrainment, 

and impingement may negatively affect resident fish 

populations. Whether and to what extent dynamic 

effects can cause reproductive failure or mortality 

on a population basis has high uncertainty. Static, 

chemical, and acoustic stressors have a medium 

potential to impact resident fish populations as a 

result of commercial installations, but the uncertainty 

ranges from medium to high, based on the lack of 

knowledge from behavioral and physical effects on 

individuals. Energy removal has an unknown effect 

on populations with high uncertainty. Using Admiralty Inlet, as an example, a large field of tidal energy 

devices could remove enough tidal energy to reduce 

the flushing of Hood Canal and other Puget Sound 

basins. During the past 10 years, fish kills, behavioral 

shifts, and other sub-lethal impacts to hypoxia have 

been documented in Hood Canal (Palsson et al. 2008). 

Decreasing flushing of this basin could increase the 

frequency of fish kills that already have removed 1/4 

to 1/3 of the rockfish and lingcod populations at one 

prominent Hood Canal locality (Palsson et al. 2008). 

The cumulative stressor effects of commercial installations were rated as medium-high, in part because 

of the energy removal effects but also on the potential for stressor interactions acting to suppress fish 

populations. The “artificial reef effect” from the static 

stressor described previously could cause resident 

fish to be continually attracted to tidal generators but 

continually removed from the population by mortality 

or injury from rotating turbine blades. This cumulative stressor has a high level of uncertainty.

Community

Community-level impacts were not fully 

considered but, at a minimum, were rated the same 

as population-level impacts. The same issues for 

population-level impacts were anticipated to affect 

communities in terms of altering species composition, including measures of species richness, diversity, and evenness. Of note, however: static effects 

were likely to greatly alter the community structure 

from fishes that would normally occupy coarse sediments found in dynamic tidal habitats to fishes that 

occupy rocky habitats with greater structural relief. 

Community-level effects could also be anticipated 

from tidal energy removal. Using the same model of 

potential far-field effects in Hood Canal, increased 

hypoxic events resulting from less flushing due to 

tidal energy removal could have community-level 

impacts affecting the species composition of rocky 

and unconsolidated habitats, as described by Palsson 

et al. (2008).

Gaps in Understanding

The greatest information gaps for dynamic and 

energy removal stressors are discussed in more detail 

in the following sections. Other significant data gaps 

are how to understand the cumulative and interactive 

impacts of the stressors to populations and biological 

communities and how acoustic and EMF stressors 

may affect fish behavior and fitness. A combination of laboratory experiments, modeling, and field 

experiments is the suggested approach to reducing the 

identified levels of uncertainty. Laboratory experiments examining behavior of fish to acoustic and 

EMF stressors could provide the basic inputs to a 
100

model that predicts fish responses to these stressors 

at a given site. Field experiments would then be used 

to monitor and test model hypotheses. In the case of 

EMF, acoustic telemetry could be used to examine if 

shark behaviors are affected by existing underwater 

transmission lines, and measurement of magnetic 

and electrical fields at existing transmission cables 

could determine whether EMFs are produced that 

are detectable (from ambient conditions). Stress and 

sub-lethal effects may occur but are poorly understood; therefore, biomarkers (such as stress hormones 

taken from blood samples) could be used to assess 

the effects of barotrauma, acoustic stimulation, and 

EMFs. Laboratory studies would first be needed 

to determine the dose-response curve. One other 

data gap is scaling up experimental findings from 

pilot-scale observations to commercial installations, 

because when turbines are grouped, the probability 

of physical interaction between the device and fishes 

increases, but the increases may not be linear.

Approaches to Monitoring

The installation of pilot- and commercialscale tidal generators would require a significant 

monitoring effort to assure that experimental and 

modeling results are valid in pilot- and commercialscale installations and that unforeseen responses or 

conditions are identified for subsequent adaptive 

management. The BACI approach was identified as 

a desired approach (Smith 2002). Monitoring data 

at the different scales before generator deployment 

would be preferred. Subsequent to deployment, 

long-term monitoring may be required to determine 

population-level impacts. Locating a suitable control 

site is often difficult in high-current areas because 

fine-scale differences in habitats or current patterns 

may not match the sites where tidal energy devices 

are deployed. For example, the BACI approach was 

ineffective at detecting changes at the RITE demonstration project. Although pre- and post-installation 

monitoring was attempted at RITE from 2005-2009, 

the dynamic nature of site did not allow for appropriate before-and-after observations, as in a river/dam 

environment (Verdant Power 2008, Colby and Adonizio 2009). However, control sites do have the potential to provide the basis to observe large-scale changes 

that may not be due to tidal device deployment. 

Cooperative monitoring among different management 

authorities may provide synergies to offset some of 

the monitoring effort. For example, fishery agencies may be conducting population surveys of fishes 

and provide the perspective to evaluate population 

impacts.

A host of monitoring tools is available, but 

some may have limited effectiveness due to the 

high currents in the area or the operation of the 

blades and turbines. These tools include Acoustic 

Doppler Current Profilers (ADCPs), water quality 

meters, remotely-operated vehicles (ROVs), scientific echosounders, mid-water and plankton nets, 

advanced acoustic or visual plankton samplers, threedimensional acoustic arrays, and acoustic telemetry 

systems. These devices could be deployed at the sites 

to measure avoidance and attraction, direct injuries or 

mortalities, alteration in current patterns, and abundance, or these devices may need to be placed or used 

outside the tidal operation areas to detect far-field 

effects. A key challenge will be deploying these tools 

during periods of turbine operation, when currents 

exceed 2 m/s.

4.5.4 Priority Area: 

Population and individual level effects due to the 

dynamic stressor

Description

Dynamic effects of device operation, especially 

rotor strikes, impingement, and entrainment of 

commercial installations have the highest potential to 

negatively affect individuals and enough individuals 

to impair population stability. 

Gaps in Understanding

The effects of physical strikes are poorly understood but have the highest population impacts in a 

commercial build-out. Although there was consensus 

among workgroup participants on the uncertainty, 

there was no agreement on the extent of knowledge 

or potential effects. Impacts to protected species 

could occur in both pilot- and commercial-scale 

installations. The greatest data gap is the frequency 

and extent of individual strikes, entrainment, and 

impingement on species expected in a project area. 

Technology does exist to evaluate species vulnerability first by quantifying expected startle thresholds, 
101

reaction distances, avoidance behavior, and swimming speeds from literature studies or laboratory 

studies. These data can be used to develop models of 

fish behavior, as suggested by Wilson et al. (2007), 

to predict collision rate as a function of encounter, 

avoidance, and evasion rates. These models need to be 

validated in the field using acoustic tags and acoustic 

receiver arrays to track three-dimensional fish movement, behavior, and collisions during pilot operations. 

However, the tagging intensity and receiver density 

required to carry out such studies may entail a high 

cost for the relevant spatial scales. Field data should 

be used to validate models of effects to individuals 

that can be subsequently used in demographic and 

viability models to evaluate population level effects. 

A data gap still exists on how tidal energy devices 

may affect eggs, larvae, and juveniles. These early 

life stages will need to be investigated in the laboratory or, potentially, with conventional plankton nets, 

high frequency sonar, or other technologies, although 

conducting these evaluations in the field will be 

extremely difficult.

Approaches to Monitoring

As stated above, acoustic telemetry and acoustic 

arrays provide several methods to monitor individual 

specimens. However, population-level surveys using 

ROVs and conventional fish surveys, such as trawl 

surveys or demographic population models, may be 

required to evaluate population-level effects. Cooperative monitoring efforts will likely produce more 

comprehensive results.

4.5.5 Priority Area: 

Far-field effects of energy removal at the 

population level

Description

Commercial installations may remove enough 

tidal energy to further decrease circulation in poorly 

flushed basins. Less tidal energy may increase the 

extent and frequency of poor water quality events 

such as hypoxia, high temperatures, and excessive 

nutrients.

Gaps in Understanding

The uncertainty level is high, with most scientists 

agreeing that energy removal may diminish flushing 

in receiving water bodies. For example, population 

impacts due to hypoxia have been well documented 

in Hood Canal, so operation of a commercial array 

of tidal generators in Admiralty Inlet could influence the frequency of fish kills. A comprehensive 

oceanographic model that predicts the circulation 

patterns, flushing rates, and water quality could be 

used to predict the influence of removing tidal energy 

in project areas. However, the effectiveness of such 

models to accurately predict the effect of perturbations may be limited (see Physical Environment: Farfield, Section 4.2). Pilot plants could be used to verify 

some model inputs and model results. However, some 

of the predictions may not be validated until a fullscale commercial project is installed.

Approaches to Monitoring

A comprehensive system of remote oceanographic sensors would be needed to monitor for 

changes in current profiles, flushing rates, and other 

oceanographic properties. If changes are found, then 

further ecological monitoring would be required to 

detect population-level impacts. This would be a very 

costly stand-alone effort and would need to leverage 

existing monitoring activities to be viable (Additional 

discussion of this topic is presented in Section 3.6, 

Energy Removal. 
102

4.5.6 Recommended References

Bortone, S.A. 2006. A perspective of artificial reef 

research: the past, present and future. Bulletin of 

Marine Science, 78(1): 1-8.

Buckley, R.M. and G.J. Hueckel. 1985. Biological 

processes and ecological development on an artificial reef in Puget Sound, Washington. Bulletin of 

Marine Science, 37: 50-69.

Colby, J. and Adonizio, M. 2009. Hydrodynamic 

analysis of kinetic hydropower arrays. Waterpower XVI, Spokane, WA. July 27-30, 2009. 

Diaz, J. 2001. Overview of hypoxia around the world. 

Journal of Environmental Quality, 30: 275-281.

EPA (U.S. Environmental Protection Agency). 1999. 

Wildlife and Oil Spills. In Understanding Oil 

Spills and Spill Response. Office of Emergency 

and Remedial Response. EPA 540-K-99-007: 

21-26. Available at http://www.epa.gov/oem/

content/learning/pdfbook.htm.

Hellinger, J. and Hoffmann, K.P. 2009. Magnetic field 

perception in the Rainbow Trout, (Oncorhynchus 

mykiss). Journal of Comparative Physiology 

A-Neuroethology Sensory Neural and Behavioral 

Physiology, 195(9): 873-879.

Kajiura S.M. and K.N. Holland. 2002. Electroreception in juvenile scalloped hammerhead and 

sandbar sharks. Journal of Experimental Biology, 

205(23): 3609-3621.

Kalmijn, A.J. 1982. Electric and magnetic-field detection in elasmobranch fishes. Science, 218(4575): 

916-918.

Lohmann, K.J. and Johnsen, S. 2000. The neurobiology of magnetoreception in vertebrate animals. 

Trends in Neurosciences, 23(4): 153-159.

Love, M.S., Schroeder, D.M. and Lenarz, W.H. 2005. 

Distribution of bocaccio (Sebastes paucispinis) 

and cow cod (Sebastes levis) around oil platforms 

and natural outcrops off California with implications for larval production. Bulletin of Marine 

Science, 77: 397-408.

McGowan, D.W. and Kajiura, S.M. 2009. Electroreception in the euryhaline stingray, (Dasyatis 

Sabina). Journal of Experimental Biology, 

212(10): 1544-1552.

Montgomery, J.C. and Walker, M.M. 2001. Orientation and navigation in elasmobranchs: Which 

way forward? Environmental Biology of Fishes, 

60(1-3): 109-116.

Öhman, M.C., Sigray, P. and Westerberg, H. 2007. 

Offshore Windmills and the Effects of Electromagnetic Fields on Fish. Ambio 36(8): 630-633.

Palsson, W.A., Pacunski, R.E., Parra, T.R. and Beam, 

J. 2008. The effects of hypoxia on marine fish 

populations in southern Hood Canal, Washington. In Mitigating Impacts of Natural Hazards 

on Fishery Ecosystems. McLaughlin, K. (Ed.). 

American Fisheries Society Symposium Series 

64: 255-280.

Smith, E.P. 2002. BACI design. In Encyclopedia of 

Environmetrics, Volume 1 (Shaarawi, A. and 

Piegorsch, W. (Eds.). Chichester, UK: John Wiley 

and Sons, Ltd. 141-148. 

Verdant Power. Roosevelt Island Tidal Energy Pilot 

License Application, FERC No. 12611. Filed 

December 2010. Volumes 1-4 available at http://

www.theriteproject.com/Documents.html.

Wilhelmsson D., Malm, T. and Ohman, M.C. 2006. 

The influence of offshore windpower on demersal 

fish. ICES Journal of Marine Science, 63: 

775-784.

Wilson, B., Batty, R.S., Daunt, F. and Carter, C. 

2007. Collision risks between marine renewable 

energy devices and mammals, fish and diving 

birds. Report to the Scottish Executive. Scottish 

Association for Marine Science. Oban, Scotland, 

PA37 1QA.
103

4.6 Marine Mammals and Seabirds

4.6.1 Introduction

There is minimal information presently available on the potential impact of tidal energy systems on 

marine mammals and seabirds. Substantial knowledge 

gaps remain on baseline natural history and habitat use 

for most of the potentially affected species, for specific 

sites, and at relevant spatial and temporal resolution. 

Such data are critical to predicting risk and type of 

interaction with tidal energy devices. Critical knowledge gaps extend to behavioral ecology and on how 

most species sense, perceive, and react to the environment and elements therein, potentially including tidal 

energy devices. Such information is also essential for 

the characterization of possible behavioral responses 

to operating devices. Acoustic effects are of particular 

concern within the context of behavioral ecology (how 

animals sense and respond to elements in their environment), and knowledge gaps extend to the lack of data 

on acoustic signatures of operating devices (at least, 

in terms of information available within the public 

domain) as well as the characterization of background/

ambient noise levels at specific sites. These knowledge gaps are exacerbated by a lack of standards 

for assessing ambient sound levels and the acoustic 

signatures of operating devices during periods of high 

current velocities (an explanation of this is contained 

in Bassett 2010).

Of the range of potential stressors considered, 

physical strike (in relation to both static and dynamic 

presence of tidal energy devices) and acoustic effects 

were considered of highest concern (noise from 

device installation was identified as a specific issue of 

concern). Both stressors are associated with high levels 

of risk and effect uncertainty. On the whole, risk levels 

were deemed low in terms of likely population-level 

impacts. However, the group recognized that critically 

small and/or sensitive populations exist in some areas 

where real or publicly perceived impacts on single 

individuals may result in drastic regulatory consequences. Impacts for commercial-level installations 

are likely larger than for pilot installations and related 

to the extent and spatial arrangement of the installation. However, scaling of impacts is not necessarily 

directly linked to the scope of installations. Regarding 

individual animals, the most likely affected receptor 

elements associated with nonoperational physical presence (i.e., collision) includes possible consequences 

ranging from minor injury to mortality. The most 

likely affected receptor elements for dynamic operation of devices include all levels of physical injury 
104

already associated with static presence, as well as 

possible impacts on foraging and migratory behaviors or population displacement. Most likely affected 

receptor elements associated with acoustic effects 

include local habitat use and foraging behavior, as 

well as migratory pathways. Insufficient time was 

available to evaluate other stressors.

The significance and uncertainty associated with 

stressor/receptor interactions are summarized in 

Figure 35 for pilot-scale deployments and in Figure 

36 for commercial-scale deployments. The colors 

denote significance and triangles denote uncertainty, 

as defined in Figure 24.

Figure 35 – Receptor matrix: Marine mammals and seabirds – pilot-scale deployment

4.6.2 Receptor Matrix
105

Figure 36 – Receptor matrix: Marine mammals and seabirds – commercial-scale deployment
106

4.6.3 Discussion

Many of the considerations raised and discussed 

in this group are specific to tidal energy device 

installation sites, technology, and the natural history 

of the resident or migratory species potentially 

affected by installation, presence, or operation of tidal 

energy devices. It was noted that, while impacts or 

effects may exist, these are not always negative. For 

example, migratory routes may be affected by tidal 

energy devices resulting in altered pathways without 

any detectable or implicit effect on individual animal 

energetics, survival, or reproductive success. Generally, commercial-scale impacts and concerns are 

likely larger and higher than for pilot-scale installations and may be related to installation scope (extent 

and spatial arrangement), although impacts cannot 

necessarily be directly scaled to project size (e.g., 

installed generating capacity). 

Physical presence (static and dynamic) and, 

specifically, physical strike, and acoustic effects were 

identified as environmental issues of top priority. 

Physical presence, excluding strike, may result in 

altered migratory pathways or in population displacement, including blocking effects at locations of 

constricted topography that may occur outside of 

migratory pathways. These effects could alter the use 

of an area or the use of resources within an area. 

The species in this receptor group are very 

heterogeneous in natural history and habitat use. Not 

all technologies/designs have the potential to affect 

seabirds, with designs protruding above water level 

more likely to result in effects on seabird. Subsurface 

devices are commonly located at depths where interactions with birds are unlikely. All technologies may 

potentially affect marine mammals.

4.6.4 Priority Area: Physical presence

Description

The primary consideration for the physical presence of tidal energy devices is strike, through either 

static presence or dynamics of operating devices. The 

consequences of strike range from non-injury contact 

to minor or even fatal injuries. Indirect effects are 

possible, including mortality resulting from entrapment/entanglement and drowning. Secondary effects 

of physical presence were discussed, including potential function of tidal energy devices as prey aggregation or debris aggregation devices. Prey aggregation 

was deemed less likely due to high currents at installation locations (although fish aggregations have been 

observed in the wake of a test turbine at the EMEC 

during currents less than 1.2 m/s). Debris aggregation could occur (in part, due to high currents) and 

may have impacts on marine mammals and seabirds. 

Dynamic presence may also affect local habitat use 

and foraging behavior (i.e., through altered currents/

upwellings and prey fields) and may result in area 

avoidance with possible impacts on migratory 

behavior and pathways, as well as increased energy 

demands associated with behavioral changes.

Gaps in Understanding

Workgroup participants agreed that likelihood and potential impacts of effects from static or 

dynamic presence are associated with high levels of 

uncertainty in general and also in relation to different 

technologies (i.e., shrouded versus open turbine 

designs). This uncertainty is directly related to the 

paucity of information on how most of the potential 

target organisms perceive the environment at relevant 

scales, how they might detect and respond to a tidal 

energy device, and what options animals might have 

to avoid a tidal energy device. Data scarcity specifically includes variation in behavioral ecology and 

habitat use with respect to locations, seasons, and age 

and sex of potentially affected organisms. 

Participants also noted and discussed the difference between likely or actual impact versus perceived 

impact of tidal energy devices, especially in terms of 

public opinion. Even the perception of lethal impact 

on marine mammals, in particular, may result in 

extreme regulatory constraints on device operation.
107

Key knowledge gaps identified by the group 

include sufficiently detailed information on the 

basic natural history and habitat use for most of the 

potentially affected species, at the relevant temporal 

and spatial scales. For example, in some areas, local 

population sizes, vital rates, and demographics are 

not sufficiently well described to populate a risk 

matrix. Although migratory pathways are known for 

some species, this information is often available at 

larger temporal and spatial scales than required for 

assessments of the risk of adverse modifications in 

relation to tidal energy devices, particular at the pilot 

scale. Other examples include lack of information 

on area-specific habitat use, including area-specific 

prey selection, again at relevant spatial and temporal 

scales. This (required) information is likely specific to 

species, sites, and seasons. Such information is essential for the development of risk models and also as 

baseline data for the monitoring of potential impacts.

Key knowledge gaps also exist on how animals 

perceive elements of their environment, including 

how they might sense an operating tidal energy 

device. Sensory capabilities and sensory pathways are 

not well described for many species. Consequently, 

predictions of behavioral responses, energetic consequences, and risk assessments are impossible to 

provide.

Approaches to Monitoring

Rather than presenting specific monitoring 

techniques or specific experimental designs, the 

group decided to highlight conceptual approaches 

and elements. In addition, the group recognized the 

importance of developing a comprehensive research 

and monitoring plan that should be based on a 

broad consensus amongst technology companies, 

researchers, agencies, non-government organizations, 

and other involved parties, and should involve local 

stakeholders as much and as early as possible and 

practical. 

The group briefly discussed the possibility of an 

adaptive research approach based on first monitoring 

for and identifying ultimate effects (i.e., populationlevel impacts, changes in vital rates) and progressively moving towards more proximate assessments 

of effects and, possibly, mechanisms for any species 

potentially affected. However, this approach was 

deemed impractical due to empirical difficulties and 

also due to the low likelihood of finding (or modeling) 

population level effects exceeding natural variability, 

in particular for pilot-scale deployments.

An alternate approach was proposed, based on 

assessments that move from possible proximate 

effects and mechanisms (i.e., individual animal 

behavioral responses or energetics effects) to more 

ultimate effects. In order to effectively allocate 

limited resources, this approach might be more 

fruitful if possibly affected species are ranked in order 

of concern or likelihood of impact. 

The group recognized that physical strikes as one 

of the highlighted areas of concern may represent rare 

events, which may require a significant amount of 

resources for detection/quantification. This potential 

tradeoff between cost and knowledge gained needs to 

be considered within the comprehensive, consensusbased plan, and while weighing potential populationlevel impacts — particularly for critically small or 

sensitive populations. Within this context, the empirical distinction between hypothetical strike-related 

mortalities (proximate cause) and population displacement (a hypothetical ultimate effect, dependent on 

monitoring approaches utilized) may be very important. Research and monitoring approaches can build 

on existing and well-proven technologies and experimental designs, while considering or expanding the 

use of novel techniques, where appropriate. Details 

of the marine mammal monitoring and mitigation 

effort undertaken by Marine Current Turbines Ltd. are 

described in Section 1.6.3 of this report. 

Either type of approach should be tailored to the 

needs (including resolution) of the issue at hand, with 

comprehensive project and research plans updated 

as results are obtained. All data and results should be 

made available in the public domain.
108

Although potential effects of tidal energy devices 

on marine mammals and seabirds are likely specific 

to sites and seasons, monitoring should not be 

restricted to locations and seasons of operation but 

should extend to larger spatial and temporal scales 

for the purpose of comparability and for the integration of effects that may transcend more directly 

affected areas. For example, ultimate effects of the 

proximally created impacts of tidal energy devices 

may only become apparent at distant sites of reproduction. Furthermore, any assumed alterations of 

population trajectories have to be viewed within the 

context of non-anthropogenic variance, cycles, and 

trends. There are, however, two challenges to such 

studies for marine mammals and seabirds whose 

life stages involve large spatial scales. First, study 

methodology would need to discriminate between 

ultimate effects from tidal energy devices and other 

proximate anthropogenic stressors in order to test 

specific hypotheses (Further discussion is contained in 

Section 3.7.6, Cumulative Effects). Second, the cost 

of life-cycle monitoring could be very high and, as 

with the question of blade strike, the tradeoff between 

the knowledge likely to be gained and study cost must 

be considered. However, without studies to establish 

the linkage between proximate stressors and ultimate 

effects, regulatory agencies may be required to take 

the precautionary approach of limiting exposure of 

some populations to proximate stressors.

4.6.5 Priority Area: Acoustic effects

Description

Acoustic effects may result in altered area use 

and foraging behavior, potential impact on migratory pathways, and population displacement, as well 

as interference with navigation and communication. 

Population displacement was considered as a distinct 

issue from migratory behavior, in part because of 

the possibility of distinct mitigation measures (i.e., 

in relation to timing of migration). In both (hypothetical) instances, individuals may avoid areas with 

operating tidal energy devices, but impacts may affect 

distinct life-history stages or portions of annual life 

cycle, and may or may not include critical habitat for 

protected species. Noise related to device installation 

is of particular concern, because higher sound pressure levels and impulse-type sound are more likely, 

and the potential for injurious sound pressure levels 

are much higher, than during continued operations. 

Thus, the potential impact during installation may be 

high, although this would be of shorter duration than 

for the continued operation of a tidal energy device. 

However, more mitigation opportunities with respect 

to installation noise effects may exist (as discussed in 

Section 3.4.4). 

Gaps in Understanding

The group noted a nearly complete lack of 

information/data on noise signatures of tidal energy 

devices in the public domain (see Section 3.4, 

Acoustic Effects). This contributes to the high levels 

of uncertainty associated with assessment of risks 

and potential impacts of acoustic effects. Marine 

mammals are much more likely to be affected by 

noise from tidal energy devices than are seabirds. 

Noise is not considered a problem for seabirds 

— even if they can perceive it, they are known to 

habituate to noise. Conversely, the receptor elements 

considered problematic for marine mammals are 

driven by issues that may not be resolved through 

habituation (i.e., masking of acoustic communication 

and navigation functions). Species relying on sonar 

for orientation, navigation and feeding, or underwater 

acoustic communication were considered by the 

group to be more likely to be affected by tidal energy 

devices.

Virtually no information exists on the behavioral 

response of species of concern to acoustic signals, in 

relation to intensity, type, frequency, etc. This is, in 

part, due to regulations on marine mammal research. 

When coupled with the absence of data (in public 

domain) on noise types and levels generated by tidal 

energy devices and on ambient and background noise 

levels, predictions of behavioral responses, energetic 

consequences and risk assessments are impossible to 

provide. 
109

Approaches to Monitoring

In addition to the general monitoring discussion in the previous section, a few select specific 

approaches, experimental designs, or techniques were 

mentioned or briefly discussed. Acoustic controlled 

exposure experiments were specifically recommended 

to establish biologically relevant exposure levels, as 

well as behavioral response parameters and thresholds. It was noted that the National Marine Fisheries 

Service exposure thresholds for behavioral disturbance from continuous noise (120 dB RMS) are based 

solely on studies of large whales and limited observations. Thus, these thresholds are not very robust. 

There is a need to standardize exposure criteria and 

thresholds (Southall et al. 2007). The use of both 

moored active sonar for near-field monitoring, and 

passive acoustic listening were techniques mentioned 

as having potential, as was high resolution behavioral 

telemetry. However, the primary bands or side bands 

for active sonars used to make these observations 

may be audible to marine mammals and result in 

confounding avoidance behavior, and the engineering 

required to design moorings for high current environments is non-trivial. 

4.6.6 Recommended References

Southall, B.L., Bowles, A.E, Ellison, W.T., Finneran, 

J.J., Gentry, R.L., Greene, C.R., Kastak, D., 

Ketten, D.R., Miller, J.H., Nachtigall, P.E., Richardson, W.J., Thomas, A. and Tyack, P.L. 2007. 

Marine Mammal Noise Exposure Criteria: Initial 

Scientific Recommendations. Aquatic Mammals, 

33(4): 411-521.

Wilson, B., Batty, R.S., Daunt, F. and Carter, C. 

2007. Collision risks between marine renewable 

energy devices and mammals, fish and diving 

birds. Report to the Scottish Executive. Scottish 

Association for Marine Science. Oban, Scotland, 

PA37 1QA.
110

4.7 Ecosystem Interactions

was geographically diverse, with experience in or 

knowledge about high-energy tidal systems in Puget 

Sound, Alaska and the United Kingdom. All of the 

session participants were active in the wide-ranging 

discussions.

The significance and uncertainty associated 

with stressor/receptor interactions are summarized 

in Figure 37 for pilot-scale deployments and in 

Figure 38 for commercial-scale deployments. The 

colors denote significance and triangles denote 

uncertainty, as defined in Figure 24.

4.7.1 Introduction

For this work group session, participants 

attempted to integrate the possible environmental 

effects of tidal energy development across the 

receptor groupings, whereas, the cumulative effects 

session was intended to integrate across the stressor 

groupings. Accordingly, the discussion in this session 

largely addressed processes amongst the receptors, 

focusing largely, but not solely, on food web interactions and trophic dynamics. The breakout group 
111

Figure 38 – Receptor matrix: Ecosystem interactions – commercial-scale deployment

Figure 37 – Receptor matrix: Ecosystem interactions – pilot-scale deployments

4.7.2 Receptor Matrix
112

4.7.3 Discussion

Because of the complexity of these systems, 

generalizations have limited value, and site-specific 

measurements are essential to understanding the 

possible or probable effects in any given system with 

a given technology and magnitude of development. 

In this context, pilot-scale projects and site-specific 

baseline and monitoring programs are considered 

very important. These systems are so turbulent that 

the conceptual approaches of water column stratification and stability, critical depth, and pelagic-benthic 

decoupling seem largely inapplicable at potential 

project sites, although these conceptual approaches 

may be key to understanding any far-field ecosystem 

interactions related to energy removal.

It is important to consider that there can be positive effects as well as negative ones. With changes 

brought about in ecosystem interactions, there are 

likely to be “winners” and “losers” in the species 

affected. These changes will be appropriately 

judged in the context of the overall integrity of the 

ecosystem, the specific management goals established 

for the ecosystem, and consideration of species or 

populations known to be at risk.

The relative spatial scales of tidal energy conversion operations (local) versus the spatial scales of the 

ecosystem (e.g., regional scale) were judged by the 

participants as likely to prevent significant system 

scale effects (i.e., environmental impacts) through 

ecosystem interactions, per se. There was no readily 

apparent nexus or pathway (at the level of a fatal 

flaw) between the envisioned stressors and the food 

web and trophic dynamics, as understood at a general 

level. However, given projects of sufficiently large 

size or number, ecologically significant effects would 

likely occur.

Uncertainty was generally moderate to high for 

effects seen as highly likely to have a substantial 

impact and generally low for effects seen as unlikely 

to have a substantial impact. That is, the group had 

much more confidence in its ability to rate effects as 

unlikely or low significance, as opposed to measurable and ecologically significant effects. 

Trophic-dynamic ecosystem effects were viewed 

as being highly likely at local scales (even with a pilot 

project) and, perhaps, regional scales (with a commercial build-out), driven by attraction of predators and, 

possibly, by changes in the distribution and abundance 

of prey (especially forage fish) in both the pelagic and 

benthic habitats. This does not, however, mean that 

these effects will necessarily constitute significant 

deleterious impacts (see prior discussion of spatial 

scales). Although there was only moderate uncertainty 

about the high likelihood of trophic changes overall, 

there was high uncertainty about the likelihood of true 

top-down trophic changes (i.e., driven by changes in 

predation at the higher trophic levels). These latter 

effects were seen as equally likely for pilot- versus 

commercial-scale build-outs, but with expression at 

much broader spatial scales with a single or multiple 

commercial build-outs.

Energy removal was seen as having a low to 

moderate likelihood of mediating effects at the 

ecosystem scale with very large commercial buildouts, although the proportional amount of energy 

withdrawn from the system is probably quite low as 

predicted by initial efforts at modeling. These effects 

would be expressed in hydrology/hydrography and 

water chemistry in dead-ended systems (i.e., in estuaries and fjords but not in open-ended straits or passes 

between islands in archipelagos), where mixing at 

the landward end is largely dependent of the amount 

of tidal energy supplied. For example, deep-water 

replacement in inner basins, which is often density 

driven and episodic, could be reduced and exacerbate 

or result in hypoxic or anoxic conditions.

There was agreement that bioaccumulation could 

be of concern. However, it was viewed as highly 

unlikely that any project activity (e.g., transmission 

cable trenching and burying) would be allowed to 

take place in highly polluted sediments without strict 

mitigation measures. The group did not consider the 

accumulation of metals (e.g., copper or zinc) in the 

sediment from antifouling coatings because the highly 

energetic environment would largely prevent its 

sedimentation in the near field. There is a sense that 

antifouling coatings will not be maintainable in the 

near-benthic portion of the water column, as saltating 
113

particles will effectively “sandblast” the structures (discussed in Section 3.3, Chemical Effects,). 

However, this process would likely remove settling 

or newly settled propagules from the near-bottomfouling community as well.

Pilot projects were generally viewed as not likely 

to have significant effects on ecosystem interactions. 

However, as shown in the Receptor Matrix, food web 

changes may be measureable at the pilot scale and, 

hence, important to measure and document before 

continuing to the commercial scale. Environmental 

studies need to focus on very explicit questions about 

the potential effects and support addressing management issues within the adaptive management realm.

Project construction and decommissioning will 

likely cause local and transient effects but were 

not judged likely to have a measureable effect on 

ecosystem interactions. Accidents — for example 

spills during servicing — were, likewise, seen as local 

and temporary. Thus, the group focused its attention 

on the longer-term operational effects.

4.7.4 Priority Area: Top-down ecosystem effects

Description

Top-down effects are a high priority, because 

a combination of stressors may cause significant 

changes in trophic structure and energy flow (in a 

food web context) by altering the relative abundance 

and distribution of predators and the availability 

of appropriate prey, especially forage fishes. It is 

plausible that the additive effect of small to moderate 

changes in each of the species involved could add 

up to a significant integrated effect, as expressed in 

trophic dynamics. The specific stressors would likely 

include fish attraction and artificial reef effects and, 

possibly, changes in benthic sediment in the far field, 

and strike effects on certain groups of organisms such 

as forage fish. 

The level of uncertainty is moderate to high, and 

agreement among the group was relatively high.

Gaps in Understanding

The basic information gap in this area is the lack 

of detailed information on food web structure and 

energy flow for tidal systems suitable for hydrokinetic generation. Participants with field experience in 

these high-energy systems pointed out the difficulty 

in simply determining presence and absence of most 

species with traditional sampling methods. Even 

“slack” tides may be characterized by significant 

shear in the water column.

Approaches to Monitoring

Participants in this breakout group agreed that 

techniques and protocols appropriate for monitoring 

ecosystem interactions in high-energy tidal environments are generally not available. Practical metrics 

for these types of interactions have not been identified. However, new active acoustic techniques show 

promise in documenting the behavior of diving 

birds, marine mammals, and large and migratory 

fish, as well as their distribution and abundance in 

high-energy environments. This documentation is 

particularly important in the very nearfield (i.e., the 

immediate vicinity of the tidal energy device). The 

United Kingdom has several active programs to 

develop this type of information.

4.7.5 Priority Area: Energy removal

Description

Energy removal is a top priority because, even 

with a low to moderate likelihood of measureable 

expression, the consequences could be systemic, 

especially in a fjord environment or any other system 

limited by flushing. Changes in mixing rates at 

the terminus of the system could cause changes in 

hydrology/hydrography, water chemistry and deepwater replacement. Group members concurred that 

projects that take ecologically significant amounts 

of energy out of tidal systems are unlikely to be 

permitted (or consented). The obvious corollary to 

this observation is that the scientific community (or 

risk assessors) needs to provide adequate technical 

information about the relationship between energy 

removal and ecological effects to support environmental risk management.
114

The level of uncertainty is low to high, depending 

on the relative physical and hydraulic complexity and 

the spatial scale of the system. Agreement among the 

group was relatively high.

Gaps in Understanding

Hydrodynamic models validated and calibrated 

for specific locations where development may occur 

are needed to address information gaps related to 

this topic. These models will need to be informed 

by appropriate field measurements (as discussed in 

Section 4.2, Physical Environment: Far-field).

Approaches to Monitoring

Required protocols for monitoring the effects 

of energy removal comprise measurements of the 

stressor itself, as well as conservative and nonconservative measures of mixing. However, changes 

in primary production rates and the dominant species 

of phytoplankton would be appropriate indicators of 

bottom-up ecosystem effects. Protocols for sampling 

and measuring plankton species and primary and 

secondary production rates are well documented in 

the research literature.
115

The premise of the tidal energy workshop is that 

ocean energy can provide clean, reliable power, and 

emerging turbine designs will make production of 

electricity from ocean energy technologically and 

economically feasible. Tidal energy projects could be 

a viable renewable energy source, displacing fossil 

fuel-based energy resources, providing benefits to 

the marine environment through the mitigation of 

carbon dioxide production (which can lead to ocean 

acidification, climate change) and a reduction in the 

risk of catastrophic spills associated with fossil fuel 

extraction and transportation. However, the risk to 

the marine environment and marine organisms from 

tidal energy generation is not well known. In order 

to appropriately site and operate tidal power installations, a better understanding of the risks of the 

technology is needed, in order to explore the potential 

contribution tidal power can make to a renewable 

energy portfolio. 

Throughout the workshop, participants returned 

to the theme of data and information gaps as they 

considered the likely stressors associated with tidal 

energy development and environmental receptors. 

These gaps are compounded by the difficulty of 

working in the marine environment at locations with 

strong tidal currents. Operational challenges include 

the durability of in situ monitoring instruments, 

anchoring instrumentation in high current speeds, and 

the high cost of marine operations. Four major challenges are discussed below, encapsulating recurring 

themes from throughout the workshop. 

1. Critical knowledge gaps hinder 

evaluation of environmental impacts. 

Despite modest government investment in tidal 

power research and development, permitting of tidal 

device deployment remains a considerable barrier to 

advancement. The tidal power industry and regulators 

have identified uncertainty regarding environmental 

effects as one of the top barriers to getting tidal 

devices in the water (Bedard 2008). 

 5. Workshop Outcomes: Challenges

Workshop participants identified numerous areas 

of uncertainty regarding stressor/receptor interactions, 

including the following priority challenges: 

Existing data used to evaluate environmental 

effects are often from poor analogues, or data from 

tidal device operation are proprietary and not available.

Relatively little data about environmental effects 

have been collected from operating tidal energy 

projects, and any data that are available relate to a 

particular device design. Because these data have 

been collected by device developers at considerable 

expense, most are proprietary and, in many cases, not 

publically available. 

Industrial analogues to tidal energy include oil 

and gas development, military sonar use, offshore 

wind development in European countries, shipping, and general marine construction. These activities have generated considerable information about 

baseline environmental conditions and species- and 

population-level effects. However, these are of limited 

utility in assessing a number of potentially significant 

stressor/receptor combinations, such as blade strike. 

Environmental effects are difficult to generalize 

among different projects, and the significance of an 

effect may differ between species and individuals of 

the same species. Depending on the context for tidal 

energy development, environmental concerns vary 

greatly for the same stressor/receptor combinations. 

For example, when endangered species could be 

negatively affected, the significance of an interaction may increase acutely. Because of this variability, 

general conclusions about the significance of stressor/

receptor interactions remain elusive.
116

Understanding marine mammal-device interaction is a critical challenge because few impact data 

exist, many marine mammal populations are at risk, 

and marine mammal regulatory protections are 

stringent. 

Common to many locations in the United States 

where ocean energy devices may be sited, uncertainty 

regarding possible interactions between devices and 

marine mammals is the most likely “show-stopper”. 

This area of uncertainty has dramatic potential to 

impact development of the industry, because many 

populations of marine mammals are at risk and 

regulatory protections are robust, especially those 

for endangered or threatened stocks. Lack of understanding, combined with very low risk tolerance 

(as required by law), means that this concern could 

prohibit development if not addressed with improved 

effects data and mitigation techniques. 

The factors that make this an issue of major 

concern will also apply, to a lesser extent, to other 

protected species, such as turtles, some sea birds, 

and some fish, depending on the location and turbine 

technology.

 Potential energy removal effects for commercial 

arrays cannot be determined by scaling up measurements from pilot-scale installations.

Potential commercial-scale energy removal 

effects are not well understood and could result in 

significant negative impacts to marine ecosystems. 

Pilot projects are not effective ways to improve this 

understanding, because these effects are not likely 

to be measurable at the pilot-scale. Indirect study 

through numerical, physical, or analytical modeling 

is also problematic, because implementation, validation, and calibration are resource-intensive activities. 

Other challenges include the potential for ecosystem 

“tipping points” (where a small increase in extraction would result in a disproportionally large change 

to the regional physical environment or habitat), the 

existing, natural variability in the hydrodynamic 

regime, and understanding the ecosystem response to 

natural variability. In order to organize information/

data gaps into actionable areas of focus, the workshop 

steering committee categorized information needs into 

four types that correspond to stages of tidal project 

development:

• Information that can be gained prior to deploying 

a small number of devices at the pilot scale;

• Information that can be gained by monitoring 

pilot deployments that will inform deployments at 

both pilot and commercial scales;

• Information needed to responsibly deploy a large 

number of devices at the commercial scale; and 

• Information required to understand environmental 

effects that will only be obtainable (i.e., measureable) at commercial scale through post-installation studies.

The purpose of Table 6 and Table 7 is to relate 

information needs to the stage of project development 

where the information is required or can most beneficially be gained. Table 6 summarizes priority areas 

identified by stressor groups and Table 7 summarizes 

priority areas for receptor groups. A precautionary 

approach is taken in assembling these tables, emphasizing information needs highlighted by either stressor 

or receptor groups on each side of priority areas. For 

some of the cases summarized in these tables, the 

stressor and receptor are both reasonably understood 

and emphasis is on improving understanding of the 

stressor/receptor interaction (e.g., blade strike to an 

individual). In others, information gaps related to a 

specific stressor or receptor must first be addressed 

before stressor/receptor interactions can be evaluated (e.g., noise and electromagnetic fields created 

by device operation; species sensitivity to particular 

stressors). 

In many cases, information needs at the commercial scale (both pre-deployment and baseline postinstallation monitoring) will be determined by the 

results of pilot-scale activities. 
117

Table 6 – Information needs to close critical gaps in understanding (stressor groups).

Table 6 – continued on following page
118

Table 6 – continued from previous page
119

Table 7 – Information needs to close critical gaps in understanding (receptor groups).
120

2. A lack of clearly identified research 

priorities leaves researchers and 

developers with little guidance about 

the most pressing stressor/receptor 

interactions.

Not all possible stressor/receptor interactions 

(i.e., environmental effects) are likely to rise to the 

level of deleterious ecological significance (i.e., 

environmental impacts), particularly for pilot-scale 

developments. In light of the sheer number of 

possible interactions, an approach to prioritizing 

high-risk interactions is needed to guide research 

dollars and mitigation strategies. Through the process 

of developing matrices for each stressor and receptor 

session, workshop participants identified those effects 

of greatest potential significance and highest uncertainty. However, in a number of cases, the assessment 

of similar stressor/receptor interactions varied among 

workshop breakout groups because of the underlying 

uncertainties and group-specific assumptions. Such 

factors may complicate high-level prioritizations. 

Two examples include:

• Effects on fish — Both migratory and resident fish work groups adopted similar receptor 

elements, but the migratory fish group expected 

generally higher significance from tidal energy 

stressors than the resident fish group at both pilot 

and commercial scales of development.

• Ecosystem interactions — When considering 

their stressor’s effect on ecosystem interactions, most stressor groups expected moderately 

to highly significant ecosystem interactions at 

the commercial scale with high uncertainty, but 

the “Ecosystem Interactions” receptor group 

expected generally low to moderate significance 

for these stressors with low uncertainty. 

Some uncertainties are compounded by knowledge gaps about how receptors respond to existing, 

analogous anthropogenic stresses. Evaluating the 

effects of tidal energy development requires a better 

understanding of stressor/receptor interactions in 

the natural environment. Tidal energy project and/

or device developers acknowledge the spectrum of 

data needed to support environmental impact analysis 

and decision making but are not able to bear the cost 

of addressing all uncertainties, even for the highpriority areas summarized in Table 6 and Table 7. 

Workshop participants agreed that tidal energy project 

developers cannot be expected to support basic 

oceanographic research and stock assessments that 

are disproportionally large compared to their project 

scopes. Workshop participants further noted that the 

United States currently lacks a mechanism to evaluate 

and prioritize critical information needs for tidal 

energy projects and to fund information collection. 

This would require an appropriate division of public 

and private/industry resources reflecting national 

energy policy priorities and energy developer 

responsibilities. 

3. Technologies required to monitor 

high-priority stressor/receptor 

interactions are underdeveloped 

and costly.

The instrumentation required to monitor several 

high priority stressor/receptor interactions is either 

not at a sufficient technical maturity to deploy at tidal 

energy projects or its deployment is prohibitively 

expensive for project developers. In addition, the 

available instrumentation may produce vast streams of 

data that are not suitable for decision making without 

extensive post-processing. Workshop participants 

agreed that it is not enough to simply collect environmental data; these data must be in a form suitable for 

decision making, some of it in real time.
121

Participants identified a number of common 

reasons for these technology gaps including:

• Some interactions may be rare, requiring a high 

level of effort to capture;

• Tools that are effective for stock assessments are 

not well suited to detect effects below the population level.

• Existing methods for data collection and monitoring may be ineffective at tidal energy sites, due 

to high current velocities; and

• Mutual interference between instruments may 

limit the capability to simultaneously monitor a 

range of interactions.

4. Appropriate mitigation strategies 

for unavoidable environmental 

impacts are not well-developed. 

Some environmental impacts that cannot be 

avoided may be sufficiently mitigated by installation/

decommissioning procedures, operational adjustments, or design improvements. Development of 

mitigation strategies, which will be critical for moving 

the industry forward, requires an understanding of 

stressor/receptor interactions and clear guidance from 

environmental statutes and regulatory agencies on 

permissible levels of impact. Because of the newness 

of tidal technology in the United States, regulatory 

agencies struggle with the same information gaps as 

others and are working with industry to develop 

guidance. 
122

6. Workshop Outcomes: Recommendations

Breakout group discussions generated a number of 

recommendations that fall into three broad categories:

1. Approaches to reducing uncertainties around 

potential impacts (i.e., those effects which may be 

ecologically significant for one or more receptors); 

2. Approaches to mitigating environmental 

stressors; and 

3. Development of strategic and coordinated technologies and capabilities.

Recommendation details, organized by general 

category, are presented below. 

6.1 Approaches to Reducing 

Critical Uncertainties

Avoiding or mitigating impacts requires sufficient 

information to assess the magnitude of the impact 

and the effectiveness of mitigation strategies. This 

includes life-history data for animals of concern and 

device operational parameters. In general, stressor 

groups emphasized the need to quantify the magnitude of the stressor, while receptor groups emphasized 

the need for information to place the stressors from 

tidal energy development in the context of existing 

stressors from other activities. 

Priority research areas should be established for 

stressor/receptor interactions.

As discussed in Section 5, research efforts must 

be prioritized in order to make best use of limited 

funding and address the most pressing issues in a timely 

manner. As tidal technologies and environmental understanding evolve, risk assessment may provide a mechanism to evaluate and compare risks associated with 

specific stressor/receptor interactions in order to support 

research, permitting, and siting decisions. 

As an initial attempt at this type of prioritization, 

the workshop organizing committee created high-level 

stressor/receptor matrices of significance and uncertainty. This synthesis is based on a review of session 

matrices, session narratives, and priority area information gaps identified in Table 6 and Table 7. Results are 

shown in Figure 39 for pilot-scale deployments and 

Figure 40 for commercial-scale deployments.

Although no stressor/receptor interactions with 

high potential significance and low uncertainty are 

identified at the pilot-scale, a number of high uncertainty interactions with high potential significance are 

apparent. These should be prioritized for investigation 

at the pilot scale.

• Marine mammal-device interactions: Because 

many marine mammal populations are already 

at risk from existing stressors, accurate information about device or array impacts to populations, 

especially endangered or threatened species, 

is essential for the industry to move forward. 

Interactions include stressors associated with the 

presence of the device (static and dynamic) and 

behavioral changes due to noise.

• Fish-device interactions: These concerns 

are analogous to those discussed for marine 

mammals and are most acute for endangered 

species. For fish-device interactions, the priority 

should be on decreasing the uncertainty around 

potential impacts caused by presence of the 

device (static and dynamic) and behavioral 

changes due to electromagnetic fields. 

• Cumulative effects: Uncertainty around cumulative effects is high. Pilot projects present an 

opportunity to better understand the extent of 

stressors on individuals of a species. A better 

understanding of particular stressors is the first 

step in identifying potential synergies between/

among stressors. 

• Chemical spills: Although the risk for large 

chemical spills at the pilot scale is low, the impact 

of such spills on multiple receptors is relatively 

certain. Effective spill response procedures 

for tidal energy environments are required and 

should be developed if not already in place.
123

Figure 39 – Pilot-scale deployment generalized stressor/receptor significance (on a gradient green = low, red = 

high) and uncertainty (one green triangle = low uncertainty, two yellow triangles = moderate uncertainty, three red 

triangles = high uncertainty).

At the commercial scale, the potential significance of a particular environmental effect generally 

increases relative to the pilot scale. Energy removal, 

which is not a high priority issue at the pilot scale, 

emerges as a priority area of concern at the commercial scale. Because measurements from pilot projects 

cannot be scaled up to address this effect, research 

should be initiated to identify environmental “tipping 

points” (e.g., large environmental changes in response 

to incremental energy removal). This is a matter of 

particular concern for sites with the potential for 

multiple commercial-scale deployments. Information 

about environment “tipping points” would also inform 

market acceleration activities about the appropriate 

scales of development at specific sites.
124

Figure 40 – Commercial-scale deployment generalized stressor/receptor significance (on a gradient green = low, 

red = high) and uncertainty (one green triangle = low uncertainty, two yellow triangles = moderate uncertainty, 

three red triangles = high uncertainty).

A first step to understanding many environmental 

impacts can be achieved only through monitoring 

of pilot-scale deployments. 

Monitoring of pilot-scale projects is a critical step 

for closing information gaps for a number of high 

priority stressor/receptor combinations. Table 6 and 

Table 7 indicate that carefully monitored pilot-scale 

deployments are the first step in understanding the 

vast majority of critical uncertainties and are likely to 

provide more information than additional pre-device 

installation studies. For many, but not all, highpriority research areas, the emphasis at the pilot scale 

will be on monitoring effects on individual organisms in order to evaluate the potential for population 

effects at a commercial scale, and to inform baseline 

monitoring requirements for other pilot and commercial projects. As part of the permitting process for 

pilot projects, regulatory agencies should provide 

active, specific guidance as to what data and analysis 

products are required of tidal energy site developers. 

Efficiently closing knowledge gaps will require broad 

cooperation between site developers and regulatory 

agencies.
125

A phased approach to installation and operation 

may be required to mitigate potentially significant 

environment risks with high uncertainty, and longterm pilot projects may be required. For example, 

disturbance to the marine environment from project 

maintenance activities such as the removal of hard 

substrate from the tidal environment, cannot be fully 

assessed until device developers have verified that 

their maintenance intervals are technically achievable 

over the design life of a device. 

It may be desirable to conduct pilot projects at 

dedicated test sites, where the physical and biological 

environment are well-characterized. Although there 

are no such test sites in the U.S. at this time, such 

facilities could be patterned after the European 

Marine Energy Center (EMEC) or Fundy Ocean 

Research Centre (FORCE). The U.S. Department of 

Energy is currently undertaking a strategic review of 

testing needs for marine renewable energy, including 

tidal energy.

The public sector must play a role in funding 

the study of high-priority stressor/receptor 

interactions, particularly for baseline assessments.

The public good that can be derived from the 

development of a clean renewable energy source 

requires that responsibility for environmental data 

collection and its costs be shared appropriately by 

industry and public interests. In the near-term, public 

funding should be used to enhance pilot-scale monitoring being undertaken by industry. This could occur 

at either dedicated test sites or individual technology 

demonstrations. As previously discussed, the technologies required to monitor some high-priority stressor/

receptor interactions are underdeveloped and costly to 

deploy. Public funding for monitoring would reduce 

the burden on site developers and guarantee that the 

knowledge gained would enter the public domain in a 

timely manner.

National policy priorities should also guide 

investment of public dollars in environmental 

monitoring of regional or national importance. The 

Strategic Environmental Assessment (SEA) process 

commonly applied in Europe and Canada is one 

model for this type of strategic, regional, cost-sharing 

approach to data collection. SEA provides a mechanism to plan for pilot- or commercial-scale tidal 

energy development, identify research needs, and 

address cumulative impacts at a regional scale. The 

SEA approach, or a framework with similar goals, 

should be considered for the U.S., in order to guide 

data collection and to support permitting and siting 

decisions. 

The effort to share relevant marine energy 

information through the International Energy 

Agency’s Ocean Energy System Implementing 

Agreement (IEA-OES-IA) Annex IV should be 

continued, and other strategies to share data 

while protecting intellectual property should be 

developed. 

The U.S. Department of Energy is leading an 

effort by IEA-OES-IA countries to compile existing 

information from marine energy projects and relevant 

technology analogues as part of the International 

Energy Agency’s (IEA) Annex IV. In doing so, the 

annex will identify crucial information gaps and case 

studies from around the world, providing best practices for the marine energy industry. IEA-OES-IA 

activities under Annex IV began in 2009 and will 

continue through 2013.

Information from existing projects is needed to 

prioritize monitoring strategies. Intellectual property 

and competitive considerations for device developers 

decrease the likelihood that data collected from pilot 

projects will be freely placed in the public domain, 

especially when the collection of such data has come 

at high cost to the developer. One alternative to public 

disclosure would be the creation of a metadata archive 

describing, in detail, the types of data collected by 

ongoing projects and key lessons learned. Researchers 

and regulatory agencies would be required to negotiate access to these data on a case-by-case basis but 

would be aware of the data’s existence.

In addition to these international efforts, provisions to ensure timely delivery of research and development results are needed. 
126

Analogous and existing data should be compiled 

and reviewed to avoid duplication of data 

collection and monitoring efforts, particularly for 

baseline monitoring. 

Assessing priority stressor/receptor interactions 

may be facilitated by the use of analogous, and betterunderstood, interactions. Analogues may include 

models of fish behavior, stock assessments, and 

the effects of noise on marine mammals. Although 

stressor analogues may be imperfect when applied 

to tidal energy devices, in some cases (e.g., artificial 

reef effects), these may provide useful insight for 

assessing environmental effects. Because analogies 

may be poor in some cases, a careful evaluation of 

applicability should precede their use. IEA-OES-IA 

Annex IV will investigate analogues to marine and 

hydrokinetic devices, including tidal devices.

Project and device developers should work 

with oceanographers and other researchers 

to share monitoring data collection, modeling 

methodologies, and study results. 

High-priority concerns for tidal energy 

are also active areas of physical and biological 

oceanographic research. Summaries of the existing 

physical oceanographic data at potential development sites and biological oceanographic data on 

affected species could help to avoid duplication of 

effort in collecting baseline data for tidal energy 

development. Conversely, although tidal energy 

project developers cannot be expected to carry out 

large-scale physical or biological oceanographic 

research, the data collected during baseline or project 

monitoring may be of interest to oceanographic 

researchers. Efforts should be made to integrate 

baseline and monitoring data collection with broader 

efforts in relevant fields (e.g., in partnership with 

regional ocean observing initiatives).

6.2 Approaches to Mitigating 

Environmental Stressors

For environmental effects that have the potential 

to significantly impact one or more environmental 

receptors, mitigation strategies may be able to reduce 

that impact to an acceptable level. Table 8 summarizes proposed mitigation strategies made by stressor 

breakout groups. In a few cases, these recommendations address multiple stressors. For example, 

streamlining support structures would help to reduce 

the static effects of device presence and the effect of 

energy removal.
127

Table 8 – Potential mitigation strategies for environmental stressors.
128

6.3 Development of Strategic and 

Coordinated Technologies and 

Capabilities

Workshop participants discussed several technical capabilities and tools that require development, 

but will be essential for addressing uncertainties 

and evaluating environmental impacts. These are 

discussed below and include generally accepted 

monitoring protocols, monitoring instrumentation, 

and hydrodynamic modeling capabilities. 

Consistent, clear monitoring protocols should 

be developed and used by those conducting 

environmental research.

General protocols for pilot project monitoring 

(baseline and post-installation) should be drafted that 

specify the type of data to be collected, mechanisms 

for collection, and how these data will be used to 

address environmental uncertainties. Such protocols 

must retain some flexibility for site-specific considerations. To maximize the benefit of pilot projects, 

the lessons learned from these activities should enter 

the public domain in ways that benefit researchers 

and regulators, while protecting the intellectual property of device developers. 

Meaningful monitoring protocols require an 

understanding of natural variability in order to 

establish thresholds for detecting measurable effects. 

Protocols must place the potential effects of tidal 

energy development within the context of natural 

mortality to aquatic species, changes to the physical 

environment (e.g., isostatic release on sea level), 

and changes to habitat from extreme weather events 

(e.g., shoreline erosion, seabed scour by debris). 

Innovative approaches to monitoring 

instrumentation should be developed by 

partnerships between research institutions, 

industry, and funding agencies. 

Monitoring instrumentation must be cost 

effective and should be adaptable between project 

sites. Although techniques to monitor aspects of 

the physical environment are relatively mature 

(e.g., measurements of water currents by Doppler 

profilers), approaches to monitoring the biological 

environment are less developed. Because advancing 

biological monitoring technologies would be of 

benefit to the broader oceanographic community, site 

developers should not be expected to bear the full 

cost of this instrumentation development. 

A high-priority area of concern is mortality to 

fish and marine mammals from the rotating turbine 

blade (strike or impingement). Cost-effective instrumentation is required to detect, classify, and identify 

species moving in close proximity to an operating 

tidal energy device and make automated decisions 

based on the risk profile (e.g., temporary device 

shutdown if strike is imminent). This could involve 

integrating multiple types of instrumentation — 

acoustic telemetry (tags and receiver arrays), passive 

acoustics (hydrophones), and multi-scale sonar 

arrays — and pairing the output with a detection and 

classification algorithm to assess species-specific 

responses to device operation. Integrated monitoring 

systems will require significant hardware and software development.

Validated and calibrated hydrodynamic and 

ecosystem models can effectively address some 

critical uncertainties. 

Not all concerns can be addressed by monitoring 

pilot projects. Because measurements are always 

sparse, modeling must play an important role. Two 

types of models are required:

• Turbine-scale: Models of the near-field hydrodynamic environment should be verified against 

measurements from pilot projects. In the longer 

term, the output of turbine-scale models could 

be used to investigate fish interactions and the 

fate of chemical contaminants (coatings and 

lubricants).
129

• Estuary-scale: Models of the far-field hydrodynamic environment, including provisions for 

power extraction by tidal turbines, will eventually 

be needed for project planning and permitting. It 

will be desirable to incorporate hydrodynamic, 

chemical, habitat, and biological linkages (e.g., 

larval transport). Because pilot projects are 

unlikely to measurably change aspects of the 

far-field physical environment, a fundamental 

challenge for such models is the validation of 

predictive cases with kinetic power extraction. 

Novel approaches are required to address this 

limitation.

Development of models at both scales will require 

rigorous validation and calibration. Once validated 

hydrodynamic models are in place, additional 

dynamics can be incorporated to model other aspects 

of the biogeochemical environment (e.g., sedimentation, dissolved oxygen, nutrients, productivity). It may 

be desirable to compile a list of validated hydrodynamic models covering potential development sites 

and to fund the development of hydrodynamic models 

at sites where no suitable model exists. An effective 

way to leverage modest investments in this area may 

be to contribute to the support or improvement of an 

existing model with the understanding that results will 

be made available for tidal energy project goals. In 

the near-term, models could be leveraged to provide 

preliminary assessments that guide high-priority 

monitoring activities. Model development will be an 

iterative process.

Expanded opportunities for interdisciplinary 

collaboration will promote improved experimental 

design and data collection. 

Better coordination and synchronization among 

practitioners is required, with respect to experimental 

design and data collection; this could be achieved by 

expanding the forums for information sharing among 

disciplines (e.g., oceanography and engineering) 

and affiliation (e.g., universities and industry). For 

example, technical expertise is often compartmentalized between stressors and receptors (e.g., most 

marine mammal researchers are not trained in acoustics or chemistry and vice versa). An annual scholarly 

forum for exchanging information among practitioners would be helpful.

Future workshops on specific stressor or receptor 

topics were suggested by workshop participants as the 

industry moves forward and the need to understand 

and mitigate for environmental impacts becomes 

more acute. Examples include workshops on strategies to monitor for and mitigate against potential 

impacts to fish and marine mammals.
130

The scientific workshop in March 2010 provided 

a unique forum to identify and prioritize critical 

knowledge gaps about the potential impacts of tidal 

energy generation devices on the environment. The 

diversity of invited participants and the workshop 

format resulted in lively evaluation and brainstorming 

discussions. 

Two overarching conclusions can be drawn from 

the long list of specific knowledge gaps presented in 

Table 6 and Table 7: 

• The next step to reducing critical uncertainties is 

careful monitoring of pilot-scale device deployments; and

• Research efforts must be prioritized and leveraged in order to effectively direct limited research 

dollars and resolve key uncertainties in a timely 

manner.

Some important uncertainties and potential 

concerns, however, can only be addressed by rigorous 

post-installation monitoring of commercial-scale 

arrays. When conducting research or directing funds 

7. Concluding Remarks

to close high-priority uncertainties, the appropriateness of hypothesis testing at a particular scale of 

development should be critically assessed (i.e., in 

some cases, the significance of an effect and the 

ability to detect it will be dependent on project scale). 

Participants found the structure of the workshop 

useful for eliciting and organizing environmental 

effects of tidal energy development and associated 

uncertainties. Future workshops on specific stressor 

or receptor topics were suggested, as the industry 

moves forward and the need to understand and 

mitigate for environmental impacts becomes more 

immediate. Participants also suggested that additional workshops focused on policy and management 

issues associated with tidal energy development may 

be useful, especially in light of federal- and statelevel coastal and marine spatial planning efforts.1

 A 

secondary benefit of the workshop is that it provided 

a productive learning opportunity for tidal energy 

experts and novices alike. Nearly 80% of participants 

agreed to a moderate or great degree that the workshop increased their understanding of the potential 

environmental impacts of tidal energy development. 

1

 More information on this process and efforts in the United States 

can be found at http://www.msp.noaa.gov/.
131

 

Appendix A — Glossary

Adaptive management an approach to natural resource management that involves evaluating the results of 

management actions and modifying subsequent actions

Ambient signals or stressors of nonhuman origin; background

Anadromous species of fish that primarily live in the ocean and breed in fresh water

Anthropogenic of human origin

Antifouling paint a paint containing a biocide that is used to inhibit growth of fouling communities 

on manmade surfaces

Array a gridwork; in this context, one comprised of tidal energy devices

BACI before-after/control-impact study to identify environmental changes

Baseline environmental conditions prior to device installation

Benthic living on or in the substrate at the bottom of the water column

Biofouling the buildup of fouling community organisms (e.g., algae, barnacles) on manmade 

structures

Biological productivity in this context, primary productivity; the mechanism by which nutrients and carbon 

dioxide are converted to organic matter

Capacity the maximum electrical power output from a tidal energy device

Cetaceans the group of marine mammals that includes both the baleen (mysticetes) and 

toothed whales (ondontocetes)

Clupeids herring, shad, sardines, and other forage fish 

Commercial of or related to large arrays of devices installed for a period of many years for the 

purpose of generating utility-scale power at a cost competitive with other forms of 

electricity

Conspecifics two or more individual organisms, populations, or taxa

dB decibels; in this context, a measure of sound pressure relative to 1 μPa

Diadromous species of fish that migrate between salt water and fresh water at different life 

stages
132

DOE the United States Department of Energy; specifically the Advanced Waterpower 

Program under Energy Efficiency and Renewable Energy

Ecological in this context, pertaining to the interaction among organisms in the marine environment.

EIS environmental impact statement

Elasmobranchs cartilagionous fishes, including sharks, skates, and rays

EMF electromagnetic field

Environmental in this context, pertaining to water, nutrients, habitat, and organisms.

Environmental effects the broad range of potential measurable interactions between tidal energy devices 

and the marine environment; for potential effects, there is uncertainty around the 

fundamental nature of the interactions

Environmental impacts environmental effects that, with high certainty, rise to the level of deleterious 

ecological significance;for potential impacts, there is uncertainty around the details 

of the interaction (e.g., frequency, species-specific response) that would elevate the 

effect to the level of ecological significance

ESA federal Endangered Species Act of 1973 

FAD fish attraction device

Far-field the region over which perturbations from tidal device operation are no longer 

distinguishable from other natural or anthropogenic perturbations, as distinguished 

from the near-field; depending on the tidal energy stressor, the distance from the 

turbine at which stimuli merge into the far-field might be on the order of few meters 

(for underwater visual stimuli), greater than tens of meters (for hydrodynamic 

disturbances from rotor or support structure), or greater than hundreds of meters 

(for acoustic stimuli)

Flatfishes a family of fish evolved as side-swimmers, including flounder, sole, and halibut

Forage fishes smaller fishes that are important sources of food for larger fish, birds, and marine 

mammals including osmerids and clupeids

Foul-release paint an inert coating that is used to inhibit growth of fouling communities on manmade 

surfaces

Foundation the anchoring system securing a tidal energy device to the seabed

Hydrodynamic of or related to the motion of water
133

Hydrokinetic of or related to renewable energy involving the extraction of energy from moving 

fresh or oceanic water

Intertidal zone an area exposed to air during low tides and submerged during high tides

Invasive species undesirable species that tend to dominate habitats at the expense of more desirable 

species; most are non-indigenous

Invertebrates animals without backbones; in this context, including crustaceans (e.g., crabs, 

lobsters, shrimp), barnacles, and sponges

Isobath a contour of equal bottom depth

Kinetic power density kinetic energy flux per unit area; proportional to the cube of current velocity

kW kilowatt

MHK marine and hydrokinetic

Migratory fish fish that follow predictable movements through the environment during their life 

cycles

Mitigation an action taken to prevent or avoid an ecological effect

Mooring the mechanical linkage by which the rotor and drive train on a tidal energy device 

are connected to the foundation

MW megawatt

Near-field the region over which perturbations from tidal device operation may be readily 

differentiated from other natural or anthropogenic perturbations, as distinguished 

from the far-field; depending on the tidal energy stressor, the distance from the 

turbine that would be considered near-field ranges from a few meters (for underwater visual stimuli), to within tens of meters (for hydrodynamic disturbances from 

rotor or support structure), or to within hundreds of meters (for acoustic stimuli)

Nearshore close to shoreline; in this context referring to shallow, biologically productive areas

NMFS NOAA National Marine Fisheries Service

NOAA National Oceanic and Atmospheric Administration; a branch of the Department of 

Commerce

Pelagic Pertaining to an organism living in the water column or the water-column habitat
134

Photic zone the depth of water over which solar energy plays a significant biological role; in 

a tidal energy context, depending on turbidity, this distance can vary from a few 

meters to tens of meters

Pilot of or related to single devices or small arrays installed for short durations for the 

purpose of research and development

Pinnipeds a group of marine mammals comprised of walruses, seals, and sea lions

Plankton plants or animals that drift in water without sufficient swimming capability to 

counter currents

Power train the mechanism by which rotational, mechanical energy from a tidal turbine rotor is 

converted to electrical energy; parts of the power train include a generator and may 

include a gearbox

Propagules biological units capable of propagating new individuals or colonies; may be vegetative or reproductive

Receptor those elements of the marine environment that may be affected by stressors

Recruitment the process by which young are added to a population

Resident fish fish that maintain home ranges or that stay in a relatively stable geographic area 

throughout most of their life cycles

Risk assessment an evaluation of the potential adverse effects of an action

Rotor the component of a tidal energy device that extracts the energy in tidal currents and 

converts it to rotating mechanical energy.

ROV remotely operated vehicle; in this context an unmanned, submersible vehicle with 

propulsion, tethered to the surface by a power and data cable 

Sacrificial anode aAn expendable piece of metal, generally zinc, that protects iron and steel from 

electrolysis in seawater

Salmonids a family of fish that includes salmon, trout, whitefish, and greylings

Saltating the process of particle transport by fluid

Scombrids a family of fish that includes tunas and mackerels

Scorpaeniforms a family of fish that includes rockfish, greenlings, sculpins, and ling cod

SEA Strategic Environmental Assessment

Spatial in space
135

Stressor those factors that may occur as hydrokinetic tidal energy systems are installed, 

operated, or decommissioned

Substrate tn this context, referring to the seabed or its physical composition

Take tn this context, anthropogenic actions leading to the harassment, injury, or death of 

a fish or marine mammal; generally discussed in the context of project permitting.

Temporal in time

Tidal energy device a device that extracts kinetic power from fast-moving tidal currents and converts 

that power to electricity; components include the rotor, power train, mooring, and 

foundation.

Tipping points critical thresholds, beyond which incremental changes caused by tidal energy 

devices result in disproportionately large changes in the marine environment

Trophic level the position an organism occupies in the food chain

Turbine in this context, shorthand for either the entire tidal energy device or only the device 

rotor

Wake a lower-velocity region downstream of a blockage in a fluid flow, characterized by 

relatively more intense shear and mixing; in this context, the blockage is the tidal

energy device rotor, power train, mooring, or foundation

Water quality a measure of the physical, biological, and chemical properties of water, including 

turbidity, dissolved oxygen, chlorophyll, and nutrients
136

Appendix B — Plenary Session 

Extended Abstracts

For the March 2010 workshop, five plenary 

speakers were invited to introduce various aspects of 

environmental effects of tidal energy. The first two 

speakers provided an overview of the tidal energy 

industry in the United States and shared lessons 

learned from the Bay of Fundy in Nova Scotia, 

Canada. The next three speakers described the physical habitats and natural resources of the three selected 

sites: Coastal Maine, Puget Sound, Washington, and 

Cook Inlet, Alaska. These talks are summarized as 

extended abstracts in the following sections.

B.1 Tidal Technologies, Industry 

Overview, and the U.S. Department 

of Energy Water Power Team

Alejandro Moreno and Simon Geerlofs

U.S. Department of Energy

Introduction

This abstract provides an overview of tidal power, 

including the potential size and nature of tidal power 

resources, the technologies and devices used to capture 

tidal energy, the state of the tidal power industry, and 

the U.S. Department of Energy’s efforts to support 

the responsible deployment of tidal power and other 

marine and hydrokinetic energy technologies.

Tidal power holds promise as a significant 

source of carbon-free, renewable, and predictable electrical energy located close to coastal load 

centers with high electricity demands. However, 

the tidal power industry is still in an early developmental phase worldwide and faces a number of 

technical and non-technical challenges to deploying 

devices, whether pilot-scale demonstration projects 

or commercial-scale device arrays. Although tidal 

power technology is developing rapidly, overcoming 

these challenges will require: continued research; 

development, and demonstration of devices; consistent testing and validation of device performance; and 

a focused, collaborative approach to understanding 

and addressing potential environmental risks. Environmentally responsible pilot projects and openwater 

testing opportunities, utilizing adaptive management principals and conducted in coordination with 

industry, regulators, national laboratories, universities, 

and other stakeholders, will be critical to realizing the 

potential for generating clean energy from the tides. 

Tidal Power Potential

Ocean tides are driven by the combined gravitational forces exerted by the earth, moon, and sun, and 

by the rotation of the earth. Strong tidal currents result 

when rising and falling tides flow through constricting 

coastal and bathymetric features. Tidal currents 

contain an enormous amount of predictable, renewable energy in close proximity to coastal population 

centers with high demands for electricity. Estimates 

of the extractable tidal power potential in the United 

States vary widely: a preliminary study of seven sites 

in North America by the Electrical Power Research 

Institute found a potential extractable resource of 19.6 

terawatt-hours per year (TWh/yr) (Bedard et al. 2007), 

and a 2009 study found that between 47 and 95 TWh/

yr could be technically generated from tidal power 

across the country, based on an upscaled estimate of 

the resource available in Puget Sound (Polagye 2009)1

. 

The large discrepancy between these two estimates 

results from the methodologies and assumptions used 

in the studies, which can lead to both over- and underreporting the available resource. The U.S. Department 

of Energy continues to refine tidal energy assessments 

and is funding Georgia Institute of Technology to 

conduct a comprehensive assessment of both tidal and 

in-stream hydrokinetic resources in the United States; 

this assessment will be completed in 2010. 

1

 The study’s author notes that this is an order of magnitude 

estimate, assuming that Puget Sound accounts for 5-10% of the 

national resource and that device capacity factors range from 30% 

to 40%. The author cautions that, although technically feasible, 

dissipation of tidal energy of this magnitude could result in reduction of tidal transport and ecological changes within basins where

tidal power is extracted. Refining future resource estimates will 

require a substantial modeling effort, a clear discussion of the 

cumulative effects of extraction, and an accounting of potential 

ecological and social limits to development. 
137

Significant tidal power resource sites in North 

America include the Bay of Fundy, Cook Inlet in 

Alaska,Puget Sound, Western Passage in Maine, and 

Nantucket Sound in Massachusetts. Tidal power is 

being explored in other coastal states as well, and 

additional tidal resources may become available as the 

technology develops. 

Tidal Power Technologies

Early tidal power projects utilized dam-like 

barrages to impound tidal flows within an estuary 

or bay, creating hydraulic head. Impounded water 

was then released through turbines, similar to how a 

conventional river-based hydropower system functions2

. Tidal barrages have high capital costs and 

significantly alter coastal and estuarine ecology. By 

contrast, tidal power development in the United States 

today uses tidal in-stream energy conversion devicesto 

capture energy from freely flowing tidal currents. 

These devices function without use of impoundments 

or barrages, similar to how a wind turbine draws 

energy from moving air. 

Generally, tidal in-stream energy conversiontechnologies can be divided into three categories: axial-flow 

turbines, cross-flow turbines, and reciprocating devices.

• Axialflow or horizontal-axis turbines typically consist of three or more blades that form a 

rotor. The flow of water is parallel to the rotor’s 

axis. The kinetic flow ofthe water current over 

the blades creates lift,which causes the rotor to 

turn and drive an electrical generator. Axial flow 

turbines sometimes utilize a shroud to protect the 

turbine and accelerate the flow of water past the 

blades.

• Cross-flow turbines typically have two or three 

blades mounted along a shaft to form a rotor. The 

flow of water is perpendicular to the turbine’s 

axis. The kinetic flow ofthe water current over the 

blades creates lift,which causes the rotor to turn 

and drive an electrical generator.These devices 

can extract energy from multidirectional flows 

without the need to orient to the direction of the 

flow. 

2 The most well known tidal barrage currently in operation is La 

Rance tidal power plant in Brittany, France, which was completed 

in 1966. La Rance has a peak capacity of 240 MW.

• Reciprocating devices generate electricity 

through an oscillating motion, similar to the tail 

motion of a fish or whale, caused by the lift and 

drag forces of the water stream. Mechanical 

energy from this oscillation feeds into a power 

conversion system.

All tidal in-stream energy conversiontechnologies 

share some common characteristics, which include 

moorings, foundations, rotors or oscillating structures, 

a power conversion system, and transmission cables. 

Tidal Power Industry

Technology developers based in the United 

Kingdom were quick to develop and deploy tidal 

power devices during the late 1990s and early 2000s 

to take advantage of the strong tidal flows located 

in U.K. waters. The first grid-connected axial flow 

turbine, known as Seaflow, was installed in May 

2003 off the North Devon Coast of the U.K. Marine 

Current Turbine’s 1.2 megawatt (MW) SeaGen project 

in Strangford Lough, Northern Ireland, has been 

connected to the electric grid since 2003. The European 

Marine Energy Centre in Scotland’s Orkney Islands 

serves as an industry testing site for both tidal power 

and wave energy technologies. Compared to the United 

States, industry in the European Union has experienced 

greater access to capital and more extensive testing 

and pilot project resources. Aside from the United 

Kingdom, international development of tidal power is 

taking place in New Zealand and South Korea.

Exploration of tidal power technology in the 

North America is taking place in Nova Scotia, 

Maine, Washington, British Columbia, and Alaska. 

Verdant Power was the first company to deploy tidal 

power technology in the United States, installing six 

prototype units on monopoles in New York’s tidallyinfluenced East River. Verdant Power is currently 

working with the U.S. Navy on a pilot deployment in 

Admiralty Inlet in Puget Sound. Clean Current tested 

a single turbine offshore of Race Rocks in the Strait 

of Juan de Fuca from 2006-2008, and has installed a 

device in Minas Passage in the Bay of Fundy. Marine 

Current Turbine is also planning to deploy in Minas 

Passage, and OpenHydro deployed a 1 MW turbine 

in Minas Passage in November 2009. OpenHydro 

has also been selected by Snohomish County Public 
138

Utility District for a pilot project in Admiralty Inlet. 

In March 2010, Ocean Renewable Power Company 

deployed a 60-kilowatt (kW) unit on a mobile testing 

barge off Eastport, Maine, to collect data in preparation for a pilot project license application. Ocean 

Renewable Power Companyis also working through 

the Federal Energy Regulatory Commission licensing 

process for a project in Cook Inlet.

A complete description of the global tidal power 

industry is contained in the International Energy 

Agency annual report for 2009. 

Key Industry Challenges

The tidal power industry is still in a relatively 

early stage of development, although technology 

development is progressing rapidly, informed by 

lessons learned from wind power and advancements 

in ocean engineering. Device deployment is necessary 

in order to test and validate technologies and to gain 

better understanding of the potential environmental 

effects of tidal power. However, a complex regulatory 

and permitting situation, in addition to the technical 

challenges posed by the harsh marine environment, 

can complicate the deployment of tidal power devices.

Major industry challenges to the deployment of 

ocean energy devices include: technical risk and 

uncertainty regarding device cost, performance, and 

survivability prohibiting financing of development 

and demonstration projects; a lack of design tools, 

standards, and validation of data; the lack of reliable 

policy incentives to encourage the deployment and 

subsequent cost-reduction of new and innovative 

energy technologies; lengthy and complex permitting 

processes at both federal and state levels; a dearth of 

environmental and competing-use impacts data; and 

a need to integrate national energy priorities within 

coastal and marine spatial planning processes.

Overcoming Challenges—

DOE Water Power Activities

The mission of the U.S. Department of Energy’s 

Water Power Team is to develop and employ novel 

technologies, improved operational procedures, and 

rigorous analysis to:

• Assess the potential extractable energy from 

domestic rivers, estuaries, and marine waters; and 

• Support industry to harness this renewable, 

emissions-free resource through environmentally 

sustainable and cost-effective electric generation. 

Although research and development in the marine 

and hydrokinetic energy industry has increased in 

recent years, no single design or technology has 

emerged as a clear leader. Until full-scale or near 

full-scale demonstration projects are deployed in 

realistic open-water conditions, such a determination 

will be very difficult to make. The U.S. Department 

of Energy is currently working to support the design, 

development, and testing of a variety of marine and 

hydrokinetic systems and identifying key cost drivers, 

performance characteristics, and technology improvement opportunities. 

The U.S. Department of Energy leverages its 

extensive expertise in technology development to 

identify and fund research in areas where industry 

currently lacks either the capabilities or financial 

resources. It conducts research in six key areas that 

have been identified as critical to the success of the 

marine and hydrokinetic industry: 

• System development, deployment, and verification to improve device functionality, to generate 

cost, performance and reliability data, and to test 

systems in relevant openwater settings; 

• Research tools to develop design codes and 

models necessary for supporting system development and testing; 

• Adequate test centers and facilities to generate 

and collect system data; 

• Technology characterization to analyze and 

evaluate test data; 
139

• Resource assessments to quantify energy availability and location; and 

• Studies and projects to evaluate and minimize 

key environmental risks to permitting and deployment of demonstration projects. 

The U.S. Department of Energy’s Water Power 

Team collaborates with federal and state agencies, 

industry, national laboratories, national marine renewable energy centers, universities, and other stakeholders to carry out its activities.

Summary

Tidal power represents a regionally significant 

clean, renewable, and predictable energy resource. 

Modern tidal power technologies are designed to 

capture energy from the tides, convert that energy 

to electricity, and transmit the electricity to shore, 

all without use of dams or impoundments and with 

minimal environmental effect. Development of these 

technologies is still at a relatively early stage, but 

technology advancement is happening swiftly, with 

a number of devices tested worldwide. Nevertheless, the tidal power industry faces technical, regulatory, and environmental challenges and needs to test, 

deploy, and monitor devices in operational environments. No commercial-scale tidal power device arrays 

currently exist, and pilot project permitting is expensive and time-consuming. The Water Power Team 

is leveraging funding through industry and public 

partnerships to address key challenges and overcome 

information barriers that impede the responsible 

deployment of tidal power projects.
140

B.2 Ecological Effects of Tidal 

Energy: Experience from the 

Bay of Fundy

Graham R. Daborn

Acadia Centre for Estuarine Research, 

Acadia University

Introduction

Tidal power is an old technology. Mechanical 

mills driven by tidal movements in estuaries have 

been widespread in Europe for at least a thousand 

years, used variously for grinding grain or pumping 

water. Production of electricity from tidal waters has 

been a dream for a little over 100 years but, in that 

time, only three plants of commercial size have been 

completed: at Khislaya Guba (Russia), La Rance 

(France), and Annapolis Royal (Canada). All three are 

barrage-based systems, designed to convert the potential energy stored behind the barrage into electricity. 

Numerous other similar developments have been and 

are being considered in many countries, but many 

have not been pursued for economic or (occasionally) 

environmental reasons. The substantial environmental 

effects of barriers constructed in tidal estuaries —

whether for power production, water storage, flood 

control, or transportation —have greatly diminished 

enthusiasm for such tidal barrage-based systems, 

although tidal lagoons and shore-fast reservoirs are 

still under active consideration. 

The present focus on arrays of tidal in-stream 

energy converter (TISEC) devices arises, in part, 

because of the adverse effects expected from barrages, 

but also because arrays of TISEC devices offer the 

benefits of an incremental approach both to the investment required and for the assessment of long-term 

environmental effects

Tidal Power and the Bay of Fundy

Within the next two years is the centennial of 

Turnbull’s original proposals (1910, 1912) for generating electrical energy from the tides in the Bay of 

Fundy. In those past 100 years, there have been four 

major and numerous minor proposals for large-scale 

tidal power development in the Bay. Most of these 

involved the creation of one or more barrages, but 

at least one (the Clarkson proposal of 1915) was for 

a kinetic energy conversion. Apart from the earliest 

studies of fisheries in the Outer Bay (1898-1911), 

tidal power proposals were responsible for surges in 

research activity in the Bay in every decade of the 

20th century. Arguably, most of what isknown about 

the Bay ecosystem has resulted from the dreams of 

harnessing its energy (Daborn 2007).

In the 1970s, rising oil prices triggered an extensive examination of the potential for barrage-based 

tidal power development in the Upper Bay of Fundy. 

A review of existing knowledge (Daborn 1977) 

established that environmental and ecological information was too sparse to enable assessment of the 

environmental implications of any tidal power barrage 

in the Upper Bay, although hydrodynamic modeling 

did indicate that extraction of energy from the tides 

could have significant effects on the whole of the 

Fundy ecosystem and might even extend through the 

Gulf of Maine for the largest proposed development. 

It was recognized that the Upper Bay was biologically productive, but, because of the high levels of 

suspended sediment and the consequent lack of light, 

it was not clear on what this productivity was based.

In order to address the numerous questions 

presented by the proposed tidal power development, a 

major collaborative research network called the Fundy 

Environmental Studies Committee (FESC) brought 

together researchers from government agencies, local 

universities, and engineering companies, in a multidisciplinary, multi-institutional, collaborative effort 

that lasted from 1977 to 1984. The highly integrated 

program addressed all of the major research issues, 

from modeling of tides and currents to the dynamic 

properties of sediments, marshes, and mudflats and 

the migratory movements of fish, birds, and mammals. 

The final FESC report (Gordon and Dadswell 1984) 

represented a major increase in the understanding of 

the Bay of Fundy and its unique properties. In spite 

of seven years of integrated, collaborative efforts of 

more than 50 scientists, many questions remained 

unanswered when the FESC was terminated in 

1984. In order to continue the integrated, collaborative, multi-institutional programinitiated by FESC, 

the Acadia Centre for Estuarine Research (ACER) 

was established at Acadia University in 1985. Since 
141

that time, ACER associates from several universities and government agencies in Canada, the United 

States, Argentina, and the United Kingdom have 

carried out numerous investigations into the Bay of 

Fundy ecosystem, from sediments to marshes to fish. 

Advantage was taken of the Annapolis Tidal Generating Station, which was opened at Annapolis Royal, 

Nova Scotia, in 1985, to examine the questions of fish 

passage through a tidal power barrage. As in previous 

decades, collaborative research investigations added 

enormously to the scientific knowledge and understanding of the Bay of Fundy system.

Tidal in-stream technology and the Bay of Fundy

The present considerations for tidal power 

conversion in the Bay of Fundy are primarily based 

upon new designs for TISEC devices, although there 

are also proposals for tidal lagoons or shore-fast 

impoundments. Most of the more mature TISEC technologies are either horizontal- or vertical-axis designs, 

and the ones closest to commercial development for 

grid-connected application, tend to be horizontalaxis. Locations with strong tidal currents suitable for 

TISEC devices occur at a number of sites in the Bay 

of Fundy, especially at the entrances to Passamaquoddy Bay and Minas Basin. 

In 2007, the government of Nova Scotia decided, 

once again, to explore the prospects for generating 

electricity from the tides of the Bay of Fundy and, 

to that end, decided to have a test facility built in the 

Minas Passage that would accommodate commercialscale TISEC devices. The Fundy Tidal Test Facility is 

designed to accommodate three separate devices at a 

time, with grid connections and a supportive research 

facility on shore. These facilities are currently under 

construction, but one device, a 1.2-MW Open-Centre 

Turbine sponsored by Nova Scotia Power, Inc., was 

installed onsite without connections to the grid in 

November 2009. The remaining berths will house a 

20-m diameter Clean Current turbine and a gravitybased version of the two-propeller SeaGen produced 

by Marine Current Turbines.

In 2008, university and government scientists 

in the region met to consider the research needs 

presented by proposals for TISEC development in the 

Bay of Fundy. The research questions identified are 

probably similar to most other potential locations. 

They can be summarized as follows:

• How much energy is available? Current assessments of the amount of energy available at sites 

in the Bay of Fundy are based upon several alternative numerical models that can give widely 

divergent results. Although not really required 

for demonstration scale installations, effective, 

validated hydrodynamic models are essential 

foundations for economic and environmental 

assessments of commercial-scale developments.

• How much energy can be extracted? There 

are two aspects of this. One, relating to the 

efficiency of a device’s energy conversion, is 

of primary interest to the designer and proponents. The more difficult and important aspect, 

however, is at what point does the extraction of 

energy begin to cause unacceptable changes to 

the ecology or to other resources of the system? 

Resolution of this question also depends upon 

validated hydrodynamic models.

• What are the effects of energy removal on 

sediment dynamics? This is a critical environmental question for many of the sites proposed 

for tidal-stream energy extraction, primarily 

because of the profound and complex ecological 

significance of sediments in macrotidal systems. 

The fundamental research involved here generally falls outside the scope of environmental 

assessments for demonstration projects but is 

essential for assessments of commercial scale 

arrays.

• What environmental signals (e.g., vibrations or noise) are emitted by energy conversion devices, and how do these signals affect 

marine life? Technology developers address 

concerns about vibrations that might affect the 

efficiency or durability of their devices, but 

there are great uncertainties about the potential 

effect of such signals on marine life, particularly 

mammals, birds, and fish. Presently-available 

technologies for monitoring movements of fish or 

birds in the vicinity of turbines have so far proved 

to be not only very expensive but also often less 

effective than expected under naturally occurring 

conditions.
142

• What (if any) are the effects of electromagnetic fields generated by submarine electrical 

transmission lines? Research into electromagnetic field effects is not new, but many questions 

remain unanswered about the ecological effects 

of electromagnetic fields and species-specific 

responses. 

• What are the implications of submersed ice 

or other debris? Ice is an issue that applies in 

many but not all northern latitude sites where 

marine energy may be developed. The research 

questions have to do with the effects of ice on 

energy conversion devices (e.g., the potential for 

non-buoyant ice to be a threat to the devices in 

the Upper Bay of Fundy) but also the effects of 

energy extraction on the formation, persistence, 

and movements of ice (e.g., as a result of reduced 

mixing between fresh water and salt water in 

estuaries). In many estuaries, the presence of 

logs and other debris derived from shoreline 

erosion, resource harvesting,or other sources may 

represent significant threats to the integrity and 

efficiency of energy conversion devices.

• What is the potential for energy extracting 

devices to affect the presence, mobilization, 

and effects of contaminants —both those 

associated with the devices and those occurring as a result of other activities? Although 

the potential contaminant hazard of the devices 

themselves tends to be small, commercial-scale 

development will require consideration of larger 

cumulative effects. In turbid systems such as the 

Bay of Fundy, contaminants become closely associated with sediments, particularly those of finer 

grain sizes, so that contaminant fate becomes tied 

up with sediment dynamics. 

• What are the indirect effects of marine energy 

developments on marine biota? In addition to 

direct ecological effects associated with changes 

in flows, sediment dynamics, noise, and strike 

effects on fish and mammals, alluded to previously, there may be other ecological effects that 

are, at present, unknown. These include: mortality 

effects on non-commercial species; indirect 

effects associated with changes in predators or 

prey; and ecosystem effects of habitat alterations. Answers to these questions require new 

investigations of behavior, application of new and 

improved models, and field-based monitoring and 

experimental studies. They are complex, timeand resource-consuming, and difficult to conduct. 

It seems that only a collaborative approach 

involving developers and university and government scientists is likely to lead to a progressive 

and well-founded marine energy industry. 

These questions relate primarily to the perceived 

environmental effects of tidal (or wave) energy developments. However, the coastal marine ecosystem 

is already a well filled environment, with numerous 

other industries vying for access. Interference with 

those activities may trigger other social and environmental consequences. Public attitudes toward alternate energies are important, potentially mutable, and 

poorly known; these will play a major role in determining the public support for marine energy developments. 

The past three decades of research on the Bay 

of Fundy have demonstrated unequivocally that 

macrotidal systems such as the Bay do not exist in 

isolation. Through the motions of the tides and the 

movements of fish, birds, and mammals, the Bayis 

physically and biologically connected to the Canadian Arctic, the eastern seaboard of the United States, 

Central and South America, and Europe. Some of 

the species involved are rare or endangered. The 

implications of energy extraction from the Bay of 

Fundy system must, therefore, be assessed carefully 

in the full context of these international biophysical 

linkages, and this may well apply to most other sites 

in the world that exhibit high potential for TISEC 

development.

Stressors, Receptors, and Risk.

As indicated, the major environmental questions raised by TISEC developments are familiar 

enough. The primary stressors include: changes to 

hydrodynamic characteristics; changes to sediments 

and substrates; noise during construction and noise 

and vibrations during operation; pressure changes; 

ice and debris; and contaminants. The receptors 

of most concern in the Bay of Fundy are marine 

mammals, fish (especially endangered and migratory 

species),benthic communities, plankton, and a few 
143

marine diving birds. However, in spite of all of the 

past work on the ecology of the Bay, it remains difficult to assess the true risk of TISEC development to 

these receptors. The difficulty arises in several ways:

• Many of the potential effects are indirect, resulting from changes to ecosystem 

processes. For example, the footprint of a 

TISEC array and the immediate changes 

to the substrate are easy to assess, but the 

secondary effects of changes in energy levels 

and, therefore, sediment distributions and 

dynamics may have greater effects on farfield benthic habitat.

• Monitoring for and detecting these secondary 

effects in a highly dynamic system that 

is continually undergoing changes from 

other forces, natural and anthropogenic, 

is extremely difficult. Far-field ecological 

changes attributable to energy development 

may be difficult to distinguish from natural 

perturbations.

• Many standard monitoring technologies 

do not work as well under the extreme 

flow conditions of some of these sites. For 

example, some acoustic devices used for 

monitoring fish and their movements appear 

less effective if levels of turbulence, turbidity, 

and entrained air are very high.

• Too little is known about the behavior of 

many species, especially during their migration and in the vicinity of TISEC devices.

A preliminary assessment of risk, recognizing 

differences in the near-field and far-field and the 

potentially different scales of demonstration/pilot 

projects and commercialarrays, has been conducted 

for the Bay of Fundy. The greatest uncertainties are 

associated with the behavior of fish and mammals 

in the vicinity of turbines. Previous monitoring 

conducted at the Roosevelt Island site by Verdant 

Power showed that very few fish were present in 

the experimental array; however, it was unclear 

whether this was because of active avoidance or 

simplybecausefish were scarce in that portion of 

the river. It was anticipated that the deployment of 

commercial-scale devices in the Bay would enable a 

first-order evaluation of the reactive behavior of fish 

and mammals as they approached a working turbine; 

however, the apparent inadequacy of existing technologies and the difficulties of maintaining monitoring 

equipment in place has shown that this is a much 

more challenging task than previously thought.

Adaptive management 

In recognition of these uncertainties, federal and 

provincial governments and the developers of the 

Minas Passage (Bay of Fundy) project have instigated 

an adaptive management process to address the environmental implications of tidal energy conversion in 

the Bay. Following preparation of an Environmental 

Effects Monitoring Plan (EEMP), an independent 

Environmental Monitoring Advisory Committee that 

is responsible for examining the outcomes of monitoring activities and advising on the technologies and 

methodology on a continuing basiswas convened. The 

objective is to ensure that the EEMP delivers, over 

time, the answers needed by regulators, the scientific 

community, developers, and the public. 

Reducing the uncertainties requires research that 

goes beyond the usual scope of environmental impact 

assessments. In recognition that successful demonstration of these commercial-scale devices will lead 

quickly to proposals for arrays, collaborative research 

projects involving regional universities, government agencies, and the consortium of developers 

(represented by the Fundy Ocean Research Centre 

for Energy or FORCE have been initiated in the 

following areas:

• Active and passive tracking of fish, lobsters, and 

mammals in the vicinity of the test site;

• Development of hydrodynamic and sediment 

models that can address the near- and far-field 

effects of energy extraction;

• Monitoring of sediment distributions and benthic 

populations;

• Monitoring of mammal and marine bird activities 

in the passage; and

• Investigation of the formation and fate of ice and 

the movements of large debris.
144

It is also anticipated that additional research into 

the development of new, robust monitoring technologies will be initiated in recognition of the exceptional 

needs for monitoring in these dynamic environments. 

After 100 years, it seems that the dream of 

Fundy tidal power will continue to be a stimulus for 

innovation and a generator of new knowledge for 

decades to come.

References

Daborn, G.R. (Ed.). 1977. Fundy Tidal Power and 

the Environment: Proceedings of a workshop 

on Environmental Implications of Fundy Tidal 

Power at Wolfville, N.S., Nov. 4-5, 1976. Publication No. 28. Nova Scotia, Canada: Acadia 

University Institute. 

Daborn, G.R. 2007. Homage to Penelope: Unraveling the ecology of the Bay of Fundy system. 

In Challenges in Environmental Management in 

the Bay of Fundy—Gulf of Maine. Proceedings of 

the 7th Bay of Fundy Workshop, St. Andrews, NB, 

October 24-27, 2006. Poehle, G.W., P.G. Wells 

and Rolston, S.J. (Eds.). BoFEP Technical Report 

No.3. 12-22.

DFO (Fisheries and Oceans Canada). 2008. Potential 

Impacts of, and mitigation strategies for, smallscale tidal generation projects on coastal marine 

ecosystems in the Bay of Fundy. Canadian 

Science Advisory Secretariat Science Response, 

2008/013.

Gordon, D.C. and Dadswell, M.J. 1984. Update on 

the marine environmental consequences of tidal 

power development in the upper reaches of the 

Bay of Fundy. Canadian Technical Report of 

Fisheries and Aquatic Sciences, 1256. 
145

B.3 Physical Habitat and Natural 

Resources: Maine

James McCleave, Gayle Zydlewski, 

Huijie Xue and Michael Peterson

University of Maine

Interest in tidal power development in Maine 

coastal waters comes from the high tidal currents 

and energy densities. These features are caused by 

the Gulf of Maine-Bay of Fundy basin being in near 

resonance with the principal lunar semidiurnal (M-2) 

tidal constituent of the North Atlantic Ocean. The Electric Power Research Institute (Hagerman and Bedard 

2006) listed 36 potential tidal plant sites in Maine, with 

eight optimistically listed as having 10 MW or greater 

electricity generating potential. The Maine Department of Environmental Protection (DEP 2010) added 

five sites and listed nine sites with active preliminary 

permits. The reason so many potential sites exist is that 

the last glaciations resulted in a series of parallel narrow 

estuaries and bays with numerous constrictions where 

high tidal flows occur.

This presentation considers four environmental 

aspects important during consideration of tidal power 

generation in Maine. It describes the physical settings 

of potential tidal energy sites, describes the biological 

and ecological settings, identifies ecologically significant features and sensitive areas, and mentions some 

species of particular concern.

The emphasis is on “Downeast” Maine, where 

potential sites could be termed bay sites, but also 

considers other parts of Maine briefly, where some sites 

are better termed estuarine sites. Four sites illustrate the 

latter. The Sasanoa “River” connects Sheepscot Bay 

and the Kennebec River, with Lower Hell Gate as the 

prospective site. Through here, the tide floods saline 

water into southern Hockomock Bay and the Kennebec 

River. The tide ebbs from both, receiving low-salinity 

water from the Kennebec River. Mean monthly 

discharge of the Kennebec ranges about 240-1100 m3

s-1. Cowseagan Narrows connects between the Sheepscot River and northern Hockomock Bay; the narrows 

are about 3 km long.

The primary site in the Penobscot River is about 

5 km along the Verona Island narrows, immediately 

above the widening into Penobscot Bay. Tidal currents 

are strong, and the large freshwater discharge enhances 

currents, especially during the spring freshet (mean 

April discharge is >1,000 m3

 s-1). The Bagaduce River 

narrows and Castine Harbor are listed by the Electric 

Power Research Institute as having a combined 10 MW 

potential, but that is doubtful. The practical importance of these sites is as a tidal energy demonstration 

and evaluation site for Maine Maritime Academy, in 

collaboration with the University of Maine.

In Maine, current development activity is focused 

on Cobscook Bay and the Western Passage of Passamaquoddy Bay, which differ in some ways and are 

similar in others. Both, especially Cobscook Bay, have 

complex geomorphology because of glacial action 

(Kelley and Kelley 2004). Glaciated estuaries, 

typical of the northeastern United States, do not 

fit the traditional conceptual models of increasingly fine sediment material found farther up the 

estuary. Instead, bedrock structures and glacial 

deposits control the shape and tidal flow and, 

hence, sedimentation. Subtidal areas are dominated by gravel, cobble, boulders, and bedrock. 

Intertidal areas are about half mudflat. Both 

bays, especially Cobscook, have limited freshwater input, so riverine sediment is lacking. 

The Dennys River, largest in Cobscook, has a 

maximum discharge of ~8 m3

 s-1. The St. Croix 

River, largest in Passamaquoddy, discharges 

45-150 m3

 s-1 seasonally. In contrast, 0.5 km3

of water goes in and out of Cobscook each tide 

— approximately equal to the Mississippi River 

discharge in the same time. There is even greater 

flow through Western Passage into Passamaquoddy. Mean tides in Western Passage are ~5.7 

m. Extreme spring tides are ~7.6 m. Most of the 

flow into both bays comes through Head Harbor 

Passage on the Canadian side of the border.

Modeled flow and energy density during tidal 

cycles shows where tidal energy potential is greatest. 

However, the model does not capture the extreme 

turbulence to the flow, especially in Western Passage, 

where the flow through Head Harbor Passage makes 

a 90° turn. This results in a famous whirlpool, “Old 
146

Table 9 – Differences and similarities of Cobscook and Passamaquoddy Bays

Sow,” on flood tides, along with smaller whirlpools and 

general turbulence.

Flow into Cobscook and Passamaquoddy originates from the mouth of the Bay of Fundy, where the 

upwelling and mixing from the decreasing depth of 

water contributes three important characteristics to 

the water entering the bays: marine salinity of ~30 ppt 

in most areas; boreal, moderated temperatures with 

seasonal range ~0-12 C; and high nitrate concentration 

year-round.

These bays have long been noted for high productivity and biological richness, without much assessment of why, until a concerted effort was published 

in 2004. Nitrate and ammonium, necessary for plant 

growth, are part of the ecosystem flow of energy and 

production. Nitrate is high in Passamaquoddy and 

Outer and Central Cobscook (Garside and Garside 

2004). Because of limited freshwater discharge, the 

only source of nitrate sufficient to support the observed 

primary productivity is the sea. Primary productivity of 

six different groups of taxa provides the organic material available to higher trophic levels.

Conventional wisdom is that increased tidal mixing 

results in increased nutrient availability, which results 

in increased phytoplankton production. But annual net 

primary productivity of phytoplankton in Cobscook 

is similar to non-macro-tidal estuaries (Phinney et al. 

2004). Overall phytoplankton production is high, but 

biomass is very low because of high flushing and high 

turnover. Benthic micro-algal production is about 100 

times the integrated water column phytoplankton value 

in Cobscook because light can penetrate to the bottom; 

the situation in Passamaquoddy is probably about 

reversed.

Rockweeds, primarily Ascophyllum nodosum and 

Fucus vesiculosus, dominate northeastern U.S. coasts in 

the intertidal and sublittoral fringe zones in both highand low-flow areas (Vadas et al. 2004a). Ascophyllum 

productivity in Cobscook Bay is near the high end of 

other studies in the northeast. The high areal coverage 

in Cobscook, coupled with high productivity and 

two-year turnover time, means that rockweed contributes a huge amount of organic carbon to the marine 

ecosystem.

Canopy-forming kelps (e.g., Laminaria longicruris) are abundant along boreal, subarctic shores as 

narrow subtidal fringes (Vadas et al. 2004b). Highest 

biomass occurs in summer and is greater at low-flow 

than high-flow sites. Kelp growth continues through 

the summer, when growth of most other algae slows, 

because kelp can store nitrogen for use when watercolumn nitrogen is low. Kelp turns over three to four 

times per year, becoming detritus or being consumed 

directly by herbivores. Kelp contributes substantially 

to the organic carbon pool in Cobscook and less so in 

Passamaquoddy.

Several species of foliose and filamentous red and 

green algae are common on Maine’s shores (Vadas et 
147

Table 10 – Primary producers and production on Cobscook Bay

al. 2004c). Palmeriaare common red algae; Ulva and

Enteromorpha are common green algae. Because of the 

extensive intertidal and shallow subtidal areas, these 

algae contribute a surprising amount of organic carbon 

to the ecosystem.

Seagrasses, especially Zostera marina, are abundant in protected intertidal and sublittoral fringe 

habitats (Beal et al. 2004). Production is greater in the 

sublittoral fringe than in the intertidal. Again, because 

of the extensive eelgrass beds in Cobscook (490 hectares) and two-month turnover time, seagrass contributes 

large amount of organic carbon to the ecosystem.

Phytoplankton, benthic microalgae, and rockweeds 

make the greatest contribution of fixed carbon to the 

ecosystem of Cobscook Bay. Productivity per unit 

area or per unit volume would be similar in Passamaquoddy Bay, but the proportions of the total contributed 

by the six groups would be very different, because the 

percentage of the area of Passamaquoddy Bay that is 

intertidal is much lower than in Cobscook Bay. Phytoplankton plays the dominant role in Passamaquoddy 

Bay. Recognizing that the values in Table 10 are based 

on different methods by different authors and mostly 

represent net production, not gross production, they 

should be viewed as estimates.

The macroinvertebrate fauna of Cobscook Bay and 

Passamaquoddy Bay is exceedingly diverse. Trott’s 

(2004a) historical checklist of the benthic macroinvertebrates spanning 162 years lists 775 species in 17 

phyla. The list is a thorough inventory and includes 

species not present today. Mollusca (187 species), 

Annelida (183), Arthropoda (149), and Cnidaria 

(95) dominate the list. A survey limited to 11 shallow 

subtidal stations in the eastern part of outer Cobscook 

Bay in 1975 yielded 172 species in 12 phyla (Larsen and 

Gilfillan 2004). Only 200.1 m2

 grab samples were taken. 

Annelida (59 species), Arthropoda (47), and Mollusca 

(44) dominated those samples.

There have been two published bottom-trawl surveys 

of fishes in Passamaquoddy Bay, neither of which is 

current, and there have been downward trends in many 

species in the meantime. Tyler (1971) caught 39 species 

in bottom tows over a 16-month period in 1965-1966 

at a station north of Western Passage, 45 years ago. He 

categorized the fishes as summer periodic (four species), 

winter periodic (four), regular (13), and occasional (18). 

Regular species included commercially harvested fish, 

such as Atlantic herring (Clupea harengus), haddock 

(Melanogrammus aeglefinus), Atlantic cod (Gadus 

morhua), and winter flounder (Pseudopleuronectes 

americanus), and non-commerciallysought fish such as 

longhorn sculpin (Mtoxocephalus octodecemspinosus) 

and ocean pout (Macrozoarces americanus). Important 

summer periodics were silver hake (Merluccius bilinearis), white hake (Urophycis tenuis), and the anadromous alewife (Alosa pseudoharengus). Winter periodics 

included the little skate (Raja erinacea) and pollock 

(Pollachius virens). 

MacDonald et al. (1983) trawled at Tyler’s station, 

at a station farther up Passamaquoddy Bay, and at a 

station in Head Harbor Passage about monthly from 

1976-198130 years ago. They categorized 62 species as 

Tyler did, including 49 species caught at Tyler’s station. 

There were some qualitative differences, mainly because 

MacDonald et al. (1983) categorized greater percent-
148

ages of the species as either summer or winter periodics 

and they considered separately adults and juveniles of 

haddock, Atlantic cod, pollock, and winter flounder.

There are no published studies of pelagic fishes in 

Passamaquoddy or Cobscook Bays. Personal observations suggest that juvenile Atlantic herring are very abundant in summer, despite MacDonald et al.’s (1983) claim 

that they are a winter periodic. Tremendous schools 

of herring were identified during acoustic surveys in 

Western Passage and Outer Cobscook Bay in August and 

September 2009. Atlantic mackerel (Scomber scombrus) 

were also abundant then, feeding on herring.

Migratory species are not well represented in the 

bottom surveys. Alewife, blueback herring (Alosa aestivalis), rainbow smelt (Osmerus mordax) and American 

eels (Anguilla rostrata) migrate through as juveniles and 

as adults. Atlantic salmon (Salmo salar) are rare in the 

Dennys River in Cobscook Bay, but juveniles and adults 

migrate through Passamaquoddy Bay to rivers in New 

Brunswick, Canada.

Marine mammals were especially abundant in 

Western Passage and Head Harbor Passage in 2009. 

Several species are present, commonly minke whales 

(Balaenoptera acutorostrata), fin whales (B. physalus), 

harbor seals (Phoca vitulina) and harbor porpoises 

(Phocoena phocoena), and, occasionally, endangered 

northern right whales (Balaena glacialis) and humpback 

whales (Megaptera novaeangliae).

Astounding numbers of seabirds are present as 

residents, migrants, and overwinterers. Many congregate along tidal fronts, either passively or actively. At 

some times as many as 25,000 Bonaparte’s gulls (Larus 

philadelphia), 15,000 herring gulls (L. argentatus), 3,000 

black-backed gulls (L. marinus),and 3,000 black-legged 

kittiwakes (Rissa tridactyla) may be present in the area. 

Red-necked phalaropes (Phalaropus lobatus) once were 

far and away the most common (as many as 2,000,000 at 

a time in 1977), but are rare now for unknown reasons. 

Similarly, the kittiwakes have declined from a high in 

1996 of 65,000. A variety of ducks and common terns 

(Sterna hirundo) and Arctic terns (S. paradisaea)are also 

present.

One could argue that all of Cobscook Bay is an 

ecologically important and sensitive feature for several 

reasons. There is high species diversity. The extensive 

stands of rockweed, kelp, and seagrass provide nursery 

areas and habitat for numerous sessile and mobile 

organisms as well as foraging habitat for many species, 

including seabirds. The detritial food web is important because of the extensive areas of plants and their 

high turnover rates. As many as a hundred species of 

invertebrates that, elsewhere, are only found subtidally 

are found intertidally in Cobscook, for two reasons. 

Extreme spring low tides occur in early mornings and 

late afternoons, so low intertidal areas are not exposed 

to noonday sun. Because of the cool water in summer, 

heavy fog develops, insulating intertidal organisms 

from the summer sun. Gigantism occurs in several 

invertebrate species (e.g., sea stars, brittle stars, tunicates, sea urchins, and periwinkles) in Cobscook and 

Passamaquoddy.

However, Cobscook Bay and Passamaquoddy Bay 

are not pristine. Rockweeds are species of concern. 

There is a controversy over how much can be safely 

harvested without damaging the multiple roles that 

rockweeds play in the ecosystem. Species diversity 

in Cobscook and, probably, in Passamaquoddy has 

declined substantially in the last 30-35 years. Accumulated mud sediment has occluded normal interstices 

in gravel and boulder habitats, especially in inner 

Cobscook. Extensive stands of kelp have disappeared 

there, making kelp a species of concern.

Mussel beds have become dominant in many areas 

where they were rare before 1980. Invasive European 

green crabs(Carcinus maenas) have contributed to the 

decline of periwinklesnails (family Littorinidae), as 

has commercial harvesting. Mussel beds trap sediment, but where does the sediment come from, given 

the lack of riverine input? Trawling for scallops and 

sea urchins produces plumes of sediment, and the 

sediment spreads on the tidal flow and re-deposits 

everywhere. Sea urchin trawling didn’t start much 

before 1987. Blue mussels (Mytilus edulis), soft-shell 

clams (Mya arenaria), sea scallops (Placopecten 

magellanicus),urchins, and periwinkles are all species 

of concern.
149

In Passamaquoddy and Cobscook, an ecologically significant feature is the predator-prey food 

web, based on Atlantic herring as the forage base. 

The summer abundance of juvenile herring schools 

attracts periodic fishes, such as Atlantic mackerel, 

resident fishes, such as haddock, many species of 

seabirds, and several species of marine mammals. 

Adult herring provide food for marine mammals. In 

all areas of Maine, the decline of Atlantic herring is of 

concern from the food web aspect to the lobster bait 

and human food aspect.

In other areas of Maine, estuaries and bays are 

important corridors for migratory fishes. The Penobscot, Sheepscot, Sasanoa, and Kennebec rivers are 

corridors for Atlantic sturgeon (Acipenser oxyrhynchus) 

and endangered shortnose sturgeon (A. brevirostrum) 

and overwintering areas for shortnose sturgeon. The 

Atlantic sturgeon is under consideration for listing as 

threatened. Thus, the sturgeons are species of concern. 

Maine is making significant efforts to restore anadromous alewife, blueback herring, American shad (Alosa 

sapidissima) and Atlantic salmon (Salmo salar) to 

rivers, so these are also species of concern.

A plan is in place for turbine removal and 

improved fish passage facilities in the Penobscot 

River and other rivers where anadromous fishes are or 

were present. A question worthy of thought would be 

whether people are simply proposing to replace river 

turbines with tidal turbines?

References

Beal, B.F., Vadas, R.L., Wright, W.A. and Nickl, 

S. 2004. Annual aboveground biomass and productivity estimates for intertidal eelgrass (Zostera marina) 

in Cobscook Bay, Maine. Northeastern Naturalist, 

11(Special Issue 2): 197-224.

Department of Environmental Protection. 2010. 

Status of tidal power project proposals in Maine as of 

January 1, 2010. Maine Department of Environmental 

Protection. Unpublished document. Available at http://

www.maine.gov/dep/blwq/docstand/dams/hydro_

FERC_process/index.htm.

Garside, C. and Garside, J.C. 2004. Nutrient 

sources and distributions in Cobscook Bay. Northeastern Naturalist, 11(Special Issue 2): 75-86.

Hagerman, G. and Bedard, R. 2006. Maine Tidal 

In-Stream Energy Conversion (TISEC): Survey and 

Characterization of Potential Project Sites. Palo Alto, 

CA: Electric Power Research Institute, EPRI-TP- 003 

ME Rev 1. 

Kelley, J.T. and Kelley A.R. 2004. Controls on 

surficial materials distribution on a rock-framed, glaciated, tidally dominated estuary: Cobscook Bay, Maine. 

Northeastern Naturalist, 11(Special Issue 2): 51-74.

Larsen, P.F. 2004. Introduction to ecosystem 

modeling in Cobscook Bay, Maine: A boreal, 

macrotidal estuary. Northeastern Naturalist, 11(Special 

Issue 2): 1-12.

Larsen, P.F. and Gilfillan, E.S. 2004. A preliminary survey of the subtidal macrobenthic invertebrates 

of Cobscook Bay, Maine. Northeastern Naturalist, 

11(Special Issue 2): 243-260.

Macdonald, J.S., Dadswell, M.J., Appy, R.G., 

Melvin, G.D. and Methven, D.A.. 1983. Fishes, fish 

assemblages, and their seasonal movements in the 

lower Bay of Fundy and Passamaquoddy Bay, Canada. 

Fishery Bulletin, 82: 121-139.
150

Phinney, D.A., Yentsch, C.S and Phinney, D.I. 

2004. Primary productivity of phytoplankton and 

subtidal microphytobenthos in Cobscook Bay, Maine. 

Northeastern Naturalist, 11(Special Issue 2): 101-122.

Trott, T.J. 2004. Cobscook Bay inventory: A 

historical checklist of marine invertebrates spanning 

162 years. Northeastern Naturalist, 11(Special Issue 2): 

261-324.

Tyler, A V. 1971. Periodic and resident components 

of communities of Atlantic fishes. Journal of the Fisheries Research Board of Canada, 28: 935-946.

Vadas, R.L., Beal, B.F., Wright, W.A., Emerson, 

S. and Nickl, S. 2004. Biomass and productivity of red 

and green algae in Cobscook Bay, Maine. Northeastern 

Naturalist, 11(Special Issue 2): 163-196.

Vadas, R.L., Beal, B.F., Wright, W.A., Nickl, S. and 

Emerson, S. 2004. Growth and productivity of sublittoral fringe kelps (Laminaria longicruris) in Cobscook 

Bay, Maine. Northeastern Naturalist, 11(Special Issue 

2): 143-162.

Vadas, R.L., Wright, W.A. and Beal, B.F. 2004. 

Biomass and productivity of intertidal rockweeds 

(Ascophyllum nodosum) in Cobscook Bay. Northeastern Naturalist, 11(Special Issue 2): 123-142.
151

B.4 Physical Habitat and Natural 

Resources: Puget Sound, Washington

Andrea Copping, Ph.D. and Brie Van Cleve

Pacific Northwest National Laboratory, 

Marine Sciences Laboratory 

The Puget Sound system and how it was formed

Puget Sound is a large, fjord-like estuary encompassing the second largest watershed area in the 

United States. It is the southern portion of the greater 

Puget Sound-Georgia Basin that is shared with British 

Columbia in Canada (Figure 41). 

From the Canadian border south to Olympia and 

west to the Pacific Ocean, the Puget Sound basin 

comprises 7,252 square kilometer of inland marine 

waters and 4,023 km of shoreline. Puget Sound is 

connected to the Pacific Ocean through the Strait of 

Juan de Fuca to the west and the Strait of Georgia and 

Johnstone Strait in British Columbia. Together these 

water bodies are known as the Salish Sea, in recognition of Native American inhabitants of the area. 

Puget Sound is approximately 160 km long with 

average depths of 62 m and maximum depths of 280 

m. Meltwater flowing southward beneath the ice is 

believed to have scoured the major troughs that define 

Puget Sound today (Burns 1985). Glacial moraines 

created shallow sills at the mouths of several of the 

basins in Puget Sound, creating constrictions with 

strong reflux and tidal currents. The two major sills 

responsible for circulation in Puget Sound are located 

at Admiralty Inlet (near Port Townsend, Washington) 

and the Tacoma Narrows. The majority of the Sound’s 

marine water enters through Admiralty Inlet. This 

inlet is constricted by topography (Point Wilson 

and Admiralty Head) and vertically constricted by a 

shallow sill making it an area of swift tidal currents 

(>3 m/s). 

An estuarine system with lots of people

A number of major river systems bring freshwater into Puget Sound, making it one of the most 

productive estuaries in the county, which, in turn, 

has supported the development of one of the largest 

shipping ports in the country, a robust tourism and 

recreation industry, a substantial fishing industry, 

and major military installations. Nearly 4.5 million 

people live in the Puget Sound region and another 1.3 

million are expected by 2025. The majority of inhabitants live in major cities on the eastern shore between 

Bellingham and Olympia, with Seattle and Tacoma 

boasting the largest populations. 

The Puget Sound region is an important 

economic, security, and environmental asset. Total 

maritime trade in Washington averages $12 billion 

in exports and $60 billion in imports.1

 The Ports 

of Seattle and Tacoma are together the third largest 

container port in the United States. Over 80 percent 

of waterborne cargo moving from the lower 48 states 

to Alaska passes through Puget Sound ports.2

 Other 

maritime industries include shipyards, boat and shipbuilding and repair, naval facilities, cruise ships, and a 

large oil refinery.

Puget Sound is home to the majority of the 

Alaska fishing fleet — the largest fishing fleet in the 

United States — and is the point of entry of 50% of 

the seafood entering the country.3

 Approximately 

10,000 jobs in the Puget Sound region and $3.5 

billion in gross sales are attributed to the fishing 

industry.4

 Washington produces the largest amount 

of farmed shellfish in the United States, the majority 

from Puget Sound.5

 Aquaculture alone is worth 

$110 million in the region and supports thousands 

of jobs.6

Recreational boating is a major activity in 

Puget Sound, accounting for $489 million in spending 

annually.7

 Puget Sound wildlife provide a basis for 

an ecotourism industry 80 boats strong, and visitors 

come from across the country to view the region’s 

iconic killer whales. 

1

 FAST Corridor: The Fast Partnership helps move our Economy. 

April, 2006. www.psrc.org/fastcorridor/ 2

 Commit to Compete: Maritime transportation is critical to the 

future of the Pacific Northwest Economy. 2003

3

 Ibid and International Center of Maritime Industries fact sheet 

by the Trade Development Alliance of Greater Seattle.

4

 International Center of Maritime Industries fact sheet by the 

Trade Development Alliance of Greater Seattle.

5

 Focus on Puget Sound: Economic Facts by Washington State 

Department of Ecology, October 2008. 

6

 http://www.pcsga.org/pub/farming/farm_benefits.shtm

7

 Focus on Puget Sound: Economic Facts by Washington State 

Department of Ecology, October 2008.
152

Table 11 – Examples of Puget Sound plant and animal life

Who lives here and who is at risk

The shape of Puget Sound results in a narrow 

fringe of vegetated habitat types. These habitats (e.g., 

kelp forests, eelgrass beds, mudflats, coastal marshes 

and embayments, rocky reefs, and open water) host 

rich plant and animal diversity including over 230 

species of marine and anadromous fish, 13 species 

of marine mammals, 165 marine dependant birds, 

and 3,000 species of marine invertebrates. Puget 

Sound is also home to five species of Pacific salmon, 

many populations of which are listed as threatened 

or endangered under the federal Endangered Species 

Act, as well as a population of endangered Southern 

Resident killer whales. 

Table 11 – Examples of Puget Sound plant and animal life

Puget Sound supports abundant natural resources, 

making timber harvest, fishing, and shellfish harvest 

important regional industries. Indicators of stress to 

the ecosystem resulting from industrial and residential development include a loss of 25% of forest 

lands in the past 15 years, nearshore habitats such 

as eelgrass under stress, declines in commercial fish 

harvest, water quality issues such as beach closures 

and hypoxic zones, less than half of the Puget Sound 

herring stocks considered “healthy,” and economically 

and culturally important species threatened by extinction. Three endangered species especially susceptible 

to potential negative impacts from tidal energy development are Southern Resident killer whales (currently 

85 individuals in the population), Chinook salmon 

runs, and the marbled murrelet seabird. 

How exactly tidal energy development will affect 

the Puget Sound ecosystem and especially these 

key species is poorly understood, making securing 

environmental permission under regulatory statutes 

challenging, time-consuming, and costly. Initial 

modeling estimates indicate that there is unlikely to 

be a measurable change in tidal prism from removal 

of energy from pilot-scale deployments at Admiralty 

Inlet or other locations in Puget Sound (Polagye 

2009). Possibly additive or synergistic effects of 

tidal energy development with existing environmental issues, such as water quality, habitat impacts, 

and species population declines, further add to the 

uncertainty associated with development. In spite of 

technical and environmental challenges of tidal power 
153

generation in Puget Sound, there is strong interest 

in renewable energy generation among public and 

private entities, and Puget Sound offers sites with 

abundant power densities in close proximity to load 

centers. 

Proposed tidal projects 

At locations in Admiralty Inlet, there are two 

distinct efforts to test and develop tidal energy. One 

project is proposed by the Snohomish County Public 

Utility District (SnoPUD), using OpenHydro devices. 

A second project is lead by U.S. Navy Region Northwest, using Verdant Power devices. There are several 

other potential tidal energy sites in Puget Sound (e.g., 

Tacoma Narrows) that are not under active development. 

In early 2007 SnoPUD received preliminary 

permits from the Federal Energy Regulatory Commission (FERC) to study seven locations in and around 

Puget Sound for tidal energy development. The 

seven sites combined could provide as much as 100 

MW of energy —or enough power for about 70,000 

residences. Following a screening process, SnoPUD 

narrowed its focus to two sites: Deception Pass and 

Admiralty Inlet. Only Admiralty Inlet is under active 

development. 

In April 2009, SnoPUD selected OpenHydro, 

an Irish tidal turbine developer, to design, build, and 

install up to two hydrokinetic turbines at a project site 

in northern Admiralty Inlet, west of Whidbey Island 

(Figure 42). InDecember 2009, SnoPUD submitted 

a draft license application to the FERC to install one 

or two tidal power generation turbines off Admiralty 

Head. A 10-meter diameter OpenHydro design is 

proposed for deployment in >60 meters of water on 

the cobble seabed in late 2011 or early 2012. This 

water depth will avoid interactions with shipping 

traffic and mayhelp to limit environmental impacts. 

At peak performance, each unit is expected to produce 

about 600 kilowatts (kW)of electricity, enough to 

power about 500 homes. Washington State law 

now requires the utility to meet 15% of its load with 

renewable resources (not including additional traditional hydropower) by 2020. 

Since 2007, SnoPUD and its contractors have 

carried out a number of studies to characterize the 

physical and biological environment in the project 

area. Owing to the intense tidal currents in the area, 

preexisting data are limited. Characterization studies 

have included:

• Tidal currents (Acoustic Doppler Current 

Profilers)

• Ambient noise (recording hydrophones)

• Aquatic species abundance (vessel-based 

hydroacoustic surveys, both mobile for broad 

area assessment and moored for assessment of 

“fish flux” through a fixed site)

• Marine mammal sighting and passive acoustic 

surveys (focusing on the endangered Southern 

Resident killer whales, but also including seal, 

sea lion, and porpoise populations)

• High resolution bathymetric survey (including 

ROV surveys of the seabed); and

• Water quality measurements

These studies suggest significant spatial and 

temporal variations in the physical and biological 

environment at the proposed development site.

U.S. Navy Region Northwest was directed by 

Congress to carry out research and development 

activities in tidal power in Puget Sound. A one-year 

demonstration project is planned at a site further south 

in Admiralty Inlet off Marrowstone Island (Figure 2) 

using Verdant Power turbines. As with the SnoPUD 

project, deployment of three to six turbines could 

take place in late 2011 or early 2012. Each turbine 

would generate 40 kW of electricity at rated capacity 

and supply power to one building and the lights in a 

parking lot at the U.S. Navy’s magazine on nearby 

Indian Island. Although the Navy is not required to 

obtain a pilot demonstration license from FERC, the 

U.S. Navy’s environmental planning process follows 

internal guidelines and the National Environmental 

Policy Act, which requires compliance with applicable federal and state statutes. Consequently, the 

permitting process and time lines are very similar to 

those for the SnoPUD project. 
154

Figure 41 – The Puget Sound-Georgia Basin is bisected by the U.S.-Canadian border.
155

Figure 42 – Sites of Puget Sound pilot tidal projects.

Reference

Polagye, B. 2009. United States National Tidal 

In-stream Resource Estimate. Technical Report to 

US Department of Energy by Northwest National 

Marine Renewable Energy Center, University of 

Washington, Seattle, WA. 
156

B.5 Physical Habitat and Natural 

Resources: Alaska, with a Focus 

on Cook Inlet

 Sue Saupe

Cook Inlet Citizens Regional Advisory 

Committee

Background – Alaska Tidal Resources

Alaska has more than 70,000 km of coastline; 

more than double that of the rest of the U.S. coastal 

states combined. This extensive coastline and the 

unique regional tidal ranges and currents create 

enormous tidal energy potential, primarily in areas of 

the Gulf of Alaska. Most of the Gulf of Alaska has 

mixed semi-diurnal tides, and the Aleutian Islands 

and western and northern Alaska have predominantly 

diurnal tides and have much lower tidal ranges. The 

location of the Gulf of Alaska basin relative to the 

North Pacific amphidromic point and the complex 

interaction of the M2

 (lunar semi-diurnal) tidal wave 

with the Gulf of Alaska’s coastline and its bays and 

estuaries results in tidal ranges and currents that vary 

significantly throughout the Gulf. For example, the 

tide is focused into the narrow ends at the head of 

Cook Inlet, an extension of the northwestern Gulf of 

Alaska, and the natural period of oscillation in this 

long, narrow inlet is similar to that of the tides, amplifying the tides even further.

In 2003, the Alaska State Legislature commissioned an Alaska Energy Policy Task Force1

 to 

develop a long-term energy policy for Alaska to: 

promote research, development, and demonstration 

of clean and renewable energy; promote conservation and energy efficiency across all of Alaska; 

increase the proportion of renewables in long-term 

fuel sources. An Alaska Renewable Energy Atlas 

was published and most recently updated in 2009 to 

include the most current information on the potential 

for developing geothermal, wind, solar, hydroelectric, 

tidal, and wave energy resources (AEA 2009). Since 

2006, the Alaska Energy Authority has partnered with 

the Electric Power Research Institute (EPRI) to study 

tidal energy potential in Alaska and has identified 

three main areas of interest that were highlighted in 

1

 Established by HCR 21; sunset in April 2004.

the Renewable Energy Atlas of Alaska — Cook Inlet, 

specific areas of southeast Alaska, and several Aleutian 

Island passes (Figure 43). Also shown in Figure 43 are 

other areas where there has been interest in tidal energy 

development, as evidenced by current, proposed, or 

expired FERC permits2

. In 2008 the Alaska Legislature 

established a Renewable Energy Grant Fund,3

 authorizing the Alaska Energy Authority to distribute renewable energy grants based on an annual funding of $50 

million (with an additional $50 million added in FY09). 

Despite the massive tidal energy potential in 

Alaska, the lack of extensive infrastructure for much of 

coastal Alaska (roads, transmission lines, and docks) 

presents major challenges to developing tidal energy 

resources. However, there are several areas where tidal 

energy potential is high and can be linked to existing 

power grids or can be delivered to specific locales. 

Specifically, upper Cook Inlet is of high interest, 

given its proximity to energy demands and electrical 

infrastructure. More specifically, an area west of Fire 

Island in upper Cook Inlet is under intense evaluation 

for the planned in-water installation and testing of a 

group of TideGen turbines by Ocean Renewable Power 

Company, LLC (ORPC) by 2011 or 2012. Several 

other areas of Cook Inlet have also been identified as 

having potential (Figure 43), including Turnagain Arm, 

the Forelands, Kalgin Island, and Harriet Point. In 

Cook Inlet, pending preliminary permits to FERC have 

been submitted by ORPC to explore the resources at the 

East Foreland and by Turnagain Arm Tidal Energy for a 

tidal fence near the mouth of Turnagain Arm (Table 12). 

Several other FERC permits for Cook Inlet were either 

expired or were withdrawn or dismissed for various 

reasons – including areas near Kalgin Island and in 

Kachemak Bay. 

Southeast Alaska is another area of Alaska with 

potential for tidal energy development (Figure 43). 

Cross Sound and Icy Strait show substantial energy 

potential (Polagye and Bedard 2006) that could meet 

energy needs for local communities as well as supply 

energy via inter-tie to Canada and the Pacific Northwest. Other very local but high quality sites have been 

identified, mainly in areas that funnel southeast Alas2 http://www.ferc.gov/industries/hydropower/indus-act/hydrokinetics.asp

3

 Established by HB 152
157

ka’s tidal energy through very narrow passes. Natural 

Currents Tidal Development, LLC has obtained 

preliminary permits from the FERC for Icy Strait and 

Port Clarence and has permits pending for Kootznahoo 

Inlet and Gastineau Channel4

. 

The Renewable Energy Atlas (AEA 2009) also 

identifies several eastern Aleutian Island passes as 

having exploitable tidal power resources (Figure 43). 

Although the tidal ranges are low compared to other 

areas of the Gulf of Alaska, significant currents are 

produced by tidal flushing between the north Pacific 

and the Bering Sea through the numerous deep and 

narrow passes between the various Aleutian Islands as 

well as atmospheric-induced barotrophic flow and the 

baroclinic flow of the Alaska Coastal Current. Except 

for a few specific locations, there is low potential for 

tidal energy development further east and north in the 

Bering Sea and Arctic regions due to their significantly 

lower tides and heavy winter ice. 

The focus in the next section is on upper Cook 

Inlet, due to the current interest in the area and because 

a pilot project is currently permitted with plans for 

in-water turbine deployment in 2011 or 2012. The 

physical habitat and natural resources of this area will 

be the presented, as well as briefer descriptions for 

other areas of interest in Cook Inlet, Southeast Alaska, 

and the Aleutians.

Cook Inlet Physical Environment

Cook Inlet has attracted the most recent attention 

for tidal energy development in Alaska for several 

reasons – strong semi-diurnal tides and associated 

currents, proximity to infrastructure for deploying 

equipment and personnel during research and development, and the ability to distribute energy to the 

adjacent city of Anchorage or other areas of the 

Alaska Railroad railbelt. The electric grid of the 

railbelt is along the Alaska Railroad that extends 

from Fairbanks to Anchorage and south to Whittier 

in Prince William Sound and Seward on the Kenai 

Peninsula and provides electrical power to more 

than two-thirds of the entire population of the state. 

Despite the proximity of Cook Inlet’s tidal energy 

4

 http://www.ferc.gov/industries/hydropower/indus-act/hydrokinetics.asp

resources to this infrastructure, extreme tidal ranges, 

suspended sediment loads, and seasonal broken sea 

ice in the upper Inlet create an unusual environment of 

extreme tidal currents, ice scouring and transport, and 

sediment erosion and deposition, creating challenges 

to any marine development or operation in the area. 

The main body of Cook Inlet is a roughly 290 

km-long tidal estuary along a southwest to northeast 

axis extending from the western Gulf of Alaska in the 

North Pacific Ocean (Figure 44a). At its mouth, the 

inlet is more than 120 km wide and narrows northward. Upper Cook Inlet also includes Turnagain and 

Knik arms, extending about 60 km to the east and 

north, respectively. Upper Cook Inlet is the area north 

of a constriction point called the Forelands, where the 

Inlet narrows to less than 20 km. Everything south 

of the Forelands is considered Lower Cook Inlet, 

although some documents further divide it into the 

central (or middle) and lower portions of the Inlet. 

Kachemak and Kamishak Bays are two additional 

major areas of the Inlet, inside the mouth on the east 

and west sides, respectively. 

Cook Inlet is generally less than 70 m deep, 

although depths are much greater at the entrance and 

in several deep channels (Figure 44a). Wide shallow 

areas ring much of the upper and western Inlet, often 

revealing kilometers-wide mudflats during low tides. 

The standing wave around the North Pacific 

amphidromic point pushes into the mouth of Cook 

Inlet and the shape of the Inlet basin promotes resonance of the Gulf of Alaska M2

 tide and focuses its 

energy at its narrow and shallow head. This amplifies the tide height compared to the rest of the Gulf of 

Alaska, creating a significant difference in tidal range 

from an average of 2-3 m at the mouth and 8 m at the 

head, with extreme tidal ranges approaching 12 m 

in the upper Inlet. These large tides produce strong 

currents, with some places in the Inlet averaging 2 kts 

and exceeding 8 kts during maximum tides in areas of 

extreme constriction such as between McKenzie and 

Cairn Points and between the West and East Forelands 

(Figure 44a).

The Cook Inlet watershed drains over 100,000 

km2 (Glass et al. 2004) and is bordered by the Chigmat 

and Alaska Ranges to the west and northwest, by the 
158

Chugach Range and smaller Talkeetna Range to the 

north and northeast, and by the Kenai Mountains to the 

east. These ranges have ice fields and glaciers as well 

as significant snowfall that all contribute to seasonal 

inundations of freshwater to the Inlet. The interaction of Cook Inlet’s unique bathymetry and geography 

(channels, shallow flats, constrictions, embayments, 

and changes in the direction of its main axis) with tidal, 

geostrophic, and baroclinic currents creates a complex 

hydrographic regime throughout the Inlet. The significant freshwater inputs into the upper Inlet create a 

density-driven western boundary current from north to 

south along the west side of upper Cook Inlet, resulting 

in ebb-tidal currents that are greater than flood-tidal 

currents. In the lower Inlet, the Alaska Coastal Current 

flows west and north into Cook Inlet and upwelling 

of colder, nutrient-rich water occurs near the entrance 

onto the shallow shelf. As these sources of water are 

transported north and west in the Inlet, they mix with 

the fresher water flowing south along the west side. The 

combination of barcolinic circulation, bathymetry, tidal 

forces, and geography results in especially complex 

circulation patterns throughout Cook Inlet, with strong 

vertical mixing, gyres, and shear zones that occur where 

southward-flowing lower salinity water meets seawater 

intruding westward from the entrance. 

The low-salinity waters of upper Cook Inlet allow 

ice formation when air and water temperatures drop 

in late fall. Typically, by mid-November (November 

24th, on average), sea ice has formed in the upper Inlet 

and, on average, the termination of significant ice is 

April 8 (Nelson and Whitney 1996). Much of the ice 

forms initially as shore-fast ice that is subsequently 

floated by high tides and remains broken and mobile. 

The ice can become entrained in surface currents 

and transported into shipping lanes, temporarily 

re-grounded elsewhere, converge at frontal zones, or 

become concentrated due to prevailing winds temporarily concentrating and packing the ice. Multiple 

grounding and refloating of ice pans can create multilayered ice that can be up to 10 m thick and pose 

significant risk to ships or infrastructure. 

The rivers that discharge into upper Cook Inlet 

also introduce considerable loads of suspended 

sediments, mainly as glacial flour. The strong tidal 

currents maintain these clay particles in suspension 

and transport them to the very shallow nearshore areas 

or areas of lower energy downstream. In the upper 

Inlet, suspended sediment loads exceeding 10,000 

mg/l have been measured, concentrations greater than 

2,000 mg/l are common, and average values are about 

200 mg/l (Feely and Massoth 1981). In contrast, 

significantly lower suspended sediment concentrations are found in lower Cook Inlet, reflecting the 

intrusion of seawater into the lower Inlet. The 

enormous plumes of sediment in upper Cook Inlet are 

visible in satellite imagery (Figure 44b) and provide 

a visual “proxy” for the transport of freshwater from 

the upper to the lower Inlet along the west side. The 

interaction of suspended sediments, currents, and 

bluff erosion plays a major role in structuring nearshore and benthic habitats throughout Cook Inlet. 

Cook Inlet Biological Habitats and Resources

The marine habitat and resources of upper Cook 

Inlet are influenced by extreme tides and currents, 

the reworking of sediments by currents and seasonal 

ice, high suspended sediment loads and subsequent 

low light transmission through the water column, 

low in situ primary production, and extreme salinity 

gradients. In Cook Inlet, these factors create a general 

trend of decreased marine species diversity in upper 

Cook Inlet, compared to the middle and lower Inlet. 

Despite these differences, the upper Inlet has recently 

been described as more productive than previously 

believed, with the transport of terrigenous and salt 

marsh carbon described as the likely carbon source to 

the nearshore food web (Houghton et al. 2005a). 

Habitat

Overall, Cook Inlet is represented by a diverse 

array of intertidal and subtidal benthic habitats. 

Substrate sediment grain size is a significant factor 

defining the infaunal and epifaunal communities that 

dominate in the different habitats. The sediment 

grain size is, in turn, influenced by currents and wave 

energy. For example, the strong currents of the upper 

and central Inlet prevent subtidal deposition of most 

of the glacial flour that is introduced into the upper 

Inlet, and a significant portion is swept out of the 

Inlet. For much of the upper and central Inlet, especially in the channels, the strong currents ensure that 

the benthic habitat is swept clear of sand and mud so 
159

that gravel (from cobbles to boulders) habitat dominates. Other subtidal habitats include areas dominated 

by sand waves (lower Cook Inlet near the entrance) and 

silt/clay sediments (deepest Kachemak Bay). 

Deposition of fine-grained sediments occurs in 

the lower energy environments of the shallow nearshore, quiet embayments, and in the eddies that form 

behind land projections, such as the Forelands and 

Point Possession. This allows mud and sandy mud 

to dominate in the mid- and lower intertidal and very 

shallow subtidal zones of upper and western Cook Inlet, 

especially in Knik and Turnagain arms, the Susitna and 

Beluga River deltas, Trading and Redoubt bays, and the 

backs of most of the bays on the west side of the Inlet. 

Invertebrates

The extensive mud flats of Cook Inlet are an 

important stopover for a variety of migrating shorebirds and seabirds, including sandpipers, plovers, and 

dunlin (Gill and Tibbits 1999). They also provide ideal 

habitat for the deposit-feeding clam, Macoma balthica, 

which is especially abundant in muddy areas near river 

sources and in the lee of promontories (Lees et al. 2001) 

and is a major prey item of the migratory birds. This 

bivalve is one of the few intertidal invertebrates that 

occurs in upper Cook Inlet. They are the only food 

source for over-wintering Pribilof rock sandpipers 

(Calidris ptilocnemis ptilocnmeis) in Cook Inlet (Gill 

et. al. 1999), which hostsa large proportion of this rock 

sandpiper subspecies’ entire population. Tidal currents 

create icescouring that scrapes the mud flats and 

provides ice-free areas for the birds to forage, despite 

the severe Cook Inlet winter conditions. M. balthicaisalso an important prey for other shorebirds, diving 

birds, crabs, isopods, and fish. 

Subtidal invertebrates that have been documented 

in upper Cook Inlet include isopods (Aregia pugettensis, 

Onisicidea), Alaska bay shrimp (Crangon alaskensis), 

California bay shrimp (C. franciscorum), blacktail 

shrimp (C. nigricauda), sand shrimp (Crangon spp.), 

brine shrimp (Lagunogrammarus setosus), mysids 

(Mysis litoralis, Neomysis sp., N.kadiakensis, N. rayii, 

N. mercedis), nereid polychates (Neanthes limnicola), 

stink bug (Pentatomidae), and aquatic sow bug (Saduria 

entamom) (Houghton et. al. 2005a and 2005b).

Fish

In Cook Inlet, salmon are important subsistence, 

recreational, personal-use, and commercial fish. Five 

salmon species occur in Cook Inlet, and all five of these 

species spawn in the main rivers of upper Cook Inlet. 

These include chinook or king salmon (Oncorhynchus 

tshawytscha), red or sockeye salmon (O. nerka), silver 

or coho salmon (O. kisutch), dog or chum salmon (O. 

keta), and pink or humpback salmon (O. gorbuscha). 

Adult salmon return between May and October to their 

natal rivers and streams to spawn, and the timing of 

their return within that window is species-dependent. 

Pink salmon can also spawn intertidally. Salmon 

smolts out-migrate from freshwater to the oceans from 

mid-April through mid-July, although they have shown 

up in beach seine surveys throughout the year. 

Other fish species that occur in upper Cook Inlet 

include the demersal starry flounder (Platichthys 

stellatus), yellowfin sole (Limanda aspera), rock sole 

(Lepidopsetta bilineata), Pacific cod (Gadus macrocephalus), and Pacific staghorn sculpin (Leptocottus 

armatus). Dominant seasonally-abundant forage fish 

include threespine stickleback (Gasterosteus aculeatus), 

Pacific herring (Clupea pallasi), walleye pollock 

(Theragra chalcogramma), capelin (Mallotus villosus), 

Pacific sandlance (Ammodytes hexapterus), eulachon 

(Thaleichthys pacificus), longfin smelt (Spirinchus 

thaleichthys), saffron cod (Eleginus gracilis), pacific 

sandfish (Trichodon trichodon), and ninespine stickleback (Pungitius pungitius) (Houghton et al. 2005a, 

2005b, Moulton 1997).

Birds

In addition to the migrating birds previously 

described as associated with foraging on tidal mud 

flats, there are numerous other birds that use Cook 

Inlet, including 30 waterfowl species, 29 shorebird 

species, 16 jaeger, gull, or tern species, 5 loons or 

grebes, 3 merganser species, 2 heron and crane species, 

2 auk or puffin species, 1 shearwater species, 1 rail, and 

1 cormorant. In upper Cook Inlet, the shorebirds and 

waterfowl are the most common. 

Marine Mammals

There are few resident marine mammals in upper 

Cook Inlet. Beluga whales (Delphinapterus leucas) are 
160

the most abundant marine mammal species in Upper 

Cook Inlet, despite the fact that the population of this 

genetically isolated stock has declined to the point that 

it has recently been listed as endangered. In addition, their summer feeding range has contracted and 

is focused in upper Cook Inlet, critical habitat area for 

these whales. Harbor seals (Phoca vitulina) have occasionally been sighted in upper Cook Inlet, using the 

mud and sand flats to haul out (Rodrigues et. al. 2006). 

Other occasionals include gray Stellar sea lion (Euretopias jubatus), sea otter (Enhydra lutris), Dall’s porpoise 

(Phocoenoides dalli), harbor porpoise (Phoecena 

phoecena), minke whale (Balaenoptera acutorostrata), 

fin whale (Balaenoptera physalus), and killer whale 

(Orcinus orca).

Biological Habitat and Resource Differences in 

Lower Cook Inlet

In general, lower and eastern Cook Inlet havewider 

ranges of intertidal habitats than does upper Cook Inlet 

and include much more rocky habitat and its associated 

epifauna. For example, Kamishak Bay has extensive 

unprotected rocky wave-cut platforms and rocky reefs. 

The combination of upwelled nutrients, circulation, and 

other environmental factors led Hood and Zimmerman 

(1986) to describe areas of lower Cook Inlet as being 

some of the most biologically productive ecosystems in 

the Gulf of Alaska. 

Unlike the mud flats of upper Cook Inlet —where 

the infaunal Macoma balthica clam dominates and 

where few epifaunal organisms can find appropriate 

attachment sites or can survive the scouring sediments 

and seasonal ice—epifaunal algae and invertebrates 

dominate in the rocky intertidal habitats. Depending 

on wave exposure and substrate, common algae in the 

lower and eastern Inlet include the rockweed (Fucus 

distichus =gardneri),red algae such as Palmaria mollis, 

P. hecatensis, P. callophylloides, Odonthalia flocossa, 

Neorhodomela aculeata, and Develeria ramentacea

(which dominates some exposed tidal flats in Kamishak 

Bay),green algae such as Ulva spp., Monostroma sp., 

Chladophora sericea, and Acrosiphonia arcta, kelps 

such as Alaria spp., Laminaria spp., Agarum spp., 

Saccharina latissima, and S. groenlandica, and the 

canopy kelps: bull kelp (Nereocystis leutkeana) and 

bull kelp (Eularia fistulosa). 

Dominant rocky intertidal epifaunal invertebrates 

include blue mussels (Mytilus trossulus) and barnacles 

(Balanus glandula, Semibalanus balanoides, S. cariosus, and Chthamalus dalli). Grazers include limpets 

(Lottia persona, L. pelta, L. scutum), the perriwinkle 

snails Littorina sitkana and L. scululata, and numerous 

chitons. Numerous bryozoans, sea stars, whelks, sea 

cucumbers, urchins, nudibranchs, and other invertebrates 

occur in the low intertidal and shallow rocky nearshore 

environments. Lower and eastern Cook Inlet infaunal 

invertebrates are adapted to coarser-grained sediments, 

including the commercially and recreationally harvested 

razor clams (Siliqua patula), littleneck clams (Leucoma 

staminea), and butter clams (Saxidomas gigantea), as 

well as the soft-shell clam (Mya arenaria), numerous 

polychate worms, and other burrowing invertebrates. 

In the 1970s and early 1980s, tanner crab (Chionocetes bairdi), red king crab (Paralithodes camtschaticus), Dungeness crab (Metacarcinus magister), 

northern shrimp (Pandalus borealis), coonstripe shrimp 

(P. danae), humpy shrimp (P. goniurus), sidestripe 

shrimp (Pandalopsis dispar), and scallop (Patinopecten 

caurinus) were all commercially harvested from lower 

Cook Inlet. These populations rapidly declined in the 

mid-1980s and have not returned to commercially 

harvestable levels, although several species have recently 

been open to personal-use harvests, and scallops have 

been commercially harvested in Kamishak Bay. 

All of the birds that were reported for upper Cook 

Inlet also use habitat throughout the rest of Cook Inlet. 

The threatened Steller’s eider (Polysticta stelleri) is 

also found in Cook Inlet, south of the Forelands. The 

marbled murrelet (Brachyramphus marmoratus) has 

been observed nesting in Cook Inlet and is considered a 

Bird of Conservation Concern in Alaska by the U.S. Fish 

and Wildlife Service. As well, most of the fish species 

reported in upper Cook Inlet also occur in lower Cook 

Inlet. However, many of them occur in much higher 

numbers and in commercially or recreationally harvestable sizes. Other species,such as arrowtooth flounder 

(Atheresthes stomias), butter sole(Pleironectes isolepis), 

and black cod or sablefish (Anoplopoma fimbria), occur 

in lower Cook inlet that have not been reported for upper 

Cook Inlet. Gray whales (Eschrichtius robustus) and 

humpack whales (Megaptera novaeangliae) are also 

commonly seen seasonally in lower Cook Inlet. 
161

Cook Inlet – Potential Stressors of Tidal Energy 

Development

As previously described, there is significant 

interest in tidal energy development projects in upper 

Cook Inlet, as well as in other areas throughout the 

Inlet. Currently, the area west of Fire Island in upper 

Cook Inlet is under intense evaluation for the planned 

in-water installation and testing of a group of TideGen 

turbines by Ocean Renewable Power Company, LLC, 

(ORPC) by 2011 or 2012. Environmental and site 

characterization studies have been ongoing, as has 

consultations with federal and state agencies. Many of 

the required studies have been completed, and concerns 

raised by most agencies have already been addressed. 

The main concerns for this project have included:

• Conflict with existing uses, such as shipping and 

commercial fishing (nearby salmon set-net sites)

• Difficulty in maintaining turbines in high 

suspended sediment and seasonal sea ice environment 

• Turbine strikes on fish and marine mammals, 

especially to endangered beluga whales. 

• Changes to hydrodynamics and sediment transport that might impact sediment deposition for 

important prey species such as Macoma clams 

that rely on a specific habitat for deposit-feeding. 

• Alterations to marine habitat and benthos (vegetation and invertebrates) due to dredging or infrastructure placement

• Avoidance of habitat by mobile organisms such 

as forage fish —prey of beluga whales

• Collisions/entanglements 

• Underwater noise/vibration; and

• Electromagnetic radiation fields.

Field surveys and studies, literature reviews, 

modeling, and negotiated mitigation measure development are on-going by ORPC and its contractors. 

These data will be used to determine detailed monitoring that will be required during in-water deployments of the turbines. 

Biological Habitats and Resources of Other 

Potential Tidal Energy Sites in Alaska

The currents in Cross Sound and Icy Strait areas 

of northern Southeast Alaska (Figure 43) have the 

potential to produce enough energy to meet regional 

needs and for export (Polagye and Bedard 2006). 

These areas are the main routes of tidal exchange for 

water moving from the northern part of the southeast 

Alaska panhandle to the Gulf of Alaska. However, 

before placing in-water turbines in the area, there 

are concerns particular to these areas that must be 

considered. The strait is an important shipping route 

for vessels that use the inside passage (inland water of 

southeast Alaska panhandle) before entering the Gulf 

of Alaska and is a scheduled route for Alaska Marine 

Highway ferries. Thus any infrastructure would have 

to allow for safe shipping navigation.

The area is a significant feeding and refuge 

area for many marine species that thrive in these 

extremely productive waters, including many important commercial, subsistence, personal-use, and sport 

harvests. For example, all five species of Pacific 

salmon, as well as Dungeness, tanner, and king crabs, 

scallops, shrimp, black cod, and herring are supported 

by these waters. The strong currents and tidal mixing 

in the area provide nutrients for primary production and secondary production that is transported 

throughout the area and concentrated by local flow 

patterns and frontal systems. These concentrations 

attract small schooling fishes such as herring and the 

nearshore areas are important habitat for other forage 

fish such as juvenile walleye pollock, juvenile salmonids, sandlance, and capelin. These concentrations 

of pelagic food attract feeding marine mammals, and 

there is significant use by humpback whales. 

Concentrations of zooplankton and herring attract 

feeding marine mammals. Humpback whales heavily 

use some concentration areas of Icy Strait. Sea otters 

have recently been re-colonizing the waters of Icy 

Strait and Cross Sound and rely on nearshore areas for 

foraging. Any development of tidal energy projects 

in these waters must progress with careful attention to 

protecting sensitive environments and species through 

close consultation with state, federal, and local laws 

and regulations.
162

Table 12 – Pending and Issued FERC permits for hydrokinetic energy projects in Alaska.

In addition to the major tidal energy potential 

described for Icy Strait and Cross Sound, numerous 

high quality (strong power density) but small (in 

terms of cross-sectional area) sites have been identified that can provide local power (Polagye and Bedard 

2006). These areas tend to be in narrow passes or 

inlets and have the potential to interfere with safe 

navigation. They are often important passages for 

marine fish, feeding birds, and marine mammals. 

The abundance of rocky nearshore habitat and high 

currents in these areas are prime conditions for 

canopy kelps. Three canopy kelps occur in nearshore 

waters of southeast Alaska, including bull kelp, 

dragon kelp, and giant kelp (Macrocystis porifera = 

integrifolia). All of these provide important habitat 

for many invertebrates and fish, including early life 

stages of many commercially important species. 

Discussions on tidal energy development in 

Alaska have also included the potential in numerous 

eastern Aleutian Island Passes (Figure 43). The 

Unimak Pass is a major transportation route for ships 

transiting a great circle route from the west coast of 

the United States and Asia. The major flow through 

Unimak Pass is from the Gulf of Alaska into the 

Bering Sea. This flow periodically reverses itself, 

given the right atmospheric storm conditions. The 

pass is approximately 18 km wide at its narrowest 

point and, generally, is less than 100 m deep —relatively shallow in comparison with major passes 

farther west in the Aleutian chain. 

Areas within about 10 km of land in these 

narrow straits between islands are generally less 

than 60 m deep, and several shallow banks occur in 

the area. These can be important feeding areas for 

marine mammals and, together, the passes comprise 

a major migration corridor for mammal populations 

entering and leaving the Bering Sea, especially for 

gray and humpback whales. There are two records 

of another endangered whale, the right whale (Eubalaena glacialist) reported from Unimak Pass. Steller 

sea lions are year-round residents and have numerous 

haul-outs in the Aleutian Islands. Sea lion populations have followed a downward trend in the eastern 

Aleutian Islands since the late 1970s. 

Again, any development of tidal energy projects 

in these waters must progress with careful attention to 

protecting these area-specific, sensitive environments 

and species through close consultation with state, 

federal, and local laws and regulations.
163

Figure 43 – Areas of significant hydrokinetic energy potential in Alaska (yellow triangles) and areas with pending or 

issued FERC permits (red triangles, Table 12).

Figure 44 – Cook Inlet bathymetry (left) and satellite image showing suspended sediment plumes (right, ORBIMAGE)
164

References

Alaska Energy Authority. 2009. Renewable Energy 

Atlas of Alaska: A Guide to Alaska’s Clean, 

Local, and Inexhaustible Energy Resources. 

Report by Alaska Energy Authority and Renewable Energy Alaska Project. 

Bartsch-Winkler, S. and Ovenshine, A.T. 2004. 

Macrotidal subarctic environment of Turnagain and Knik arms, upper Cook Inlet, Alaska; 

sedimentology of the intertidal zone. Journal of 

Sedimentary Research, 54(4): 1221-1238. 

Feely, R.A. and Massoth, G.J. 1982. Sources, composition, and transport of suspended particulate 

matter in Lower Cook Inlet and northwestern 

Shelikof Strait, Alaska. NOAA Technical Report 

ERL-415 PMEL-34.

Gill, R.E., Jr. and Tibbitts, T.L. 1999. Seasonal 

shorebird use of intertidal habitats in Cook Inlet, 

Alaska. Final Report. U.S. Department of Interior, 

U.S. Geological Survey, Biological Resource 

Division and OCS Studies, MMS 99-0012.

Glass, R.L., Brabets, T.P., Frenzel, S.A., Whitman, 

M.S. and Ourso, R.T. 2004. Water quality in 

the Cook Inlet basin Alaska, 1998– 2001. U.S. 

Department of Interior, U.S. Geological Survey, 

Circular 1240. 

Haley, B., Tomlins, G., Smith, O., Wilson, W. and 

Link, M. 2000. Mapping Cook Inlet rip tides 

using local knowledge and remote sensing. 

Report prepared by LGL Alaska Research Associates, Inc., Anchorage, AK, Pacific Geomatics, 

Ltd., Surrey B.C, Canada, and the University of 

Alaska, Anchorage, AK., for the U.S. Department 

of Interior, Minerals Management Service. 

Hood, D.W. and Zimmerman, S. (Eds.). 1986. The 

Gulf of Alaska: Physical Environment and 

Biological Resources. U.S. Department of 

Commerce, National Oceanic and Atmospheric 

Administration.

Houghton, J., Starkes, J., Chambers, M. and Ormerod, 

D. 2005a. Marine fish and benthos studies in 

Knik Arm, Anchorage, Alaska. Report prepared 

for the Knik Arm Bridge and Toll Authority, 

and HDR Alaska, Inc., Anchorage, AK, by 

Pentec Environmental, Edmonds, WA.

Houghton, J., Starkes, M. Chambers, and D. Ormerod. 

2005b. 2004-2005 marine fish and benthos 

studies-Port of Anchorage, Anchorage, Alaska. 

Report prepared by Pentec Environmental, 

Edmonds, WA, for Integrated Concepts and 

Research Corporation.

Lees, D.C., Driskell, W.B., Payne, J.R. and Hayes, 

M.O. 2001. Final report of CIRCAC intertidal 

reconnaissance survey in Upper Cook Inlet. 

Prepared for Cook Inlet Regional Citizens Advisory Council, Kenai, AK.

Naidu, A.S., Feder, H.M., Foster, N., Geist, C. and 

Rivera, P.M. 1992. Macoma balthica monitoring 

study at Dayville Flats, Port Valdez. Draft final 

report. Submitted to Alyeska Pipeline Service 

Company, Anchorage, AK.

Nelson, W.G. and Whitney, J.W. 1996. A description 

of summer and winter environmental conditions 

within Cook Inlet, Alaska. Society of Petroleum 

Engineers paper #SPE 35688 presented at the 

Western Regional Meeting, Anchorage, AK, May 

22-24, 1996.

Polagye, B. and Bedard, R. 2006. Tidal in-stream 

energy resource assessment for southeast Alaska. 

Report to Alaska Energy Authority, Electric 

Power Research Institute Tidal In Stream Energy 

Conversion Reports, TP-003.

Polagye, B. and Previsic, M. 2006. System level 

design, performance, cost and economic assessment – Knik Arm Alaska tidal in-stream power 

plant. Electric Power Research Institute Tidal In 

Stream Energy Conversion Reports, TP-006. 

Rodrigues, R., M. Nemeth, T. Markowitz, and D. 

Funk. 2006. Review of literature on fish species 

and beluga whales in Cook Inlet, Alaska. Final 

report prepared by LGL Alaska Research Associates, Inc., Anchorage, AK, for DRven Corporation, Anchorage, AK.

Whitney, J. 2002. Cook Inlet, Alaska: Oceanographic and Ice Conditions and NOAA’s 18-year 

Oil Spill Response History 1984-2001. NOAA 

HAZAMAT Report 2003-01.
165

Appendix C — Workshop Participant List

Adonizio, Mary Ann Verdant Power Fish: resident Devices: dynamic effects

Agness, Alison NOAA Fisheries, Northwest Marine mammals and seabirds Devices: dynamic effects

Region, Protected Resources

Division

Ainsworth, David Marine Current Turbines, Ltd. Marine mammals and seabirds Devices: dynamic effects

Chemical effects

Albertson, Skip Washington Dept. of Ecology Physical environment: far-field Cumulative effects

Anderson, Richard Pacific Northwest Fish: migratory Chemical effects

National Laboratory

Baldwin, David NOAA Fisheries - Northwest Physical environment: far-field Chemical effects

Fisheries Science Center

Balla-Holden, Andrea U.S. Navy Physical environment: far-field Energy removal

Barr, Sue OpenHydro Group, Ltd. Ecosystem interactions Devices: dynamic effects

Bhuyan, Gouri Powertech Labs Physical environment: near-field Electromagnetic effects

Bishop, Alicia NOAA Fisheries, Northwest Ecosystem interactions Electromagnetic effects

Region, Hydropower Division

Boyd, Ian Sea Mammal Research Unit, Ecosystem interactions Cumulative effects

University of St. Andrews

Breen, Joe Northern Ireland Marine mammals and seabirds Cumulative effects

Environment Agency

Brennan, Jim Washington Sea Grant Fish: migratory Cumulative effects

Browne, Peter HDR, Inc. Habitat and invertebrates Acoustic effects

Boehlert, George Oregon State University Steering Committee Steering Committee

Cada, Glenn Oak Ridge National Laboratory Habitat and invertebrates Devices: dynamic effects

Collar, Craig Snohomish County Habitat and invertebrates Devices: static effects

Public Utility District

Copping, Andrea Pacific Northwest National Steering Committee Steering Committee

Laboratory

Couch, Scott University of Edinburgh Physical environment: far-field Energy removal

Courtenay, Simon Fisheries and Oceans Canada Fish: resident Devices: static effects

Daborn, Graham Acadia University Habitat and invertebrates Cumulative effects

Dahl, Peter University of Washington Physical environment: near-field Acoustic effects

Session chairs and their sessions are presented in boldface type.

Name Affiliation Receptor Group Stressor Group
166

Eckert, Ginny University of Alaska - Fairbanks Ecosystem interactions Devices: static effects

Fresh, Kurt NOAA Fisheries - Northwest Fish: migratory Devices: dynamic effects

Fisheries Science Center

Geerlofs, Simon U.S. Department of Energy Habitat and invertebrates Acoustic effects

Gill, Andrew Cranfield University Fish: migratory Electromagnetic effects

Gill, Gary Pacific Northwest National Physical environment: near-field Chemical effects

Laboratory

Goetz, Fred U.S. Army Corp of Engineers Fish: migratory Devices: dynamic effects

Goodman, Layna U.S. Navy Physical environment: near-field chemical effects

Hanson, Brad NOAA Fisheries - Northwest Marine mammals and seabirds Devices: dynamic effects

Fisheries Science Center

Horning, Markus Oregon State University Marine mammals and seabirds Electromagnetic effects

Jacobson, Paul Electric Power Research Institute Ecosystem interactions Chemical effects

Johnston, Sam Hydroacoustic Technology, Inc. Fish: migratory Devices: static effects

Johnson, Jerry University of Alaska - Fairbanks Physical environment: near-field Electromagnetic effects

James, Scott Sandia National Laboratories Physical environment: far-field Energy removal

Kajiura, Stephen Florida Atlantic University Fish: resident Electromagnetic effects

Kagley, Anna NOAA Fisheries - Northwest Fish: migratory Devices: static effects

Region, Science Center

Kawase, Mitsuhiro University of Washington Physical environment: far-field Energy removal

Kirkendall, Keith NOAA Fisheries, Northwest Steering Committee Steering Committee

Region, Hydropower Division

Kramer, Sharon H.T. Harvey & Associates Fish: resident Devices: static effects

Livingston, Pat NOAA Fisheries - Alaska Fish: resident Cumulative effects

Fisheries Science Center

Mate, Bruce Oregon State University Marine mammals and seabirds Acoustic effects

McCleave, Jim University of Maine Fish: migratory Devices: static effects

McClure, Bob BioSonics, Inc. Fish: resident Acoustic effects

McMahon, Neil Alaska Energy Authority Physical environment: near-field Energy removal

McMurray, Greg Pacific Energy Ventures Ecosystem interactions Electromagnetic effects

Mumford, Tom Washington Department of Habitat and invertebrates Cumulative effects

Natural Resources

Norris, Jenny European Marine Energy Ecosystem interactions Cumulative effects

Center

Palsson, Wayne Washington Department Fish: resident Devices: static effects

of Fish and Wildlife

Session chairs and their sessions are presented in boldface type.

Name Affiliation Receptor Group Stressor Group
167

Parrish, Julia University of Washington Marine mammals and seabirds Devices: static effects

Polagye, Julia University of Washington Steering Committee Steering Committee

Previsic, Mirko re vision consulting, LLC. Physical environment: far-field Electromagnetic effects

Rawson, Kit Tulalip Tribes Fish: migratory Acoustic effects

Redman, Scott Puget Sound Partnership Ecosystem interactions Chemical effects

Ruggerone, Greg Natural Resource Consultants Fish: migratory Devices: dynamic effects

Saupe, Sue Cook Inlet Regional Citizens Ecosystem interactions Cumulative effects

Advisory Committee

Savage, Kate NOAA Fisheries - Alaska Marine mammals and seabirds Electromagnetic effects

Regional Office, Protected

Resources Division

Savidge, Graham University of Queens Physical environment: near-field Energy removal

Simenstad, Charles (Si) University of Washington Habitat and invertebrates Energy removal

Simmons, Harper University of Alaska - Fairbanks Physical environment: far-field Energy removal

Smith, Joanna The Nature Conservancy Marine mammals and seabirds 

Spring Harris, Melanie NOAA Fisheries, Office of Fish: resident Devices: static effects

Habitat Conservation

Thomson, Jim University of Washington Physical environment: near-field Acoustic effects

Thresher, Bob National Renewable Energy Physical environment: near-field Devices: dynamic effects

Laboratory

Tollit, Dominic Sea Mammal Research Marine mammals and seabirds Acoustic effects

Unit, Ltd.

Trim, Heather People for Puget Sound Habitat and invertebrates Chemical effects

Van Cleve, Brie Pacific Northwest National Steering Committee Steering Committee

Laboratory

Wainstein, Michelle Washington Sea Grant Steering Committee Steering Committee

Walker, Sue NOAA Fisheries - Alaska Steering Committee Steering Committee

Region, Habitat Conservation

Worthington, Monty Ocean Renewable Power Marine mammals and seabirds Energy removal

Company

Wyllie-Echeverria, Tina Wyllie-Echeverria Associates Fish: resident Acoustic effects

Young, Tina U.S. Environmental Protection Habitat and invertebrates Chemical effects

Agency

Zydlewski, Gayle University of Maine Marine mammals and seabirds Devices: dynamic effects

Session chairs and their sessions are presented in boldface type.

Name Affiliation Receptor Group Stressor Group
168

Monday, March 22

Opening Lecture: Changing Tides – Developing Best Practices for the Tidal Energy Industry

Sue Barr, Open Hydro ......................................................... 1900-2030: 110 Kane Hall

Tuesday, March 23

Plenary Sessions................................................................. 0830-1230: Mary Gates Hall Auditorium

• Simon Geerlofs, U.S. Department of Energy

• Graham Daborn, Acadia University

• Jim McCleave, University of Maine

• Andrea Copping, Pacific Northwest National Laboratory

• Sue Saupe, Cook Inlet Regional Citizens Advisory Committee

Stressor Breakout Groups ................................................ 1400-1630: Mary Gates Hall breakout rooms

Stressor Group Recap ....................................................... 1630-1730: Mary Gates Hall Auditorium

Evening Reception............................................................. 1800-2000: Burke Museum

Wednesday, March 24

Regroup............................................................................... 0830-0900: Mary Gates Hall Auditorium

Receptor Breakout Groups............................................... 0900-1130: Mary Gates Hall breakout rooms

Stressor Breakout Groups ................................................ 1400-1530: Mary Gates Hall breakout rooms

Wrap Up ............................................................................. 1530-1600: Mary Gates Hall Auditorium

Appendix D — Workshop Agenda
169

Appendix E — Workshop Evaluation Results

1. Rate the overall quality of the workshop 

(42 responses)

2. The goals of the workshop were clear 

(42 responses)

3. Select all that apply to the balance between 

presentations (plenary) and breakout groups 

(42 responses)

4. The design of the workshop facilitated exchange of 

expertise among participants (42 responses)

5. Did this workshop increase your understanding of 

potential impacts of tidal energy development on 

the ocean environment? (40 responses)

6. Has this workshop provided you new viewpoints 

and insights? (40 responses)
170

7. Will you apply information learned at this 

work shop to tidal energy-related projects? (39 

responses)

8. What was most valuable about this workshop?

• Diversity of expertise assembled to address 

questions.

• Stressor/receptor breakout group discussions.

• Interaction and networking opportunities.

9. What was least valuable about this workshop?

• Time spent populating stressor/receptor 

matrices.

• Time limitations for breakout groups.

• Frustrations with having to generalize 

stressor/receptor interactions when concerns 

were specific to sites, species, and devices.

10. How would you improve similar workshops?

• Additional time within each breakout group 

(+1 day).

• Focus on specific scenarios, rather than 

general cases.

• Presentations by device developers on what 

monitoring and mitigation approaches have 

been employed as part of their projects.