NOAA Technical Report NMFS 40

The Potential Impact of

Ocean Thermal Energy

Conversion (OTEC)

on Fisheries

Edward P. Myers

Donald E. Hoss

Walter M. Matsumoto

David S. Peters

Michael P. Seki

Richard N. Uchida

John D. Ditmars

Robert A. Paddock

June 1986

U.S. DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

National Marine Fisheries Service
NOAA TECHNICAL REPORT NMFS

The major responsibilities of the National Marine Fisheries Service (NMFS) are to monitor and assess the abundance and geographic distribution of fishery resources, to

understand and predict fluctuations in the quantity and distribution of these resources, and to establish levels for their optimum use. NMFS is also charged with the development

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and economic analysis programs, and mortgage insurance and vessel cunstruction subsidies. It collects, analyzes, and publishes statistics on various phases of the industry.

The NOAA Technical Report NMFS series was established in 1983 to replace two subcategories of the Technical Reports series: "Special Scientific Report-Fisheries" and

"Circular." The series contains the following types of reports: Scientific investigations that document long-term continuing programs of NMFS; intensive scientific reports on

studies of restricted scope; papers on applied fishery problems; technical reports of general interest intended to aid conservation and management: reports that review ill cun·

slderable detail and at a high technical level certain broad areas of research; and technical papers originating in economics studies and from management investigations Since

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5285 Port Royal Road, Springfield, VA 22161. Although the contents have not been copyrighted and may be reprinted entirely, reference to source is appreciated.

1. Synopsis of biological data on the Blue Crab, Callinecles sapidus Rathbun, by

Mark R. Millikin and Austin B. Williams. March 1984, 39 p.

2. Development of hexagrammids (Pisces: Scorpaeniformes) in the Northeastern

Pacific Ocean, by Arthur W. Kendall, Jr., and Beverly Vinter. March 1984,44 p.

3. Configurations and relative efficiencies ofshrimp trawls employed in southeastern

United States waters, by John W. Watson, Jr., Ian K. Workman, Charles W. Taylor,

and Anthony F. Serra. March 1984, 12 p.

4. Management of northern fur seals on the Pribilof Islands, Alaska, 1786-1981, by

Alton Y. Roppel. April 1984, 26 p.

5. Net phytoplankton and zooplankton in the New York Bight, January 1976 to

February 1978, with comments on the effects of wind, Gulf Stream eddies, and slope

water intrusions, by Daniel E. Smith and Jack W. Jossi. May 1984, 41 p.

6. lchthyoplankton survey of the estuarine and inshore waters of the Florida Everglades, May 1971 to February 1972, by L. Alan Collins, and John H. Finucane. July

1984, 75 p.

7. The feeding ecology of some zooplankters that are important prey items of larval

fish, by Jefferson T. Turner. July 1984, 28 p.

8. Proceedings of the International Workshop on Age Determination of Oceanic

Pelagic Fishes: Tunas, BUtfishes, and Sharks, by Eric D. Prince (convener and editor),

and Lynn M. Pulos (editor). December 1983, 211 p.

9. Sampling statistics in the Atlantic menhaden fishery, by Alexander 1. Chester.

August 1984, 16 p.

10. Proceedings of the Seventh U.S.-Japan Meeting on Aquaculture, Marine Finfish

Culture, Tokyo, Japan, October 3-4, 1978, by Carl 1. Sindermann (editor). August 1984,

31 p.

II. Taxonomy of North American fish Eimeriidae, by Steve.! Upton, DlVid W.

Reduker, William L. Current, and Donald W. Duszynski. August 1984, 18 p.

12. Soviet-American Cooperative Research on Marine Mammals. Volume I--Pinnipeds, by Francis H. Fay, and Gennadii A. Fedoseev (editors). September 1984, 104 p.

13. Guidelines for reducing porpoise mortality in tuna purse seining, by James M.

Coe, David B. Holts, and Richard W. Butler. September 1984, 16 p.

14. Synopsis of biological data on shortnose sturgeon, A1:ipenser breviroslrnm leSueur

1818, by Michael 1. Dadswell, Bruce D. Taubert, Thomas S. Squiers, Donald Marchette, and Jack Buckley. October 1984, 45 p.

15. Chaetognatha of the Caribbean sea and adjacent areas, by Harding B. Michel.

October 1984, 33 p.

16. Proceedings of the Ninth and Tenth U.S.-Japan Meetings on Aquaculture, by Carl

1. Sindermann (editor). November 1984, 92 p.

17. Identification and estimation of size from the beaks of 18 species of cephalopods

from the Pacific Ocean, by Gary A. Wolff. November 1984, 50 p.

18. A temporal and spatial study of invertebrate communities associated with hardbottom habitats in the South Atlantic Bight, by E. L. Wenner, P. Hinde, D. M. Knott,

and R. F. Van Dolah. November 1984, 104 p.

19. Synopsis of biological data on spottail finfish, Dip/odu; ho/brooki (Pisces'

Sparidae), by George H. Darcy. January 1985, II p.

20. lchthyoplankton of the Continental Shelf near Kodiak Island, Alaska, by Arthur

W. Kendall, Jr., and Jean R. Dunn. January 1985, 89 p.

21. Annotated bibliography on hypoxia and its effects on marine life, with empha""

on the Gulf of Mexico, by Maurice L. Renaud. February 1985, 9 p.

22. Congrid eels of the eastern Pacific and key to their Leptocephali, by Solomon

N. Raju. February 1985, 19 p.

23. Synopsis of biological data on the pinfish, Lagodoll r/IO/Ilboides (Pisccs:Sparidae).

by George H. Darcy. February 1985, 32 p.

24. Temperature conditions in the cold pool 1977-81: A comparison between southern

New England and New York transects, by Steven K. Cook. February 1985, 22 p.

25. Parasitology and pathology of marine organisms of the world ocean, by Wilham

1. Hargis, Jr. (editor). March 1985, 135 p.

26. Synopsis of biological data on the sand perch, Dip/eclrum formosum (Pisces:

Serranidae), by George H. Darcy. March 1985, 21 p.

27. Proceedings of the Eleventh U.S.-Japan Meeting on Aquaculture, Salmon Enhance..

ment, Tokyo, Japan, October 19-20, 1982, by Carl J. Sindermann (editor). March 1985,

102 p.

28. Review of geographical stocks of tropical dolphins (Slenella spp. and De/phinus

de/phis) in the eastern Pacific, by William F. Perrin, Michael D. Scott, G. Jay Walker,

and Virginia L. Casso March 1985, 28 p.

29. Prevalence, intensity, longevity, and persistence of Anisakis sp. larvae and Lacisrorhynchus tenuis metacestodes in San Francisco striped bass, by Mike Moser, Judy

A. Sakanari, Carol A. Reilly, ar.d Jeannette Whipple. April 1985, 4 p.

30. Synopsis of biological {ata on the pmk shrimp, Panda/us borealis Kr6yer, 1838,

by Sandra E. Shumway, Herbert C. Perkins, Daniel F. Schick, and Alden P. Stickney.

May 1985, 57 p.

31. Shark catches from selected fisheries off the U.S. east coast, by Emory D. Anderson, John G. Casey, John J. Hoey, and W. N. Witzell. July 1985, 22 p.

32. Nutrient Distributions for Georges Bank and adjacent waters in 1979, by A. F.

1. DraxJer, A. Matte, R. Waldhauer, and 1. E. O'Reilly. July 1985, 34 p.

33. Marine flora and fauna of the Northeastern United States. Echinodermata:

Echinoidea, by D. Keith Serafy and F. Julian Fell. September 1985, 27 p.

34. Additions to a revision of the shark genus Carcharhinus: Synonymy of Aprionodon and Hypoprion, and description of a new species of Carcharhinus (Carcharhinidae),

by 1. A. F. Garrick. November 1985, 26 p.

15. Synoptic review of the literature on the Southern oyster drill Thais haemnstoma

jlvridana, by Philip A. Butler. November 1985, 9 p.
NOAA Technical Report NMFS 40

The Potential Impact of

Ocean Thermal Energy

Conversion (OTEC)

on Fisheries

Edward P. Myers

Donald E. Hoss

Walter M. Matsumoto

David S. Peters

Michael P. Seki

Richard N. Uchida

John D. Ditmars

Robert A. Paddock

June 1986

u.s. DEPARTMENT OF COMMERCE

Malcolm Baldrige, Secretary

National Oceanic and Atmospheric Administration

Anthony J. Calio, Administrator

National Marine Fisheries Service

William G. Gordon, Assistant Administrator for Fisheries
The National Marine Fisheries Service (NMFS) does not approve, recommend

or endorse any proprietary product or proprietary material mentioned in this

publication. No reference shall be made to NMFS, or to this publication furnished by NMFS, in any advertising or sales promotion which would indicate

or imply that NMFS approves, recommends or endorses any proprietary

product or proprietary material mentioned herein, or which has as its purpose

an intent to cause directly or indirectly the advertised product to be used or

purchased because of this NMFS publication.

ii
Contents

Introduction 1

Background 2

The OfEC Principle 2

Application 3

U.S. Legislation 3

Estimated Operating Conditions

for Initial U.S. OfEC Deployments 4

General Site Characteristics 4

Temperature, Salinity and Density Profiles 4

Currents 4

General Plant Characteristics 4

Type of Plant 4

Plant Capacity 4

Plant Dimensions 4

Power System

Working Fluids 4

Heat Exchangers 4

Biofouling Control 7

Operating Efficiencies 7

Seawater Systems

Warm Water Intake 7

Cold Water Intake 7

Discharge 7

Physical Interaction with the Environment 8

Cold Water Intake 8

Warm Water Intake 8

Effluent Discharge 8

Regional Influence 11

Biological Interaction with the Environment 12

Biological Characteristics of the Environment 12

Location 12

Phytoplankton 12

Zooplankton 13

Fisheries 14

Eggs and Larvae of Important Species 15

Other Important Biological Components 15

Factors that may Affect Fish 16

Attraction/Avoidance 16

Impingement 17

Primary Entrainment 18

Temperature 18

Pressure 19

Chemical Additions 19

Secondary Entrainment 20

Ocean Water Mixing 20

1Il

The Potential Range of Ecological Effects

Resulting from OfEC Operations 21

Impingement 21

Primary Entrainment of Plankton 21

Secondary Entrainment 22

Impacts on Fishery Food Chains 23

Potential Impact on Fisheries 23

Measures to Reduce Potential Effects to

Fisheries 24

Cold Water Intake 25

Warm Water Intake 25

Discharge Location and

Configuration 26

Chemical Additions 'lJ

Research Priorities 'lJ

Investigations on Fish Distribution 'lJ

Studies on the Effects of Entrainment 'lJ

Biostimulation/Inhibition 'lJ

Early Life History Studies 'lJ

Dynamics of Fishery Populations 28

Ciguatera 28

Construction Effects 28

Conclusions 28

References 29

The Potential Impact of

Ocean Thermal Energy

Conversion (OTEC)

on Fisheries

EDWARD P. MYERS

Ocean Minerals and Energy Division,

Office of Ocean and Coastal Resource Management,

National Ocean Service, NOAA,

Page 1 Building, Room 105,

2001 Wisconsin Avenue NW,

Washington, D. C. 20235

DONALD E. HOSS

DAVID S. PETERS

Southeast Fisheries Center,

Beaufort Laboratory,

National Marine Fisheries Service, NOAA,

Beaufort, NC 28516-9722

WALTER M. MATSUMOTO

MICHAEL P. SEKI

RICHARD N. UCHIDA

Southwest Fisheries Center,

Honolulu Laboratory,

National Marine Fisheries Service, NOAA,

2570 Dole Street,

Honolulu, HI 96822-2396

JOHN D. DITMARS

ROBERI' A. PADDOCK

Energy and Environmental Systems Division

Argonne National Laboratory

Argonne, lL 60439

ABSTRACf

The commercial development of ocean thermal energy conversion (IDEC)

operations will involve some environmental perturbations for which there is no

precedent experience. The pumping of very large volumes of warm surface water

and cold deep water and its subsequent discharge will result in the impingement,

entrainment, and recmtribution of biota. Additional stresses to biota will be caused

by biocide usage and temperature depressions. However, the artificial upwelling

of nutrients associated with the pumping of cold deep water, and the artificial

reef created by an 0fEC plant may have positive effects on the local environment.

Although more detailed information is needed to assess the net effect of an

0fEC operation on fISheries, certain assumptions and calculations are made supporting the conclusion that the potential risk to fisheries is not significant enough

to deter the early development of IDEe. It will be necessary to monitor a commercial-scale plant in order to remove many of the remaining uncertainties.

INTRODUCTION _

Under the Ocean Thermal Energy Conversion (OfEC) Act of 1980,

the National Oceanic and Atmospheric Administration (NOAA) was

given responsibility for licensing U. S. commercial OfEC operations and determining the potential environmental effects associated

with this development and operation. NOAA (1982), in an environmental research plan required by the Act, identified two high-priority

research areas that could be addressed with the available resources:

1. Determining the region of influence of an OfEC operation

on mixing and redistribution of water masses, and

2. predicting the potential effects on fisheries.

Research in the first area has resulted in development of a model

to predict the spatial scale and degree of perturbation to ocean waters

(Wang 1984). This development responds to a direct licensing requirement of the Act and, in addition, has resulted in information

useful in the determination of biological effects.

The second area, prediction of potential fishery effects, was considered a high priority because of the commercial and recreational

value of fisheries and because of NOAA's responsibilities for

fisheries through the National Marine Fisheries Service (NMFS).

In fact, in its environmental research plan for OfEC, NOAA (1982)

noted that the "Achilles heel, " if any, to OfEC siting and operation could well be the effect on fisheries or other biologically important resources such as corals.

The concern over fisheries is primarily related to the entrainment

and impingement that would result with the pumping of large

volumes of seawater through an OfEC plant, the secondary entrainment caused by the discharge of OfEC waters, the use of

biocides, and the redistribution of ocean properties (e.g., nutrients,

trace metals, heat). The very presence of an OfEC structure might

add to these factors due to the attraction or avoidance of fish and

other biota to OfEC structures. There are other potential problems

(NOAA 1981a), e.g., the leakage or spilling of working fluids to

the environment, that are not discussed in any detail in this report.

The report has focused on those problems associated with the normal everyday operating conditions of an OfEC plant.

NOAA believed that there was much information available that

would be useful in making preliminary estimates of OfEC effects

on fisheries. This includes information on the oceanographic

characteristics of marine waters near potential OTEC sites, on the

fates and effects of substances such as biocides, trace metals, and

nutrients, and on other problem areas such as entrainment and impingement. Some of this available information is rather general,

some site-specific, and some related to experiences from the operation of conventional and nuclear power plants.

A synthesis of pertinent information to assess the potential effects on fisheries was initiated in FY 1982 and culminated in this

report. The effort focuses on the Caribbean and the North Pacific,

since these are regions where U.S. OfEC interests have the greatest

potential for development. It also emphasizes the nearshore application of OfEC more than the open-ocean case. The rationale for

this emphasis is that at the present time there appears to be more

interest in the nearshore application of OfEC, and there is definitely

more reason for concern over the coastal areas as compared to the

open ocean, at least during the early development of OfEC.
BACKGROUND _

The OTEC Principle

Ocean thermal energy conversion (arEC) is a renewable energy

technology which produces power using a heat engine driven by

the temperature difference between warm surface ocean waters and

cold deep ocean waters (Gritton et al. 1980). The heat engine can

take the form of a closed-cycle process (Fig. I) which employs a

working fluid (e.g., ammonia or FreonTM) which is evaporated by

warm seawater. The expanding gas drives a gas turbine, is then

recondensed by cold seawater, and the process is repeated. The

open-cycle process is quite similar to the closed-cycle process, with

the exception that the warm seawater, acting as the working fluid,

is flash-evaporated and the resulting vapor passed through a turbine. A big advantage of the open-cycle process is that the condensate can be used as a freshwater source.

There are several possible locations and construction strategies

proposed for arEC plants. The plants could be land-based, be

mounted or moored on the continental shelf, or be open-ocean plantships (NOAA 198Ia). A land-based plant would be constructed

onshore with the needed warm-water, cold-water, and discharge

pipes extending offshore to reach the desired intake and discharge

conditions. A plant mounted on the continental shelfmight be similar

to an offshore oil rig. A moored plant would be a floating plant

that is moored (anchored) to the seafloor. All of the above designs

could be used to supply baseload electricity to existing electrical

grids. A plantship, on the other hand, would be a ship equipped

with an arEC plant and could utilize suitable thermal resources

wherever they existed. The power produced by a plantship could

be used to produce energy-intensive products such as hydrogen,

ammonia, and methanol (Francis and Dugger 1980; NOAA 1981a;

Dugger et al. 1982; Avery et al. 1985).

ElectriC Power

Output

Low Pressure

NH3 Liquid

Low Pressure

NH3 Vapor

20°C

Turbine

Generator

Liquid

Pressurizer

High Pressure

NH3 Liquid

...............

.............. . ............. . . . . . . . . . . . . . . . .............

............ .

.+.

WARM WATER INTAKE

Depth: 20 m

Flow Rate: 4 m3/s per MWe

Flow Velocities:

Outside intake, 0.25·0.30 m/s

In pipe, 1.5-2.5 m/s

Water Temperature: 25°C

High Pressure

NH3

Vapor

MIXED DISCHARGE

Depth: >30 m

Flow Rate: 8 m3/s per MWe

Flow Velocity 1.5-2.5 m/s

Water Temperature: 15°C

COLD WATER INTAKE

Depth: 750-1000 m

Flow Rate: 4 m3 /s per MWe

Flow Velocity: 1.5-2.5 m/s

Water Temperature: 5°C

Figure I.-Schematic diagram of a c1osed-cycle OTEC system. (adapted from U.S. Department of Energy 1979). (Note: Newer designs can achieve

somewhat higher temperature changes across the heat exchangers with slightly less flows; Avery 1984).

2
Application

A temperature difference of approximately 20°C is needed to make

the OfEC process sufficiently efficient to be cost-effective (Myers

and Ditmars 1985). Such temperature differences exist between the

ocean surface and depths of about 1000 m in most coastal and openocean areas within about ±20° of the Equator, and in some areas

outside of this band (United Nations 1981). These areas include

approximately 70 developing nations with an adequate thermal

resource (Table 1). Although temperature differences represent only

one ofthe various forms of renewable ocean energies (e.g., biomass,

waves, tides, currents, salinity gradients), it has been concluded

that this form of ocean energy potential offers much promise by

the year 2000 (United Nations 1981).

Countries that presently have an interest in developing OfEC

technology include the United States, France, Japan, Sweden, and

the Netherlands. The U.S. Department of Energy has supported

design studies for a 40 megawatt-electric (MWe) pilot plant that

would be located at Kahe Point, Oahu, Hawaii. During the conceptual design phase of this work, two closed-cycle designs were

under development: An artificial island design by Ocean Thermal

Corporation (OTC) (1983) that would be located about 550 m offshore, and a tower-mounted concept by General Electric (1983)

to be located about 2200 m offshore. The OTC plant was chosen

over that of General Electric for the second phase of the projectpreliminary design. The OTC plant would utilize the thermal

discharge from the Hawaiian Electric Company's (HECO) conventional power plant at Kahe Point to supplement the thermal resource

of the ambient seawater. The intake of ambient warm water would

be near the surface at the plant with the intake of cold water further offshore at a depth of about 700 m. Both warm and cold waters,

once used, would be discharged as a mixture at a depth of about

100 m.

The French government has been performing preliminary studies

related to a 5-MWe prototype open-cycle plant in Tahiti. Japanese

companies have designed, built, and operated a land-based closedcycle 100-kWe plant for the island of Nauru in the North Pacific.

Although this demonstration plant has been shut down, there are

plans for a 2.5-MWe plant at the same site. Sweden's interest has

principally been in building plants or components of plants and selling to developing countries. For instance, they have had discussions with Jamaica for a plant. Certain Dutch companies have similar

interests.

U.S. Legislation

Two legislative acts were passed by Congress in 1980 to facilitate

the commercial development of OfEC: The Ocean Thermal

Energy Conversion Research, Development, and Demonstration

Act; and the Ocean Thermal Energy Conversion Act of 1980. The

purpose of the OfEC Research, Development, and Demonstration

Act (P.L. 96-310) is to accelerate OfEC technology development;

the designated lead agency is the U. S. Department of Energy. The

purpose of the OfEC Act of 1980 (P.L. 96-320) was to create a

legal regime that would facilitate the commercialization of OfEC

in a manner compatible with the protection of the marine environment and other marine resources; the lead agency is the National

Oceanic and Atmospheric Administration.

Table I. Some developing nations with adequate ocean thermal resources (after United Nations 1981)

Distance from Distance from

AT (0C) resource to AT (OC) resource to

Region/nation Lat. Long. 0-1000 m shore (km) Region/nation Lat. Long. 0-1000 m shore (km)

Africa Latin America

Angola 60 S -ISoS II °E -14°E IS-22 65 Bahamas 25°N 77°W-79°W 20-22 15

Benin 6°N 3°E -4°E 22-24 50 Barbados 13°N 5soW-600W 22 1-10

Congo 4°S _5 0 S 22°E -12°E 20-22 50 Belize 16°N-17°N S7°W-SSoW 22 50

Gabon ZON-4°S 9°E -2ZOE 20-22 50 Brazil 4°N-32°S 35°W-55°W 20-24 75

Ghana 5°N-6°N 3°W_I oE 22-24 50 Colombia 2°N-12°N 63°W-79°W 20-22 50

Guinea 9°N_Il oN 24°W-15°W 20-22 SO Costa Rica SON-12°N S3°W-S5°W 21-22 50

Guinea-Bissau II 0N-13°N 15°W-lrW IS-19 60 Cuba 200N-23°N 75°W-S5°W 22-24 I

Ivory Coast 5°N 3°W-SoW 22-24 30 Dominica 15°N-16°N 61°W-62°W 22 1-10

Kenya 2°S -5 0 S 34°E -41 °E 20-21 25 Dominican Republic IsoN-200N 6soW-72°W 21-24 I

Liberia 5°N-17°N SOW-23°W 22-24 65 Ecuador 2°N-4°S 79°W-SloW IS-20 50

Madagascar 100S -25°S 45°E -500E IS-21 65 EI Salvador 13°N-14°N SrW-90oW 22 65

Mozambique 200 S -25°S 35°E -400E IS-21 25 French Guiana 4°N-5°N 500W-52°W 22-24 130

Nigeria 4°N-6°N 4°E _9°E 22-24 30 Grenada 13°N 61 0W-62°W 27 1-10

Rio Muni 2°N-3°N 100E 20-22 30 Guatemala 14°N-17°N SsoW-94°W 22 65

Sao Tome and 00N-2°N 7°E _9°E 22 1-10 Guyana 5°N-soN 5SoW-600W 22-24 130

Principe Haiti IsoN-200N 72°W-75°W 21-24 I

Senegal 13°N-17°N 16°W-17°W IS 50 Honduras 14°N-16°N S3°W-SSoW 22 65

Sierra Leone rN-9°N 12°W-14°W 20-22 100 Jamaica IsoN-19°N 76°W-78°W 22 1-10

Somalia lOoN-2°S 41 °E -500E 18-20 25 Lesser Antilles 12°N-18°N 61°W-65°W 22-24 I

Togo 6°N 2°E _3°E 22-24 50 Mexico 17°N-22°N 104°W-I08°W 20-22 32

United Republic 3°N-4°N 9°E _lO oE 22-24 65 Nicaragua I ION-14°N 84°W-86°W 22 65

of Cameroon Panama SON-9°N 76°W-S3°W 21-22 50

United Republic 50 S _lOoS 35°E -400E 20-22 25 St. Lucia 13°N-14°N 61 0W-62°W 22 1-10

of Tanzania St. Vincent and 13°N-14°N 61°W-62°W 22 1-10

Zaire 50 S -60 S 12°E 20-22 50 the Grenadines

Suriname 4°N-5°N 52°W-58°W 22-24 130

Trinidad and lioN 61°W 22-24 10

Tobago

Venezuela 8°N-lZOW 600W-73°W 22-24 50

U.S. Virgin Islands 18°N 65°W 21-24 I

3
Under its responsibilities of the arEC Act of 1980, NOAA has

issued regulations for licensing commercial arEC plants (NOAA

1981 b), an environmental impact statement on the licensing of commercial plants (NOAA 1981a), a technical guidance document on

the environmental requirements of the regulations (NOAA 198Ic),

and a research plan for assessing environmental effects that may

accompany the commercialization of arEC (NOAA 1982).

ESTIMATED OPERATING

CONDITIONS FOR INITIAL

U.S. OfEC DEPWYMENTS _

This chapter presents preliminary estimates of site characteristics

and operating conditions for early arEC developments. Two areas

are so characterized because of the interest for arEC in these areas:

The western coast of Oahu, Hawaii, in the vicinity of Kahe Point

(Fig. 2); and the southeastern coast of Puerto Rico in the vicinity

of Punta Tuna (Fig. 3). Both near/onshore and open-ocean sites

near Oahu and Puerto Rico are considered in the following description which is primarily based on an evaluation of information

presented by Bathen (1975, 1977, 1978), EG&G (1980), Miller

(1977), Noda et al. (1980), Ocean Data Systems, Inc. (l977a,b),

and Wolff (1978).

General Site Characteristics

Temperature, Salinity, and Density Profiles-In the vicinity of

Kahe Point, Oahu, Hawaii, the probable surface temperature varies

from 24.1 °C in late winter to 26.9°C in midsummer. The likely

range of surface temperatures is generally within 1.2°C of these

probable values. At a depth of 700 m the probable temperature varies

from 5.2 to 5.5°C. At a depth of 1000 m the temperature is about

4.2°C with very little variation. The thickness of the mixed layer

typically varies from as little as 10 m to as much as 180 m; however,

the probable thickness of the surface mixed layer varies from 40

to 100 m, being deepest during the winter and shallowest in the

summer. The average nearsurface salinity is about 34.8 ppt and

increases to about 35.1 ppt at the bottom of the surface waters (a

depth of 100-125 m), and then decreases again to about 34.1 ppt

at a depth of about 450 m. The density profile is dominated by

temperature, but salinity variation has some effect due to the salinity

maximum occurring near the thermocline (just below the bottom

of the surface mixed layer).

In the vicinity of southeastern Puerto Rico the probable surface

temperature varies from 26.ZOC in winter to 29.ZOC late summer

and early fall. The likely range of surface temperatures is generally within ±2.3°C during spring and fall. At a depth of 700 m the

probable temperature is 7.9-8.2°C. At a depth of 1000 m the

temperature is about 5.3 °C with very little variation. The thickness

of the mixed layer typically varies from as little as 10 m to as much

as 140 m; however, the probable thickness of the surface mixed

layer varies from 40 to 100 m, being deeper during the winter and

shallower in the summer. The nearsurface salinity is about 35-36

ppt and increases to a maximum of about 36.7 ppt at a depth of

100-125 m. The salinity minimum is about 35 ppt at a depth of

700-900 m.

Currents-The ocean currents near Kahe Point, Oahu, Hawaii, are

fairly complex, being a combination of tidal (i .e., depth-averaged,

shelf) currents, geostrophic (i.e., upper water column of deep water)

4

flow. and wind-driven (i.e.. surface) currents. The tidal current

has both a semidiurnal and a diurnal component. The flood-tide

is basically parallel to the shore, flowing in the south-southeast direction. The maximum semidiurnal component of the current is about

20-30 cm/s while the diurnal component is 10-20 cm/s. The

geostrophic flow is highly variable and can exceed 60 cm/s in larger

eddies, although near Kahe Point currents on the order of 15-25

cm/s are more typical. The magnitude of wind-driven currents (i.e.,

surface) depends on the wind strength, but values of 9-10 cm/s are

typical. Wind-driven currents tend to be shore-parallel near Kahe

Point.

The currents discussed above are highly variable in magnitude

and direction. The mean flow near Kahe Point is difficult to determine but is estimated to be on the order of or less than 10 cm/s.

In shallower areas nearshore, this flow tends to be more shoreparallel. The net flow of the surface waters in the vicinity of Hawaii

tends to be westward, being part of the North Pacific Equatorial

Current.

Ocean currents in the vicinity of southeastern Puerto Rico are

generally westward flowing due to the South Atlantic Drift, which

is driven by the North Atlantic Trades. The currents tend to follow

the bathymetric contours (and thus tend to be shore-parallel) but

are highly variable. The mean current is typically 10-40 cm/s in

the deep offshore waters « 1000 m deep) and slightly higher (60

cm/s) nearshore.

General Plant Characteristics

Type of Plant-The first arEC plants are expected to be of the

closed-cycle type using ammonia as the working fluid. Smaller

plants (of the pilot-plant scale) will probably be located on or nearshore or on bottom-mounted towers in about 100m of water. Larger

plants (of commercial scale) will likely be either on bottom-mounted

towers or offshore in the form of moored floating plants or freefloating plantships.

Plant Capacity-arEC plants are expected to be made up of multiple units which can operate independently. A typical pilot plant

might be made up of four to six IO-MWe units, while eventually

ten to twenty 25-MWe units might be typical for commercial plants

(W. H. Avery, Director, Ocean Energy Programs, Johns Hopkins

Uiliv. App!. Physics Lab., Laurel, MD, pers. commun. 1984).

Plant Dimensions-Pilot plants located on or nearshore where space

is not particularly limited will have horizontal dimensions on the

order of 100 m. Bottom-mounted plants (on towers) will make use

of the space along the vertical extent of the tower and thus will

have horizontal dimensions on the order of 50 m. Larger plants

(commercial scale) in the open ocean are expected to be 100-150

m in diameter for cylindrically symmetric designs and 50-75 m wide

x 150-200 m long for ship or barge type designs.

Power System

Working Fluids-Most designs for first-generation arEC plants

specify ammonia as the working fluid. Other fluids that have been

considered are noted in Table 2.

Heat Exchangers-Initially heat exchangers will be of aluminum

or titanium but eventually other materials may be used. Designs
Kaena .- ----J>f'.

Pt.

Kilometers

L-J

o 5

Figure 2.-The Kahe Point area, Oahu, Hawaii.

1

........-------------------------------------,19°00'N

67°00'

San Juan

PUERTO RICO

Punta

Tuna

Figure 3.-The Punta Tuna area, Puerto Rico.

5

Kilometers

o 10 20

VIEQUES

ISLAND
Table 2.-Characleristics of some candidate OTEC working fluids.

Physical Clean Water Water OSHA'

state*t Act (1977) solubility*! Flamma- Explosion Disaster 8-h exposure Human CarcinoFluid (20°C) standing (in 100 ml HzO) bility** hazard*' hazard limitstt (ppm) toxicity**·d genicity**

Ammonia Gas Hazardous 90 g (O°C) 671°C' Moderate Moderately dangerous 50 High None

substance (when (emits toxic fumes

exposed to when exposed to heat)

flame)

FreonTM 22 Gas Not Insoluble 63rC' No data Dangerous (emits No data Low None

regulated highly toxic fumes

when heated to

decomposition or on

contact with acid or

acrid fumes)

Atmospheric release

may contribute to

potential degradation

of the ozone layer.

FreonTM II Liquid Not InSOluble No data Reacts Dangerous (emits No data Low None

regulated violently highly toxic fumes of

with molten fluorides and chlorides

aluminum when heated to

decomposition)

Atmospheric release

may contribute to

potential degradation

of the ozone layer.

Methyl Gas Toxic 400 g 63rC' Mode,ate Dangerous (emits 100 Moderate None

chloride pollutant <O°Cb (Reacts highly toxic fumes

violently when heated to

with decomposition; reacts

aluminum) vigorously with

oxidizing materials)

Methylene Liquid Toxic 2 g (20°C) 615°C' None under Dangerous (emits 500 Moderate None

chloride pollutant ordinary highly toxic fumes

conditions when heated to

decomposition)

Nitrogen Gas Hazardous 7 g (O°C) No data Reacts Dangerous (emits 5 High None

dioxide substance violently highly toxic fumes

with when heated to

aluminum decomposition. reacts

with water or steam

to produce heat and

corrosive fumes)

Methyl Liquid Not 30 g (20°C) 465°C' Moderate Dangerous (emits 100 Moderate None

formate regulated -rcb (when toxic fumes when

exposed 10 exposed to heat or

heat or name~ reacts

flame) vigorously with

oxidizing materials)

Methyl Gas Not 807 g (12°C) 430°C' Moderate Dangerous (reacts 10 Moderate None

amine regulated O°C' (when vigorously with

exposed to oxidizing materials)

spark or

flame)

Ethyl Liquid Not Soluble 385°C' No data Dangerous (reacts 10 High None

amine regulated < _17°C' vigorously with

oxidizing materials)

aAutoignition temperature SOURCES; * P. Holtzclaw. U.S. EPA. 401 M St. SW,

'Flash point Wash., D.C.• pers. commun. 1981.

'Occupational Safety and Health Administration t Hodgman, 1959

dLow - causes readily reversible tissue changes which disappear after exposure ceases. ** Sax, 1979

Moderate - may cause reversible or irreversible changes to exposed tissue, no permanent injury or death. tt United States Department of Labor, 1972

High - capable of causing death or permanent injury in normal use; poisonous

6
suitable for afEC applications involving tube-in-shell, plate types,

and folded tube heat exchangers have been successfully tested at

small scale under afEC conditions (Avery, pers. comrnun. 1984).

Biofouling Control-Most designs will use periodic (daily) chlorination for biofouling control. Some designs also plan to use mechanical cleaning methods, such as AmertapTM balls or M.A.N.TM

brushes, in conjunction with chlorination. The dose of chlorine

needed to prevent biofouling will be somewhat dependent on sitespecific characteristics; however, recent studies suggest doses on

the order of 0.07 mglL (70 ppb) injected I hourlday may be sufficient (Larsen-Basse and Daniel 1983).

Operating Efficiencies-Overall thermal operating efficiencies for

most afEC plants are expected to be in the 2-3% range. However,

certain pilot-plant designs use larger than normal warm-water flow

rates to take advantage of less expensive heat exchangers. Such

designs will have efficiencies in the 1.0-1.5 % range.

The thermal efficiency is the fraction (usually expressed as a percent) of the heat energy extracted from the warm water that is converted into net electrical energy. For normal afEC operating

temperatures, this efficiency is limited to 6.0-7.5% by the basic

laws ofthermodynamics. Therefore, a more useful quantity might

be the "effectiveness" of the plant which is the ratio of the net

electrical power available for external use to the gross power produced by the turbo-generator system. This ratio is 65 to 75 % for

typical designs (increases rapidly with delta-T) and may fall to 35 %

for shore-based sites where the needed cold-water pipe lengths require higher pumping power (Avery, pers. commun. 1984).

Seawater Systems

Warm Water Intake

Depth and location-The warm-water intake will be located in the

upper part of the surface mixed layer of the ocean to take advantage of the warmest water available. Intakes for pilot plants will

be about 10 m deep, while intakes for larger commercial plants

will have to be about 20 m deep due to the larger intake flow-rate

requirements.

Shape and orientation-The intake structure will generally be constructed to produce horizontal flows external to the structure because

it appears that fish can sense and avoid horizontal flows better than

vertical flows (see Impingement section). The structure will also

be much larger in the horizontal direction than in the vertical direction to keep intake velocities low and yet keep the structure nearsurface where the warmest water is located.

Flow rates and intake velocities-Typical warm-water flow rates

for OTEC designs are in the range of 3-5 m3 ·s-I.MWe- l .

However, flow rates as high as 8.5 m3 ·s-l •MWe- 1 are proposed

for plants intending to trade larger flow rates for less expensive

heat exchangers. Flow velocities in the warm-water pipes and conduits will generally be in the 1.5-2.5 mls range, but intakes are

expected to be designed to reduce the velocity to 0.25-0.30 mls

outside the intake structure. The low intake velocities can lead to

rather large intake area requirements for large (loo-MWe) plants.

7

Cold Water Intake

Depth and location-The cold-water intake for most afEC designs

will be at the end of a long pipe extending to a depth of 750-1000

m. The selection of the depth at which the cold water will be

withdrawn is the result of a trade-off between the efficiency gained

by colder temperatures and the added expense of constructing and

operating a longer cold-water pipe.

Shape and orientation-Because the cold-water intake will be

located in an area of low biological activity, little effort has gone

into design of the intake structure; most likely, it will be an openended pipe with bar screens placed to keep out relatively large

objects.

Row rates and intake velocity-Typical afEC designs call for coldwater flow rates comparable to the warm-water flow rate, in the

range of 3-5 m3 ·s-I.MWe- 1• However, some designs try to

reduce the cold-water requirements because of the expense of obtaining water from such depths. Flow velocities in the cold-water

pipe will generally be in the 1.5-2.5 mls range. Intake velocities

may be of this same order because it is generally thought that there

is no need to reduce the intake velocity at the great depths involved.

However, lower intake velocities can be achieved, if needed, by

use of a flared pipe section. Ocean Thermal Corporation will use

such a section to reduce the cold-water intake speed to 0.3 mls for

the Kahe Point design.

Discharge

Depth and location-Most afEC designs will try to locate the

discharge so as to reduce the potential for recirculation of effluent

into the warm-water intake. Although this may be accomplished

through either separate or mixed effluent discharges, most designs

depend on the density of the effluent being greater than the density

within the mixed layer so that the effluent will come to equilibrium

near the bottom of the mixed layer, out of the influence of the intake. For nearshore plants this may involve the use of a discharge

pipe leading offshore. In deeper waters it is anticipated that the

discharge will generally be located at a depth of 30 m or greater

to avoid recirculation.

It is expected that the temperature of the warm water and cold

water will decrease about 2-3°C during passage through the heat

exchangers. For representative warm and cold waters of 25°C and

5°C, respectively, temperatures of separate warm and cold

discharges would then be about 22-23°C and 7-8°C, respectively.

For this situation, a mixed discharge would have a temperature near

15°C.

Shape and orientation-Most proposed designs do not involve the

use of any special discharge structures such as multiport diffusers

(see Effluent Discharge section). Thus, the discharges will be from

open-ended round pipes directed either downward or horizontally

(often with a downward component).

Row rates and discharge velocity-Discharge flow rates must equal

intake flow rates due to continuity. Typically, discharge velocities

will be in the 1.5-2.5 mls range.
PHYSICAL INTERACTION

WITH THE ENVIRONMENT _

The presence of an OfEC plant will cause a physical interaction

with the marine environment. However, with the exception ofsome

small modification of water movement in the immediate vicinity

of a plant, the principal physical interaction will be due to the intake and discharge of the relatively large volumes of water needed

for an OfEC operation. These topics are discussed in this section

since they are so important to the definition of biological interaction

taken up in the later section on Biological Interaction.

Cold Water Intake

The cold water intake provides the cold water needed for the condensing part of the OfEC cycle. Given a certain surface temperature, a cold water pipe (CWP) will have to be extended deep enough

to obtain cold water at a temperature low enough to assure a

temperature difference (liT) of about 20°C. Certain engineering

constraints will be present, however, in obtaining the cold water,

e.g., the large pipe diameters and depths required for bottornmounted pipe installations both exceed the demonstrated capability of the offshore pipe laying industry (Brewer 1979). However,

it is believed that these problems may be overcome with a minimum

extension of present technology. The CWP may either be

1. emplaced on a shelf, extending to the needed depth for a landbased OfEC plant;

2. placed vertically within the structure of a shelf-sitting tower

to the needed depth, or to the seabed and then extended on the shelf

to the needed depth; or

3. placed vertically to the required depth beneath an open ocean

plantship.

To obtain a liT of about 20°C, the CWP intake will need to be

located at a depth of about 800-1000 m in most locations. At this

depth the induced flow will not interact with other intake and

discharge flow fields, and the interaction with the environment will

depend primarily on the volumetric flow rate (Paddock and Ditmars 1983). Therefore, the intake depth, volumetric withdrawal

rate, and velocity are the three principal variables that will define

the interaction.

Warm Water Intake

Like the need for cold water, a relatively large volumetric rate of

warm water is needed for the evaporation part of the OfEC cycle

(see section on Flow Rates and Intake Velocities).

In general, the warm water intake will draw water from a range

of depths, dependent upon the ambient density stratification in the

vicinity of the intake, the flow rate at which water is withdrawn,

and the size and shape of the intake structure (Paddock and Ditmars

1983). The volumetric flow rate at which water will be withdrawn

will depend, among other factors, on thermodynamic needs of the

power cycle and the efficiencies of the heat exchangers. Once the

volumetric flow rate is established, however, a trade-off is involved

between the intake dimension and the velocity of the flow-the less

the intake dimensions, the greater the intake velocity and vice versa.

For example, consider the intake of 140 m3/s of warm water for

a 40-MWe OfEC plant (i.e., 3.5 m3 . S-I. MWe- I

). Using an intake pipe of 34 m diameter would result in an intake velocity of

15 cm/s, whereas an intake pipe of 17 m would impart an intake

8

velocity of 62 cm/s. Using an intake pipe of 10 m diameter would

result in an intake velocity of 178 cm/s for which the power loss

due to friction would be small, whereas an intake diameter of 5

m would entail a velocity of 713 cm/s which would cause an unacceptable friction loss (Avery, pers. commun. 1984).

The effect of the warm water intake on the flow field in the vicinity

of the intake structure will also be dependent upon a number of

factors. To provide an idea of the possibilities, three induced flow

patterns are indicated in Figure 4 for three simplified hypothetical

intake situations:

1. Intake flow field in the presence of an ambient current for

an intake distributed uniformly over the mixed layer where the density is constant above and below a strong thermocline (Fig. 4a);

2. intake flow field in the presence of an ambient current for

a point intake within the mixed layer, again where the density is

constant above and below the thermocline (Fig. 4b); and

3. intake flow field for a point intake in a stagnant, linearly

stratified environment (Fig. 4c).

These hypothetical scenarios provide an indication of the variety

of cases that will determine where seawater and organisms are

withdrawn. The quantification of the pertinent variables for such

cases has been discussed by Paddock and Ditmars (1983).

Most ocean environments exhibit some variations ofseawater density vvith depth (i.e., density stratification) such as shown in Figures

5 and 6 for Kahe Point and Punla Tuna, respectively. In the case

of intake withdrawal from a density-stratified environment, selective withdrawal occurs. Selective withdrawal involves the flow of

water from discrete layers centered about the elevation of the intake as shown in Figure 4c. The thickness of the layer withdrawn

(0) is inversely proportional to the degree of stratification, so that

thinner layers will be withdrawn when strong stratification is

present.

Effluent Discharge

The discharge of used warm and cold OfEC waters may be either

separate or mixed. Additionally, a discharge could be through a

single discharge pipe, through a number of discharge pipes if the

dimensions of a single discharge structure became unrealistic, or

through a multiple port diffuser. Multiple port diffusers are commonly used for the discharge of municipal waste to ocean waters

(Koh 1983) and have been considered in hydraulic studies of OfEC

discharges. Although multiple port diffusers could ensure a greater

degree of dilution of an OfEC effluent, it is not obvious that this

is the desired objective, as discussed below. Furthermore, problems

with construction, head losses, and additional pump requirements

might outweigh possible advantages of a multiple port diffuser, to

say nothing of additional biological concerns over the greater volume

of dilution water needed.

A separate discharge scheme would involve separate discharges

for both the warm and cold waters, whereas a mixed discharge

scheme would utilize the same discharge structure for both water

types. Although the initial physical fates of the discharged water

would vary according to the scheme employed, the physics that

define these fates are the same for both cases and relate to the

behavior of buoyant discharges.

The behavior of positively or negatively buoyant discharges has

been studied analytically as well as through the use of physical

models. Initially these studies were conducted to evaluate the

behavior of cooling water discharges from conventional power plants

and of effluents from sewage outfalls; recently such studies have
T. "C (e)

0 5 10 15 20 25 30 .__ ~--,------..J

0T (0)

22 23 24 25 26 27 28

0 22.72

- 22.97

100

200

300

::'j; 400

:i

fa..

LU 500 0

600

700

800

900 -27.43

I

I

1000 I

'-{-L~ --___

a

d-,;:-------__-

p

Figure S.-One temperature and density profile offshore Kahe Point, Oahu,

Hawaii (from Noda et aI. 1981a; site 1, cast 1, 6 November 1980).

T. "C (e)

0 5 10 15 20 25 30 L--I

0T (0)

22 23 24 25 26 27 28

0 23.17-

100

200

300

400

::'j;

If- 500 a..

LU

0

600

700

800

900

1000 -27.77

b

c

Figure 4.-a. Schematic of the intake flow field in the presence of an ambient

current for an intake distributed uniformly over the mixed layer (from Paddock

and Ditmars 1983). b. Schematic of the intake flow field in the presence of an

ambient current for a point intake within the mixed layer (from Paddock and

Ditmars 1983). c. Schematic of the intake flow field for a point intake in a stagnant, linearly-stratified environment (from Paddock and Ditmars 1983).

Figure 6.-0ne temperature and density profile offshore Punta Tuna, Puerto Rico (from Vargo et a!. 1981; daycast, PROTEC-13).

9
been applied to arEC discharges (Allender et al. 1978; Ditmars

1979; Ditmars and Paddock 1979). Although details of such

assessments may be quite complex and dependent upon site-specific

factors, generalities can be made for certain simplified situations

(Paddock and Ditmars 1983). As discussed by Paddock and Ditmars, different phenomena govern the different regions of the flow

that develop, termed the near-field, intermediate-field, and far-field

(Figs. 7, 8). Momentum and buoyancy dominate in the near-field,

gravity and interfacial shear in the intermediate field, and advective and dispersive mechanisms in the far field.

The important parameters about the near-field region are primarily

the depth where the discharge plume reaches neutral buoyancy

(equilibrium depth), the average dilution achieved by the discharge

plume upon reaching the equilibrium depth (initial dilution), and

the trajectory from the point of discharge to the equilibrium depth.

Paddock and Ditmars (1983) present methods for quickly estimating

these parameters for simplified situations. As an example, consider

the discharge from 40-MWe hypothetical arEC plants located offshore of (1) Kahe Point, Oahu, Hawaii, and (2) Punta Tuna, Puerto

Rico. The plants pump 140 m3/s of both cold and warm water for

a total flow and discharge of 280 m3/s. Four cases are considered

to give an indication of the range of behavior that might be expected:

I. Separate horizontal round discharges to nearsurface waters

(20 m);

2. separate horizontal round discharges at depth (100 m);

3. mixed horizontal round discharge to nearsurface waters (20

m); and

4. mixed horizontal round discharge at depth (100 m).

For all four cases, it is assumed that stagnant conditions prevail,

the density profiles of Figures 5 and 6 apply, and the intake waters

are from 20 m and 1000 m with the following ambient properties:

Salinity

Temp. (0C) (ppt) 0,

Kahe Point

Warm Water 26.6 34.9 22.8

Cold Water 3.8 34.5 27.4

Punta Tuna

Warm water 27.7 36.0 23.3

Cold Water 5.4 35.2 27.8

It is also assumed that the warm water will undergo a temperature

drop of 2°C and that the cold water will undergo a temperature

increase of 2°C. Based on tables of seawater density in Fischer

et al. (1979), these temperature changes would produce sigma-t's

(a,) of approximately 23.4 for the warm water side and 27.2 for

the cold water side at Kahe Point, and 23.9 for the warm water

side and 27.5 for the cold water side at Punta Tuna. All discharges

are made through lO-m diameter pipes, whether separate or mixed.

For the case of mixed discharges, the discharge velocity is kept

constant at 1.8 m/s by using two IO-m diameter pipes. It is assumed

that the discharges do not interfere with each other. Using the approximation methods of Paddock and Ditmars (1983) leads to the

following results.

I------++Intermediate Field -+- Far Field -----

J- Cold-Water Intake

Figure 7.-Typical discharge flow field for an OTEC plant located in deep water (from Paddock and

Ditmars 1983).

10

Figure 8.-Typical discharge flow field for an OTEC

plant located in shallow water showing flow along the

bottom (from Paddock and Ditmars 1983).
Regional Influence

Warm 30 4

Cold 55 5.5

Warm 75 5

Cold 160 7

Mixed 45 4.5

Mixed 115

Level of neutral

Discharge buoyancy, m Dilution

Warm 50 6.5

Cold 80 7

Warm 95 4

Cold 145 6

Mixed 75 6.5

Mixed 120 4.5

Kahe Point

Separate to nearsurface

(20 m)

Separate to depth

(l00 m)

Mixed to nearsurface

(20 m)

Mixed at depth

(l00 m)

Punta Tuna:

Separate to nearsurface

(20 m)

Separate to depth

(100 m)

Mixed to nearsurface

(20 m)

Mixed at depth

(l00 m)

Although the above results are only rough approximations, they

provide insights that are useful for defining physical interaction with

the environment. In general, it can be seen that initial dilution for

afEC discharges will be in the range of about 1 to 10. The strong

effect of density stratification is also apparent and suggests that

wherever an afEC discharge plume encounters a strong density

gradient, its further vertical motion will be limited. Not only do

strong density gradients arrest a plume's trajectory, they also limit

the amount of dilution that can be achieved. The presence of currents would act to lengthen the trajectory of the discharge plume

and increase the dilution achieved; accordingly, the depth of neutral

buoyancy of an effluent plume might be somewhat less for a

negatively buoyant discharge.

Using approximation methods discussed by Paddock and Ditmars

(1983), it can be shown that the above initial dilutions and levels

of neutral buoyancy will occur in a time frame on the order of a

minute. Referring back to Figures 7 and 8, it can then be inferred

that the intermediate and far field processes will have a greater influence on regional environmental impacts. Examining a hypothetical40-MWe afEC plant in typical tropical ocean conditions, Jirka

et al. (1980) analyzed the spreading of a mixed discharge plume

in a density stratified environment. The results indicated the effluent plume to be about 10 m thick and 5 km wide. This size is

comparable with island shelf areas and warrants an analysis of the

regional environmental influence of even a small afEC plant.

Aware that the regional influence of an afEC operation could

be considerable, NOAA initiated a research effort in 1982 with

Argonne National Laboratory to develop a model that could define

this influence. To come to an understanding of the influence, a

description was needed of the physical processes associated with

the discharge of large volumes of water into the upper ocean by

afEC plant operations. The approach taken departed from previous

mathematical modeling investigations of afEC plant interactions

with the ocean environment. In previous modeling, effluent plumes

and intake flows have been superimposed on fixed ambient ocean

waters; that is, no attempt was made to model changes in the ocean

resulting from their presence. The Argonne model simulates the

II

interaction of an afEC discharge with the ocean, thereby permitting discharge-induced modifications to the ambient ocean to be

determined. Changes in ambient circulation, temperature structure,

and concentration of effluent and water column constituents are

modeled. The general approach was to modify an existing threedimensional model for limited-area coastal regions (Wang 1982)

by incorporating simulations of the effluent flows due to an OTEC

operation. The effect of the intake flow was found to be minimal

and thus is not included in the model.

The Argonne model was applied to a base case of a 280 m3/s

mixed discharge from a 40-MWe afEC plant into coastal waters

for various ambient ocean conditions, and then was used to examine

the effect of two nearby 40-MWe plants and that of an 80-MWe

plant. Applied to the case of a mixed discharge from a 40-MWe

afEC plant located in deep water on a coastal margin, the Argonne

model indicated the effluent plume will be confined mostly to the

top of the thermocline. In the case of an ambient alongshore current of 20 cm/s, the addition of a conservative dye to the discharge

indicated the effluent plume to be about 20 m thick, 2 km wide,

and 4 km long (Fig. 9), and diluted by a factor of20-100. Because

the plume is mainly driven by the buoyant discharge, the regional

influence does not depend on the details of the mode of discharge

(e.g., single or multiple outlet discharge). Temperature perturbations are caused by the dilution of the effluent and by the redistribution of ambient temperature structure. For a 40-MWe afEC plant

discharge, temperature perturbations are less than 0.2 °C and are

distributed almost uniformly between the bottom of the mixed layer

and the top of the thermocline.

The circulation induced by interaction of the buoyant discharge

and the ocean not only influences plume dilution and temperature

structure but also contributes to the redistribution of other ocean

constituents. A computation of a nitrate profile subjected to only

the physical (conservative) aspects of afEC operation indicated

that the nitrate flux into the upper ocean is derived both from the

mixed-discharge effluent (i.e., cold water influence) and from

discharge-induced deep upwelling. For a base condition where the

nitrate level is very little in the upper 90 m and increases to some

higher level in the depth interval of 90-130 m, the two processes

contribute about equal amounts of the afEC-induced nitrate flux

into the upper ocean.

Using the Argonne model to examine the effects of discharges

of two adjacent afEC plants showed that the regional influence

may be computed as a superposition of two individual plumes, given

reasonable separation between plants. When two 40-MWe afEC

plants are separated by 2 km alongshore, the effluent concentration near the up-current plant is about the same as the effluent concentration of a 40-MWe afEC single plant, where the effluent concentration near the down-current plant is increased by about 25 %

(Fig. 10). When two plants are separated by only a few hundred

meters, which is equivalent to the case of a single 80-MWe afEC

plant, significant interaction occurs and the effluent concentration

is increased by about 100% from that of a single 40-MWe afEC

plant.

The regional influence is not very sensitive to the effects of the

coastal boundary. On the other hand. the dilution of the effluent

plume is greatly reduced for effluents discharged in shallow water

or along the bottom. For a 40-MWe afEC plant with bottom

discharge, the maximum effluent concentration will be about 10%

ofthe initial concentration, which is about twice the maximum concentration of the effluent plume from the nearsurface discharge.

The plume also penetrates deeper into the thermocline than in the

case of nearsurface discharge.
E E 0" 0"

0

.<: 0 0.1 Vl .<:

0> Vl

o~ C 0>

0 C

« 0

«

2

E

0"

o

.<:

Vl

0>

C

o

«

\ \

0.1

o~

0

2 0 2

Offshore (km) Offshore (km)

3 4

E \

0" 0.1

W

0

.<:

Vl

0>

C

0

«

Figure 9.-Horizontal distribution of dye at 10

m (level 1),30 m (level 2), SO m (level 3), and 70

m (level 4) from a model ofthe regional innuence

of a 4O-MWe OTEC plant (initial concentration

= 10; ambient current = 20 cm/s alongshore)

(from Wang 1984).

2

Offshore (km)

o 2

Offshore (km)

The applications of the Argonne model to several OTEC configurations have demonstrated the importance of the dischargedinduced circulation, or interactions between the discharge and ambient ocean. The region of influence of an OfEC facility clearly

is greater than simply the geometric extent of the plume detennined

from integral jet models and superimposed on a fixed ambient ocean.

For the purpose of investigating regional influence in a generic

sense, model applications have been restricted to a simple coastal

geometry and steady ocean currents. In the case of a more complex geometry, the effluents that are advected downcurrent may

accumulate in a convergence zone. The effluent plume also may

be swept away by storm currents and impinging eddies.

BIOLOGICAL INTERACTION

WITH THE ENVIRONMENT _

Biological Characteristics of the Environment

This section briefly summarizes information presented in reports

by Hoss et al. (1983) and Uchida (1983) (both efforts being part

of this overall study), on pertinent biological information from the

Caribbean and Pacific, respectively. For specific details those

reports should be directly consulted.

Location-There are no areas in the Caribbean which lie outside

of existing or potential Exclusive Economic Zone claims of some

nation. It is likely that OfEC operations by U.S. corporations will

be within the Fishery Conservation Zone (equivalent to the Exclusive

Economic Zone in the U.S.) surrounding Puerto Rico and the U.S.

Virgin Islands (Fig. 11). Several sites in the Pacific have been

studied for possible land-based OfEC plants including Keahole Point

and Kahe Point in the Hawaiian Islands and Cabras Island, Guam.

Additional areas in the open Pacific (e.g., between lat. 5 0 _WO N

and long. 90 0

-95°W) have been investigated and found to be excellent for OfEC plantship operation.

Phytoplankton-Primary production in Hawaiian and open tropical

Pacific waters is low relative to that of Continental Shelf areas in

the Pacific (estimated to be on the order of 200 g C·m-2 .y-')

(Platt and Rao 1975). Noda et al. (1982) estimated the annual

primary production off Keahole Point to range from 4.2 to 72.6

g C·m-2 .y-'; measurements off Kahe Point are similar, with

Noda et al. (1981 a) determining average annual primary produc12
2

, ,

I" .-

; --- ""--

E --- ,-- E e-'"

,............. e-'" .,

....

0 0 .c ......... ...... .c III III

0> 0> l: " "- ... l: 0

\, 0

<{ , .. <{ .. 1 ,

E

e-'"

o

.c

III

0>

l:

o

<{

o

o

2 4

Offshore (km)

3

2

Offshore (km)

I~

o

.c

III

0>

l:

o

<{

o 2

Offshore (km)

4

2 4

Offshore (km)

Figure to.-Horizontal distribution of velocity

and dye for two adjacent 4O-MWe OTEC plants

at 10 m (level 1), 30 m (level 2), SO m (level 3),

and 70 m (level 4) (velocity scale = 20 cm/s

alongshore; initial dye concentration = 10; contour interval = 0.1) (from Wang 1984).

tion at 60.4 ± 15.6 g C' m-2. y-I. Slightly higher values, 120 to

144 g C'm-2 'y-l, have been reported from the open ocean (EISayed and Taguchi 1979). Bienfang and Szyper (1982) demonstrated

that enriching the photic zone with upwelled nutrients can increase

production.

Production in the Caribbean is also generally low, typical of areas

without a pronounced admixture of nutrient-rich water from below.

Average daily production rates reported from various areas (Sander

and Steven 1973; Steven 1971; Beers et al. 1968; and Steeman

Nielsen and Jensen 1957) correspond to annual rates ranging from

20 to 105 g C' m- 2 .r I. The variation is associated with input of

nutrients to the surface: where water passes over shallow banks,

at the edge of eddies which form in the wake ofislands, at upwellings along the South American coast, and in upwellings on the

periphery of eddies of Amazon river water. Potential OfEC sites

near Puerto Rico and the U.S. Virgin Islands may be particularly

low in primary and secondary production due to the thick wedge

of low-density surface water present which may reduce nutrient

advection.

Phytoplankton standing crop is similar at oceanic sites in the

Caribbean, Hawaii, and the mid-Pacific. Surface chlorophyll-a concentration from eight Caribbean locations (Marshall and Solder

13

1982; Knauer and Flegal 1981; Sander and Steven 1973; Malone

1971; and Hargraves et al. 1970) averaged 0.13 mg m- 3. Off

Keahole Point in Hawaii it ranged from 0.03 to 0.18 mg m- 3

(Noda et al. 1982) and in the open tropical Pacific the average value

was 0.12 mg/m3 (EI-Sayed and Taguchi 1979).

Investigations of plankton near oceanic islands have repeatedly

revealed that taxonomic composition, standing crop, and production change with distance from shore. The intensity of this "island

mass" effect and the area influenced are generally greater on the

leeward side of the island. Data from Barbados (Sander and Steven

1973) showed that moving from 2 to 10 km offshore reduced cell

concentration and production rates by a factor of four and increased

the relative abundance of blue-green algae by a factor often. Because

the intensity of this island mass effect varies with location, sitespecific studies are particularly important at potential sites which

are nearshore.

Zooplankton~Althoughzooplankton have not been studied extensively in either Hawaii or the Caribbean, the data available indicate

similar abundance in both areas. In dry weights per sample from

the Caribbean oceanic water, the range (0.3 to 12 mg/m3) is

similar to that found in Hawaiian nearshore samples, 0.14 to 25
PUERTO RICO

and the

U.S VIRGIN ISLANDS

MARITIME REGia

22"N

20"

18"

- 16"

Q

68 • 66" 54"W

Cl>

C ,.. .- Cl>~-J_

c "' Cl> u: E .Cl>

"?

::>2c

UJ

Figure H.-The Fishery Conservation Zone surrounding

Puerto Rico and the U.S. Virgin Islands (U.S. Department

of State 1982).

mg/m) (Noda et al. 198Ia). The average displacement volume,

0.20 to 0.30 ml/m3, and average dry weight, 2.4-3.3 mg/m3 , are

very similar among oceanic studies from the Caribbean (Moore and

Sander 1977; Deevey 1971; Margalef 1971; and Moore 1967). The

importance of an island effect on zooplankton abundance is evident from studies near Jamaica and Barbados where respective dry

weights inshore were 1.7 and 2.5 times those found offshore (Sander

and Steven 1973; Moore 1967).

Abundance of zooplankton decreases considerably with depth.

Off Bermuda, total abundance in the upper 500 m was 8, 19, and

39 times that found at respective depths of 500-1000 m, 1000-1500

m, and 1500-2000 m (Deevey and Brooks 1971). In the mid-Pacific,

Hirota (1977) showed the highest concentration in the upper 150

m and moderately high concentration between 200 and 900 m. Standing stocks in the upper 200 m varied about 50-90% of that in the

upper 1000 m. Off of Kahe Point in Hawaii, Noda et al. (198Ia)

observed an approximate tenfold difference between surface samples

and those from 600-1000 m.

Although diel migration of zooplankton has been observed but

not extensively documented in Hawaii and the Caribbean, the

phenomenon is general and fairly well known. "Diel vertical

movements occur in all planktonic phyla and in most of the smaller

taxonomic groups" (Longhurst 1976). In general this consists of

a migration from deep water toward nearsurface layers. where

plankton spend the night and then descend again at dawn. The

plankters do not necessarily rise all the way to the surface; aggregations tend to occur at the level of the deep chlorophyll maximum,

and abundance in the surface water may even decrease during the

night as a result of downward migration of surface zooplankters

to the chlorophyll maximum layer.

Fisheries-The major thrust of the commercial fishery in Hawaii

is in the open ocean beyond 200 m in depth, where pole-and-line

sampans catch skipjack tuna; and longline, handline, and charter

boats harvest yellowfin and bigeye tuna, albacore, striped blue and

black marlin, swordfish, spearfish, sailfish, wahoo, and mahimahi.

Nearshore fisheries include a variety of commercial handline, net,

trap, and recreational boats which catch a wide variety of demersal and bathypelagic species including pink, red, and grey snappers. goatfishes, seabass, and bigeye and mackeral scad. The scad

landings are of considerable importance, being second only to tuna

and billfishes.

The area near Kahe Point sustains a varied and valuable fishery.

In the years from 1976 to 1980. 101 different species were identified in the harvest from the area. Hawaii Division of Aquatic

Resources records show that the average annual catch was about

219 metric tons with an annual yield to commercial fishermen of

$350,000.

The commercial fishery in the oceanic waters of the Caribbean

is basically a long-line fishery for tunas. The fishery is dominated

by large modem vessels from Japan, Korea, Taiwan, and Venezuela.

The commercial fishery in nearshore waters can be described in

terms ofseveral main components which overlap slightly. The most

important of these, both in weight and value, is the demersal fishes

component, in which fish pots and hand lines are used to catch

shallow reef species and deep-water snappers and groupers. This

component of the fishery accounts for about 70% of the catch in

Puerto Rico and 53% of its value. The second component of the

fishery is for coastal pelagic fishes, using troll lines, beach seines,

and gill nets; this component accounts for about 21 % of the total

catch and 16% ofits value in Puerto Rico. Shellfish, the third com14
ponent, accounts for only about 15 % of the Puerto Rico catch but

about 30% of its value. Spiny lobster landings are over 50% of

the shellfish catch, yet 70% of its value; the other major shellfish

species is the queen conch.

Although the economic importance of the recreational fishery has

not been evaluated, it is of considerable importance to the tourism

industry and the local residents. Its importance in Puerto Rico is

reflected in a catch of 1,361 blue and white marlin and sailfish from

May 1977 to April 1978, about half of which were caught by vessels

from outside the area. Other species for which the area is known

are yellowfin tuna, wahoo, bonefish, some of the larger reefspecies,

and billfishes. Billfishes are already overexploited in the Atlantic,

so the future of that recreational fishery is uncertain.

Eggs and Larvae of Important Species-Data on abundance and

distribution of the early life stages of important species is rather

scant; thus, it is difficult to make a general comparison of larvae

from Hawaii and the Caribbean. Based on reproductive stages of

adult fish in the Caribbean (Munro et al. 1973), it appears that reef

fish eggs and larvae will be most abundant during February through

April. However, the eggs and larvae of tuna and billfishes will be

most abundant during the summer, with some species present at

lower numbers in spring and fall (Matsumoto et al. 1984; Uchida

1981 ; Yoshida 1979; Shomura and Williams 1975; Miller et al.

1979; Idyll and deSylva 1963).

Spatial distribution of larvae is quite complicated depending on

both the reproductive habits of the fish and water movement in and

near the spawning area. Most of the important reef species have

pelagic eggs and appear to be spawned at times and locations where

the eggs will be quickly moved offshore to areas where predators

may be less abundant. This pattern has been substantiated in Hawaii

by Leis (1982) who found reef fish eggs were more abundant 3.0

Ian from shore than 0.2 Ian out, and Miller (1974) who reported

larvae of some fish were more abundant 50 Ian off Oahu than 5

Ian out. Dekhnik et al. (1973) found the same larval pattern off

Cuba and several studies have shown the same pattern with fish

eggs at other Caribbean sites (Moore 1967; Sander and Steven 1973;

Moore and Sander 1976). Larval distribution of pelagic species may

be much different. Miller et al. (1979) reported tuna larvae were

much more abundant nearshore and on the leeward rather than windward coast. It appears likely that high surface densities of larvae

are produced by wind-driven upwelling of layers of water containing fairly dense larval concentrations.

Comparing absolute abundance of larvae between areas is particularly difficult because various investigators use different techniques, including sampling at different depths, and because the

samples display considerable variability. The larval abundance of

oceanic species in the Caribbean (Richards 1981), however, appears similar to that in the eastern tropical Pacific (Ahlstrom 1971,

1972). The Caribbean may have a more diverse assemblage with

15 families accounting for about 70% of the larvae (Richards 1984)

in comparison to the Pacific, where 10 families constituted 90%

of the larvae. It is likely that in both regions the larvae are most

abundant nearsurface. In the mid-Pacific, Hirota (1977) found:

1) that the larvae of commercially important tuna occur more

abundantly in the neuston layer than from 1-200 m,

2) the species in the 1-200 m layer are primarily midwater forms,

and

3) very few larval fish occur between 200-1000 m.

Off Puerto Rico the vertical trend is similar with few fish below

200 m and the highest number between 0 and 25 m (Vargo et al.

1981).

15

Other Important Biological Components-Other biological components such as coral reefs, mangroves, and sea grass beds are all

very important habitat types for numerous fishery resources, at least

during some portion of the individual species' life cycle. Impacts

on such fishery habitats may be of greater importance than direct

impact on the species themselves (eggs, larvae, adults), particularly for near/onshore OTEC sites (1. Naughton, Southw. RegionWest. Pacific Program Staff, Natl. Mar. Fish. Serv., NOAA,

Honolulu, HI, pers. commun. 1984). In addition, the destruction

of coral reefs can sometimes lead to an increase in the incidence

of ciguatera poisoning, caused by the ingestion of fish contaminated

with a paralytic neurotoxin of natural origin (see Research Priorities

section). It is important that all efforts be made·to minimize the

impact of OTEC operations on such biological resources.

In a strict interpretation, protected species such as marine mammals may not be "fisheries" resources. However, they are important components of the biota at the potential OTEC sites and impacts

on them will have to be evaluated on a thorough basis. As noted

in Table 3, a number of species are listed as threatened or endangered in Hawaiian and Caribbean waters. The humpback whale,

Table 3.-Threatened (T) and endangered (E) marine

species (Source: 50 eFR 17.11-12).

Hawaii Virgin Islands

Marine mammals

Right whale Balaena glacialis* E

Sei whale

Balaenoptera borealis E

Blue whale

Balaenoptera musculus E

Finback whale

Balaenoptera physalus E

Humpback whalc

Megaptera novaeangliae E

Hawaiian monk seal

Monachus schauinslandi E

Spenn whale Physeter calOdoll E

Caribbean monk seal

Monachus tropicalis E

West Indian manatee (Florida)

Trichechus manatus E

Sea Turtles

Loggerhead sea turtle

Caretta caretta T T

Green sea turtle

Chelonia mydas E T

Leatherback sea turtle

Dermochelys coriacea E E

Hawksbill sea rurtle

Eretmochelys imbricata E E (=carey)

Kemp's Ridley sea turtle

(=Atlantic)

Lepidochelys kempii E E

Olive Ridley sea turtle (Pacific)

Lepidochelys olivacea T

Birds

Newel's shearwater

Puffillus auricularis newelli T

Hawaiian dark-romped petrel

Petrodroma phaeopygia

sandwichensis E

'Not considered part of the normal cetacean fauna in

Hawaiian waters.
Megaptera novaeangliae, one of the most abundant cetaceans in

Hawaii, is an endangered species which migrates into Hawaiian

waters in winter to breed. A second endangered species, the

Hawaiian monk seal, Monachus schauinslandi, is present; however,

the population resides in the Northwestern Hawiian Islands and away

from potential OTEC sites. Of the five sea turtles that have been

reported off Hawaii, the green sea turtle (Chelonia mydas) is the

most abundant. A single green sea turtle has been observed repeatedlyon the reef directly off the Kahe Point power station.

A number of marine species listed as threatened or endangered.

including several turtles, are found in the waters off Puerto Rico

and the Virgin Islands. Of particular importance are the leatherback and hawksbill turtles which nest in potential OTEC areas, and

humpback whales which calve and mate in the region from January

through April.

Factors That May Affect Fish

Organisms entrained by the intakes of an OTEC plant will either

be impinged on screens placed to prevent larger objects from entering and clogging critical parts of the plant, or entrained and

transported through the plant and then discharged. In passage

through the plant, entrained organisms will be subject to a number

of stresses such as temperature and pressure changes, and chemical

additions. Upon discharge to the environment, entrained organisms

will be redistributed in the water column along with additional

organisms entrained into the discharge plume. The artificial upwelling of nutrients and other constituents contained in the deeper, colder

waters and their subsequent redistribution may also effect some

biological changes.

AttractionlAvoidance-The attraction or avoidance of fish towards

objects, light and noise is a known phenomena that is expected to

occur with OTEC operations, whether they be open-ocean plantships, stationary towers, moored platforms, or land-based plants.

For the purpose of this study, Seki (1984) has summarized available

information on this topic and related it to OTEC development; the

following is a brief synopsis of his findings.

The attraction of fish to free-floating and anchored objects or

structures has been studied throughout the world's tropical and subtropical waters. The objects with which fish have been observed

to associate include drifting seaweed (Senta 1966), driftwood (Yabe

and Mori 1950; Inoue et al. 1963; Hunter and Mitchell 1967; Inoue

et al. 1968), manmade rafts (Kojima 1960; Gooding and Magnuson

1967), and artificial surface or rnidwater structures, including commercial fish aggregating devices (FAD's) (Hunter and Mitchell 1968;

Klima and Wickham 1971; Wickham et al. 1973; Wickham and

Russell 1974; Matsumoto et al. 1981). Tunas dominate the catch

of the pole-and-line, trolling, handline, and purse seine boats fishing

around FAD's, as evidenced by some catch data obtained from

Kiribati, Western Samoa, Fiji, and Hawaii (Shomura and Matsumoto 1982). The experimental study by Matsumoto et al. (1981)

provided the most detailed records of catches around FAD's in the

Pacific. Matsumoto reported that skipjack tuna, Katsuwonus

pelamis, represented nearly 90% of the catch by the pole-and-line

boats. These fish ranged from 0.9 to 5.4 kg and sometimes over

9.1 kg. Unlike pole-and-line boats, trolling boats hac a much more

diversified catch. Tunas (mostly yellowfin tuna, 1hunnus albacares,

and skipjack tuna, Katsuwonus pelamis) still dominated the catch,

although mahimahi, Coryphaena hippurus, constituted the largest

percentage of single species caught.

16

Another tuna fishery which utilizes FAD's (in conjunction with

an artificial light source) in Hawaii is the ika-shibi or the night

handline fishery for tuna. Although this rapidly growing fishery

utilizes extremely simple gear (a single hook and a line) as compared

with the longliners and large purse seiners, it is an extremely effective method as indicated by the mean catch rate of approximately

two fish per hook per night (Yuen 1979).

In comparison to floating OTEC structures, the tower and manmade island designs of OTEC plants are expected to function as

artificial reefs, duplicating those conditions that cause concentrations of fishes and invertebrates on natural reefs and rough bottom

areas. The effect of tower designs would be similar to that of offshore oil platforms, which have resulted in an increase in offshore

sport fishing in the immediate area.

Numerous studies have described the variety of fish which have

been attracted to artificial reefs at various sites. In all studies, the

many different species found generally represent similar basic broad

behavioral classes, such as the Turner et aI. (1969) reef or nonreef

associates (the former further split into resident or semiresident).

Four reefs were established at various sites in Hawaii between 1960

and 1973, using primarily car bodies, damaged concrete pipes, and

old car tires filled with mortar. The southern boundary of a reef

created on one of these sites (Waianae) on the western coast of the

Island of Oahu is at lat. 21 °25. I'N, long. 158° 1l.6'W (Kanayama

and Onizuka 1973) only 3 miles from the present OTEC benchmark

survey site at lat. 21 0

19.5'N, long. 158 0 12.5'W offshore of Kahe

Point. Sampling along a fish transect established before the reef

construction indicated the presence of 32 different species and a

standing crop density of 103 pounds of fish per acre. The reef was

constructed in two sections, one composed of car bodies and the

other of damaged concrete pipes. Thirty species of fishes (standing

crop estimated at 1,271 pounds/acre) were present at the car body

section. This was a tenfold increase over the pre-reef count. The

concrete pipe section showed a fivefold increase of 45 fish species

and a standing crop estimated at 496 poun.ds/acre.

Although attraction of fish to man-made structures is well

documented, questions still arise regarding the relationship between

artificial structures and fish production. Mallory (1965) believed

that a structure concentrated the fish which constantly migrated in

and out, thus serving as an orientation point. This was true for a

number of species (primarily the game fishes) associated with flotsam. Stroud (1965) felt that since the artificial habitat provides food

and shelter, reproduction will be enhanced resulting in an increase

in production and yield of fish. A third hypothesis discussed by

Carlisle et al. (1964), Turner et aI. (1969), and Dugas et aI. (1979),

combines both viewpoints; fish are concentrated by recruitment,

and, as the colonization progresses on the structures, a reproducing

resident fish community may evolve. Although this may hold true

for many of the reef fishes, this hypothesis falls short of accounting for overall fish attraction as evidenced primarily for such species

as the deeper water pelagic scombrids and billfishes.

The attraction of various marine organisms to light is a phenomenon that has been used in the harvesting of fish for many years.

Mackerel scad, Decapterus macarellus, and bigeye scad, Selar

crumenophthalmus (Yamaguchi 1953; Powell 1968), various species

of tuna (Yuen 1979), and squid (Ogura and Nasumi 1976), are

caught by the use of night lights. How much of an effect the lights

from an OTEC facility will have on the tuna is not presently known.

As indicated by Laevastu and Hayes (1981), every species has a

particular optimum light intensity in which its activity is at a maximum. It is probable that the intensity of the artificial light would

fall within the thresholds of some species.
Regarding avoidance traits of marine biota to structures and operations in the ocean, published information is virtually nonexistent.

Yuen (1981) indicated that the endangered and threatened species

would probably avoid the area due to human presence and to the

noise emitted from the plant. Among the few studies that address

avoidance was one on the negative phototactic behavior of fish.

Dragesund (1958) found that herring would sometimes display a

shock response That is, when the light was turned on, the fish would

make a sudden upward movement towards the light only to later

disperse or school and descend. Studies on other aspects of

avoidance, such as of the physical structures, are nonexistent in

published literature. Future studies should be directed in this area.

Impingement-·lmpingement at coastal power plants has been an

ecological problem (loss of a large number of organisms), an operational problem (reduction in cooling water flow), and a cost problem (removal and disposal of organisms). Impingement occurs when

organisms too large to pass through the intake screen, are pulled

against it, and are unable to escape due to the current velocity.

Schooling fishes are especially susceptible, and impingement mortalities may involve millions ofindividuals. In one incident, 2 million

menhaden at the Millstone Plant in Connecticut were impinged and

caused a shutdown of the plant by reducing the cooling water flow.

These mortalities are believed by some ecologists to be reaching

proportions which may cause population damage (Van Winkle

1977). As a result, data on impingement of fish have been collected

from many operating plants (Adams 1969: Marcy 1971; Jensen

1974; Uzie! 1980).

Variation in impingement on intake screens is related, among

other things. to season, swimming speeds, intake location, and

operating schedules of the power plant. Screen catches at most

coastal power plants studied in temperate waters fluctuate markedly with season, due to migrations into and out of intake areas and

to changes in water temperature that affect the fishes' ability to swim

successfully against intake currents. In tropical areas, where OfEC

plants will be located, impingement may be less variable because

there is generally less migrational movement of populations and

the water temperature is essentially the same the entire year.

The swimming speed of an organism determines whether or not

it will escape impingement or entrainment once in the vicinity of

an intake. Eggs and larvae of marine fish drift passively in the ocean

within the zooplankton community. Early larval stages utilize swimming only to capture prey, escape predation, or migrate vertically.

In general, sustained swimming speeds of fish larvae fall into a range

of 2-4 body lengths/second for larvae in advanced development or

for juveniles (Blaxter 1969; Bainbridge 1960). Table 4 lists representative species, including a few freshwater species, for individuals

up to 6 cm in length. For most fishes, relative speeds decrease as

size increases above that shown in Table 4, and absolute speed increases as size increases.

Table 4.-Sustained swimming speeds of some larval and juvenile fish species (adapted from Marcy et al. 1980).

Length Speed Temp Time Body lengths

Species (mm) (mm/s) (0C) maintained per second Author

European plaice 7.5 12 6.5-7.5 A few s Ryland (1963)

9.5 27 6.5-7.5 A few s

Whitefish 10-12 16 4 ? 1.6 Braum (1964)

29 16 2.4

Common roach 35-45 138 I min 3.1-3.9 Aslanova quoted by Radakov

(1964)

Common bream 45-55 126 I min 2.3-2.8

Carp 50-60 129 I min 2.1-2.6

Horse mackerel 30-40 136 I min 3.4-4.5

Mullet 35-45 128 I min 2.8-3.6

Mullet 45-55 156 I min 2.8-3.5

White bream 18-26 330 ? 12.7-18.3 Radakov (1964)

Atlantic herring 6.5-8 5.8 ?(14) 45 min 0.7-0.9 Bishai (1960)

Atlantic herring 12-14 10 9-10 60 min 0.7-0.8 Blaxter (1966)

Sole 4 6-9 15 Long periods 1.5-2.2 Rosenthal (1966)

intermittent

swimming

Bleak 0.26 g (wet wt) 29.8 20 Ivlev (1960)

Smallmouth bass 22 146-312 20-35 3 min 6.6-14.2 Larimore and Duever (1968)

Yellow perch 6.5 5.5 13 60 min 0.8 Houde (1969)

7.5 14.0 13 60 min 1.9

8.5 24.0 13 60 min 2.8

9.5 27.5 13 60 min 2.9

10.5 32.0 13 60 min 3.0

13.5 46.0 13 60 min 3.4

Walleye 7.5 5.0 13 60 min 0.7 Houde (1969)

8.5 13.0 13 60 min 1.5

9.5 29.0 13 60 min 3.0

10.5 32.0 13 60 min 3.0

11.5 37.5 13 60 min 3.3

13.5 42.0 13 60 min 3.1

14.5 46.0 13 60 min 3.2

Lake whitefish 15.2 35 7.5 I min 2.4 Hoagman (1974)

15.8 58 11.5 I min 3.7

19.7 71 11.5 1 min 3.6

21.3 76 14.5 I min 3.5

28.8 115 14.5 I min 4.0

17
Among the fastest burst swimmers are yellowfin tuna, which as

adults can swim 27 body lengthsls for 5 seconds (Walters and

Fierstine 1964). Although larvae do not have strong sustained swimming ability, they possess impressive darting or burst speeds relative

to their size. Blaxter (1969) suggests bursts of lO body lengthsis

which, for most larvae (up to 25 mm), would limit their speed to

less than the 0.25-0.30 mls suggested as typical of OfEC plant

warm-water intake velocity (see Seawater Systems section). Scombrid larvae have not been measured for burst swimming performance, but Pacific mackerel up to 3.6 cm in length swam up to

26 cmls, counting time spent in rest and feeding (Hunter 1980).

Swimming ability is a function of morphological shape, stage of

development, length, ambient temperature and light, and the duration required for the performance (Tsukamoto et al. 1975; Hartwell and Otto 1978; Rulifson 1977; Pavlov et al. 1968; Larimore

and Duever 1968; Hunter and Kimbrell 1980). Knowledge of these

factors and the types of species likely to be near the OfEC plant

site is necessary to predict the potential of larvae and juveniles to

escape intake currents.

Morphologically, the fastest species have a high aspect ratio of

the caudal fin (ratio of the square of the caudual fin depth to the

surface area) (Lighthill 1970). Species with high aspect ratios are

those with the carangiform (e.g., Carangidae, Clupeidae, Pomatomidae) and thunniform (e.g., Scombridae, Istophoridae, Xiphiidae, Stromateidae) swimming motion. Anguilliform swimmers

(e.g., Anguillidae, Pleuronectiformes), subcarangiform swimmers

(e.g., Gadiformes, Salmonidae), or ostraciiform swimmers (e.g.,

Ostraciidae, Tetraodontidae, Lophiiformes) have a low caudual fill

aspect ratio and are relatively slow.

The effects of temperature on swimming speeds are probably

unimportant in predicting susceptibility ofsmall fish to entrainment

in an OfEC plant. While Hettler (1979) found that a lOoC increase

in temperature caused the swimming speed for two carangiform

juveniles to increase by a factor of 1.6, the relatively consistent

temperature in the tropics is unlikely to cause large seasonal changes

in susceptibility to entrainment.

The design of the water intake structure will greatly affect current velocity. It has been shown that fish are better able to orient

to a horizontal flow than a vertical flow. Intake structures placed

or capped so that intake flows are in the horizontal plane enable

fish to orient to the flow and more effectively avoid the intake

(Langford 1983).

Because of the large volume of water required by OfEC plants

and the relatively high flow rate at the screens, impingement of

organisms on the warm-water intake screens will assuredly be a

visible effect and may, in some cases, be ecologically important.

Impingement rates will depend on intake location and velocity, time

of day, behavior characteristics of the populations of organisms

associated with the plant site and, to some extent, season of the

year, although this will be a relatively minor factor in tropical

waters. Another important factor is that the plant may serve as a

fish-attracting device and concentrate large numbers of organisms

where they are in danger of being impinged or entrained (Seki 1984).

Impinged organisms generally fall into the micronekton size

category (2-20 cm) and include fishes, macroplanktonic crustaceans,

cephalopods, and gelatinous organisms such as coelenterates, salps,

and ctenophores. Micronekton are an important intermediate step

in the food chain between the zooplankton and commercially important fishes. The significance of large-scale mortalities due to impingement at coastal power plants in temperate waters has not been

quantified from field data and there is presently no conclusive

evidence of actual population declines in any species due to imp18

ingement losses.

Attempts have been made to model the effects on populations

(see section on Potential Range of Ecological Effects) but there is,

in general, a lack of needed data on natural mortality rates. In

general, the data base for tropical-subtropical waters is even more

deficient than for temperate waters. Very few quantitative studies

have been made in tropical-subtropical waters to systematically collect samples of micronekton. Therefore, it is very difficult to

estimate the impingement rate. Sullivan and Sands (1980), using

data from water off Oahu, Hawaii, estimated a daily impingement

of 420 kg for the warm-water screen of a 400-MWe OfEC plant,

and concluded that this loss is probably insignificant when the

replacement ability ofthe micronekton population in the surrounding region is considered.

Primary Entrainment-Any organism small enough to pass

through the intake screens (approximately 1.3 em; Sands 1980) will

be entrained in the seawater flowing through the heat exchangers

(primary entrainment). During this period, organisms are subjected

to thermal and mechanical stresses as a result of changes in pressure

and temperature, shear and acceleration forces, abrasion, and collision with structures. In addition, organisms will be subjected to

biocides used to clean the surfaces of the heat exchangers, anticorrosion agents, and corrosion products. Effects on organisms will

be due to a combination of these factors.

The effects of primary entrainment at conventional power plants

have been extensively studied and a number of reviews have been

reported (e.g., Schubel and Marcy 1978). There is general agreement that while a great many species of organisms cannot survive

passage through the cooling water system, there is a wide range

of tolerance among species, and plant design and operating

characteristics are critical factors. Mechanical damage is probably

the major single factor contributing to primary entrainment mortality. The importance of thermal and chemical stress will vary

depending on thermal exposure, biocide treatments, and corrosion

rates.

Entrainment effects associated with OfEC will no doubt be one

of the most important factors to consider with respect to fisheries.

Because of the low thermal efficiency of OfEC plants the amount

of water needed is extremely large; generally between 6 and 10

m3 . S-I. MWe- ' for the total combined warm and cold water flow

(see Seawater Systems section), as compared to an average of 0.05

m3 .s- I . MWe-1 for condensing water for a nuclear plant. Because

of this large water requirement, the number of organisms subject

to entrainment will be large.

Temperature-Organisms entrained in conventional power plants

are subjected to rapid increases in temperature as they pass through

power plant condensers. The near instantaneous temperature changes

(~T) may range from less than 6°C to more than 19°C (Schubel

and Marcy 1978), and the exposure time to these elevated temperatures may range from several minutes to an hour (including time

in the discharge canal) depending on the plant design. Laboratory

research on the larvae of four species of temperate subtropical

marine fish (Atlantic menhaden, Brevoortia tyrannus; spot,

Leiostomus xanthurus; pinfish, Lagodon rhomboides; and flounder,

Paralichthys sp.) has shown that their survival following entrainment in a once-through cooling water system will depend on the

increase in condenser water temperature over ambient water

temperature and the length of exposure (Hoss et al. 1971,1974).

Studies designed to evaluate a hypothetical offshore conventional

power plant with a ~T of lO-12°C and an ambient temperature of
l5-l6°C indicate that spot, Leiostomus xanthurus, eggs may be more

affected by heat shock during their first day of life than at later

stages as embryos (Hettler and Coston-Clements 1978). Eggs of

black sea bass, Centropristis striatus, did not show this same effect, so it appears that stage of development at time of shock may

be important, but must be determined on an individual species basis.

Spot eggs that were slowly returned to ambient temperatures had

a much better survival than those subjected to a rapid return. The

larvae of spot (1-21 days old) showed no apparent relationship

between age and survival following thermal shock (Hettler and

Coston-Clements 1978).

Unlike conventional power plants where organisms experience

only an increase in temperature as they pass through the condensers,

organisms entrained in arEC plants will experience both increases

and decreases in temperature. Organisms entrained in the warm

water will pass through the evaporator, where the temperature will

be decreased by 2-3°C, while organisms entrained in the cold water

will pass through the condenser, where temperature will be increased

2-3°C (U.S. Dept. of Energy 1978). Additionally, organisms will

be subject to larger temperature changes upon mixing of the two

effluents (if practiced) and/or discharge to the environment. For

instance, a mixed discharge would effect a temperature drop of about

lOoC for the warm-water organisms and a lOoC increase for any

cold-water organisms. Entrained organisms will also experience a

redistribution in the water column when discharged with effluent

waters. This redistribution could also expose organisms to a different temperature regime.

No literature was found on cold shock in fish for the temperature

range and aT expected for the arEC discharge. Cold shock literature is limited to describing effects of rapidly reduced temperatures

during the cooler months to new temperatures at or near the low

lethal temperatures, which produce death by the formation of ice

in the tissues or induce primary (respiratory) or secondary (nerve

blockage) chill comas. All reported fish kills or experimental cold

shocks involved species in temperate climates. Chittenden (1972)

found that young Alosa sapidissima exposed to abrupt temperature

decreases from 24°C to 12°C were not affected, but below 12°C

even gradual decreases caused sublethal behavioral problems. Terpin

et al. (1977) showed that Anchoa mitchilli died at lOoC when acclimated to 22°C and subjected to a 12°C decrease in 29 hours.

However, no mortality occurred at decreases of 4°C and rc.

Becker et al. (1977), although not working with marine species,

showed that differences in response to abrupt temperature changes

were found between species, inferring that a general prediction of

the effect of cold shock cannot be made to a number of species.

Further, knowledge of thermal requirements of the adults of a

species may not be sufficient to predict those of egg and larval forms.

• In Brett's (1956) review, he states that" ...the thermal requirements

in the very early stages are more exacting than in the adult." For

eggs and larvae of stenothermal species, reduced temperatures,

although not actually "cold," will retard development and may

cause abnormalities. Harada et al. (1978) found that no yellowfin

tuna larvae developed normally in temperatures below 20°C.

Pressure-Rapid change in hydrostatic pressure is one ofthe stresses

to which organisms are subjected during entrainment. These

pressure changes may be either negative (vacuums within the pump)

or positive, and the magnitude of the change is dependent on design

of the plant.

It has been suggested that rapid changes in pressure that occur

in power plant cooling water pumps may be potentially damaging

to entrained fish (Marcy et al. 1980). Although much research has

19

been conducted on the effect of pressure change on fish, very little

of it has any direct relevance to the relatively small pressure changes

(1-5 atmospheres; 1 atmosphere change equivalent to a lO-m depth

change) to which fish are subjected in power plant cooling systems.

Much less entrainment of organisms is expected in the cold water

intake of an arEC plant, but any entrained organisms will be exposed to a pressure change of 70-100 atmospheres depending on

depth of the intake pipe. Entrained fish larvae possessing a swim

bladder would be very vulnerable to rapid changes in pressure of

this magnitude (Hoss and Blaxter 1979; Blaxter and Hoss 1979).

Chemical Additions-Due to the low thermodynamic efficiencies

available through the arEC system (Myers and Ditmars 1985), the

heat transfer rate at the heat exchanger surfaces will be critical.

The inhibition of biofouling due to microorganisms must thus be

an integral aspect of arEC operations. As in coastal power plants,

current thought here supports the need for intermittent chlorination to keep biofouling to a sufficiently low level. As noted by Hoss

and Peters (1983), there is concern over the use of chlorine because

of its toxicity. It has been shown that added chlorine can seriously

affect the growth and survival of entrained organisms (Schubel and

Marcy 1978), although there are species-to-species variations and

certain synergistic effects with temperature and trace metals (Hoss

et al. 1975, 1977).

The biocide concern is amplified in an arEC operation because

of the large volumes of water involved, i.e., the achievement of

a certain concentration for biocidal effectiveness will require the

application of large quantities of biocide. Although the required

dose of chlorine will be somewhat site-specific, recent studies indicate that concentrations of total residual chlorine of about 0.07

mg/L may achieve the desired results (Larsen-Basse and Daniel

1983). This is well below the new source performance standards

(NSPS) requirement for chlorine discharges from steam electric

generating stations, the standards which would most likely apply

to arEC discharges (Myers and Ditmars 1985). For plants with

a steam electric generation capacity of 25-MWe or more, the NSPS

specify the total residual chlorine (TRC) in the cooling water

discharge from any single generating unit shall not exceed 0.20

mg/L, and that the duration of chlorine discharge shall not exceed

2 hours/day.

Although chlorine bioassay studies by Venkataramiah et al.

(l98Ib) suggest that levels less than or equal to 0.5 mg/L may be

generally safe, there are still concerns regarding cumulative effects

of continuous discharges that must be further addressed (Venkataramiah et al. 1981a; U.S. Department of Energy 1981). There

is also a potential for synergistic reactions of chlorine with trace

metals and ammonia leaks. Recent studies (Venkataramiah et al .

1981a,b) on marine fishes and zooplankton have shown that the

toxicity of ammonia and chlorine varies with habitat of the species

and with duration of exposure. Within the same species (gray mullet,

MugU cephalus), smaller fish were more sensitive than larger fish.

This work confirms past research on other species and provides

further evidence that exposure to chlorine in marine waters, while

not well understood, may present a serious problem and should

receive additional study.

Because of the large surface areas required for arEC heat exchangers [about 9.3 m2/kWe for closed cycle (NOAA 198Ia»),

heat exchangers are considered one of the principal sources oftrace

metal release. Myers and Ditmars (1985) have used the results of

DOE-supported corrosion tests (Tipton 1980) to make worst-case

estimates of trace metal concentrations in OTEC discharges (Table

5). In general, the concentrations of trace metals in an arEC
Table S.-Estimates of OTEC effiuenl. trace metals concentrations due to heat exchanger corrosion and erosion.

Trace constituent concentrations

in arEC discharge effluentd

(ng/g)

Cleaning

environment Material' b

Material loss/unit area

3-mo exposure"

(mg/cm2

)

------------

Alclad 3003

5052 AI

CA 706 Cu-Ni

AI-6X Steel

Ti

Brush + chlorine

Brush + chlorine

Brush

Brush

Brush

34.3

10.1

87.5

0.02

<0.01

AI, 66; Zn, I

AI, 19; Mg, 0.49; Cr, 0.05

Cu, 151; Ni, 17; Fe, 2.4

Fe, 0.02; Ni, 0.01; Cr, 0.01;

Mo,O.OO2

Ti, <0.02

'Material composition: Alclad 3003 is 99% AI, 1% Zn; 5052 AI is 97.5% AI, 2.5% Mg, 0.25%

Cr; CA 706 Cu-Ni is 88.6% Cu, 10.0% Ni, 1.4% Fe; AI-6X Steel is 50% Fe, 24% Ni, 20% Cr,

6% Mo; and titanium is commercially pure.

bCleaning environment is either M.A.N.<Il (American M.A.N. Corp., N.Y.), brushing with 3 roundtrips/day or brushing plus continuous chlorination at 0.1 mg/L concentrations.

cFrom Tipton (1980); largest alloy losses from 3-mo exposure reported here.

dCalculated assuming alloy loss (from Tipton 1980), heat exchanger surface areas of 9.3 m2/kWe

(NOAA 198Ia), and OTEC seawater flows of 6 m3

s-IMWe- l

•

discharge are estimated to be on the order of 100 ng/g (100 J.lg/L)

or smaller. With the possible exception of copper, these estimates

suggest that the release of trace metals from heat exchanger surfaces would not pose significant concern. Worst-case estimates of

the release of copper from a Cu-Ni alloy (i.e., CA 706) indicate

concentrations above 100 ng/g, in the acute toxicity range of copper in seawater based on a number of observations of copper toxicity (Klapow and Lewis 1979).

With the exception of catastrophic accidents, any leaks of working fluids will be diluted by the large volumetric flow of seawater

through the plant, to the point that problems should not arise. For

instance, with the Ocean Thermal Corporation OTEC design for

Kahe Point, it is predicted that normal leaking of ammonia could

result in an increase of 2.4 J.lg/L above the ambient level of 10.7

J.lg/L in the mixed discharge (Ocean Thermal Corporation 1983).

Upon reaction with the seawater, only about 5% of this increase

would remain as un-ionized ammonia, the principal toxic form. The

concentration of un-ionized ammonia in the discharge would then

be about 0.66 J.lg/L, well below a reported minimum-risk level of

10 J.lg/L (U.S. Environmental Protection Agency 1973) and only

0.12 J.lg/L greater than the ambient concentration of un-ionized

ammonia.

Secondary Entrainment-Secondary entrainment refers to the capture of organisms in discharge waters (effluent plume) as a result

of turbulent mixing or behavioral responses. The rate at which

organisms are entrained in this manner will depend on the discharge

flow rate, the near-field dilution, and the average population density

along the near-field trajectory of the plume (Paddock and Ditmars

1983).

Most of the same stresses encountered in primary entrainment

will also be encountered in secondary entrainment, the difference

being that the magnitude of the stress will, in general, be much

less. Determining the effects on fisheries organisms of secondary

entrainment will be even more difficult than for primary entrainment, and results from previous power plant studies are limited in

their usefulness.

Ehrlich (1977) reported that the hatching success of California

grunion (Leuresthes tenuis) was significantly reduced by a nonthermal but unknown component of the effluent from a California

power plant. Large variation in hatching success suggested that the

unknown hatching inhibitor in the water fluctuated during plant

operation. It is possible that trace metals in the effluent caused the

variation, since previous work by Rosenthal and Alderdice (1976)

showed reduced hatching in herring eggs exposed to trace metals.

The effects ofsmall changes in water temperature have been shown

by Peters and Angelovic (1973) to be an important factor in controlling fish feeding and growth. Small changes in temperature

(either increases or decreases) in the discharge plume may,

therefore, have an effect on larval fish growth, but this will be very

dependent on the depth at which the discharge occurs and the total

area that is impacted.

Ocean Water Mixing-An OTEC plant's displacement of large

quantities of deep ocean water can cause an upwelling effect that

may disturb the natural temperature structure, salinity gradient and

levels of dissolved oxygen, nutrients, and trace metals in the surface waters. Artificial upwelling is not a characteristic of conventional power plants; therefore, there is little direct analogy to the

OTEC situation. However, some studies that have been made on

nutrient distribution and changes in trace metal levels may be of

some use in predicting upwelling effects.

In general, it is thought that the pumping of large amounts of

deep nutrient-rich ocean water to the surface layer may have positive

effects ifthe same type of biostimulation occurs near OTEC plants

as occurs near areas of natural upwelling. However, whether upwelling will be harmful or beneficial to local ecosystems will depend

on many factors, as discussed in the section Impacts on Fishery

Food Chains.

The concentration of trace metals in surface water may increase·

due to upwelling of metal-rich deep water or the formation of corrosion products. The impact of these increases will depend in large

part on the amount and chemical form ofthe metals involved. The

free ion activity, not the total metal concentration, determines

biological availability and effect. Increases in the bioavailability

of micronutrients, e.g., iron, manganese, and copper, could increase

production of the algae community. Similarly, toxicity could result

from high availability of metals, such as copper, zinc, or cadmium,

which could be detrimental to biological production. If the trace

metal complement of the effluent water is harmful, the potential

biostimulatory effect of upwelled nutrients may either not occur

or be unnoticeable. The trace metal complement will change with

time through a variety of processes, and a bloom may be merely

delayed. With current information it is not possible to predict what

20
effect the altered trace metal regime will have on the utilization

of upwelled macronutrients, nor is it clear whether the effects will

differ with location.

The Potential Range of Ecological Effects

Resulting From OTEC Operations

Marine ecosystem impacts which may result from OfEC operations can be described only in very general terms. This section attempts to estimate the upper and lower bounds of these effects for

a 40-MWe shorebased plant with the effluent plume coming to

equilibrium near the bottom of the mixed layer (see Effluent

Discharge section). Impacts which we consider include impingement, primary and secondary entrainment, and nutrient enrichment.

This or any estimate of impacts is limited by the environmental data

available and by an incomplete understanding of the amounts and

types of ecological compensation which may occur. Also, evaluating

the importance of projected effects will be particularly difficult and

dependent upon resource and system boundaries.

Impingement-Impingement rates will depend on volume and speed

of the intake waters and the abundance of animals larger than the

mesh size of the intake screen and their ability to avoid the intake.

An animal's ability to avoid the intake depends on (I) rheotactic

behavior, (2) visual perception in low light environments, and (3)

swimming speed. Swimming speed depends on (a) species limitations (form or hydrodynamics), (b) temperature, and (c) physical

condition. Physical condition depends on (i) nutritional state, and

(ii) presence of disease or injury. While neither abundance or

avoidance capability is well documented, reasonable estimates are

possible. Fish, in general, can swim about 3-6 body lengths per

second and will avoid intakes which are visible and in a horizontal

flow field (Hocutt and Edinger 1980). With estimated intake

velocities of 0.25 to 0.30 m/s (see Seawater Systems section), it

is unlikely that fish over 10 cm in length will be impinged, and

many smaller ones could probably avoid the screens. The minimum

length of fish impinged will be several times the screen mesh size.

Thus, most impinged animals will be in a size range probably narrower than from 3 to 10 cm.

While there are no measurements of the absolute abundance of

animals susceptible to impingement by an OfEC plant, trawl surveys

conducted near Hawaii (Maynard et al. 1975) and Puerto Rico

(Vargo et al. 1981) may be used to provide estimates of impingement rate. While catch efficiencies of the trawls are not known,

we assume the fishes' susceptibility to capture by net is about the

same as by impingement. Although the nets were pulled several

times faster than plant intake velocities, most animals caught were

of the same small size «10 cm) which is most susceptible to entrainment or impingement. By adjusting the reported trawl catches

for items identified as undersized or soft-bodied (entrainable rather

than impingeable) and oversized (those which can probably avoid

an intake), we can estimate expected impingement.

In both areas surveyed, fishes were the most abundant group,

with crustaceans and cephalapods also present. In Hawaii surfacewaters, a combined catch of all three groups was 0.2 mg/m3 during the day and 5.4 mg/m3 at night. Micronekton sampling near

Puerto Rico revealed an average biomass of 2.7 mg/m3• Adjusting

the Caribbean catch for the 60% "residue" of entrainable size

organisms, which those samples contained, results in estimates of

1.1 and 2.5 mg/m3 for day and night, respectively, or an average

1.8 mg/m3 of animals large enough to get caught on surface intake screens. In these samples, there appeared to be few animals

21

which were large enough to escape intake velocities. In Hawaii the

net was pulled faster than in Puerto Rico (1.7 vs 1.0 rnIs) and larger

animals were collected. Adjusting the nocturnal catch in Hawaii

for those fish weighing more than 10 g (those most likely to be

able to avoid impingement) results in estimates of the biomass of

animals which will be impinged at night (4.6 mg/m3). The average

impingeable biomass over a 24-hour period is 2.4 mg/m3. Similar

calculations with data from deeper water result in an estimate of

impingeable biomass at the cold water intake of 3.4 mg/m3 in the

Caribbean and 4.2 mg/m3 in Hawaii.

Multiplying the average concentrations of impingeable biomass

from the two studies (2.1 mg/m3 at the surface and 3.8 mg/m3 in

deep water) times estimated flow rates results in an estimate of impingement rates. A 4O-MWe plant with surface and deep intake rates

of 120-200 m3/s (i.e., 3-5 m3 ·s-I.MWe- 1 for each intake; see

Seawater Systems section) would probably impinge 20-35 kg live

weight daily from the surface water and another 40-65 kg at the

cold water intake, roughly in accord (being an order of magnitude

less) with the impingement estimated by Sullivan and Sands (1980)

for a 4oo-MWe OfEC plant in similar waters (see Impingement

section). These estimates of impingeable biomass are based on the

assumption that larger organisms can detect and avoid the intake

screens. We are unaware of any measures of the concentration of

larger organisms which could be used to estimate impingement rates

on a screen which they could not detect; thus, our estimates can

serve only as a lower bound. Higher rates are possible, but we have

no means of estimating them.

Primary Entrainment of Plankton-Plankton entrainment rates

are a function of plankton density and the rate of water intake. While

the intake rate can be predicted and information on average density

of various planktonic groups is available, their vertical stratification is, in many cases, not clearly documented. Those motile

organisms which aggregate at particular depths may be entrained

at rates vastly different than predicted from their average density

in the mixed layer.

Phytoplankton biomass is approximately the same in Hawaii and

the Caribbean. In the mixed layer at the Hawaiian Kahe Point OfEC

site the median value was 0.10 mg chlorophyll-a1m3 (Uchida

1983). The average of eight published values reported from the

Caribbean surface waters (Hoss et al. 1983) is 0.13 mg/m3• Judging from chlorophyll-a concentration at discrete depths, there is

no consistent pattern in the vertical distribution of phytoplankton

in the upper 50 m near Hawaii and Puerto Rico (Sands 1980). Thus,

average concentrations can be used to estimate phytoplankton entrainment. However, it should be recognized that while mean abundances in Hawaii and the Caribbean are similar, individual

measurements showed considerable variation, so the rate of entrainment of phytoplankton may also vary widely over time. To be conservative in estimating the range, extreme lower and upper bounds

are assumed to be 0.05 mg/m3 and 0.25 mg/m3•

'Daily phytoplankton entrainment by a 40-MWe plant, again with

surface and deep-water intake rates each in the range of 120-200

m3/s, will probably be between 0.5 kg chlorophyll-a (0.05 mg

chlorophyll-a m3 and 120 m3/s) and 4.3 kg (0.25 mg chloropyll-a

m3 and 200 m3

/s). Assuming a factor of 100 for relating

chlorophyll-a to organic carbon (Holm-Hansen 1969), we estimate

that the organic carbon of phytoplankton entrained will be in the

range 50 to 430 kg C/d. If the chJorophyll-a concentration is 0.1

mg/m3, a figure frequently used to describe subtropical oceanic

water, then phytoplankton entrainment will be in the range 100 to

170 kg C/d.
The zooplankton biomass which is subject to entrainment by an

OfEC plant consists oftwo major fractions: macroplankton caught

in conventional nets (200 lim or larger mesh) and microplankton

small enough to pass through such nets. The larger animals in surface waters have been studied enough that their density is fairly

well known. In Hawaiian water the mean dry weight biomass in

the upper 200 m was 4.9 mg/m3 and 3.3 mg/m3 in two different

sets of cruises (Noda et al. 1981b, from Uchida 1983). The average

of four published studies from the Caribbean is 2.6 mg/m3 (standard error = 0.24). Converting these dry weights to nearsurface

zooplankton carbon (Wiebe et al. 1975) yields estimates of 1.3 mg

C/m3 in Hawaii and 0.8 mg C/m3 in the Caribbean. Macrozooplankton abundance at cold-water intake depths has not been studied

as thoroughly as at the surface. The concentration clearly decreases

with depth and will probably be less than 0.24 mg C/m3 (Table

6). The 0.24 mg C/m3 average estimated from four studies (Table

6) is probably inflated because many of the samples were taken

during the day when plankton abundance is greater than the 24-hour

average and because we chose the highest of the conversion factors reported for estimating dry weight.

The smaller zooplankton, i.e., microzooplankton, have received

little study so estimates oftheir density are not very precise. While

microzooplankton density appears to vary with depth, we averaged

measurements from the top 100m of the photic zone as an indicator

of entrainable biomass. A study in Hawaii (Gundersen et al. 1976)

showed an average biomass of 0.7 mg C/m3• Holm-Hansen (1969)

reported values off southern California of 0.9 mg C/m3 . Using

0.08 as a factor to convert displacement volume to carbon (HolmHansen 1969) and the volumes given by Beers and Stewart (1969,

1971), we calculate the microzooplankton biomass averaged 2.3

mg C/m3 in the eastern tropical Pacific and 1.2 mg C/m3 in the

California current. From these estimates it appears that microzooplankton abundance is approximately the same as the average macrozooplankton density in Hawaii and the Caribbean (about 1 mg

C/m3). This similarity in biomass of these vastly different sized

animals has also been noted by Sheldon et al. (1977). With little

information indicating the factors responsible for differences in

density of microplankton, a more precise estimate of abundance

in surface water is not possible.

With micro- and macrozooplankton densities in the mixed layer

each averaging about I mg C/m3, the warm water intake of a

40-MWe plant will entrain between 10 and 17 kg C/d in each of

the zooplankton size categories. For the lack of evidence that

microplankton are abundant at such depths, we assumed that entrainment at the cold water pipe will be limited to macroplankton.

If deeper water macroplankton are present at a density of 0.2 mg

C/m3 (Table 6), then entrainment will probably range from 2 to

4 kg C/d.

Secondary Entrainment-Turbulent mixing will result in a rapid

dilution of the effluent water through the entrainment of ambient

water (see Effluent Discharge section). As a result, there is a potential for impact on the plankton present in the ambient water as they

become entrained into the discharge plume. While it is difficult to

predict the scale of impact from this secondary entrainment, the

potential effect is considerable. This impact will depend on the abundance of organisms in the dilution water, their sensitivity to the

altered water quality, and the amount of water involved.

Secondary entrainment will occur over a narrow depth range.

Because of the desire to avoid recirculation of effluent back into

the warm-water intake, the discharge location may be below 30

m. Based on the density of the effluent, relative to the density and

22

Table 6.-Estimated macrozooplankton carbon density at cold water intake

depth. ------_.

Depth of

samples Calculated

Area Source (m) Data provided (mg C/m3

)

Hawaii Uchida

1983 200·1000 0.80 mg dry wt/m3 0.26

Pacific (19°C) Vinogradov 700 0.004 m1/m3 0.17

and Sargasso 1968

Sea

Puerto Rico Vargo et al. 600-1000 0.0035 ml/m3 0.15

1981

Sargasso Sea Deevey and 500·1000 0.0108 m1/m3 0.45

Brooks 1971

1000-1500 0.0046 m1/m3 0.19

Calculations used the following conversions: wet weight = 72 % of displacement

volume; dry weight = 13 % of displacement volume; carbon weight = 32% of

dry weight (Wiebe et al. 1975)

density gradient of ambient waters near the discharge, the plume

will come to equilibrium near the bottom of the mixed layer. Thus,

it appears that the dilution water and therefore secondary entrainment of organisms will generally be from depths between 30 and

80 m. However, some recent modeling investigations (Wang 1984)

indicate that there may also be an induced upwelling from beneath

the plume which would entrain some water from below the mixed

layer (see Regional Influence section).

Several characteristics of the effluent (e.g., reduced water

temperatures, the presence of a biocide, and a supersaturation of

nitrogen gas) may adversely affect secondarily entrained organisms.

Assuming a mixed discharge, we estimate that the temperature of

the effluent at the point of discharge could be as low as 15°C. While

many ofthe organisms which could be secondarily entrained engage

in vertical migrations which expose them to a wide range of

temperatures, others, including some of the ichthyoplankton, are

not accustomed to such low temperatures. Even thermally tolerant,

temperate organisms may be immobilized or killed by sudden exposure to cold temperature (Hoss et al. 1974; Bradley 1978; Stauffer 1980). The probability of mortality is greatest when the animals

are living near their lower lethal limit. While most of the important tropical organisms have not been studied for thermal effects,

it seems likely that many of those found in surface waters are

stenothermal (e.g., tuna larvae) and may be impacted by temperature

changes during secondary entrainment.

While biocides will probably be introduced only intermittently

and at low concentrations, it is reasonable to assume that if the

biocide is concentrated enough to kill fouling organisms it may also

affect the more sensitive animals which are secondarily entrained.

Prediction of biocide impacts from current information is difficult

because most research has involved temperate organisms. Conducting additional research on biocide effects will be difficult because

likely effluent concentrations are near the limit of detectability.

Whatever biocide effects occur will be greatest in the zone of initial dilution where their concentration is greatest and thermal impacts are largest. Furthermore, previous research has shown that

thermal and chlorine effects are synergistic (Hoss et al. 1977). There

is also a possibility that temperature or chlorine effects may interact

with effects from gas supersaturation. When saturated cold water

is brought to the surface and warmed, it will be supersaturated with

nitrogen, a condition which has caused fish mortality at other types

of power plants.
With all the uncertainty surrounding the effects of water quality

on secondarily entrained organisms, any prediction of effects is

largely subjective. Until additional information is collected, it is

assumed that cold shock effects will be insignificant for short-term

temperature drops of less than 2°C, even in combinations with

biocide concentrations and nitrogen supersaturation 20% that at the

point of discharge. Ifsurface and deep water intake rates are equal,

the total discharge rate will be twice the surface intake rate. Assuming the temperature of the mixed layer to be constant, the amount

of dilution water required to reduce the temperature difference to

2°C would be 8 times the surface intake rate (a 5:1 dilution being

needed to decrease the difference between effluent temperature and

ambient temperature to 2°C). With the further assumption that the

concentration of biota in the depth interval of 30 to 80 m is the

same as used in estimating primary entrainment mortality, an upper limit on secondary entrainment mortality may then be about

8 times that lost to surface primary entrainment. If cold shock rather

than exposure to biocides, trace metals, or pressure changes is the

major factor involved in the harmful effect of secondary entrainment, then many species may suffer only slightly, the most vulnerable being non-migratory animals. This, unfortunately, includes

many fish larvae.

Impacts on Fishery Food Chains-Increased fish production can

occur through either more primary production or shorter food

chains, either of which could result from upwelling of nutrient-rich

deep water. Primary production changes will in large part be due

to the reaction of algae to nutrient and trace metal characteristics

of the effluent plume. Ifthese characteristics stimulate algal growth,

fast growing diatoms will in all likelihood account for most of the

production (Sunda and Huntsman 1983). Ifthese diatoms are large

or chain forming species they can probably be utilized directly by

macrozooplankton. This could result in a shorter food chain than

would occur ifsmall algae were eaten by microzooplankton which

were then eaten by macrozooplankton. Removal of one trophic step

could increase fish production 5 to 10 times in the receiving waters.

In general, complex food webs, which occur in potential OfEC

areas, are resilient so that most changes have little impact on

ecosystem function. Minor changes in the food web, however, may

drastically alter our acceptance of the fish produced. For example,

blooms of the dinoflagellates which cause red tide or ciguatera can

make the fish inedible. Unfortunately, the factors responsible for

blooms of these algae are not well enough understood to allow

precise estimates ofOfEC influence on them. Based on the theory

that most red tide outbreaks are associated with terrestrial runoff,

they would not be expected as a consequence of OfEC operations.

It is possible that minimizing disturbances of the benthic substrate

(Bagnis 1981) during construction or operation of an OfEC plant

will reduce the likelihood of ciguatera.

The indirect predatory effect of a 40-MWe OfEC plant on carbon or energy flow through the fishery food web is predicted to

be minimal. Based on estimates of primary and secondary entrainment and impingement of various organisms by an OfEC plant

(Table 7), the number of trophic transfers between the various

trophic levels and fishery harvest (Ryther 1969), and an assumed

trophic transfer efficiency of 15 %, calculations were made of

equivalent harvestable stock which would be lost due to OfEC

operation. If all the entrained or impinged biomass were removed

from the system, then 1.8 to 3.1 fewer kg of carbon would be

available as fish harvest each day. Based on a carbon-to-live-weight

ratio of 1: 10, about 18 to 31 kg of fishery harvest would be lost

daily. This probably overestimates actual loss because it is likely

that many of the organisms killed will be eaten and thus not be lost

from the food web.

Our projection that food chain effects will not significantly impact the fishery does not address direct effects on the harvested

species. Many of the fishes are currently being harvested at levels

equal to or greater than the Maximum Sustainable Yield (MSY).

Ifsuch assessment of harvest levels is accurate, then those stocks

may not be able to compensate for the individuals lost through entrainment or impingement, and yield will be reduced. Unfortunately,

we do not know the fine-scale temporal and spatial distribution of

the early life stages of the major species, and thus are unable to

predict the number which may be impacted by OTEC operation.

In addition, our knowledge of the survival of these early stages is

too incomplete to predict the amount of impact on the resource.

Potential Impact on Fisheries

Defining in detail what constitutes significant adverse impact on

fisheries is very subjective. Effects which reduce commercial and

recreational fisheries harvest would likely be considered adverse.

On the other hand, if the plant were to serve as a fish aggregating

phenomenon, harvest efficiency may be increased and the overall

effect considered beneficial. However, this potential beneficial effect would have to be weighed against the overall negative effect

that aggregation (see Attraction/Avoidance section) may have on

entrainment and impingement.

In predicting impacts of conventional power plant operations on

fish population levels, scientists have relied on life cycle models

which focus on those components of the life cycle which are susceptible to power plant effects at the appropriate stages. Simple models

take a gross view ofthe life cycle, examine the environment in which

the species exist, and incorporate details of the plant operations and

effects. More complex models account for increased temporal

resolution, more detailed environmental variation, and knowledge

of behavioral responses to changes in the environment.

Table 7.-Estimated loss of living carbon and equivalent harvestable stock due to entrainment

and impingement during operation of a 4O-MWe OTEC plant (kg C/d). (Based on Peters 1983).

Phytoplankton Microzooplankton Macrozooplankton Micronekton

Entrainment

Primary

Secondary

Impingement

Total

Trophic transfers

Transfer efficiency

Equivalent harvestable stock·

0.07 - 0.12 0.05-0.08

23

0.15

0.80-1.4 0.90-1.5
With OfEC, adverse impacts cannot be examined with any degree

of confidence because what information is available on fish eggs

and larvae at potential sites is not sufficiently precise. Furthermore,

effects from operations of conventional power plants can hardly

be extrapolated to that of an OfEC plant because of the unprecedented volume of water the latter is expected to pump and

the redistribution of water properties that will occur. However, in

the absence of data which can be used as input into a life cycle

model, a crude evaluation of OfEC-related impacts on fisheries

has been made by Matsumoto (1984) for the purpose of this study.

Based on a review of the combined effects of impingement, direct

entrainment, and biocide usage to fish, Matsumoto (1984) concluded

that an assumption of total mortality of all fish eggs, larvae and

juveniles, directly entrained is not unreasonable. Because the eggs

and larvae of most fishes caught commercially off Kahe Point are

buoyant and tend to reside near or at the surface, the degree ofsecondary entrainment of fish eggs and larvae will be very dependent

on the discharge depth of the effluent. Little is known regarding

the effects ofsecondary entrainment; however, Matsumoto (1984)

believes the effects would be minimal for deep (e.g., 100 m)

discharges. More information is needed, however, on the microdistribution of fish eggs and larvae to judge whether such a conclusion would be justified for shallow discharges where the degree

of secondary entrainment may be 10 to 20 times (worst case) that

of direct entrainment on the warm water side. If 100% mortality

is assumed for both direct and secondary entrainment, one must

then ask what effect this will have on fisheries.

Off Kahe Point, the principal fisheries that would be affected by

OfEC operations include six pelagic and two demersal fish groups

representing 98 % by weight of the area's total annual production.

The pelagic forms include tunas (mainly skipjack and yellowfin

tuna), billfishes (Pacific blue and striped marlin), mahimahi, wahoo,

bonefish, and jacks (principally scads), where the demersal forms

include goatfishes (six species) and snappers (eight species).

Based on density values of tuna and billfish larvae at depths near

the warm water intake and discharge points, and warm and cold

water intake rates of 160 m3/s (i.e., 4 m3 ·s-I.MWe- I

), Matsumoto (1984) has estimated the extent of damage from the planned

Ocean Thermal Corporation plant at Kahe Point. Assuming total

mortality during entrainment, it was estimated 13.7 million skipjack and 5.5 million yellowfin larvae will be killed each spawning

season. To be more realistic, these mortality figures must be adjusted for natural mortality which is estimated at 93 % for skipjack

and 91 % for yellowfin. This would result in estimates of OfECinduced mortality of 1.0 million and 0.5 million, respectively. Any

effects of secondary entrainment would add to these figures;

however, Matsumoto suspects that the effects ofsecondary entrainment would be minimal.

The OfEC plant is also expected to function as a fish aggregating

device and attract fish from adjacent areas. Any increase of large

aggregations of fishes, such as tunas, mahimahi, mackerels, and

carangids, will eventually result in concentrated spawnings around

the plant, subjecting more than the usual amounts of eggs and larvae to entrainment effects.

The impact on fisheries will be largely through the recruitment

process. Through recruitment, the impact on pelagic species, particularly tunas, is not expected to be noticeable because most of

them are migrants from the eastern Pacific fishery, the northwestern

Pacific, and from equatorial waters. The effects of recruitment on

bottom and reef-associated fishes would most likely be felt in areas

further downstream from the plant site. If the prevailing currents

carry the eggs and larvae along the coast and out into open ocean,

14

the full impact of the damages caused by the plant may not be apparent at the plant site.

Direct effects could occur, however, in the demersal fishery. For

the Ocean Thermal Corporation OfEC design for Kahe Point, Oahu

(see Application section), warm effluent from the Hawaiian Electric conventional powerplant at Kahe Point is used as a supplementary heat source, and sand particles which are contained in this effluent (McCain 1977; Coles 1980) will eventually be discharged

over the escarpment and build up over a period of time, blanketing

the rocky bottom near the discharge point. The effect would be to

force fishes such as snappers to relocate to other areas. The net

effect to the fishery should be negligible, however, since demersal

species comprise only a small portion (1. 3%) of the total fish production off Kahe Point.

Turning to Puerto Rico, we find that the principal fisheries off

Punta Tuna include four demersal and one pelagic fish groups

representing 72 % ofthe fish taken along the eastern coastline. The

demersal group includes groupers (14 species), grunts (II species),

snappers (14 species), and porgies (3 species); the pelagic group

is comprised of mackerels (2 species). Other pelagic fishes, such

as tunas, marlins, dolphins, and jacks, comprise 1.8% of the total

fish production and are caught in small numbers.

The potential effects of OfEC plant operations on pelagic fishes

off Punta Tuna are also believed by Matsumoto (1984) to be insignificant. The effects there on demersal and reef fishes, however,

cannot be estimated in the absence of appropriate data and biological

information.

MEASURES TO REDUCE

POTENTIAL EFFECTS

TO FISHERIES _

From the previous chapter and background reports, one can conclude that there will remain some level of uncertainty regarding

the potential risk to fisheries due to construction and operation of

an OfEC plant until a full-scale OfEC operation can be monitored

for some period of time. However, certain aspects of an OfEC

operation warrant enough concern to examine measures that would

minimize the risk to fisheries of early plant operations.

First, from the viewpoint of general environmental risk, proper

siting is the single most effective means to minimize the potential

for environmental damage. The avoidance of areas of high biological

productivity and others of special biological importance (e.g.,

critical habitats, spawning grounds, coral reefs) is desirable.

However, the flexibility in choice of location may be limited in many

of the islands that have a suitable thermal resource. For instance,

as noted by Uchida (1983), there are a number ofsites in Hawaiian

waters that satisfy criteria for both nearshore floating and shorebased OfEC power plants. However, on the island of Oahu, only

the area along the Waianae coast from Barbers Point to Kaena Point

was concluded to meet certain criteria for OfEC siting (Shupe

1982). Along or offshore of this part of the Oahu coast are major

coral formations and important commercial and recreational

fisheries.

Once the location has been tentatively chosen, preliminary

oceanographic information will have to be collected to identify initial engineering flexibility. This will include information on the

thermal resource. waves and tides, currents, and extreme oceanographic events.

The power produced, and thus the cost-effectiveness of a plant,

is highly dependent upon the thermal resource (aT). For an island

plant, the site selected will therefore have to offer a suitable thermal
resource within a reasonable distance of shore. One of the major

trade-offs for the conceptual design by Ocean Thermal Corporation for Kahe Point, Oahu, Hawaii (Ocean Thermal Corporation

1983), was the distance offshore for placement of their "artificial

island" system. The artificial island would require greater structural and construction costs in deeper waters; however, greater

distances offshore also reduce the cost of the cold water pipe (i.e.,

less length) required to achieve a certain aT. Greater distances offshore also reduce the cost of effluent pipes. The study conducted

by OTC indicated that a plant in about 15 m of water was optimal

for their design.

Assuming normal operation of an OTEC plant at a suitable location, the most important design features for which there is some

flexibility to reduce the potential threat to fisheries are the cold water

intake, warm water intake, discharge, and chemical additions. These

topics are discussed in the following sections.

Cold Water Intake

Generally, reviews by Hoss and Peters (1983) and Uchida (1983)

reveal that the direct environmental implications of the deep water

intake of cold water are small. The depths involved are below the

euphotic zone, estimated to be in the range of 100-150 m in subtropical waters of the Caribbean and the Pacific. As a consequence,

the entrainment of phytoplankton by the cold water pipe (CWP)

is not a concern.

The information on zooplankton distributions indicated that the

CWP will entrain certain zooplankton. It is also apparent that the

deeper the placement of the CWP intake, the fewer the number of

zooplankton that will be entrained. Ifthe CWP intake could be placed

beneath the zone within which certain zooplankton undergo diel

migrations (see Zooplankton section), this would also help to

minimize entrainment. However, the extension ofthe CWP to depths

deeper than necessary to achieve the needed aT would be very expensive, since this is one area where present technology is being

advanced. This could also totally upset the financial aspects of a

plant since the CWP construction and deployment costs will comprise a major percentage of the total construction and deployment

costs.

It might be argued that the cost of extending the CWP to deeper

depths to achieve less entrainment of zooplankton would be offset

by a decrease in seawater volume requirements, and thus pumping

requirements, if a sufficiently greater aT was obtained. Although

such trade-offs will have to be examined on a site-specific basis,

such factors tend to balance out when consideration is given to other

factors such as the increase in pipe frictional losses. Any extension

of the CWP is going to be expensive. Furthermore, although deep

zooplankton playa role in the food web and thus fisheries, it is

not a well defined role as yet. Therefore, the true benefit of trying

to avoid deep zooplankton entrainment cannot be quantified with

the present state of knowledge.

As noted by Hoss et al. (1983) and in the section on Eggs and

Larvae of Important Species, little information is available on the

vertical distribution of fish eggs and larvae in the Caribbean and

Pacific. However, it appears that they are most abundant in the upper

25 m, particularly at night. Although Miller (1979) suggests there

may be a deep source of certain larvae in waters nearshore Kahe

Point, few larvae are found below 200 m. The relative lack of information on fish larvae suggests that additional information should

be gathered at specific OTEC sites when a design is contemplated.

The most significant environmental implication of the CWP in25

take would appear to be related to the intake in these deep waters

of nutrients and other natural chemical constituents, which are

generally present in greater concentrations here than in surface

waters (NOAA 1981a). Since the potential environmental impact

does not relate to the intake as much as to the discharge of these

constituents back to the ocean near the surface, this topic is taken

up under discharges (see Discharge Location and Configuration).

To conclude this section, it is suggested that for most situations

the placement and configuration of the CWP will be driven by

economic considerations. However, the lack of flexibility in design

does not seem to imply any significant disadvantage in terms of

potential environmental impact and risk to fisheries.

Warm Water Intake

As discussed under Biological Interaction with the Environment,

the warm water intake will have significant interaction with the

biological environment, entraining or impinging phytoplankton,

zooplankton, ichthyoplankton, and fish.

Generally (see Phytoplankton), the concentration of phytoplankton

increases near tropical and subtropical islands due both to the upwelling of nutrients from depths as well as a greater input of nutrients

from the land mass. Also, in both the Caribbean and Pacific areas

under discussion, the levels of maximum phytoplankton biomass

tend to be near the l00-m level, near the bottom of the mixed layer.

For instance, for waters off Keahole Point, Hawaii, Noda et al.

(1980) reported that the subsurface chlorophyll maximum occurred

between 64 and 94 m. Chlorophyll-a levels tended to be relatively

constant in the top 40 m or so of the water column. In general,

they increase below this level to the levels found at the chlorophyll

maximum and then quickly decrease to very low values, with the

lowest values occurring beneath the euphotic zone. As noted by

Uchida (1983) for six cruises in the Kahe Point environment, Noda

et al. (1981a) observed that the chlorophyll maximum remained

relatively constant in its vertical position at 86 m as well as in its

concentration. Furthermore, this layer accounted for 77% of the

chorophyll biomass in the photic zone.

The discussion in the section Impacts on Fishery Food Chains

suggests that the predatory effect on harvestable fish stock caused

by any food chain effect of the entrainment of phytoplankton is not

a concern. However, where the design flexibility exists, it is probably prudent to avoid the direct entrainment of phytoplankton to

the extent practicable. In light ofthe information on phytoplankton

distributions, this would suggest that the warm water intake of an

OTEC plant should probably be located in shallow water (i.e., 0-40

m). The secondary entrainment of phytoplankton is a separate issue

and is discussed under the next section.

As discussed in the Zooplankton section, the abundance of

zooplankton tends to be greatest near the level of the chlorophyll

maximum, particularly at night when many zooplankters migrate

from both deeper and shallower waters to this level. Thus, the

avoidance of zooplankton to the extent practicable also suggests

relatively shallow warm-water intake depths. However, as in the

case of phytoplankton, the effect on fish stocks due to the predation of zooplankton by an OTEC plant of 40-MWe capacity is not

expected to be significant (see Impacts on Fishery Food Chains).

Like phytoplankton, zooplankton also exhibit an island mass effect with concentrations higher at nearshore locations (see

Zooplankton section). However, as evident in Table 8 for Caribbean waters, the gradient in surface zooplankton concentration is

not great enough to warrant the extension, for a land-based plant,
Table 8.-Mean displacement volume, dry weight, and abundance ofsurface zooplankton at island

sites in the Caribbean. All samples were taken with 203 I'It1 or 239 I'It1 mesh nets (from Doss

et al. 1983).

Distance Water Displacement

offshore depth volume Dry weight Abundance

Location (kIn) (m) (rnJ/m3

) (mg/m3) (no./m3) Source

Puerto Rico 0.5-1.0 10 0.086 818 Youngbluth 1979

Barbados <1 10 0.049 4.00 Sander and Steven 1973

Barbados 2 25 0.041 3.05 345 Moore and Sander 1976

Barbados 10 460 0.Q28 2.40 368 Sander and Steven 1973

Moore and Sander 1977

Jamaica I 35 0.043 8.28 1600 Moore 1967

Jamaica 8 900 0.021 3.30 823 Moore 1967

of a warm water intake to waters, say, 10 krn offshore. For instance, the data suggest that the entrainment of zooplankton might

be halved for an extension of the intake from less than 1 krn to,

say, 10 krn. However, the suggestion of an insignificant effect of

zooplankton entrainment on fisheries would not justify the benefit

of this entrainment reduction, if indeed it was to be realized. On

the other hand, if there was some flexibility over the location of

the plant, e.g., whether it could be land-based or a shelf-sitter, the

shelf-sitter with its location and intake being further offshore might

imply a lower environmental risk on qualitative grounds, other factors being equal.

The only conclusion which can be drawn from observations of

larval fish (see Eggs and Larvae section) is that the actual distributions may be quite complex. The implication is that the spatial/temporal and species distribution of larval fish should be determined

before engineering flexibility in the location of the warm water intake is considered.

From the standpoint of impingement and entrainment of adult

fish, the warm-water intake velocity is a critical factor with lower

velocities being more desirable (see Impingement section). The

general guideline regarding velocities for conventional power plant

intakes is to keep the velocity below 15 cm/s so as to allow fish

to escape the screen wells (U.S. Environmental Protection Agency 1973). Although the effectiveness of velocity caps (covers used

to create horizontal velocity fields for a vertical intake) to reduce

fish entrainment is not universally accepted, EPA recommends their

use for offshore, submerged intakes; the principle is that fish tend

to avoid horizontal velocity fields more so than vertical ones (see

Impingement section).

Discharge Location and Configuration

The discharge of effluent waters from an OTEC operation has important implications for both the operation of the plant and its environmental effect. It is of great importance that discharge waters

not recirculate to the warm water intake and thereby reduce the

effective thermal resource of the plant. However, for most situations the negative buoyancy of the discharge plume and the initial

dilutions achieved (see Effluent Discharge section) should assure

that recirculation is not a problem. It is also of great importance

that a discharge scheme be chosen so as to minimize the potential

effects to fisheries and other biological resources. As discussed,

the initial and, to a certain extent, subsequent fates of the effluent

plume will be very dependent upon the density of the discharge,

the configuration ofthe discharge outlet, the vertical ambient density distribution, and the presence of currents.

Several discharge situations were examined in the Effluent Dis26

charge section: separate and mixed discharges from a 40-MWe

OTEC plant to two water types that are representative ofsituations

found offshore of Kahe Point, Oahu, and Punta Tuna, Puerto Rico.

Discharges at depths of 20 m and 100 m were considered for both

situations.

For the Kahe Point case considered, the upper 50 m were fairly

mixed so that there was little stratification in density. The calculations showed that there would be little impedance to the sinking

of effluent plumes, whether mixed or separate, until a depth of

50-100 m was reached. Discharges at 100 m did not stray too far

from that depth because of the stronger stratification there.

Calculated dilutions were in the range of 4-7.

The Punta Tuna case was somewhat different because of the

stronger density stratification present. A separate warm water

discharge at 20 m fell to 30 m, achieving a dilution of about 4;

whereas a separate cold water discharge fell further, to 55 m with

a dilution of 5.5. A separate warm water discharge at 100 m rose,

because of its positive buoyancy at that depth, to 75 m with a dilution of 5; the separate cold water discharge at 100 m fell to 160

m with a dilution of 7. A mixed discharge at the 20-m depth fell

25 m to a depth of45 m with a dilution of4.5, and a mixed discharge

at 100 m fell 15 m to 115 m with a dilution of 5.

Although the examples offered are limited, they do provide an

indication as to how the level of neutral buoyancy (where the density

of the plume equals that of the ambient waters) and dilutions are

affected by the type of discharge. For a given situation, larger differences in density between the discharge and receiving waters will

involve longer trajectories and higher dilutions before a neutral

buoyancy is achieved. This may be desirable if dilution and removal

of certain constituents (e.g., chlorine) from the immediate environment is desired. However, it might be undesirable if the redistribution of organisms is a concern, or ifthe utilization of nutrients from

the cold water is possible and desired. Long trajectories and high

dilutions also result in larger secondary entrainment ofthe organisms

which could have an effect many times that of primary entrainment.

This brief treatment of discharge schemes provides only a glimpse

of the discharge possibilities and how they might be used to advantage. The presence of currents, occurrence of coastal upwelling,

and placement of the plant will greatly influence the final schemes

chosen. Also if the plant is land-based, an artificial island, or a shelf

sitter, the presence of the seabed may influence the selection. For

example, a mixed effluent discharged to shallow waters will probably hit the seabed before it reaches its level of neutral buoyancy.

This would affect the rate of subsequent dilution and also cause

impact to benthic biological resources in the area, such as corals.

It is obvious that the discharge scheme, more so than either of the

intakes, will have to be fine-tuned to the environmental conditions

at a site.
Chemical Additions

Chemicals will be added to the seawater pumped through an OfEC

plant by the corrosion/erosion of heat exchanger surfaces, the addition of biocides to control the biofouling of heat exchanger surfaces, and the leaking of working fluids. The release rates will be

determined by both the engineering design and the biologicalchemical characteristics of the local ambient waters. For the most

part, the normal release of working fluids and metals from heat

exchanger and other surfaces is not expected to be a problem (see

Chemical Additions section).

Given that a biocide such as cWorine may be a necessary evil

for an OTEC operation, a certain amount of engineering flexibility can still be utilized to reduce the degree or scale of potential

effects. All of the previously discussed options are definite candidates (i.e., plant location and intake/discharge schemes). For instance, achieving a high dilution and a level of neutral buoyancy

below the euphotic zone may be very desirable to limit the exposure

of biota to the biocide. This would require the identification of a

certain optimal discharge scheme. In addition, certain dosing

schemes can be used.

Flexibility in biocide dosing might involve applying the biocide

to different power modules at different times and mixing the dosed

module effluent with other module effluents to create some degree

of pre-dilution. For instance, if a 40-MWe OfEC plant was composed of four lO-MWe modules and the condenser and evaporator

could be dosed separately, a certain dose to one of the evaporator

units and subsequent mixing with the total warm and cold water

discharge would produce a dilution of 8 to I prior to discharge.

In other words, a free residual cWorine level of 0.05 JAg/g in the

effluent of the evaporator or unit in question would be diluted to

0.006 JAg/g before discharge to the environment. Initial dilutions

of 5 to 10 could further reduce these concentrations to 0.0012 and

0.0006 JAg/g, respectively.

RESEARCH PRIORITIES _

The preceding sections have presented information and inferences

regarding the potential effects of OfEC operations on fisheries. The

discussions have primarily relied upon information on power plant

effects in temperate waters and the limited biological information

available for tropical waters. Although such an assessment provides

valuable insights regarding the effects of early small-scale OfEC

development, a more thorough assessment will eventually be needed.

To do so will require much additional research of both generic and

site-specific types as defined below. However, although further

research is needed, the preceding sections also allude to areas where

additional information is either not needed or deemed to be unimportant. Specifically, the assessments in the Biological Interactions

section of the predatory effect of an OfEC plant on phytoplankton

and zooplankton (with the exception of ichthyoplankton) would suggest that the effect is so minimal as to not warrant further investigation of this topic. As emphasized below, additional information on

the eggs and larvae of fish is direly needed.

Investigations of Fish Distribution

There is almost no quantitative information available on the distribution of the early life stages (eggs to juveniles) of fish in tropical

waters. Both spatial and temporal information ofthis type is needed

27

and should be given high priority, in order to determine the potential numbers of fish that will be subjected to impingement and

primary and secondary entrainment. An understanding of the

distribution of fish in the water column may allow plant modifications to be made that will help decrease the environmental impact

of OfEC operations.

Studies on the Effects of Entrainment

Primary and secondary entrainment effects associated with OfEC

are potentially important because of the extremely large volumes

of water involved. Unlike conventional power plants where

organisms experience an increase in temperature as they pass

through the condensers, larval fish entrained in an OfEC plant will

be subjected to a decrease in temperature of about 2°C upon passage

through the evaporators. Additionally, in the case of a mixed

discharge, organisms entrained in the warm water intake will be

further subjected to a decrease in temperature of about 10°C when

the warm and cold waters are mixed. Depending on where this

discharge is made, secondary entrainment may expose additional

organisms to some temperature decreases.

Since we found no reported work on the effects of cold shock

on the young oftropical fish, research on this subject was initiated

by the National Marine Fisheries Service. This research is examining

the effects of cold shock (using realistic decreases in temperature)

that could occur as a result of entrainment. In the future, factors

such as the addition of biocides and increased levels of trace metals

in the water should be examined in conjunction with the temperature

studies.

Biostimulation/Inhibition

The OfEC plants are unique in their utilization of cold water from

the deep ocean. This use of large amounts of deep ocean water

creates a potential for changes in the upper part of the water column

similar to those caused by natural upwelling. The increased nutrient

load of cold, deep ocean waters may have stimulating, inhibiting,

or no effects on the productivity of marine fisheries.

Although some experiments have described the effect of mixing

deep water with surface waters at potential OfEC sites (e.g.,

Quinby-Hunt 1979; Szyper et al. 1984), further work is needed.

This research should look at nutrient and trace metal distributions

of waters from different depths and test their ability to affect primary

production and species composition. This type of research can be

completed in a relatively short time, and the results must then be

combined with the effects of natural nutrient fluxes to determine

the ecological significance of potential changes in primary production.

Early Life History Studies

It appears that the major direct impacts of OfEC operations on fish

will be on the early stages in their life history. In order to evaluate

OfEC impacts on these stages, we need more information on their

abundance, distribution, migration, and growth and mortality rates.

Generic information on tropical species is lacking and general principles may be applicable to many species. Such information should

be collected, starting with some of the major recreational and commercial species. The duration for this type of research is in years,

but specific parts can be completed in less time.
Dynamics of Fishery Populations

The research priorities outlined above are directed at establishing

the effects of afEC operations on the biological community which

supports and includes harvested fishery populations. Such research

should indicate whether effects may be positive or negative and

supply information needed to predict the number and life stage of

fish directly impacted. In order to evaluate any such effects as they

relate to commercial or recreational fisheries, additional information is needed. For example, while some information is available

on many of the fisheries, much more is needed, including:

1) Stock structure (i.e., the number and geographic distribution

of the stocks);

2) stock assessment over time, which depends upon age distribution of the stocks, size at age, and age-specific fecundity,

3) accurate catch and effort statistics, and

4) increased information about the factors affecting recruitment,

including development of models to predict compensation for mortality at various early life stages.

Although parts of this research area can be performed over short

time scales, the topic as a whole will require years to address

adequately.

Ciguatera

Independent of other impacts, fisheries could be severely impacted

if the fish present were inedible due to ciguatera fish poisoning,

which occurs in many tropical waters. Current information is inadequate to predict or prevent such an occurrence, and additional

information is needed, including a description of the environmental factors responsible for blooms of the toxin-producing algae,

methods of easily detecting contaminated fish, and methods of

mitigation.

Construction Effects

Further research is also needed to properly assess the effects from

disturbances to the environment (including the fisheries) by actual

construction of the afEC facility. Any dredging in open seas will

generate turbidity and sedimentation, not only in the immediate area

of construction but also in adjacent areas. Sediment in the dredging plume will settle out ofthe water column, covering and perhaps

killing some benthic life, including, possibly, coral communities.

Dredging has also been found to be correlated with outbreaks of

ciguatera poisoning. Thus, in addition to the information needed

on ciguatera, there is a need to gather data on effects of sediments

on coral reef ecosystems as well as on the downstream extent of

the dredging plume.

CONCLUSIONS _

This report examines the potential impact to fisheries due to the

operation of ocean thermal energy conversion (afEC) plants. The

effort is primarily a synthesis of existing information that has pertinence to the topic, and an extrapolation to conditions brought about

by afEC operations. The intent was to gain a perspective of the

potential risk to fisheries, to identify practicable measures that would

reduce the potential for problems, and to suggest research areas

where significant uncertainties exist, uncertainties that under certain conditions might impede the commercial development of afEC.

28

The report focused on two regions where U.S. afEC interests

might lie: the Caribbean and the Pacific. It also focused on nearshore operation of afEC as compared to open ocean application;

the rationale here is that the nearshore area is considered to be the

more ecologically sensitive as well as more likely to see afEC

development in the near term. Additionally, the report has contained

itself primarily to those factors of concern that would be associated

with the normal operating conditions of an afEC plant: the impingement and direct entrainment of biota, the secondary entrainment

of biota, the redistribution of ocean water properties, and the addition of biocides and other chemical constituents. These concerns

are highlighted by the relatively large volume of water that will

be pumped through afEC plants.

Fish impingement rates caused by these flows will depend on the

abundance of fish which are larger than the mesh size of an afEC

intake screen and on the ability of the fish to avoid the intake.

Although this avoidance ability will also depend on a number of

factors, it can be increased through the use or creation of horizontal intake flow fields. It can also be increased by keeping the flow

speeds as low as practicable. It is estimated that a 4O-MWe Hawaiian

or Puerto Rican afEC plant would impinge about 20-35 kg of

organisms daily, due to the warm water intake, and another 40-65

kg at the cold water intake. It is estimated that the effect on a fishery

of such impingement rates will be negligible compared to other

pressures on a fishery; however, the use of the above mitigating

measures and attempts to locate intakes away from areas of high

biological activity are recommended.

Organisms, including fish eggs and larvae, that are caught up

in the intake flows and not impinged, will be entrained, travel

through the plant, and then be discharged. Although the combined

effect of the various stresses that these entrained organisms would

undergo is difficult to quantify with accuracy, it is considered prudent to assume 100% mortality until better knowledge is available.

Additionally, entrainment mortality will be added to by the secondary entrainment of organisms. This entrainment is due to a

discharge plume that, in falling or rising to find its level of neutral I

buoyancy, entrains surrounding water and biota as it is diluted. With

typical dilution ratios expected to be in the range of 5: 1 to 10: 1,

the level of secondary entrainment may be quite high. However,

until further information is gathered, assessments ofthe associated

mortality are very subjective. It is concluded that cold shock to biota

may be the main concern with· secondary entrainment and that

organisms may only suffer slightly. However, the most vulnerable

of the organisms will be the non-migratory species; and these, unfortunately, include many larvae.

afEC plants have the potential of influencing the food chains

leading to fish in several ways. Increased fish production can occur through either more primary production or shorter food chains,

either of which could result from the "pumped upwelling" of

nutrient-rich deep water. On the other hand, minor changes in food

webs may drastically alter our acceptance ofthe fish produced. For

example, blooms of the dinoflagellates which cause red tides or

ciguatera can make the fish inedible. Although more information

is needed on such processes, red tide outbreaks are not expected

and the minimization of benthic disturbances during afEC construction and operation will reduce the likelihood of ciguatera

outbreaks.

In trying to examine impacts to fisheries due to mortalities

associated with OTEC operations, one key problem is the lack of

detailed information on the spatial and temporal distribution of fish

eggs and larvae, the natural mortality of most fish, and the range

of natural variability associated with the various life stages of fish.
This results in a low degree of confidence in anything beyond rather

subjective conclusions. However, even these conclusions are

valuable until further information is gained.

Design measures that might be taken to reduce the potential risk

to fisheries relate to the location ofthe plant, location and configuration of the intakes and discharges, and the mode of introducing

biocides to the system. From the viewpoint of general environmental

risk, proper siting is the single most effective means to minimize

the potential for environmental damage. Here, the avoidance of areas

of high biological productivity and of others ofspecial importance

(e.g., critical habitats, spawning grounds, coral reefs) is desirable.

For most situations the placement and configuration of the cold

water pipe will be constrained purely by economic considerations.

However, the perceived lack of flexibility does not seem to imply

any significant disadvantage in terms of potential environmental

impact and risk to fisheries. Regarding the warm water intake, it

is felt that more information is needed on the microscale distribution of fish eggs and larvae. However, in general, it is believed

that warm water intakes placed below the surface, where many fish

eggs tend to concentrate, and above the chlorophyll maximum may

be most desirable. This suggests a placement between about 10 and

40 m. Additionally, if there was some flexibility over the location

of the plant, particularly its warm water intake, a plant located further offshore might imply a lower environmental and fishery risk

on qualitative grounds, other factors being equal.

The placement and configuration of discharges will be a very sitespecific consideration. Mixed vs. separate, and deep vs. shallow,

discharges can achieve different dilutions and levels of neutral

buoyancy. Different permutations have implications regarding the

utilization of cold water nutrients, the potential for recirculation

into the warm water intake, the degree of secondary entrainment,

the amount of cold shock, and the concentration of biocides. Brief

treatment of the possibilities suggests that in deeper waters the

discharge of a mixed effluent near the surface would offer a number

of advantages. First, the cost of the discharge structure is minimized.

Second, the plume, because of the density addition provided by the

mixed cold water, would probably sink deep enough to avoid problems of recirculation into the warm water intake. Third, sufficient

dilution would be imparted to minimize potential problems with

biocides and other trace constituents. Also, the mixed discharge

would minimize the degree of cold shock to organisms secondarily

entrained. However, with the discharge near the surface, there may

be some impact associated with the entrainment of ambient water

and organisms into the discharge plume.

The presence of currents, occurrences of coastal upwelling, and

placement ofthe plant will also influence the final discharge scheme

chosen for a particular plant. For instance, for a land-based or very

nearshore plant, the effluent from a nearsurface discharge will probably hit the seabed and roll down it before the level of neutral

buoyancy is reached. Depending upon a number of factors, e.g.,

benthic resources, this might necessitate a deep discharge.

In general, it is not believed that the effect of the corrosion

products of metals will be a problem with OfEC. However, the

addition of chlorine as an antifoulant over long time periods does

create some concern. Although more information is needed on the

chemistry and long-term effects of chlorine, this concern is lessened

through the achievement of high dilutions of the biocide and/or a

level of neutral buoyancy near the bottom of the euphotic zone.

Certain dosing schemes can be utilized to achieve predilutions that,

combined with the initial dilution process would result in much lower

levels of biocides in the environment.

29

In conclusion, the potential risk to fisheries of OfEC operations

is not judged to be so great as to not proceed with the early development of OfEC. Due to the lack of a suitable precedent, however,

there will remain some level of uncertainty regarding these initial

conclusions until a pilot plant operation can be monitored for some

period of time. In the meantime, further research on fisheries should

be undertaken to assure an acceptable level of risk regarding the

larger commercial OfEC deployments.

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