A Review of National and 

International Literature on the 

Effects of fishing on Benthic Habitats

Korie A. Johnson

U.S. Department of Commerce

National Oceanic and Atmospheric Administration

National Marine Fisheries Service

NOAA Technical memorandum NMFS-F/SPO-57

August 2002
ii

A Review of National and 

International Literature on the 

Effects of Fishing on Benthic Habitats

Korie A. Johnson

Office of Habitat Conservation

National Marine Fisheries Service, NOAA

1315 East-West Highway

Silver Spring, MD 20910

NOAA Technical Memorandum

NMFS-F/SPO-57

August 2002

U.S. Department of Commerce

Donald L. Evans, Secretary

National Oceanic and Atmospheric Administration

Vice Admiral Conrad C. Lautenbacher, Jr., USN (Ret.)

Under Secretary for Oceans and Atmosphere

National Marine Fisheries Service

William T. Hogarth, Assistant Administrator for Fisheries
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ACKNOWLEDGEMENTS

David Stevenson of NMFS Northeast Region spent considerable time helping to write and 

review the summaries of research papers. Numerous others, especially Robert Reid and John 

McCarthy from NMFS Northeast Science Center, Jon Kurland and Thomas Bigford from NMFS 

Office of Habitat Conservation, and individual participants of the Workshop on the Effects of 

Fishing Gear on Marine Habitats off the Northeastern United States (Boston, Massachusetts, 

October 23-25, 2001) provided detailed comments that improved the document. 

A copy of this report may be obtained from:

NMFS Office of Habitat Conservation

SSMC3 (F/HC)

1315 East West Highway

Silver Spring, MD 20910

(301) 713-2325

Or online at:

http://www.nmfs.noaa.gov/habitat/habitatprotection/essentialfishhabitat10.htm
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TABLE OF CONTENTS

I. INRODUCTION............................................................................................. 1

A. Statutory Requirements ................................................................................ 1

B. Information Needs to Assess Habitat Impacts...................................................... 2

II. SCOPE OF FISHING GEA R EFFECTS ................................................................ 2

A. Alteration of Physical Structure...................................................................... 2

B. Sediment Suspension.................................................................................. 3

C. Changes in Chemistry.................................................................................. 4

D. Changes to Benthic Community...................................................................... 4

E. Changes to Ecosystem................................................................................. 5

III. SUMMARY OF LITERATURE ON GEAR EFFECTS .............................................. 5

A. RESEARCH APPROACHES............................................................................... 5

B. REVIEWS ................................................................................................. 6

C. SUMMARY OF AVAILABLE SCIENCE ................................................................. 8

1. Bottom Trawls .................................................................................... 8

a. Otter Trawls (Fish) ......................................................................... 8

b. Otter Trawls (Invertebrates) ............................................................... 19

c. Roller Frame Trawls......................................................................... 22

d. Beam Trawls................................................................................. 23

e. Rapido Trawls................................................................................ 26

2. Dredges............................................................................................. 27

a. Hydraulic Clam Dredges..................................................................... 27

b. Escalator Dredges............................................................................. 30

c. New Bedford Scallop Dredges............................................................... 32

d. Toothed scallop Dredges..................................................................... 35

e. Suction Dredges .............................................................................. 42

f. Other Non-Hydraulic Dredges............................................................... 44

3. Multiple Mobile Gears............................................................................ 46

4. Pots and Traps..................................................................................... 51

5. Set Gill Nets........................................................................................ 53

6. Set Longline........................................................................................ 53

D. RECOMMENDATIONS FROM THE LITERATURE ........................................................ 53

IV. STATE OF INFORMATION.............................................................................. 55

A. LIMITATIONS OF INFORMATION AND NEED FOR RESEARCH ........................................ 55

B. MANAGEMENT PHILOSOPHIES........................................................................... 56

V. CONCLUSIONS ............................................................................................. 58

VI. REFERENCES CITED...................................................................................... 59
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LIST OF TABLES

1. Summary of literature on effects of otter trawls (used to catch fish) on habitat with 

mud substrate........................................................................................................ 10

2. Summary of literature on effects of otter trawls (used to catch fish) on habitat with 

sand substrate........................................................................................................ 13

3. Summary of literature on effects of otter trawls (used to catch fish) on habitat with 

gravel substrate...................................................................................................... 15

4. Summary of literature on effects of otter trawls (used to catch fish) on coral reef habitat........... 17

5. Summary of literature on effects of otter trawls (used to catch fish) on habitat with 

mixed substrate........................................................................................................ 18

6. Summary of literature on effects of otter trawls (used to catch invertebrates) on habitat with 

mud substrate........................................................................................................ 20

7. Summary of literature on effects of otter trawls (used to catch invertebrates) on habitat with 

sand substrate........................................................................................................ 21

8. Summary of literature on effects of roller frame trawls on seagrass habitat.......................... 22

9. Summary of literature on effects of beam trawls on habitat with mud substrate..................... 23

10. Summary of literature on effects of beam trawls on habitat with sand substrate................... 25

11. Summary of literature on effects of rapido trawls on habitat with sand substrate................... 27

12. Summary of literature on effects of hydraulic dredges on habitat with sand substrate............. 29

13. Summary of literature on effects of escalator dredges on habitat with mud substrate.............. 30

14. Summary of literature on effects of escalator dredges on habitat with sand substrate.............. 31

15. Summary of literature on effects of escalator dredges on seagrass habitat........................... 32

16. Summary of literature on effects of New Bedford scallop dredges on habitat with mud substrate 33

17. Summary of literature on effects of New Bedford scallop dredges on habitat with sand substrate 34

18. Summary of literature on effects of New Bedford scallop dredges on habitat with 

mixed substrate.................................................................................................... 35

19. Summary of literature on effects of toothed scallop dredges on habitat with mud substrate...... 37

20. Summary of literature on effects of toothed scallop dredges on habitat with gravel substrate.... 40

21. Summary of literature on effects of toothed scallop dredges on livebottom habitat................. 42

22. Summa ry of literature on effects of suction dredges on habitat with mud substrate................ 42

23. Summary of literature on effects of suction dredges on habitat with sand substrate................ 43

24. Summary of literature on effects of other non-hydraulic dredges on seagrass habitat.............. 44

25. Summary of literature on effects of other non-hydraulic dredges on oyster reefs and 

mussel beds........................................................................................................ 45

26. Summary of literature on effects of multiple mobile gear on habitat with sand substrate......... 47

27. Summary of literature on effects of multiple mobile gear on habitat with gravel substrate........ 48

28. Summary of literature on effects of multiple mobile gear on habitat with mixed substrate........ 50

29. Summary of literature on effects of pots on habitat with various substrates.......................... 51

30. Summary of literature on effects of pots and traps on coral reef habitat............................... 52
1

PREFACE

This document summarizes existing information on the effects of fishing activities on benthic 

marine habitats. It was prepared by the National Marine Fisheries Service (NMFS) Office of 

Habitat Conservation with the intent of providing the Fishery Management Councils (Councils) 

with a reference document to assist in assessing adverse effects of fishing to essential fish habitat 

(EFH). The scope of this document is limited to habitat effects; thus, ecosystem effects resulting 

from physical disturbance or removal of target species and bycatch are not addressed. The first 

part of this document reviews the statutory requirements and information needed to understand 

impacts of fishing. The second part of the document provides an overview of the major types of 

effects, as provided in scientific reviews, that could occur as a result of fishing. The third part of 

this document reviews published and unpublished scientific literature, and summarizes scientific 

reviews and studies on fishing gear effects on habitat on a case by case basis. The section is 

organized by gear type, and then by habitat within specific gear types. Papers are presented 

within specific habitat type sections based on the information provided in the papers, without the 

use of any standardized habitat classification system. The summaries present methods, results, 

and conclusions as reported by the authors. There is no attempt to evaluate the validity of the 

scientific approach or the conclusions reached in each study, although most of the studies and 

reviews discussed herein have been peer reviewed. The final portion of the document reviews 

the current state of information and the range of management philosophies discussed in the 

literature regarding minimization of fishing effects.

I. INTRODUCTION

A. STATUTORY REQUIREMENTS 

The 1996 Amendments to the Magnuson-Stevens Fishery Conservation and Management Act 

(MSA) require that fishery management plans (FMPs) minimize to the extent practicable adverse 

effects on EFH caused by fishing (Magnuson-Stevens Act section 303(a)(7)). Pursuant to the 

EFH regulations (50 CFR 600.815(a)(2)), FMPs must include an evaluation of the potential 

adverse effects of fishing on EFH. The evaluation must consider the potential adverse effects of 

all fishing gear types used in waters designated as EFH, not just those gears used in the fishery in 

question. It must also consider potential impacts of fishing on different types of habitat found 

within EFH for all federally-managed species. In completing this assessment, FMPs must be 

based on the best scientific information available, and can include other appropriate information 

sources as well (e.g., economic data, anecdotal information). Included in this assessment should 

be consideration of the establishment of research closure areas and other measures to evaluate 

impacts of fishing activities that may adversely affect EFH. 

To assist Councils in meeting the above mandates, this report summarizes available information 

concerning effects of fishing on marine habitats. Information sources include peer reviewed 

scientific journals, as well as non peer-reviewed reports. Major bibliographic sources include 

Rester (2000), NMFS Alaska Fisheries Science Center bibliography (Wion and McConnaughey 

2000), and numerous ICES reports. In addition, a thorough literature search was completed to 

ensure inclusion of articles up to May 2002. This document is limited to major fishing gear 

types: trawls, dredges, traps/pots, seines, set gillnets, and set longline. Available information on 
2

mud, sand, gravel (including pebble, cobble and boulder), coral/outcrop/seamount, and seagrass 

habitats from all geographic areas is summarized. 

B. INFORMATION NEEDED TO ASSESS EFFECTS ON HABITAT

The effects of fishing gears on habitat depend on a number of factors, including the nature, 

magnitude and frequency of the impact, and the recovery time of the habitat and biological 

community affected by the gear. These factors in turn depend on characteristics of the gear (e.g., 

type, weight, towing speed, depth of penetration), the intensity and areal extent of the 

disturbance, and the biological, physical, chemical and oceanographic characteristics of the area 

impacted (Hall et al. 1993, Brylinsky et al. 1994, Hall 1994, Auster and Langton 1999, DeAlteris 

et al. 1999, Kaiser 2000). The influence of so many factors complicates understanding the 

effects of fishing gear on habitat and ultimately on the populations of fishes and invertebrates 

that utilize that habitat. 

To fully evaluate the impacts of fishing gear on habitat, and how habitat impacts affect 

sustainability of fish populations, improved information is needed on: 

1) the spatial extent of fishing-induced disturbance (fishing effort) by gear type; 

2) the distribution of habitat types; 

3) the effects of specific gear types (and configurations within gear types), along a gradient 

of effort, on specific habitat types; 

4) the relative importance of fishing gear effects and natural disturbance;

5) the role that seafloor habitats and impacts on those habitats have in the population 

dynamics of fishes; and 

6) natural changes/trends in communities and ecosystems.

II. SCOPE OF GEAR EFFECTS 

Types of potential effects on habitat from fishing fall into specific categories, including alteration 

of physical structure, sediment suspension, chemical modifications, benthic community changes, 

and ecosystem changes. These general effects are discussed below.

A. ALTERATION OF PHYSICAL STRUCTURE

Physical effects of fishing gear can include scraping, ploughing, burial of mounds, smoothing of 

sand ripples, removal of stones or dragging and turning of boulders, removal of taxa that produce 

structure, and removal or shredding of submerged aquatic vegetation (Fonseca et al.1984, 

Messieh et al. 1991, Black and Parry 1994, Gordon et al. 1998, Kaiser et al. 1998, Lindeboom 

and de Groot 1998, Schwinghamer et al. 1998, Auster and Langton 1999, Kaiser et al. 1999, 

Ardizzone et al. 2000). These physical alterations reduce the heterogeneity of the sediment 

surface, alter the texture of the sediments, and reduce the structure available to biota as habitat. 

As mobile gear is dragged across the seafloor, parts of some gears can penetrate up to 5-30 cm 

into the substrate under usual fishing conditions, and likely to greater depths under unusual 

conditions (Drew and Larsen 1994). This action can leave tracks or even trenches in the 
3

seafloor, depending on the sediment type. It is unknown whether or to what extent these manmade features might compensate for the sediment smoothing actions of the gear. 

B. SEDIMENT SUSPENSION

Resuspension of sediments occurs as fishing gear is dragged along the seafloor. Effects of 

sediment suspension can include reduction of light available for photosynthetic organisms, burial 

of benthic biota, smothering of spawning areas, and negative effects on feeding and metabolic 

rates of organisms. If resuspension occurs over a large enough area it can actually cause large 

scale redistribution of sediments (Messieh et al. 1991, Black and Parry 1994). Resuspension 

may also have important implications for nutrient budgets due to burial of fresh organic matter 

and exposure of deep anaerobic sediment, upward flux of dissolved nutrients in porewater, and 

change in metabolism of benthic infauna (Mayer et al. 1991, Pilskaln et al. 1998).

Effects of sediment resuspension are site-specific and depend on sediment grain size and type, 

water depth, hydrological conditions, faunal influences, and water mass size and configuration 

(Hayes et al. 1984, LaSalle 1990, Barnes et al. 1991, Coen 1995). Effects are likely more 

significant in waters that are normally clear compared with areas that are already highly 

perturbed by physical forces (Kaiser 2000). Schoellhamer (1996) concluded that resuspension 

by natural mechanisms in a shallow estuary in west-central Florida was less frequent and of 

smaller magnitude than anthropogenic mechanisms (e.g., fishing) and that sediments disturbed 

by fishing were more susceptible to resuspension by tidal currents. Modeling by Churchill 

(1989) concluded that resuspension by trawling is the primary source of suspended sediment 

over the outer continental shelf, where storm-related stresses are weak. In the Kattegat Sea, 

Sweden, sandy sediments above the halocline were more affected by wind-induced impacts than 

by fishing effort, but mud sediments below the halocline experienced an increase in the 

frequency of disturbance by 90% in the spring and summer and by 75-85% in the autumn and 

winter due to fishing (Floderus and Pihl 1990). Thus, even when recovery times are fast, 

persistent disturbance by fishing could lead to cumulative impacts. In contrast, Dyekjaer et al. 

(1995) found that in Denmark, although local effects of short duration might occur, annual 

release of suspended particles by mobile fishing gear is relatively unimportant compared with 

that resulting from wind and land runoff.

Chronic suspension of sediments and resulting turbidity can also affect aquatic organisms 

through behavioral, sublethal and lethal effects, depending on exposure. Species reaction to 

turbidity depends on life history characteristics of the species. Mobile organisms can move out 

of the affected area and quickly return once the disturbance dissipates (Simenstad 1990, Coen 

1995). Even if species experience high mortality within the affected area, species with short life 

history stages and high levels of recruitment or high mobility can repopulate the affected area 

quickly. However, if effects are protracted and occur over a large area relative to undisturbed 

area, recovery through recruitment or immigration will be hampered. Furthermore, chronic 

resuspension of sediments may lead to shifts in species composition by favoring those species 

that are better suited to recover or those that can take advantage of the pulsed nutrient supply as 

nutrients are released from the seafloor to the euphotic zone (Churchill 1989).
4

C. CHANGES IN CHEMISTRY

Fishing gear can result in changes to the chemical makeup of both the sediments and overlying 

water mass through mixing of subsurface sediments and porewater. In shallow water this mixing 

might be insignificant in relation to that from tidal and storm surge and wave action, but in 

deeper, more stable waters, this mixing can have significant effects (Rumohr 1998). In a 

shallow, eutrophic sound in the North Sea, fishing caused an increase in average ammonia 

content (although horizontal variations prevented interpretations of these increases) and a 

decrease in oxygen due to the mixing of reduced particles from within the sediments (Reimann 

and Hoffman 1991). Also in the North Sea, fishing enhances phosphate released from sediment 

by 70-380 tonnes per year for otter trawls and by10,000-70,000 tonnes per year for beam 

trawlers (ICES 1992). These pulses were compensated by lower fluxes after the trawl passes. It 

is important to remember that these releases are recycling existing nutrients, rather than adding 

new nutrients, such as inputs from rivers and land runoff (ICES 1992). 

It is unclear how changes in chemistry might affect fish populations. During seasons when 

nutrients are low, the effective mixing of the sediments could cause increased phytoplankton 

primary production and/or eutrophication. ICES (1992) concluded, however, that these pulses are 

compensated by lower fluxes after the trawl has passed, and that the releases from fishing gear 

that recycle existing nutrients are probably less influential than new inputs from rivers and land 

runoff (ICES 1992). 

D. CHANGES TO BENTHIC COMMUNITY

Benthic communities are affected by fishing gear through damage to the benthos in the path of 

the gear and disturbance of the seafloor to a depth of up to 30 cm. Many kinds of epibenthic 

animals are crushed or buried, while infauna is excavated and exposed on the seabed. This is in 

addition to smothering addressed above.

Specific impacts from fishing depend on the life history, ecology and physical characteristics of 

the biota present (Bergman and Van Santbrink 2000). Mobile species that exhibit high 

fecundities and rapid generation times will recover more quickly than non-mobile, slow-growing 

organisms. In Mission Bay, California, polychaetes with reduced larval phases and postlarval 

movements had small-scale dispersal abilities that permitted rapid recolonization of disturbed 

patches and resulted in maintenance of high infaunal densities (Levin 1984). Those with longlived larvae were only available for successful recolonization if the timing of disturbance 

coincided with periods of peak larval abundance, however, these species were able to colonize 

over much larger distances. Rijnsdorp and Van Leeuwen (1996) found increased growth (based 

on back calculated growth from otolith growth zones) in the smallest size classes of plaice in the 

North Sea correlated to eutrophication and seabed disturbance from beam trawls. The authors 

hypothesized that trawling caused a shift in the benthic community from low-productive, longlived species to high-productive, short-lived species that benefitted from increased nutrient 

availability due to anthropogenic activities. This potentially could have lead to increased prey 

availability, and thus, higher growth rates for the juvenile plaice. 

The physical structure of biota also affects their ability to sustain and recover from physical 

impacts with fishing gear. Thin shelled bivalves and starfish show higher damage than solid-
5

shelled bivalves in fished areas (Rumohr and Krost 1991). Animals that are able to retract below 

the surface of the seafloor or live below the penetration depth of the fishing gear will sustain 

much less damage than epibenthic organisms. Animals that are more elastic and can bend upon 

contact with fishing gear will suffer much less damage than those that are hard and inflexible 

(Eno et al. 2001). Kaiser et al. (2000a) found that chronic fishing around the Isle of Mann, UK 

had removed large-bodied fauna such that benthic communities are now dominated by smallerbodied organisms that are less susceptible to physical disturbance. Off the northwest shelf of 

Australia, a switch of dominant species from lethrinids and lutjanids (which are almost 

exclusively associated with habitats supporting large epibenthos) to saurids and nemipterids 

(which were found on open sand) occurred after removal of epibenthic fauna by trawling 

(Sainsbury et al. 1993, 1994).

Increased fishing pressure can also lead to changes in distribution of species, either through 

movement of animals away from or towards the fished area (Kaiser and Spencer 1993, 1996a, 

Ramsay et al. 1996, Kaiser and Ramsay 1997, Ramsay et al. 1998, Bradshaw et al. 2000, 

Demestre et al. 2000). Frid and Hall (1999) found higher prevalence of fish remains and 

scavengers and a lower abundance of sedentary polychaetes in stomach contents of dabs in the 

North Sea in areas of higher fishing effort. Kaiser and Spencer (1994) document that gurnards 

and whiting aggregate over beam trawl tracks and have higher numbers of prey items in their 

stomachs shortly after trawling. Based on these studies, researchers have speculated that mobile 

fishing may lead to increased populations of species that exhibit opportunistic feeding behavior. 

Fonds and Groenewold (2000) modeled results for the southern North Sea indicating that the 

annual amount of food supplied by beam trawling is approximately 7% of the food demand of 

common benthic predators. This level could help maintain populations but is insufficient to 

support further population growth.

E. CHANGES TO ECOSYSTEM

As discussed above, the use of some types of fishing gear can affect benthic community 

composition. It is possible that these changes at the community level are in turn resulting in 

effects on harvested populations and ecosystems. Ecosystem changes are not specifically 

addressed in this report due to the lack of research concerning ecosystem effects due to fishing 

activities. 

III. SUMMARY OF LITERATURE ON GEAR EFFECTS

A. RESEARCH APPROACHES

A number of research approaches have been used to assess gear impacts to habitat. One method 

compares closed (or lightly fished) areas to open (or heavily fished) areas to identify changes to 

habitat that may be attributable to fishing activities. Determining the specific cause of any 

observed differences is difficult, however, if the unfished areas are unfished precisely because 

they are ecologically different from the fished areas. Furthermore, it is important to remember 

that those areas currently closed to fishing may have been significantly altered from previous 

fishing, such that differences are masked (Margetts and Bridger 1971, Caddy 1973, McAllister 
6

and Spiller 1994, Dayton et al. 1995, Auster et al. 1996, Kaiser et al. 1996a, Bradshaw et al. 

2000, Frid and Clark 2000). 

To avoid the difficulties with control areas many researchers have undertaken small scale 

experiments looking at varying levels of fishing intensity on habitats. These types of studies 

provide information on a specific gear type on a specific habitat type, but the scale at which they 

are conducted may make it difficult to detect effects (Thrush et al. 1995, Hewitt et al. 1998, 

Cappo et al. 1998, Bradshaw et al. 2000) or allow us to extrapolate to the scale of the fishing 

grounds (Daan 1991) or to the range of habitats utilized by a given fish species (Langton et al. 

1995). 

Another approach taken to elucidate effects of fishing on habitat is the comparison of historical 

(or pre-fishing) biological community data with present day data. With this approach, the same 

area is sampled over time and the historical data is used as the control. Long-term data sets that 

allow this comparison, however, are not always available. When such data are available, it may 

be difficult or impossible to separate out effects resulting from fishing activities from effects of 

natural and other human induced effects (Hall et al. 1993, Thompson 1993, Hall 1994, Kroncke 

1995, Glemarec et al. 1996, Botsford et al. 1997, Kaiser 2000). However, Lindeboom and de 

Groot (1998) state that “combined with the results ...on the immediate effects of bottom fisheries 

on the benthos and the comparison between fished and unfished areas, it has to be concluded that 

the observed trends in benthic invertebrates were to a great extent caused by the direct and 

indirect effects of fisheries and not solely by eutrophication and/or pollution as interpreted in 

previous studies (e.g., Rachor 1990, Kronche 1995).” 

Despite limitations of study approaches, there does exist an extensive amount of scientific 

research from various geographic regions of the world’s oceans that provides us with 

information on the effects of fishing to habitat. This information must be used when addressing 

the Magnuson-Stevens mandate to minimize adverse effects of fishing to EFH to the extent 

practicable. The National Research Council (2002) report on effects of trawling and dredging 

concludes that “although there are still habitats, gears, and geographic regions that have not been 

adequately studied and characterized, there is an extensive literature on the effects of fishing on 

the seafloor. It is both possible and necessary to use this existing information to more effectively 

manage the effects of fishing on habitat.”

B. REVIEWS

A number of authors have reviewed, to verying extents, existing scientific literature on the 

effects of fishing on habitat (e.g., Auster et al. 1996, Cappo et al. 1998, Collie 1998, Jennings 

and Kaiser 1998, Rogers et al. 1998, Auster and Langton 1999, Hall 1999, Collie et al. 2000a, 

Lindeboom and de Groot 2000, Barnette 2001, National Research Council 2002).

A number of review papers have focused specifically on the physical effects of bottom trawls. 

According to an ICES working report (1973), otter trawls, beam trawls and dredges are all 

similar in their types of impacts on the seabed, but the magnitude of impact increases from 

shrimp to sole beam trawls with tickler and stone guards, to Rapido trawl, to mollusc dredge. 

Kaiser et al. (1996a) and Collie et al. (2000a) state that, because beam trawls are used almost 
7

exclusively in areas that are adapted to frequent wave/tidal action, they are less likely to result in 

adverse effects on habitat. Moran and Stephenson (2000) conclude that semi-pelagic trawls 

towed above the seafloor inflict less damage/mortality on benthos, but result in lower catches of 

target fishes and that the light trawl gear currently in use in northwest Australia results in less 

mortality (15.5% vs. 89% documented by Sainsbury et al. in 1994) than heavy gear used in the 

past. These statements should be evaluated for trawl gear used in U.S. fisheries.

In 1971, de Groot and Appledorn published a review of trawl damage to biota, and stated that 

nemertea, annelids, bivalves, and sea potatoes are all damaged extensively by trawl tickler 

chains. A review of the effects of trawling by species group in the North Sea concluded that 

nearly all coelenterates in the trawl path are destroyed, damage to bryozoans is insignificant, 

annelids suffer considerable damage, damage to molluscs depends on the thickness of the shell, 

ophiuroids and sea potatoes are badly damaged, and sea stars are readily caught in trawl nets (de 

Groot 1984). Auster et al. (1996) reviewed 3 studies of mobile fishing gear in the Gulf of Maine 

and concluded that mobile fishing gear alters the seafloor, and reduces complexity, sedimentary 

structures, and emergent epifauna. Lindeboom and de Groot (1998) conclude that while trawling 

intensity remains high, biological communities affected by trawling may never recover to their 

original condition. Collie (1998) reviewed studies from New England and concluded that results 

indicate that hard bottom benthic habitats (e.g., boulders and gravel pavement) experience 

significant impacts of bottom fishing gear, while mobile sand habitats are less vulnerable. Fonds 

and Groenewold (2000) conclude that although mobile fishing might attract scavengers to fished 

areas, the annual amount of food made accessible by beam trawling is insufficient to support 

further population growth. In contrast, de Groot (1984) had earlier thought that although 

individual animals might be affected, food sources are readily available such that disturbance is 

not affecting fish at the population level. 

Auster and Langton (1999) review 22 studies from a wide geographic range and concluded that 

mobile fishing gear reduces habitat complexity by: (1) directly removing epifauna or damaging 

epifauna leading to mortality, (2) smoothing sedimentary bedforms and reducing bottom 

roughness, and (3) removing taxa which produce structure (i.e., taxa which produce burrows and 

pits). They also concluded that for fixed gear, the area impacted per unit effort is smaller than for 

mobile gear, but the types of damage to emergent benthos appear to be similar (but not 

necessarily equivalent per unit effort). 

Jennings and Kaiser (1998) completed an extensive review and concluded that fishing activities 

lead to changes in the structure of marine habitats and influence the diversity, composition, 

biomass, and productivity of the associated biota. They further conclude that these effects vary 

according to gears used, habitats fished, and magnitude of natural disturbance, but will tend to 

increase with depth and the stability of the substrate.

Collie et al. (2000a) analyzed 39 published studies to compile and evaluate current findings 

regarding fishing gear effects on habitat. Regarding the type and use of research, the authors 

found: (1) 89% of the studies were undertaken at depths less than 60 m; (2) otter trawl gear is the 

most frequently studied; (3) most studies have been done in Northern Europe and Eastern North 

America. The authors also had several conclusions pertaining to effects of fishing gear: (1) 

intertidal dredging and scallop dredging have the greatest initial effects on benthic biota, 
8

followed by otter trawling and then beam trawling (although beam trawling studies were 

conducted in dynamic sandy areas, where effects might be less apparent); (2) fauna in stable 

gravel, mud and biogenic habitats are more adversely affected than those in less consolidated 

coarse sediments; (3) recovery appears most rapid in less physically stable habitats (inhabited 

generally by more opportunistic species); (4) we may accurately predict recovery rates for smallbodied taxa, but communities often contain one or two long-lived, vulnerable species; (5) largebodied organisms are more prevalent before trawling (Greenstreet and Hall 1996, Frid and Clark 

1999, Veale et al. 2000); and (6) the mean initial response to fishing impacts is negative (55% 

reduction of individual taxa). Based on these findings, the authors suggest that the scientific 

community abandon short-term small-scale experiments and argue for support to undertake 

larger scale experiments that mirror the timing and frequency of disturbance by commercial 

fishing.

The most recent review was completed by the National Research Council (2002), which was 

asked by NMFS to study the effects of bottom trawling and dredging on seafloor habitats. In 

their report, they concluded that: (1) trawling and dredging reduce habitat complexity; (2) 

repeated trawling and dredging result in discernable changes in benthic communities; (3) bottom 

trawling reduces the productivity of benthic habitats; (4) the effects of mobile fishing gear are 

cumulative and are a function of the frequency with which an area is fished; (5) fauna living in 

low natural disturbance regimes are generally more vulnerable to fishing gear disturbance; (6) 

fishing gears can be ranked according to their impacts on benthic organisms; and (7) benthic 

fauna can be ranked according to their vulnerability.

C. SUMMARY OF AVAILABLE SCIENCE

1. Bottom Trawls 

a. Otter Trawls (Fish) 

1. Mud

Effects and Recovery

Pilskaln et al. (1998) deployed sediment traps in two 250 m, mud-clay basins, Wilkinson Basin 

and Jordan Basin, in the Gulf of Maine. Abundances of benthic, infaunal worms with no 

documented swimming activity coincided with seasons of higher trawling activity in those areas, 

based on NMFS effort data. Sediment trap data and effort data were not collected in the same 

year, but authors speculate that occurrence of worms in the traps are a result of those animals 

being dislodged and suspended by trawling. 

Mayer et al. (1991) investigated the immediate effects of a single tow with a commercial otter 

trawl, with 90 kg doors and 18 m footrope with tickler chains, on mud substrate in a 20 m deep 

basin on the coast of Maine. Core samples were collected inside and outside of the trawl track 

before and one day after trawling. Core profiles were similar between the trawled and untrawled 

cores, indicating that a single pass with this otter trawl – unlike scallop dredging (see New 

Bedford scallop dredge - mud) – did not plow the bottom and bury surficial sediments. The 

trawl doors did produce furrows several centimeters deep. 
9

DeAlteris et al. (1999) analyzed data from a 1995 side-scan sonar survey to assess effects of otter 

trawls over sand and mud sediments in lower Narragansett Bay, Rhode Island. Scars from otter 

trawl doors were evident in the side-scan sonar images, but were confined to the deeper mudbottom channels. Tracks were 5-10 cm deep with berms that were 10-20 cm high. The longevity 

of scars was studied using SCUBA to monitor hand-dug trenches (approximately 15 cm deep and 

1.2 m long). Scars at a 14 m mud site persisted more than 60 days, and were occupied by rock 

crabs. A quantitative model was developed to compare the magnitude and frequency of trawling 

and dredging impacts to those of natural physical and biological disturbances. In shallow sandy 

areas, where sediments are eroded daily, physical effects of fishing gear may be inconsequential. 

At the deeper mud-bottom site studied, erosion was predicted to occur less than 5% of the time, 

thus physical effects from fishing would last longer.

Brylinsky et al. (1994) examined physical and biological effects of experimental trawling, with a 

18 m trawl with 200 kg doors and footrope with 29 cm rubber rollers, in a macrotidal (6-8 m at 

high tide) estuary in the Bay of Fundy, Nova Scotia. Sediments were characterized as silty and 

uniform to a depth of 10 cm. Four trawling experiments were conducted with chorophyll a (as 

indicator of benthic diatoms), meiofauna, and macrofauna samples taken inside the door furrow, 

under the area covered by the rollers, and outside the area trawled at 1-3 stations along each 

trawl. Trawl doors made furrows that were 30 cm wide and 5 cm deep, with berms of sediment 

on the outside, that were visible for at least 2-7 months, and rollers compressed sediments. 

Meiofauna were dominated by nematodes and macrofauna was limited to polychaetes and low 

densities of mud snails. Chlorophyll a and abundance of nematodes were reduced for 

approximately 1 month after trawling. Nematodes recovered fully after 4-6 weeks and 

chlorophyll a concentrations increased by fourfold after 80 days. The authors state that the quick 

recovery was expected since sediments in the area are commonly exposed to natural stresses by 

storms and winter ice. There were no consistent differences in abundance or species 

composition of polychaetes inside and outside trawl tracks. 

Sanchez et al. (2000) conducted experimental trawling with a commercial otter trawl on muddy 

substrate off the Catalan coast in Spain. Study sites were fished at two intensities, single sweep 

(3.5 hrs) or double sweep (7 hrs). Infaunal samples, collected with van Veen grabs, were 

compared over time (0, 24, 102, and 150 hrs after fishing) between swept areas and control areas. 

Percent abundance of most major taxa (e.g., polychaetes, crustaceans, and molluscs) was similar 

between fished and unfished areas throughout the experiment. The total number of individuals 

and taxa were significantly higher in the single swept area after 150 hrs, but there were no effects 

on the number of taxa or individuals in the double swept area within 72 hours after trawling. For 

some taxa, there were significant differences in abundance between the trawled and un-trawled 

sites, but this was partially because of an increase in abundance in the fished area and a large 

decrease in abundance in the unfished area. Authors speculate that the increase of some species 

is indicative of natural variability at the experimental site exceeding any effects of fishing. They 

also note that some scavengers and predators could have been attracted to the swept area after 

fishing. Side scan sonar images of the swept area showed furrows left in the sediments by the 

trawl doors which remained visible throughout the experiment.
10

Ball et al. (2000) reviewed two studies of trawling in 30-40 m water depth over mud areas of the 

Scottish Sea and Western Irish Sea (Tuck et al. 1998, Ball et al. 1999), which used closed areas 

and shipwrecks as controls for experimental trawling. Tuck et al. (1998) conducted experimental 

trawling with rockhopper ground gear in an area closed to fishing for almost 30 years. The trawl 

used in the study had no net attached, thus effects of gear were caused by doors and groundrope 

only. Trawling was conducted one day per month for 16 months. Biological surveys were 

completed after 5, 10, and 16 months of disturbance and then after 6, 12, and 18 months of 

recovery in trawled and untrawled reference area. Trawl doors left furrows in the sediment, 

which were evident by side scan sonar for up to 18 months. There were no significant 

differences in infaunal species richness in the experimental and control sites prior to the 

beginning of the experiment or during the first 10 months of trawling, but species richness was 

significantly higher in the trawled site after 16 months of trawling and throughout the recovery 

period. Total infauna abundance was significantly higher in the trawled site prior to fishing, after 

16 months of fishing, and after 12 months of recovery, but not after 18 months of recovery. 

Some species (primarily polychaetes) increased in abundance in the fished site, while others 

(e.g., bivalves) declined in abundance in the fished site. Species diversity of infauna was lower 

in the fished site prior to fishing, during 16 months of fishing, and after 12 months of recovery. 

There were no effects to total biomass. Overall, infaunal community structure in the two sites 

became significantly different after only 5 months of fishing, and remained so throughout the 

experiment. Results from Ball et al. (1999) are provided below in “Otter Trawl (Inverts)” 

section. Based on these two studies, Ball et al. (2000) concluded that prolonged trawling 

reduced the abundance of large-bodied fragile organisms and increased the abundance of 

opportunists, and ultimately resulted in an altered, but stable, community with fewer species and 

an increase in the number of small polychaetes. This altered state was maintained due to long 

recovery times (up to 18 months) of the habitats even when fishing was restricted during parts of 

the year.

Table 1. Summary of literature on effects of otter trawls (used to catch fish) on habitat with mud substrate. Bold 

references indicate peer-reviewed journals. Blank cells indicate information was not provided by the reference.

Reference Location Depth Sediment Type of Effects Recovery Comments

Brylinsky et al. 

1994

Bay of Fundy Intertidalsilt tracks in sediment, 

decrease in nematodes 

and benthic diatoms, no 

effect on polychaetes

furrows 

visible 2-7 

months; 4-6 

weeks for 

nematodes; 1 

month for 

benthic 

diatoms

experimental trawling 

DeAlteris et al. 1999 Narragansett 

Bay, Rhode 

Island

14 m mud tracks (5-10 cm) and 

adjacent berm (10-20 

cm) in sediments;

scars 

maintained > 

60 days

observations with sidescan sonar, monitored 

hand dug scars

Mayer et al. 1991 Maine 20 m mud trawl tracks, no 

difference in core 

profiles

core samples before and 

after single trawl tow

Pilskaln et al. 1998 Gulf of Maine 250 m mud and clay infauna appearantly 

dislodged and suspended

deployed sediment traps 

in fishing grounds
11

Table 1. (continued)

Reference Location Depth Sediment Type of Effects Recovery Comments

Sanchez et al. 2000 Catalan coast, 

Spain

30-40 m mud tracks in sediment, no 

difference in species 

composition, increase in 

total abundance and 

abundance of some 

species of infauna

experimental trawling in 

commercial fishing 

ground

Tuck et al. 1998 Scotland 30-35 m 95% silt and clay tracks in sediment, 

increased bottom 

roughness, in crease in 

infauna species richness, 

decrease in diversity, no 

change in total 

abundance or biomass, 

some species increased 

and others decreased in 

abundance 

physical 

effects still 

evident after 

18 months of 

recovery, 

partial 

recovery of 

infauna 

species after 

12 months 

and epifauna 

species after 6 

months

experimental trawling in 

area closed to fishing 

for 25 years

Conclusions

Three of the four papers summarized here involved experimental manipulations. Those that 

address physical effects report that trawl doors leave tracks in the sediment that remain visible 

for up to 18 months. A short-term study conducted in fishing grounds reports no change in 

species composition, but an increase in infauna abundance in response to trawling. A longterm 

study in an area closed to fishing reports that prolonged fishing results in increased species 

richness, decreased diversity, and no change in total abundance or biomass. 

2. Sand

Effects and Recovery

Diver observations in Long Island Sound 1983-1984 (Smith et al. 1985) showed minor surface 

sediment disturbance (less than 1" deep) within the sweep path of an otter trawl with 6 ft doors, 

30-60 ft scissors, 60-110 ft extended wing nets, and 3/8" chain on the footrope. Sediments in the 

study area were described as sand with mud and clay. Much of the disturbance was by wake 

turbulence suspending small epifaunal organisms, silt and flocculent material as the net passed, 

rather than by the direct physical contact of the net with the bottom. A Achumming effect@

attracted mobile predators due to exposure of prey organisms. Trawl door tracks (in sand, less 

than 2" deep; in mud, 4-10" wide, 2-6" deep) were the most notable evidence of trawl passage. 

These tracks were obscured by tidal currents, but attracted mobile predators. Alteration of 

existing lobster burrows was minor and appeared easily repairable by resident lobsters. Roller 

gear of unspecified size on mud bottom left shallow scoured depressions; spacers between discs 

reduced scouring.

In the DeAlteris et al. (1999) study in Narragansett Bay, Rhode Island (described above), handdug trenches at a 7m deep sandy site lasted 1-4 days. 

Gilkinson et al. (1998) studied the effects of otter doors on infaunal bivalves by observing an 

otter door model deployed in a test tank with sand bottom, designed to simulate the sediment of 
12

the northeastern Grand Banks. The trawl door created a berm in the sediments (average height 

5.5 cm) with an adjacent scour (2 cm) furrow. All 42 bivalves were displaced and left exposed, 

but only two were damaged.

Schwinghamer et al. (1998) examined physical effects of experimental otter trawling (31-34 

hours within a 2 month period for 3 years) over sandy habitat (120-146 m) in the Grand Banks, 

Newfoundland that had been fished extensively since the early 1980’s and then closed to fishing 

in 1992. Effects were examined 1 and 2 years after trawling stopped. The trawl used was an 

Engel 145 otter trawl with 1250 kg oval otter boards and 46 cm rock hopper gear. Trawled areas 

were smoother and cleaner while untrawled areas were hummocky, mottled, and had more 

flocculated organic matter. Tracks left by trawl doors increased the topographic relief of the area 

and were visible for at least 10 weeks, but were not visible or faintly visible after a year. Prena 

et al. (1999) compared trawl bycatch and samples taken by an epibenthic sled from trawled and 

untrawled corridors in this area and found that in trawled areas, total macrofaunal invertebrate 

biomass was 24% lower with decreases in sand dollars, brittle stars, soft corals, snow crabs and 

sea urchins. No significant effects were evident in dominant mollusc species. Kenchington et al. 

(2001) also found immediate reduction (significant in 1 of 3 years of sampling) in the total 

abundance of benthic epifauna and infauna from grab and video samples, and in the abundance 

of 13 taxa (mostly polychaetes) but concluded that there was little indication of long-term effects 

on infauna and that when disturbance was evident, it mimicked natural disturbance.

Moran and Stephenson (2000) conducted experimental otter trawling in fished and unfished 

areas on the continental shelf of northwest Australia (50-55 m). No information on bottom type 

was provided, but it was presumed to be sand (see Sainsbury et al. 1994). Macrobenthos (>20 

cm) which were dense at the study site, were surveyed in trawled and untrawled areas before and 

after four trawling events (four trawl tows per event) with 2 day intervals between each event, 

using a video camera mounted on a sled. Mean density of benthos declined exponentially with 

increasing tow numbers with four tows reducing the density by about 50% and a single tow 

reducing density by about 15%. This estimate is lower than the estimate in Sainsbury et al. 

(1994; 89%) for removal of sponges in the same general area. The disparity may be explained 

by the fact that Moran and Stephenson (2000) used a lighter trawl, with 20 cm disks separated by 

30-60 cm spacers, than Sainsbury et al. (1994). 

McConnaughey et al. (2000) sampled megafauna from 42 paired unfished (inside closed area) 

and heavily fished areas (between 44-52 m depth) using an otter trawl that was modified to catch 

and retain macrofauna in the eastern Bering Sea. Two study sites were sampled, one with sand 

substrate with ripples in 44-52 m depth and one with coarse sand substrate with occasional 4 m 

mounds at 61-82 m depth. The authors concluded that: 1) sedentary megafauna (e.g., anemones, 

soft corals, sponges, whelk eggs, ascidians), neptunid whelks and empty shells were more 

abundant in unfished areas; 2) motile groups (e.g., crabs, sea stars, whelks) and infaunal bivalves 

exhibited mixed responses, suggesting the importance of life history considerations, such as 

habitat requirements and feeding modes; and 3) overall diversity and niche breadth of sedentary 

taxa was greater in unfished areas. Furthermore, long-lived, slow-growing taxa were 

significantly more patchy in highly fished areas, suggesting a slow impact recovery process.

In addition to experimental trawling in silty sediment, Brylinsky et al. (1994) also conducted 

experimental trawling in an area of the Bay of Fundy with coarse sand overlain by a silty layer 
13

up to 10 cm deep. Two types of trawls (18 m and 24 m) and three types of doors (180 kg, 200 kg, 

and 270 kg) were used. The footrope of all trawl configurations had 29 cm rubber rollers and no 

tickler chains. With heavier gear, trawl doors scoured furrows 80-85 cm wide and 2-4 cm deep 

and rollers compressed sediments. Lighter gear compressed sediment, but did not result in any 

scouring. Furrows were visible for at least 2- 7 months. Similar to the silty sites, benthic 

diatoms and nematodes were significantly lower inside trawl furrows, decreases were not as 

severe as the silty site, however, because of lower initial abundances. Nematodes recovered fully 

after 4-6 weeks and chlorophyll a concentrations increased by fourfold after 80 days. There were 

no consistent differences in abundance or species composition of polychaetes inside and outside 

trawl tracks.

On the continental shelf (>200m) in NW Australia, research surveys documented a shift in 

finfish species dominance from those that occur predominantly within habitats that contain large 

epibenthic organisms (Lethrinus, Lutjanus, and Epinephalus), to those that favor open sandy 

habitats (Nemipterus and Saurida), in conjunction with the development of a commercialstern 

and pair trawling fishery (Sainsbury 1987 and Sainsbury et al. 1993, 1994). Trawl closure areas 

implemented in response to these changes (closed for 5 years at time of data collection) resulted 

in increased density of Lutjanus and Lethrinus and increased abundance of small benthos, but no 

changes in the abundance of large benthos. Density of these fishes and abundance of both large 

and small benthos continued to decrease in the areas open to trawling. These results, along with 

video surveys of habitat used by target fishes, indicate that changes in species abundance and 

composition were at least in part a result of the damage inflicted on the epibenthic habitat by the 

demersal trawling gear. Video observations from a camera mounted on a trawl showed that 

sponges >15 cm were removed from the substrate during 89% of observable encounters with the 

trawl groundline.

Bergman and Van Santbrink (2000) sampled benthic fauna before and 24-48 hours after a single 

sweep with a commercial otter trawl over shallow (30-40 m) sandy areas and deeper (40-50 m) 

silty sand areas in the southern North Sea. In silty sand, direct mortality of benthic megafauna 

was 0-52% for bivalves, 7% for gastropods, 0-26% for echinoderms, and 3-23% for crustaceans. 

In sand areas, mortality of sedentary megafauna was 0-21% for bivalves, 12-16% for 

echinoderms, and 19-30% for crustaceans. Some deaths were not caused directly by the passage 

of the trawl, but instead were caused by disturbance, exposure, and subsequent predation. 

Table 2. Summary of literature on effects of otter trawls (used to catch fish) on habitat with sand substrate. Bold 

references indicate peer-reviewed journals. Blank cells indicate information was not provided by the reference.

Reference Location Depth Sediment Type of Effects Recovery Comments

Bergman and Van 

Santbrink 2000

North Sea shallow, 

deep

sand (1-5% silt, 

0.2-0.37mm), silty 

sand (3-10% silt, 

0.15-0.17mm)

decrease in abundance of 

sedentary megafauna 

experimental trawling (6 

sites)

Brylinsky et al. 

1994

Bay of Fundy intertidalcoarse sand 

overlain with silty 

layer

tracks in sediment, 

decrease in nematodes and 

benthic diatoms

furrows 

visible 2-7 

months; 4-6 

weeks for 

nematodes; 1 

month for 

benthic 

diatoms

experimental trawling 
14

Table 2. (continued)

Reference Location Depth Sediment Type of Effects Recovery Comments

DeAlteris et al. 

1999

Rhode Island 7 m sand with sand 

waves

no tracks/berms evident hand dug 

scars 

recovered in 

1-4 days

observations with sidescan sonar, divers 

monitored hand dug 

scars

Gilkinson et al. 

1998

test tank to 

simulate Grand 

Banks of 

Newfoundland

sand 5.5 cm berm adjacent to 2 

cm furrow; bivalves 

displaced

observed effects of 

commercial otter door 

model in test tank

Kenchington et al. 

2001

Grand Banks, 

Newfoundland

120 m -

146 m

fine to medium 

grain sand (~0.17 

mm)

short-term reduction in 

total abundance and 

abundance of some 

infauna and epifauna in 1 

of 3 years

experimental trawling in 

area lightly fished for > 

19 years

McConnaughey et 

al. 2000

Eastern Bering 

Sea, Alaska

44-82 m 44-52 m: sand w/ 

ripples; 61-82 m: 

coarse sand w/ 

mounds 

decrease in sedentary 

megafauna abundance, 

decrease in diversity, 

decrease in habitat 

complexity (e.g., biogenic 

substrate)

patchiness of 

longlived, 

slow growing 

taxa suggests 

slow recovery

compared unfished and 

fished sites (2 sites)

Moran and 

Stephenson 2000

Northwest 

Australia

50 m –

55 m

presumed to be 

sand

significant decrease in 

macrobenthos

experimental trawling in 

unfished area

Prena et al. 1999 Grand Banks, 

Newfoundland

120 m -

146 m

fine to medium 

grain sand (~0.17 

mm)

decrease in epibenthic 

macrofauna biomass 

experimental trawling in 

area unfished for >10 

years

Schwinghamer et 

al. 1998

Grand Banks, 

Newfoundland

120 m146 mfine and medium 

grain sand (0.125-

0.250 mm)

tracks in sediment, 

smoothed sediments and 

removed biogenic mounds 

and flocculated organic 

material, organisms and 

shells organized into 

linear features 

tracks last up 

to 1 year

experimental trawling in 

area unfished for >10 

years

Sainsbury 1987, 

Sainsbury et al. 

1993, 1994

NW Australia < 200 m calcareous sands epibenthic macrofauna 

removed, change in fish 

species composition , 

increased abundance of 

small (<25 cm) benthos

some reversal 

of trends 

within 5 

years, longer 

for recovery 

of large 

epifauna

compared historical data 

(before and during 

fishery) to data 

collected after inside 

and outside area closed 

for 5 years

Smith et al. 1985 Long Island

Sound, New 

York

sand, mud/clay tracks in sediment (1" in 

sand, 4" in mud/clay), 

attraction of predators, 

suspension of epibenthic 

organisms

tracks 

"naturalized" 

by tidal 

currents

video and diver 

observations

Conclusions

Based on the results of 11 studies, 6 of which involved experimental trawling, physical effects of 

trawling on sand habitat include trawl door tracks left on the seafloor, smoothed sediments, and 

removal of biogenic mounds. At greater depths (>120 m) tracks were evident up to 1 year after 

trawling. At shallow sites (< 7 m) tracks were no longer visible after a few days. The four 

studies that examined effects of chronic trawling documented decreased abundance and biomass 

of sedentary macrofauna, decreased diversity. Studies that examined effects of short-term or 
15

pulse trawling documented changes in the abundance of some infaunal and epifaunal taxa, such 

as polychaetes, nematodes, and benthic diatoms, which mimicked natural disturbance. Recovery 

ranged from weeks in intertidal areas to possibly years at depths of 80-200 m.

3. Gravel 

Effects and Recovery

Between 1987 and 1993, modifications to fishing gear allowed fishermen to trawl previously 

inaccessible rocky, boulder habitat in the Gulf of Maine. Bottom conditions were observed in a 

July 1987 submersible dive to 94 m depth near the top of Jeffreys Ledge (Auster et al. 1996). At 

that time the presence of large (>2m diameter) boulders in the area precluded fishing. A thin 

layer of mud covered the gravel and boulders. The rock surfaces supported large numbers of 

erect sponges, as well as sea spiders, bryozoans, hydroids, anemones, crinoid sea stars, and 

ascidians. Smaller mobile fauna, including several species of crustaceans, snails, and scallops, 

were also abundant. When the area was resurveyed in August 1993, much of the mud veneer 

was gone and there was evidence that boulders had been moved, apparently by otter trawling. 

Abundance of erect sponges was greatly reduced, and most of the associated epifaunal species 

were not present. In laboratory predation experiments (Lindholm et al. 1999) decreased habitat 

complexity lead to increased predator success, and therefore, decreased survival of 0-year cod. 

Thus, authors speculate that reduction in benthic epifauna by mobile fishing could affect fish 

populations.

Freese et al. (1999) document the effects of a single passage of a bottom trawl (Nor'easter otter 

trawl with 0.6 m tire gear on the footrope and 0.45 m rockhopper discs and steel bobbins on the 

wings) over cobble-boulder habitat (93% pebble) in the eastern Gulf of Alaska (water depth 206-

274 m). The trawl moved and overturned boulders and caused significant decreases in emergent 

epifauna (e.g., anemones, sea whips and some sponges). The tire gear produced 1-8 cm deep 

imprints in less compact substrate. Of the sponges affected, 14% of finger sponges were 

knocked over, 67% of vase sponges were damaged, and morel sponges were crushed and torn 

apart. Fifty five percent of seawhips counted were broken or pulled out of the substrate. Brittle 

stars were damaged, but reticulate anenomes and motile invertebrates were not. The authors did 

not record recovery rates, but concluded that chronic trawling would probably show greater 

reduction in density of these taxa.

Table 3. Summa ry of literature on effects of otter trawls (used to catch fish) on habitat with gravel substrate. Bold 

references indicate peer-reviewed journals. Blank cells indicate information was not provided by the reference.

Reference Location Depth Sediment Type of Effects Recovery Comments

Auster et al. 1996 Gulf of Maine 

(Jeffrey's 

Ledge)

94 m gravel/boulder with 

thin mud veneer

gravel base exposed, 

decrease in epifauna 

abundance, boulders 

moved

submersible and video 

observations before and 

after trawling

Freese et al. 1999 Gulf of Alaska 200 m -

270 m

93% pebble, 5% 

cobble, 2% boulder

boulders moved, furrows 

1-8 cm in sediment, layer 

of silt removed, 

decreased abundance and 

damage to sponges, 

anemones, and sea whips

video observations 2-5 

hrs after experimental 

trawling 
16

Conclusions

Only 2 papers on the effects of otter trawls to gravel habitat were available, both of which were 

observational. These studies showed that trawling on gravel habitats removes fine sediments, 

moves stones and boulders, and decreases abundance of epibenthic macrofauna and reduces the 

cover they provide. 

4. Coral Reefs and Seamounts 

Effects and Recovery

A number of studies have recorded damage to coral reef habitats due to trawling. A single trawl 

tow over a newly discovered coral reef at 230-280 fathoms in the Gulf of Mexico brought over 

300 lbs of coral to the surface (Moore and Bullis 1960). Reports from fishermen and ROV 

observations confirm the presence of mechanically damaged corals located on trawling grounds 

on the mid-Norwegian continental shelf at 200-400 m depth (Fossa et al. 2001). A single pass 

with a trawl (otter trawl with 40/54 fly net,12.2-m headrope, and 16.5-m footrope with 30 cm 

rubber rollers and 15-cm rubber discs, 1.8 x 1.2 m China V-doors) in a hard bottom sponge and 

coral community at 20 m in Grays Reef, Georgia, damaged finger sponge, vase sponge, barrel 

sponges, whip coral, fan coral, stick coral, and stony tree coral, and caused a significant decrease 

in density of barrel sponges (Van Dolah et al. 1987). In this case, the community recovered 

within a year. The authors speculate that because these species harbor numerous invertebrate 

prey species, damage could affect important nearshore fish populations. Extensive destruction to 

bryozoan coral mounds in Tasman Bay, New Zealand during the 1970s and 1980s, which has in 

turn reduced juvenile tarakihi and snapper abundance, is thought to have been caused by chains, 

bobbins, sweep wires and otter boards of mobile fishing gear (Bradstock and Gordon 1983).

Hall-Spencer et al. (2002) conducted ROV video observations and analysis of commercial otter 

trawl catches from the West Ireland continental shelf break and West Norway to document 

effects of fishing on deep water (200 m – 1300 m) corals. Otter trawls in the commercial fishery 

were fitted with rockhopper gear and 900 kg otterboards. The skippers actively avoided fishing 

over uneven ground, thus only 5 out of 229 trawls observed included large amounts of coral as 

bycatch. In these 5, however, pieces of coral up to ~1 m2 were landed on deck. ROV videos 

documented trawled areas with sparse living coral, coral rubble littering the seafloor, and track 

marks on the seafloor. Unfished areas had no trawl marks and large expanses of coral with 

sessile macrofauna. Radiocarbon dating of the coral fragments indicate mean growth rates of 1.1 

mm/yr with ages over 4500 years.

Seamounts have also suffered extensive damage from trawl fishing. Corals from seamount slope 

areas comprised the largest bycatch in trawl tows (using otter trawls with large bobbins along the 

ground rope) taken in depths of 662-1524 m in tropical New Zealand (Probert et al. 1997). 

These coral patches may require over 100 years to recover, and many were probably crushed or 

overturned without coming to the surface in the net. Koslow and Gowlett-Holmes (1998) and 

Koslow et al. (2001) sampled benthic fish and invertebrate macrofauna over seamounts in 

Tasmania subject to varying levels of fishing effort by orange roughy otter trawls. Results 

demonstrated that in heavily fished areas, substrates were predominantly bare rock or coral 

rubble and sand, colonial corals and associated fauna were lacking, and species abundance and 

richness were lower than in lightly fished areas. Although the absence of survey information 
17

prior to fishing precludes definitive conclusions, authors attribute these differences to fishing 

effort and recommend permanent closed areas to protect the seamount ecosystem.

Table 4. Summary of literature on effects of otter trawls (used to catch fish) on coral reef habitat. Bold references 

indicate peer-reviewed journals. Blank cells indicate information was not provided by the reference.

Reference Location Depth Sediment Type of Effects Recovery Comments

Bradstock and 

Gordon 1983

New Zealand 10-35 m bryozoan coral 

mounds

destruction of mounds, 

decreased size and 

density of coral, decrease 

in abundance of juvenile 

fishes

observations 

Hall-Spencer et 

al. 2002

West Ireland, 

West Norway

200 m, 

840 m -

1300 m

deepwater coral 

reef

track marks, destruction 

of reefs, decrease in 

sessile macrofauna

> 4000 yrs ROV video observations 

and analysis of 

commercial trawl catches

Koslow and 

Gowlett-Holmes 

1998; Koslow et 

al. 2001

Tasmania 600-1500 

m 

seamounts with 

various substrates 

( e.g., mud, sand, 

rock, coral rubble, 

barnacles)

removed colonial coral, 

decrease in macrofauna 

abundance and species 

richness

compared 14 seamounts 

with various fishing 

effort 

Probert et al. 

1997

New Zealand 660-1500 

m

seamounts coral damaged and 

collected in trawls

observations of 

commercial by-catch 

Van Dolah et al. 

1987

Georgia 20 m low-relief hard 

bottom

damage to sponge and 

coral species, decreased 

density of barrel sponge

within 1 year experimental trawling (1 

trawl tow)

Conclusions

The five studies summarized here all show that otter trawls damage sponge and coral species, in 

both nearshore and seamount habitats, resulting in a decrease in fish and invertebrate macrofauna 

abundance and density. 

5. Variable habitats

Effects and Recovery

Side scan sonar and video observations were used to document the cumulative effects of various 

mobile fishing gears used in Bras D’Or Lakes and St. Peters Canal, Nova Scotia (Canadian 

Department of Fisheries and Oceans 1993). Water depths ranged from 10 - 500 m, and bottom 

sediments included rich organic mud, clay, pebbly mud, well-sorted sand, gravel and boulders. 

Otter doors left parallel marks in the sediments, with fainter marks from the footgear and 

bobbins. These marks were seen predominantly in muddy sediments. 

Engel and Kvitek (1998) compared lightly and heavily fished areas off central California with 

similar sediments (gravel, sand, silt/clay) and depth (180 m) using still and video photography, 

Smith-McIntyre grab samples and fish stomach contents (English sole, Dover sole and Pacific 

sanddab). Results indicated that the heavily fished sites had more trawl tracks, exposed 

sediment/shell fragments, fewer rocks and mounds, and less flocculent material. All invertebrate 

macroepifauna were more abundant in the lightly trawled areas, with significantly higher 
18

densities for seapens, seastars, sea anemones, and sea slugs. The number of polychaete species 

was higher in lightly trawled areas, but densities of nematodes, oligochaetes, and ophiuroids 

were higher in heavily trawled areas in all three years (although in most cases differences were 

insignificant). No differences were detected for crustaceans. One polychaete species that was 

the most important prey item for English sole, Dover sole and Pacific sanddab was more 

abundant in the heavily trawled area in all three years, with sifnificant differences in 2 of the 3 

years. The authors concluded that trawling reduces habitat complexity and biodiversity while 

increasing opportunistic infauna and prey important in the diet of some commercially important 

fish species.

Riemann and Hoffmann (1991) assessed the water column effects of otter trawling in a shallow, 

eutrophic sound (Limfjord) in Denmark. Suspended particulate matter, oxygen, and nutrient 

(phosphorus and nitrogen) levels were measured at a number of stations throughout the water 

column at a dredged and a control site in two different locations before trawling, immediately 

afterwards, and 30 and 60 minutes later. Maximum water depth was 7.5 – 11 m. No information 

on sediment type was given. Trawling was performed for 15 minutes with a small (6-m wide) 

commercial eel trawl. Average suspended particulate matter increased significantly at both sites 

immediately after trawling, but returned to pre-trawl levels 60 minutes later. There was no 

significant effect on oxygen and either minor (non-significant) increases, or no clear trends, in 

most nutrients. Ammonia increased significantly immediately after trawling at one site, but 

marked differences before trawling between the control and the experimental site complicated 

the interpretation of this result.

Table 5. Summary of literature on effects of otter trawls (used to catch fish) on habitat with mixed substrate. Bold 

references indicate peer-reviewed journals. Blank cells indicate information was not provided by the reference.

Reference Location Depth Sediment Type of Effects Recovery Comments

Bridger 1972 English 

Channel

10-20 m sand and shell with 

small stones, 

muddy sand with 

patches of flint

stones dislodged and 

overturned, sand ripples 

smoothed, ridges and 

grooves created

diver observations over 

various habitat types

Engel and Kvitek 

1998

central 

California

180 m gravel, sand, silt, 

clay

tracks in sediment, fewer 

rocks and mounds, 

decrease in flocculent 

material and abundance 

of epibenthic 

macrofauna, increase in 

density of nematodes, 

polychaetes, oligochaetes 

and ophioroids

compared epifauna and 

infauna between a 

lightly fished site and 

heavily fished site

Riemann and 

Hoffmann 1991

Denmark 7.5 m -

11 m

significant increase in 

suspended particulate 

matter

turbidity 

returned to 

normal within 

1 hour

water column sampling 

before and after 

experimental dredging 

at two locations

High 1998 Northwest 

USA

various tracks in sediment, 

increased turbidity, 

benthic fauna and rocks 

dislodged

diver observations over 

various habitat types

Conclusions

Four papers observe effects of otter trawls on habitats with a mixture of sediment types. 

Physical effects mirror those reported for sections above, including the overturning of stones, 

tracks in sediment, sediment re-suspension, and smoothing of seafloor. The one paper that 
19

addresses biological effects reports that trawling results in a decrease in epibenthic macrofauna, 

and an increase in opportunistic infauna. One paper that addresses chemical effects of trawling 

found no significant effects. No information is provided on recovery.

b. Otter Trawls (Invertebrates)

1. Mud

Effects and Recovery

Ball et al. (2000) sampled benthic macrofauna in offshore areas (75 m depth), a heavily fished 

site and a “pseudo control” shipwreck site that had not been fished for about 50 years, within 

Nephrops prawn trawl fishing grounds in the Irish Sea. Grab samples were taken before and 24 

hours after trawling. Due to the paucity of organisms and low biomass, there were no significant 

differences in macrofauna sampled before and after trawling the heavily fished site. There were, 

however, fewer species and individuals, and lower species diversity in the commercially trawled 

area than near the shipwreck. At the shipwreck site, the number of species, number of 

individuals, and biomass decreased with increasing distance from the ship. Sixty-nine species 

found at the offshore wreck site were not found at the experimental fishing site. Large 

specimens of some molluscs and echinoderms were most common near the wreck, whereas only 

juveniles of these species were sampled in the trawled area. 

Drabsch et al. (2001) sampled benthic macroinfauna prior to and 2-3 weeks after experimental 

trawling with a commercial prawn otter trawl in an area of South Australia where little to no 

fishing had occurred for 15 years. Three study sites were used, with a trawled and control 

corridor at each site. At one study site located at 20 m depth with fine silt sediments, otter 

boards left tracks in the sediments and the footline and net smoothed topographic features and 

removed 28% of epifauna. Trawling resulted in a significant decrease in total abundance and in 

the abundance of 1 taxonomic group of polychaetes. Similar changes were not evident for any 

other taxa.

Harris and Poiner (1991) compared 1964 surveys taken in water depths of 17 - 21 m in the Gulf 

of Carpentaria, Australia prior to commercial prawn fishing, with 1985-86 surveys taken in the 

same areas after 20 years of commercial fishing (otter trawls for banana and tiger prawn). 

Sediments were characterized as mud transitions zones. Between the sampling periods, total 

demersal fish abundance decreased from 897 fish/ha to 283 fish/ha, 18 of 82 species (found 

mostly at the deeper sampling depth) decreased, and 12 of 82 species (bentho-pelagic species 

found mostly at nearshore sites) increased. There were no significant correlations between 

fishing effort and changes in species abundance, but the data suggest the decreased abundance in 

18 taxa was a result of fishing effort and bycatch. The authors speculate that the increase in the 

12 bentho-pelagic taxa might be related to disposal of fish bycatch.

Hansson et al. (2000) examined effects of experimental shrimp trawling on pure clay habitats at 

75-90 m in a Swedish fjord. Benthic macrofauna were collected using a Smith-McIntyre grab 

four times (1-5 months) before and four times (5-9 months) after experimental trawling at 3 

trawled sites and 3 untrawled sites. The study sites were located in an area closed to fishing for 6 

years. The otter trawl used had a 10 m head rope, 14 m ground rope with 20 kg of lead, and 125 

kg otterboards. For 61% of the species sampled, abundances were negatively affected by 
20

trawling. Total biomass (at all 3 sites) and total abundance (at 2 sites) decreased significantly, 

but significant reductions were also observed at control sites. Individual phyla responded 

differently to trawling; echinoderm (mostly brittlestars) abundance decreased significantly, total 

abundance of polychaetes was not affected (although some families increased and some families 

decreased), and amphipods and molluscs were not affected.

Table 6. Summary of literature on effects of otter trawls (used to catch invertebrates) on habitat with mud substrate. 

Bold references indicate peer-reviewed journals. Blank cells indicate information was not provided by the 

reference.

Reference Location Depth Sediment Type of Effects Recovery Comments

Ball et al. 2000 Irish Sea 75 m sandy silt decrease in infauna and 

epifauna richness, 

diversity and abundance

compared heavily fished 

area and un - fished area 

near a shipwreck

Drabsch et al. 2001 South 

Australia

21 m fine silt significant decrease in 

total macroinfauna 

abundance 

experimental trawling (1 

station) in area with no 

trawling for 15 years

Harris and Poiner 

1991

Australia (SE 

Gulf of 

Carpentaria)

17 m -

21 m

mud transition decrease in demersal fish 

abundance

comparison of survey 

data from 1964 and 

1985/86

Hansson et al. 2000 Sweden 75-90 m clay decrease in abundance of 

70 % of macrofauna, 

signifanct decrease in 

brittlestar abundance

experimental trawling 

(for 1 year) in area closed 

to fishing for 6 years

Conclusions

The three studies summarized here do not report on physical effects. Biological effects of 

shrimp otter trawls include a decrease in species richness, abundance, diversity and biomass of 

invertebrate benthic macrofauna, and a decrease in demersal fish abundance. In two studies of 

the biological effects of shrimp trawling in areas that had not been fished for a number of years, 

many species were less abundant after a year of sustained trawling, but significant reductions in 

total macrofauna abundance and the abundance of some taxa were only noted for individual 

trawled sites. No information is provided on recovery.

2. Sand

Effects and Recovery

In addition to sampling at mud bottom in South Australia, Drabsch et al. (2001) described above 

sampled at two 20 m sites with medium-coarse sand sediments and shell fragments. As with the 

silt site, trawl boards left tracks in the sediment, smoothed topographic features and removed 

macroepifauna. In contrast to results from the mud site, trawling did not result in any changes in 

abundance of macroinfauna. The only change which was attributed to trawling was a decrease in 

the density of one family of polychaetes at one location 2-3 weeks after trawling. 

Gibbs et al. (1980) sampled benthic macrofauna (epifauna and infauna), using Smith MacIntyre 

grabs, prior to and following the seasonal commercial prawn fishery, and prior to and after 

experimental trawling repeatedly for a period of 1 week (using 10-m otter trawl with 1075 by 

537 mm flat otter boards and chain spiders) in New South Wales, Australia. Samples were taken 

in muddy sand (0-30 % mud/clay) at three sites within the fishing grounds and one unfished 

control site. Trawl footropes only lightly skimmed the bottom and disturbed very little sand. 

Trawling did create a plume of sand, but after repeated trawls, the seafloor was only slightly 
21

modified. Dissimilarity coefficient and community statistics showed no significant differences 

in macrobenthos between the 3 fished sites and the control site before or after experimental 

trawling or after the commercial trawling season. 

Frid et al. (1999) developed a priori predictions concerning the effects of fishing by Nephrops

prawn otter trawls on benthic macrofauna species abundances, and tested those predictions using 

time series (27 years) of Van Veen grab data from sand habitats in 55 m of water and silt/clay 

habitats in 80 m of water in the North Sea. The time series was broken into 3 periods of fishing 

effort: low, moderate, and high. Taxa predicted to increase with fishing effort included errant or 

mobile polychaetes and ophiuroid and asteroid echinoderms. Taxa predicted to decrease with 

fishing effort included sedentary or fragile taxa such as echinoid echinoderms, large bivalves, 

and sedentary polychaetes. Outside fishing grounds those taxa predicted to increase and/or 

decrease with fishing remained constant. Inside heavily fished areas those taxa predicted to 

increase with fishing were significantly more abundant during the period of high fishing effort, 

but those predicted to decline remained the same. Results indicate that species abundances in 

both areas were affected by natural changes in organic input, but that inside heavily fished areas 

macrofauna abundance was influenced more by fishing.

In addition to sampling at mud bottom in the Irish Sea, Ball et al. (2000) described above 

sampled benthic macrofauna in lightly-fished, inshore prawn trawl fishing grounds and at an 

unfished (for about 50 years) “pseudo” control site near a shipwreck. Both areas were at 35 m 

depth with muddy sand sediments. Differences between the fished site and the wreck site were 

similar in kind but less pronounced than at the mud, heavily fished, offshore site. There were 

reductions in species richness, total abundance, biomass, and diversity. Larger reductions in 

these parameters at the offshore site could have resulted from differences in historical fishing 

intensity, depth or substrate. Fifty-eight species found at the inshore wreck site were not found 

at the experimental fishing site. Other polychaetes were more common at the fished site.

Table 7. Summary of literature on effects of otter trawls (used to catch invertebrates) on habitat with sand substrate. 

Bold references indicate peer-reviewed journals. Blank cells indicate information was not provided by the 

reference.

Reference Location Depth Sediment Type of Effects Recovery Comments

Ball et al. 2000 Irish Sea 35 m mudy sand decrease in total 

abundance, richness and 

diversity

compared heavily fished 

area and un- fished area 

near a shipwreck

Drabsch et al. 2001 South 

Australia

20 m coarse sand with 

shells 

furrows in sedment, 

smoothing of topographic 

features, removal of 28% 

of macroepifauna, no 

effects on macroinfauna 

experimental trawling (2 

stations) in area with no 

trawling for 15 years
22

Table 7. (continued)

Reference Location Depth Sediment Type of Effects Recovery Comments

Frid et al. 1999 North Sea 55 m, 

80 m

55 m station sand 

with 20% silt/clay; 

80 m station > 50% 

silt/clay 

changes to macroinfaunal 

abundances

27 year monitoring at 

lightly and heavily fished 

sites

Gibbs et al. 1980 New South 

Wales, 

Australia

shallow 

estuary

sand with 0-30% 

silt/clay

no significant effects on 

macrobenthic infauna or 

epifauna

sampled before and after 

commercial fishing 

season

Conclusions

Three studies, all using different study approaches, are summarized here. Physical effects of 

shrimp trawls on sand habitats include tracks in the sediments and smoothing of the seafloor. 

One study, conducted at 20 m water depth, reports negative effects of trawling on the abundance 

of macroepifauna, but no effects on macroinfauna. Another study, conducted in a shallow 

estuary, concludes that there are no effects of trawling to either macroinfauna or macroepifauna. 

No information is provided on recovery of biological communities.

c. Roller Frame Trawls

1. Submerged Aquatic Vegetation 

Effects and Recovery

Studies in Florida (using “Tarpon Springs" and "St. Petersburg" shrimp roller trawls with 4.5 - 8 

inch rollers, and 75kg shrimp roller trawl with steel rollers) have shown that trawling with side 

frame trawls in seagrass beds gathers unattached algae and deciduous leaves, but does not 

decrease mean shoot density, number of blades, blade length or below ground biomass (Tabb 

1958, Futch and Beaumariage 1965, Meyer et al. 1991) as long as rake teeth do not extend below 

the roller. Authors agree, however, that shrimp trawls should include gear specifications to 

minimize damage to seagrasses. Long-term, chronic effects have not been studied.

Table 8. Summary of literature on effects of roller frame trawls on seagrass habitat. Bold references indicate peerreviewed journals. Blank cells indicate information was not provided by the reference.

Reference Location Depth Sediment Type of Effects Recovery Comments

Futch and 

Beaumariage 1965

Florida shallow Thalassia beds no significant effects on 

seagrass

experimental trawling (3 

sites)

Meyer et al. 1991 Florida shallow Thalassia beds no significant effects on 

seagrass

experimental trawling

Tabb 1958 Florida 

(Biscayne 

Bay)

shallow Thalassia beds no significant effects on 

seagrass

experimental trawling

Conclusions

Three separate experimental studies agree that roller frame trawls have no significant effects on 

seagrass habitats (all three studies were conducted in Thalassia beds in Florida).
23

d. Beam Trawls

1. Mud

Effects and Recovery

Schratzberger et al. (2002) examined effects of beam trawling on meiofauna in mud habitats at 

59 m depth in the North Sea. Meiofauna were sampled with a circular corer at trawled and 

untrawled sites both before and after experimental trawling with a 4-m beam trawl with 80 mm 

mesh and chain matrix. Sample areas were described as relatively lightly fished by the 

commercial trawl fishery. At trawled sites species richness and nematode biomass decreased 

with increased fishing effort with decreases being most pronounced immediately after trawling. 

However, changes in species richness and nematode abundance were similar at both control and 

trawled sites. Thus, the authors concluded that there were no short-term or medium-term impacts 

on meiofaunal diversity or biomass, and that any impacts due to trawling were minor in relation 

to seasonal changes in the community. 

Table 9. Summary of literature on effects of beam trawls on habitat with mud substrate. Bold references indicate 

peer-reviewed journals. Blank cells indicate information was not provided by the reference.

Reference Location Depth Sediment Type of Effects Recovery Comments

Schratzberger et al. 

2002

North Sea 59 m mud no significant differences 

in meiofauna at trawled 

and control sites

experimental trawling 

Conclusions

Results of one study conclude that beam trawling has no significant impact on meiofauna in mud 

habitat.

2. Sand

Effects and Recovery

Schratzberger et al. (2002; see above) also conducted experimental trawling at a muddy sand site 

in the North Sea. At trawled sites species richness and nematode biomass decreased with 

increased fishing effort with decreases being most pronounced 1 month after trawling. Similar 

changes occurred at control and trawled sites, leading the authors to conclude that impacts due to 

trawling were minor in relation to seasonal changes in the community.

Margetts and Bridger (1971) used SCUBA and video cameras to observe physical effects of a 9.1 

m Dutch beam trawl with 0.2 x 0.7 m runners, and 3 part bridle at a water depth of 22 m in the 

English Channel. Beam trawls left furrows in and smoothed both hard sand and mud-sand 

sediments. Furrows and sediment suspension were much more discernible on muddy sediment. 

Fonteyne (2000) used measurements of pressure change, sediment type, and side scan sonar 

images to examine the physical effects of a 4-m beam trawl with tickler chain matrix over Goote 

Bank off Belgium and the Netherlands. The author concluded that the effects on the seabed are 

related to weight of gear, towing speed, and sediment type. On densely packed fine sand 

overlaid with a silt layer, the trawls resuspended the upper 1 cm of the sediments, so that the 

resulting surface sediments were harder and less rough. In most disturbed areas, sediments 
24

recovered to pre-trawl conditions within 15 hours. Tracks remained visible, however, for 52 

hours in coarse sand and for 37 hours in fine sediments. 

Bergman et al. (1990) and Bergman and Hup (1992) studied the effects of beam trawls in the 

North Sea. Their study site was in a lightly fished area with water depth of 30 m and mediumhard sandy sediments. Experimental trawling was repeated with a 7000 kg, 12-m beam trawl 

with ticklers until full coverage of the study site was achieved 3 times. Macrofauna were 

sampled with a bottom grab and 2.8 m beam trawl before, 8 hours after, and 16 hours after 

trawling. Experimental trawling resulted in physical penetration of the gear to at least 6 cm, and 

a 40-65% decrease in density of starfishes, small heart urchins, tube-dwelling polychaete worms, 

and small crustaceans. Many other species did not change and a few increased, possibly due to a 

change in vertical distribution with trawling disturbance. The authors discuss the possibility that 

because the area has been fished, alterations to the biota may have already occurred during past 

decades.

Bergman and Van Santbrink (2000) sampled benthic ma crofauna before and 24-48 hours after 

experimental trawling (with 12-m beam trawl with ticklers, 4-m beam trawl with ticklers and 4-

m beam trawl with chain matrix) over shallow sandy areas and deep silty sand areas in the North 

Sea. Results showed a 5-40% mortality of gastropods, starfish, crustaceans, and annelid worms 

and a 20-65% mortality of bivalves. Some deaths were not caused directly by the passage of the 

trawl, but were instead caused by disturbance, exposure, and subsequent predation. Authors 

speculate that mortalities would increase in the summer months when animals migrate to the 

sediment surface. 

Philippart (1998) analyzed bycatch records of demersal fishes and macro-epifaunal invertebrates 

from commercial fishermen when the bottom fishery in the southeast North Sea changed from 

otter to beam trawling. Beam trawlers caught proportionally more invertebrate species (e.g., 

whelks, urchins, squids, and crabs) than otter trawls and had a catch efficiency (for both targeted 

and non-targeted species) of 10 times higher than that of the otter trawl. 

The effects of beam trawls have been studied extensively in two specific areas in the eastern Irish 

Sea. One site consists of stable, coarse sand and gravel and the other consists of mobile sand 

ribbons and megaribbons (Kaiser and Spencer 1996b, Kaiser et al. 1996b, 1998, 1999). 

Following experimental trawls (10-12 passes) with a 3.5 tonnes, 4-m beam trawl with chain 

matrix, sand ripples were flattened, sediments were less consolidated (due to the chain matrix), 

and fine materials were suspended and moved away by tidal currents. Short-term changes to 

biota in the more stable environment included a 54% reduction in the number of infaunal species 

and 40% reduction in individuals (due to removal of less common species), a decrease in slowmoving epifauna and an increase in mobile species. Furthermore, serpulid worm tubeheads were 

significantly lower in fished sites, but densities were unaffected at the scale and intensity of 

fishing in the study because the worms were often attached to rocks that passed through the net, 

and thus could recolonize between sampling. These changes in biota were detectable for up to 6 

months. No differences in biota were detected at the sites with more mobile sediments. The

authors comment that although effects were short-term, the length that effects endure depends on 

the timing of the impact. For example, effects might be less evident if they coincide with peak 

settlement of benthic fauna or during a time of frequent natural disturbances.
25

Rijnsdorp and Vingerhoed (2001) examined stomach contents of plaice and sole in the North 

Sea. No clear differences in stomach contents were found between areas inside and outside of 

the “plaice box” which has reduced trawling effort by 12-m beam trawls. However, a 

comparison between recent (1996) and past (~1900) data revealed a shift in major prey types 

from dominance of bivalves to dominance of polychaetes. The authors comment that the 

observed changes agree with those predicted from trawl damage studies (i.e., increase in shortlived taxa and decrease in long-lived taxa), but note that similar changes could also be a result of 

eutrophication and pollution.

Table 10. Summary of literature on effects of beam trawls on habitat with sand substrate. Bold references indicate 

peer-reviewed journals. Blank cells indicate information was not provided by the reference.

Reference Location Depth Sediment Type of Effects Recovery Comments

Bergman and Van 

Santbrink 2000

North Sea shallow, 

deep

shallow sand (1-5% 

silt, 200-370 mm), 

deep silty sand (3-

10% silt, 150-170 

mm)

decrease in benthic 

macrofauna abundance 

(epifauna and infauna)

experimental trawling (6 

sites)

Bergman and Hup 

1992

North Sea 30 m fine to mediumhard sandtrawl penetrates to 6 cm, 

decrease in benthic 

macrofauna abundance

experimental trawling (1 

site)

Fonteyne 2000 Belgium, The 

Netherlands

20-30 m coarse sand, fine 

sand with layer of 

silt

tracks in sediment; 

alteration in sediment 

composition, suspension 

of sediments

sediments 

recover in 15 

hrs, tracks 

visible for 52 

hrs on coarse 

sand, 37 hrs 

on fine sand 

with silt

observations (2 sites)

Kaiser and Spencer 

1996b, Kaiser et al. 

1996b, 1998, 1999

Irish Sea 12-20 

m, 26-

35 m

medium sand with 

ripples, coarse sand 

with gravel and 

shell debris

sediments smoothed, 

suspended, and less 

consolidated; decrease in 

benthic macrofauna 

abundance in stable 

sediments, no effects on 

macrofauna in mobile 

sediments

6 months in 

stable 

sediments

experimental trawling (1 

site)

Margetts and Bridger 

1971

English 

Channel

22 m hard sand with 

gravel and stones

15 mm tracks in 

sediment; smoothing of 

surface, stones rolled

SCUBA and video 

observations

Margetts and Bridger 

1971

English 

Channel

22 m muddy sand 80-100 mm tracks in 

sediment, smoothing of 

surface, resuspension of 

sediments

>10 min SCUBA and video 

observations

Philippart 1998 North Sea increase bycatch of 

macroepifauna

analyzed catch data over 

20 years during switch 

from otter trawl to beam 

trawl commercial 

fisheries
26

Table 10. (continued)

Reference Location Depth Sediment Type of Effects Recovery Comments

Rijnsdorp and 

Vingerhoed 2001

North Sea change in composition of 

prey species

compared 1990 stomach 

contents and 1996 

stomach contents inside 

and outside of area 

closed to fishing

Schratzberger et al. 

2002

North Sea 39 m, 

59 m

muddy sand no significant effects on 

total abundance or 

species richness of 

meiofauna

experimental trawling at 

lightly fished sites

Conclusions

Ten studies, including 6 experimental, 2 observational, 1 using time series data, and 1 examining 

fish gut contents inside and outside a closed area, were available for inclusion in this report. 

Physical effects of beam trawls on sand habitats include suspension of sediments, alteration of 

sediment composition, smoothing of the seafloor, and trawl tracks in the sediment that remain 

visible for hours to months. Results from one study conclude that beam trawling decreases 

macrofauna abundance in stable sediments, but has no effect on macrofauna in mobile 

sediments. Six additional studies report that beam trawling decreases the abundance of 

macrofauna. A change in species composition of prey species associated with prolonged beam 

trawling is also reported. No information is provided on recovery from biological effects. 

e. Rapido Trawls

Rapido trawls resemble toothed beam trawls and are used in the Adriatic Sea – in sandy offshore 

areas to harvest scallops and in muddy inshore areas to harvest flatfish. Hall-Spencer et al. 

(1999) used underwater video 1 hour and 15 hours after trawling to examine the physical and 

biological effects of a 3-m Rapido trawl towed 5 times at a depth of 25 m in the Gulf of Venice, 

Italy. Trawling erased infaunal burrow openings, decreased the abundance of slow 

moving/sessile benthos, such as scallops, sea cucumbers and large fragile bivalves, and increased 

the abundance of mobile scavengers.

Pranovi et al. (2000) used sandy sediment areas around shipwrecks (as unfished area) in the 

Adriatic Sea for experimental fishing with Rapido trawls. Trawls produced flat tracks that were 

still clearly visible after a week, disturbed the upper 6 cm of the sediment, but did not affect 

sediment grain size. Divers observed that fishing removed debris and resulted in a 50% 

reduction of epifaunal organisms. Total abundance and total biomass of infauna collected in 

core samples decreased immediately after trawling, but increased again after only 1 week. 

However, a comparison of the shipwreck control areas to fishing areas demonstrated that several 

taxa were significantly less abundant in the fished areas, which the authors suggest indicates a 

long-term cumulative effect not evident from the short-term experimental study design. The 

authors also recognized that the presence of the wreck in the control area could modify the local 

benthic community, thus confounding results.
27

Table 11. Summary of literature on effects rapido trawls on habitat with sand substrate. Bold references indicate 

peer-reviewed journals. Blank cells indicate information was not provided by the reference.

Reference Location Depth Sediment Type of Effects Recovery Comments

Hall Spencer et al. 

1999

Gulf of 

Venice, Italy

shallow sand erased burrow openings, 

decrease in slow moving 

and sessile epifaua, 

increase in scavengers

experimental trawling 

Pranovi et al. 2000 Adriatic Sea 24 m sandy removed debris from 

seafloor, decrease 

epifauna, reduction in 

infaunal abundance and 

biomass

fauna 

recovered in1 

week

experimental trawling in 

unfished area near 

shipwreck

Conclusions

Results of 2 studies indicate that rapido trawls disturb the upper 6 cm of sandy seafloor, reduce 

abundance of epifauna, and temporarily reduce the abundance and biomass of inaunal organisms. 

Infauna recovered quickly (1 week) in one study.

2. Dredges 

a. Hydraulic Clam Dredges 

1. Sand 

Effects and Recovery

Meyer et al. (1981) used SCUBA to observe effects of a small (4' wide) hydraulic clam dredge in 

a surfclam bed located near Rockaway Beach on the south shore of Long Island, New York. The 

depth was 11 m and the sediment was silty sand. The dredge formed trenches that were the same 

width as the dredge and over 20 cm deep. Mounds of sand were formed on either side of the 

trenches. The dredge raised a cloud of silt 0.5- 1.35 m in height, which settled within 4 minutes. 

Two hours after dredging trench walls began slumping. After 24 hours the dredge track was less 

distinct, appearing as a series of shallow depressions. The dredging attracted predators, with 

lady and rock crab preying on damaged clams, and starfish, horseshoe crabs and moon snails 

attacking exposed but undamaged clams. By 24 hours after dredging, the abundance of predators 

appeared to have returned to normal. 

MacKenzie (1982) sampled benthic invertebrate assemblages in three ocean quahog beds with 

contrasting fishing histories: one had never been fished, one had been actively fished for two 

years, and one had been fished for about a year and then abandoned. All three beds were in very 

fine to medium sand sediments in 37 m off southern New Jersey. No significant differences 

were found in numbers of invertebrate individuals, numbers of species or species composition 

between previously dredged and undredged areas. Hydraulic dredging thus did not appear to 

have any lasting effect on the invertebrate populations in these beds. Polychaetes and bivalves 

exposed by dredging presumably were able to reburrow and survive. 

Medcof and Caddy (1971) conducted SCUBA and submersible observations to compare effects 

of hydraulic dredges (without teeth) to non-hydraulic dredges with teeth, in shallow water (7-12 

m) sand inlets in south Nova Scotia. On sand and sand-mud habitats, hydraulic dredges left 

smooth tracks with steeply cut walls that were an average of 20 cm deep and slowly filled in by 
28

slumping, whereas non-hydraulic dredges left tracks that were 3-10 cm deep and had a raked 

appearance. The hydraulic dredge raised sediment clouds, which seldom exceeded 0.5 m in 

height and usually settled within 1 minute. Dredge tracks were still easily recognizable after 2-3 

days. 

Murawski and Serchuk (1989) used manned submersibles in 1986-1987 to observe effects of 

experimental dredging on sand and mud bottom habitats. Studies were conducted in offshore 

areas ranging from east of Delaware Bay to south of eastern Long Island (water depths not 

reported). The authors reported that hydraulic dredges in the Mid-Atlantic penetrate deeper into 

the sediments than do scallop dredges and, on a per-tow basis, result in greater short-term 

disruption of the benthic community and underlying sediments. In coarse gravel, the sides of the 

dredge-created trench soon collapsed, leaving little evidence of dredge passage. There was also 

a transient increase in bottom water turbidity. In finer-grained, hard-packed sediments, tracks 

persisted several days after dredging. Non-harvested organisms (e.g., sand dollars, crustaceans, 

worms) were substantially disrupted by the dredge. Sand dollar assemblages appeared to recover 

quickly. Starfish and benthic feeding fish were abundant in dredge tracks, probably feeding on 

exposed infauna. 

Pranovi and Giovanardi (1994) studied the effects of a 2.7 m wide hydraulic dredge in 1.5-2 m 

depths in Venice Lagoon (Adriatic Sea). In 1992, divers took sediment and infaunal sample s 

from experimentally-dredged and control areas both in and outside commercial fishing grounds 

immediately after dredging and every 3 weeks for 2 months. The dredge created 8-10 cm deep 

furrows, one of which was clearly visible 2 months later. In this study, sediment grain size was 

not significantly affected by dredging, although portions of the fishing grounds which had been 

predominantly silt and clay sediments 15 years earlier now had a considerably higher sand 

content. Within the fishing grounds, faunal numbers and biomass were significantly reduced in 

the experimental plot immediately following dredging. Densities, especially of small species, 

recovered two months later, but biomass did not. Outside the fishing grounds, immediately after 

passage of the dredge, there were no significant faunal differences between dredged and 

undredged areas. 

Tuck et al. (2000) examined the effects of a hydraulic (water jet) dredge on the seabed and 

benthic community in a shallow (2-5 m), sandy site in the Outer Hebrides, on the west coast of 

Scotland. In the study area, sediments consisted of moderately well-sorted medium or fine sand 

and tidal currents reached speeds as high as 3 knots. Core samples and diver and video 

observations were taken before, during, immediately after, 5 days after, and 11 weeks after 

dredging, inside and outside 6 dredge tracks. Immediately after dredging, sediments had dredge 

tracks with a depth similar to the dredge blade and distinct vertical walls that collapsed once the 

dredge was hauled. The sediment within the tracks was fluidized to a depth of approximately 0.3 

m, and there was significantly more silt in the sediments outside the tracks than inside. After 5 

days, tracks and depth of fluidized sediments remained the same, but the change in silt 

composition was no longer evident. After 11 weeks the tracks were no longer visible, but 0.2 m 

of sand was still fluidized. Immediately after dredging, the number of species and total 

abundance was lower in fished tracks. At 5 days, number of species and total abundance 

recovered, but there was a significant decrease in the proportion of polychaetes and an increase 

in the proportion of amphipods. Bivalves were not affected by dredging. The biological 
29

community recovered completely within 11 weeks. Owing to the strong currents, epifauna in the 

area was very sparse: the only change observed after dredging was the attraction of crabs into the 

area to scavenge on material disturbed by the dredge. 

Table 12. Summary of literature on effects of hydraulic dredges on habitat with sand substrate. Bold references 

indicate peer-reviewed journals. Blank cells indicate information was not provided by the reference.

Reference Location Depth Sediment Effects Recovery Comments

Meyer et. al., 1981 Long Island, 

New York

11 m silty sand >20 cm deep trench, sand 

mounds, silt cloud, 

attraction of predators

trench nearly 

indistinct, 

predator 

abundance 

normal after 

24 hours; silt 

settled in 4 

minutes

SCUBA observations 

MacKenzie, 1982 Southern New 

Jersey

37 m very fine to 

medium sand

no significant differences 

in number of individuals 

or species (infauna)

comparison of heavily 

fished, recently fished 

and never fished area

Medcof & Caddy 

1971

Southern Nova 

Scotia

7-12 m sand and sand-mud smooth tracks with steep 

walls, 20 cm deep; 

sediment cloud

sediment 

plume lasted 1 

minute; 

dredge tracks 

still clearly 

visible after 2-

3 days

SCUBA & submersible 

observations

Murawski & Serchuk 

1989

Mid-Atlantic sand, mud and 

coarse gravel

trench cut, increased 

turbidity, disruption of 

benthic organisms in 

dredge path, attraction of 

predators

trench filled 

quickly in 

coarse gravel, 

but took 

several days 

in fine 

sediments

submersible observations 

Pranovi & 

Gionovardi 1994

Adriatic Sea 

(Italy)

1.5-2 m sand 8-10 cm deep furrow; 

immediate decrease in 

abundance and diversity 

of benthic infauna in 

fishing ground; no effects 

outside fishing ground

after 2 mos, 

furrows still 

visible, 

infaunal 

densities in 

fishing 

ground 

recovered, 

biomass did 

not

experimental dredging in 

previously dredged and 

undredged areas in 

coastal lagoon

Tuck et al. 2000 Outer Hebrides, 

Scotland

2-5 m medium to fine 

sand

steep-sided trench (30 

cm deep), sediments 

fluidized up to 30 cm, 

significant decrease in 

number of infaunal 

species and total 

abundance, polychaetes 

most affected

trench no 

longer visible 

but sand still 

fluidized after 

11 weeks, 

species 

diversity and 

abundance 

recovered 

within 5 days, 

abundance of 

all species 

recovered 

after 11 weeks

diver observations and 

experimental dredging
30

Conclusions

Results of six studies indicate that hydraulic clam dredges create a steep-sided trench up to 30 

cm deep that persists from 1 day to >2 months, and a sediment cloud in the dredge path that lasts 

for a few minutes. One study showed that dredging also fluidized sand within the dredge track 

for at least 11 weeks. Two studies showed that dredging resulted in temporary disruption of 

infaunal species, and decreased species abundance and diversity, with recovery in approximately 

8-11 weeks. In one study, there was evidence that infaunal communities in previously dredged 

locations were more severely affected than those in previously un-dredged locations. In contrast, 

one study found no significant differences in the numbers of infaunal individuals or species in 

heavily dredged, recently dredged, and undredged areas. 

b. Escalator Dredges 

1. Mud

Effects and Recovery

Effects of escalator dredging on water quality and benthic infauna were examined in an 

intertidal, mud flat habitat (<94% silt/clay before harvest) in Maine (Kyte et al. 1975, 

summarized in Coen 1995). Variables studied were hydrography, grain size, salinity, pH, 

dissolved oxygen, hydrogen sulfide, suspended sediments, nutrients, benthic infauna, and direct 

physical effects of the gear (tracks and trenches). Samples were taken prior to, during, and 10 

months after dredging. Turbidity plumes only lasted for a short time and often did not reach 

ambient seston levels. There were few consistent effects on water column chemistry. Infauna l 

community effects were limited due to rapid recruitment of affected invertebrates in the path of 

the dredge. 

Table 13. Summary of literature on effects of escalator dredges on habitat with mud substrate. Bold references 

indicate peer-reviewed journals. Blank cells indicate information was not provided by the reference.

Reference Location Depth Sediment Effects Recovery Comments

Kyte et al. 1975 Maine intertidalmud turbidity plumes, few 

consistent effects on water 

chemistry, limited effects 

on benthic community

rapid 

recruitment of 

benthic 

organisms

experimental dredging 

Conclusions

Results of one study indicate that escalator dredges do not have lasting adverse effects on 

intertidal mud habitat.

2. Sand

Effects and Recovery

Maier et al. (1995) assessed the effects of mechanical escalator dredges in muddy sand tidal 

creeks in South Carolina by comparing pre- and post-dredging turbidity levels and benthic 

infaunal assemblages. Turbidity was monitored 2 weeks before, during, and 2 weeks after 

dredging at one location and during and immediately after dredging at another. Infaunal samples 

were collected 3 weeks before and 2 weeks after dredging in a harvested creek and in an 

unharvested creek. No commercial clam dredging had taken place in either of these creeks for 5 

years. Turbidity was elevated in the vicinity of the dredge and immediately downstream while it 

was operating, but the sediment plumes only persisted for a few hours. Sampling failed to detect 
31

any significant changes in the abundance of dominant infaunal taxa, or in the total numbers of 

individuals, after dredging. Effects of escalator dredging had no detectable effects on water 

quality at several sites with coarse-grained sediments in Washington (Tarr 1977). This 

information was summarized by Coen (1995).

Table 14. Summary of literature on effects of escalator dredges on habitat with sand substrate. Bold references 

indicate peer-reviewed journals. Blank cells indicate information was not provided by the reference.

Reference Location Depth Sediment Effects Recovery Comments

Maier et al. 1995 South Carolina muddy sand turbidity plumes, no 

significant changes in 

abundance of dominant 

infaunal taxa or total 

number of individuals 

after dredging.

turbidity 

plumes 

persisted for a 

few hours

before and after dredging 

study in harvested and 

un-harvested tidal creeks

Tarr 1977 Washington coarse-grained 

sand

no effects on water 

quality

see Coen (1995) –

primary source not 

available

Conclusions

Two studies indicated that escalator dredges fluidize sand, create trenches up to 30 cm deep, and 

resuspend fine sediments, but effects on water quality and benthic infauna appear to be minimal 

and short-term.

3. Submerged Aquatic Vegetation 

Effects and Recovery

Godcharles (1971) conducted experimental escalator dredging in seagrass beds, Caulerpa algae 

beds, and sand bottoms in Tampa Bay, FL. The dredge water jets were capable of penetrating 

the sediments to a depth of 7 inches and left trenches that were 5 inches deep. Virtually all 

attached vegetation in the path of the dredge was uprooted leaving bare, open bottom areas. 

Dredges also uncovered a deep stratum of broken shells. Trenches were visible from 1-86 days, 

and while most sediments had hardened within a month, some remained soft over 500 days. 

Differences in silt/clay content between tracks and undisturbed areas became negligible after a 

year, but seagrasses had still not recolonized. Based on these findings, the author recommends a 

complete prohibition of dredging in areas with seagrasses and algae.

Damage to submerged aquatic vegetation (SAV) caused by escalator dredges in Chincoteague 

Bay, Virginia, was investigated by Orth et al. (1998). They reported a large number of circular 

“scars” in the vegetation, with 70-100% seagrass cover outside the scarred areas, an abrupt 

reduction to 15% or less at the scar edge, and low percent cover (<15%) across the scar until a 

second abrupt increase in cover occurred at the center where seagrass had not been disturbed. 

There were no measurable differences in percent cover estimates in the scarred portions of areas 

that were dredged during 1998 and 1 and 2 years previously, indicating that revegetation was 

proceeding very slowly. The authors concluded that even the most lightly impacted areas would 

require a minimum of 5 years to fully recover. Increased turbidity caused by persistent hydraulic 

clam dredging in shallow water where sediments have a high percentage of silt and clay could 

also inhibit light required by SAV for photosynthesis and growth (Ruffin 1995).
32

Table 15. Summary of literature on effects of escalator dredges on seagrass habitat. Bold references indicate peerreviewed journals. Blank cells indicate information was not provided by the reference.

Reference Location Depth Sediment Effects Recovery Comments

Godcharles 1971 Tampa Bay, FL sand with seagrass 

and algae

water jets penetrate to 7 

cm, create trenches 5 cm 

deep; uprooted vegetation, 

increased silt/clay content 

in dredge tracks

trench present 

up to 3 

months, 

softened 

sediments 

>500 days; 

after 1 year, 

sediment 

content 

returned to 

normal, but 

seagrass still 

unrecovered

experimental dredging 

Orth et al. 1998 Chincoteague 

Bay, Virginia 

seagrass beds circular “scars” left by 

dredges, severe loss of 

grass in dredge track

revegetation 

slow, 

estimated to 

take at least 5 

yrs in lightly 

disturbed 

areas

observations

Conclusions

Two studies indicate that escalator dredges used in shallow, sandy SAV habitat uproot seagrass, 

leave large holes in the bottom, fluidize sediments, and create trenches 5 cm deep. Trenches 

persisted for as long as 3 months and the silt/clay content returned to normal after a year. The 

time required for the bottom to “harden” was extremely variable (1 to more than 16 months). 

Revegetation of areas affected by dredging was shown to take more than a year and may take 

more than 5 years.

c. New Bedford Scallop Dredges 

1. Mud

Mayer et al. (1991) investigated the immediate effects of scallop dredging at a shallow (8 m), 

nearshore site on the Maine coast with a mixed mud, sand, and shell hash substrate. The site was 

dragged once with a New Bedford style chain sweep dredge and core samples were collected 

before and one day after dragging. Dragging lowered the substrate by 2 ±1 cm and tilled the 

sediment to a depth of 9 cm, causing finer material (sand and mud) to be injected into the lower 

5-9 cm of the sediment profile and a coarsening of the sediment above 5 cm. Organic matter 

profiles were strongly affected by dragging. Total organic carbon and nitrogen at the new 

sediment-water interface were markedly reduced in concentration after dragging and carbon 

increased significantly at the 5-8 cm sediment depth intervals. A diatom mat on the surface of 

the sediment was disrupted by the dredge and partially buried. The microbial community of the 

surface sediments increased in biomass following dragging.
33

Table 16. Summary of literature on effects of New Bedford scallop dredges on habitat with mud substrate. Bold 

references indicate peer-reviewed journals. Blank cells indicate information was not provided by the reference.

Reference Location Depth Sediment Effects Recovery Comments

Mayer et al. 1991 Gulf of Maine 8 m mud with sand 

and shell hash

tilled sediment to 9 cm and 

left trenches up to 2 cm; 

decrease in fine sediments 

and organic matter at 

surface but increase at 5-9 

cm depth; disruption of 

surface diatom mat

surface 

biomass 

increased 

within 1 day 

experimental dredging 

Conclusions

One study indicates that a New Bedford scallop dredge tilled muddy sediments, decreased fine 

sediments and organic matter at the sea surface, and left tracks in the sediments. 

2. Sand 

Effects and Recovery

Sidescan sonar over Stellwagen Bank (depths of 20-55 m) showed that scallop dredging 

disturbed sand ripples and dispersed shell deposits in the troughs of sand waves (Auster et al. 

1996). These features are restored periodically when large storms pass through the area.

Visual and photographic observations were made from a submersible before (1986) and after 

(1987) heavy commercial dredging at an offshore, gravelly sand bank (56 to 84 m) in the Gulf of 

Maine (Fippennies Ledge; Langton and Robinson 1990). Sediments throughout the area 

averaged 84% sand, with some gravel and a very small amount (<1%) of mud. Sediments in 

dredged areas changed from more organic-silty sand to a sandy gravelly appearance, apparently 

due to the disruption of amphipod tube mats. Piles of rock and scallop shells were observed, 

apparently deposited there when dredges were emptied at the surface. In addition, the density of 

three dominant megafaunal species (scallops, burrowing anemones and a tube-dwelling 

polychaete) decreased significantly between pre- and post-dredging observations. 

The geochemical and biological effects of scallop dredging were examined in a shallow (15 m), 

silty-sand estuarine environment on the Maine coast (Watling et al. 2001). Bottom samples for 

sediment chemistry, microbiology and benthic infauna and epifauna were collected by divers in a 

control and an experimental plot before and after intensive dredging using a 2 m wide New 

Bedford style dredge. The dredge was equipped with chain sweeps, but no cutterbar. Sampling 

was conducted 4 and 5 months before dredging, immediately before and after dredging, and 4 

and 6 months after dredging. The immediate effects of dragging were the loss of the fine 

fraction of the top few centimeters of sediment and a reduction in the food value of the sediment 

(significant reductions in enzymatically hydrolysable amino acids and total microbial biomass). 

Fine sediments still had not been restored six months after dragging, whereas the food value of 

the sediments in the experimental plot showed relatively complete recovery within 4-6 months. 

There was no difference in the number of macrofauna taxa present after dragging, but total 

abundance was reduced for up to four months. Differences were no longer detectable after 6 

months. 
34

Table 17. Summary of literature on effects of New Bedford scallop dredges on habitat with sand substrate. Bold 

references indicate peer-reviewed journals. Blank cells indicate information was not provided by the reference.

Reference Location/Date Depth Sediment Effects Recovery Comments

Auster et al. 1996 Stellwagen 

Bank, Gulf of 

Maine

20-55 m sand smoothing of ripples 

and waves, dispersal of 

shell deposits in wave 

troughs

bottom 

features reformed by 

large storms 

(>1 yr)

side-scan sonar survey

Langton & 

Robinson 1990

Fippennies 

Ledge, Gulf of 

Maine

56-84 m gravelly sand with 

some shell hash and 

small rocks

coarser substrate, 

disruption of amphipod 

tube mats, piles of small 

rocks and scallop shells; 

reduced density of tube 

dwelling polychaete and 

burrowing anemone

submersible and photo 

observations before and 

after dredging

Watling et al. 2001 Damariscotta 

River, Maine 

15 m silty sand loss of fine surficial 

sediments, lowered 

food quality of 

sediment, reduced 

abundance of some 

species, no changes in 

number of taxa

benthic fauna 

recover after 6 

months, 

recovery of 

food value 

within 4-6 

months

experimental dredging at 

1 site

Conclusions

Three studies of the effects of New Bedford scallop dredges on sand habitat types are 

summarized. Dredging smoothed sand ripples, dispersed shell deposits, rocks and cobble, 

resuspended fine sediments, and left flat dredge tracks in the sediment. Dredging also reduced 

biogenic structure by disrupting amphipod tubes and reduced the abundance of tube-dwelling 

polychaetes and anemones. One study documented recovery of benthic infauna within 6 months.

3. Variable Sediments

Effects and Recovery

Caddy (1968) described diver observations of dredge effects in shallow scallop (Placopecten 

magellanicus) beds in the Gulf of St. Lawrence. The depth was about 20 m and the sediments 

ranged in texture from mud to clean sand. Fishing operations were conducted with a 2.4 m wide, 

0.36 mt weight, offshore chain sweep scallop dredge (no teeth) that was modified to reduce its 

weight by replacing the forward drag bars with chains. The lateral skids produced two parallel 

furrows approximately 3 cm deep; a series of smooth ridges between them were caused by the 

rings in the chain belly of the dredge. Dislodged pieces of dead shell were more evident within 

the drag tracks than on the surrounding bottom.

Caddy (1973) used a two-man submersible to observe the effects of a 2.4 m wide offshore chain 

sweep scallop dredge (no teeth, weight 0.6 mt or 1300 lb out of the water) and a gang of three 

0.8 m wide inshore Alberton style toothed dredges in Chaleur Bay, Gulf of St. Lawrence. Depth 

varied from 40 to 50 m, and the substrate was sand overlaid by glacial gravel, 1-10 cm in 

diameter, with occasional boulders up to 60 cm across embedded in the gravel. Scallops were 

harvested with Alberton dredges in this location beginning in 1969. Visual, photographic and 

video observations were made inside and outside the dredge tracks within an hour of each tow. 

Dredging suspended fine sediments and reduced visibility from 4-8 m to less than 2 m within 20-

30 m of the track. Turbidity dispersed within 10-15 min of the tow, coating the gravel in the 

vicinity of the track with a thin layer of fine silt. The offshore dredge left a flat track in the 
35

sediment surface. Gravel fragments were less frequent inside the track, and many were 

overturned. Rocks 20-40 cm in diameter were dislodged, some boulders were overturned and 

others were plowed along, leaving a groove several meters long.

Table 18. Summary of literature on effects of New Bedford scallop dredges on habitat with mixed substrate. Bold 

references indicate peer-reviewed journals. Blank cells indicate information was not provided by the reference.

Reference Location/Date Depth Sediment Effects Recovery Comments

Caddy 1968 Northumberland 

Strait, Gulf of 

St. Lawrence, 

Canada

20 m mud and sand tracks (2 cm deep) in 

sediments, ridges from 

rings, dislodged shells 

in dredge tracks

diver observations 

Caddy 1973 Chaleur Bay, 

Gulf of St. 

Lawrence, 

Canada

40-50 m sand over gravel, 

with occasional 

boulders

suspended sediment, 

tracks in sediment, 

gravel fragments less 

frequent, rocks 

overturned, dislodged 

or plowed along 

bottom

submersible and photo 

observations 

Conclusions

According to two studies on habitat with variable sediment types, New Bedford scallop dredging 

leaves tracks in the sediment, dislodges shells and rocks, and resuspends sediments. 

d. Toothed scallop Dredges

1. Sand 

Effects and Recovery

A detailed study of the physical and biological effects of scallop dredging was conducted in a 

large, semi-enclosed, predominantly tidal embayment (Port Phillip Bay) in southeast Australia in 

1991 (Currie and Parry 1996, 1999, Black and Parry 1994). The depths at the three study sites 

were similar (about 15 m), but the sites had different sediments and were exposed to different 

current strengths and wave characteristics. Sediments at the three sites, respectively, were 

predominantly fine and very fine sand, medium-fine sands, and silt and clay with shell 

fragments. Experimental plots were located in areas that were undredged by the commercial 

fishery for 3 years. Plots were experimentally dredged repeatedly over a 2-3 day period by 

commercial draggers using toothed “Peninsula” style dredges fitted with cutter bars that did not 

extend below the skids. The biological impacts of dredging were evaluated using a BACI 

(before, after, control, impact) experimental design. Recovery from the physical and biological 

impacts of dredging was monitored over a 14 month period.

Experimental dredging in the same location disturbed the top 10-20 mm of sediment, but

sometimes penetrated up to 60 mm in softer sediments (Black and Parry 1994). Turbidity 

plumes extending 1-2 m into the water column were created within 2-16 seconds immediately 

behind the dredge, reaching sediment concentrations 2-3 orders of magnitude greater than the 

turbidity caused by storms. Sediment concentrations returned to natural storm levels after about 

9 minutes at sites 60 and 80 m downcurrent of the experimental dredging plots. Smaller sediment 

plumes were also produced by the skids. Dredging smoothed sand ripples (Curry and Parry 

1999) and biogenic mounds (Currie and Parry 1996) and produced parallel tracks up to 25 mm 

deep in the sediments. Tracks were still visible a month after dredging, but not after six months. 
36

Sand ridges re-formed immediately following a storm that occurred five days after the area was 

dredged. Biogenic mounds re-formed after six months. Eleven months after dredging there were 

no visible differences in topography between the control plots and the dredged plots. 

At one of the three sites in Port Phillip Bay, there was a significant decrease in the number of 

species in the dredged plot that persisted for 14 months (Currie and Parry 1996). In the 3.5 

months following dredging, 6 of the 10 most common benthic species at this site showed 

significant decreases in abundance; most species decreased in abundance by 20-30%. Of the 6 

species whose abundance was reduced, two were affected for 3.5 months, two for 8 months, and 

two for 14 months. Dredging impacts became undetectable for most species following their 

annual recruitment (6 months after dredging). Species that occurred on or near the sediment 

surface (e.g., tube-dwelling amphipods) were released into the water column by the first pass 

with the dredge, and species inhabiting deeper sediments (e.g., burrowing polychaetes) were 

dislodged as dredging continued. More mobile, opportunistic species inhabiting surface 

sediments increased in abundance during the 3.5 months after dredging. The maximum 

difference between the two plots occurred three weeks after dredging, suggesting that there are 

indirect effects such as increased predation of infaunal organisms that were uncovered by 

dredging. Only two and three of the ten most common species at the other two sites were 

significantly reduced in abundance, but authors note that reduced sampling intensity limited the 

statistical power of the tests (Currie and Parry 1999). The authors concluded that although 

scallop dredging results in biological impacts to benthic habitats, the reductions in density caused 

by dredging were small compared to effects from differences in sediment types or from natural 

changes in population densities, which occurred at the control sites during the year (Currie and 

Parry 1996, 1999). 

Butcher et al. (1981) documented diver observations of scallop dredging in Jervis Bay, New 

South Wales, Australia, over large-grained firm white sand shaped in parallel ridges at depths 

below 13 m. The dredge design was not described, but had teeth which extended up to 5 cm 

below the leading edge of the dredge. Operation of the dredge flattened sand ridges and 

produced a sediment plume extending up to 5 m into the water column that settled out within 15 

minutes. Dredge paths were clearly visible and “old” dredge paths could be seen. 

Thrush et al. (1995) conducted an experimental study of scallop dredging at two high energy 

sites in the Mercury Bay area of the Coromandel Peninsula in New Zealand in 1991. One site 

was regularly exploited by commercial scallop fishermen and the other was not. The sediment at 

both sites was coarse sand, but was more poorly sorted and had a large fraction of shell hash at 

the exploited site. The depth was about 24 m at each site. Divers collected core samples and 

made visual observations in dredged and undredged areas at each site before dredging, within 2 

hrs of dredging, and 3 months after dredging. At both sites, the dredge broke down the natural 

surface features (e.g., emergent tubes and sediment ripples) and the teeth created grooves 

approximately 2-3 cm deep. Changes in macrobenthic community structure in dredged areas 

differed from undredged areas for at least three months at each site. At both sites, significant 

differences in benthic community structure, and decreases in the density (mean number per core) 

and number of taxa of common macrofauna were apparent immediately after dredging. Three 

months later at the unexploited site, total density and the densities of 4 of the 13 most common 

taxa were still lower in the dredged plots. At the exploited site, total density in the dredged plot 
37

recovered after 3 months, but some species were still less abundant while others had increased in 

abundance. The authors concluded that the differences in recovery processes at the two sites 

were likely related to differences in the initial community composition and to differing 

environmental characteristics.

Eleftheriou and Robertson (1992) examined the effects of repeated scallop dredge tows in a 

shallow, sandy bay on the west coast of Scotland using photographic observations and grab 

samples of epifauna and large infauna before and after dredging. The authors note that there was 

no control in this study, and therefore no statistical tests of location or temporal effects on the 

benthic fauna. The depth at the study site was about 5 m and the sediment was well-sorted sand 

(mean grain size 0.194-0.205 mm). A 1.2-m wide scallop dredge with nine, 12-cm long teeth and 

chain bag removed was towed over the same track 25 times during a 9 day period. Dredge teeth 

penetrated the bottom to a depth of 3-4 cm. Dredging created furrows, eliminated natural bottom 

features, and dislodged large shell fragments and small stones. Dredging had no effect on the 

vertical distribution of grain size, organic carbon, or chlorophyll a. Grooves and furrows created 

by the dredge were eliminated shortly after dredging by wave action and tidal conditions. 

Infaunal invertebrates that were adapted to the stresses of a high-energy environment (e.g., 

amphipods and bivalves) were not affected, the number of small crustaceans increased 

significantly with successive tows, and crabs and starfish were attracted to feed on dead and 

damaged organisms left behind the dredge. There were no significant changes in biomass of the 

different taxonomic groups. The plowing effect of the dredge buried, damaged, or chased away 

organisms such as sea urchins, starfish, scallops, razor clams and sand eels (Ammodytes spp.), 

brittlestars, burrowing anemones, and swimming crabs. 

Table 19. Summary of literature on effects of toothed scallop dredges on habitat with mud substrate. Bold 

references indicate peer-reviewed journals. Blank cells indicate information was not provided by the reference.

Reference Location Depth Sediment Effects Recovery Comments

Black & Parry 1994, 

1999

Port Phillip 

Bay, SE 

Australia 

15 m muddy sand (0.09-

0.22 mm mean 

grain size, 7.2-

30.1% mud)

sediment plume, 

smoothing of seafloor, 

disturbance up to 6 cm 

into bottom

turbidity returned 

to normal storm 

levels within 9

minutes

experimental 

dredging (3 sites) 

Butcher et al. 1981 Jervis Bay, 

New South 

Wales, 

Australia

> 13 m sand sediment plume, 

flattening of sand ridges

plume settled 

within 15 minutes

diver observations

Currie & Parry 

1996, 1999

Port Phillip 

Bay, SE 

Australia 

15 m fine/very fine sand 

(15% mud, 0.09 

mm mean grain 

size)

smoothing of mounds, 

depressions filled, tracks 

in sediment; reduced 

species diversity, reduced 

abundance of 6 of 10 

most common species

mounds re-formed 

after 6 months, 

tracks visible 1-6 

months; most 

species recovered 

within 6 mos, but 

some had not after 

14 months

experimental 

dredging (1 site)

Currie & Parry 1999 Port Phillip 

Bay, SE 

Australia 

15 m medium-fine sand 

(7.2% mud, 0.22 

mm mean grain 

size)

removal of sand ripples, 

significant decrease in 

abundance of 3 of 10 

infauna species 

ripples re-formed 

by storm in 5 days 

experimental 

dredging (1 site)

Currie & Parry 1999 Port Phillip 

Bay, SE 

Australia 

15 m muddy sand with 

shell fragments 

(30.1% mud, 0.14 

mm mean grain 

size)

significant decrease in 

abundance of 2 of 10 

infauna species

experimental 

dredging (1 site)
38

Table 19. (continued)

Reference Location Depth Sediment Type of Effects Recovery Comments

Eleftheriou & 

Robertson 1992

Loch Ewe, 

Scotland

5 m sand no lasting physical 

effects; no significant 

effects on infauna 

adapted to high-energy 

environment; damage or 

mortality of larger 

epifauna, razor clams, 

and sand eels; 

aggregations of predatory 

species

experimental dredging

Thrush et al. 1995 New Zealand 24 m coarse sand surface sediment features 

removed, tracks 2-3 cm 

deep from teeth; change 

in community structure, 

reduced abundance of 

common taxa and 

number of taxa

after 3 months 

benthic 

community 

recovered at 

exploited 

sited, partially 

recovered at 

unexploited 

site 

experimental dredging

 (2 sites)

Conclusions

Evidence provided by seven studies in four different sandy bottom locations indicates that 

toothed dredges eliminate seafloor features, flatten sand ridges and remove sand ripples. 

Dredging also creates sediment plumes, but turbidity plumes dispersed within minutes. In lowenergy environments, dredge tracks were still visible after 1 month, but after 6 months tracks 

were gone and biogenic mounds had reformed. Biological effects included damage or mortality 

of large epifauna and, in low or moderate-energy environments, reduced species diversity, 

numbers and abundance of many infaunal taxa. Most taxa recovered within 3-6 months, but 

some required more than 14 months. A study conducted in a shallow, high-energy environment 

that is regularly disturbed by storms indicated that none of the observed physical or biological 

effects of dredging – aside from the immediate mortality of large epifauna in the dredge track –

lasted for more than a few days.

2. Gravel 

Effects and Recovery

Samples of epibenthic bycatch were collected with a gang of four Newhaven type (springtoothed) scallop dredges in June and October 1995 on 13 different commercial fishing grounds in 

the Irish Sea that had been exposed to different amounts of fishing effort during the preceding 60 

years (Veale et al. 2000). Depths ranged from 20 to 67 m and sediment types were generally 

coarse sand and gravel, overlain with pebbles, cobbles, and dead shell. The dredges were 

equipped with short teeth (76 mm) and small belly rings (57 mm). Species diversity and richness, 

total number of individuals, biomass, and the production of most of the major individual taxa 

investigated all decreased significantly with increasing fishing effort, whereas species dominance 

increased with effort. Of all the environmental parameters examined (including depth, bottom 

hardness and texture), a combination of long- and short-term fishing effort best explained the 

observed differences in bycatch assemblages across sampling sites.
39

Kaiser et al. (1996a) compared the immediate effects of beam trawling and scallop dredging on 

benthic communities on a heavily fished scallop ground off the southwest coast of the Isle of 

Mann, adjacent to the closed area studied by Bradshaw et al. (2000). Three parallel waylines 

were established: one was fished 10 times with a 4 m commercial beam trawl fitted with a 80 

mm diamond mesh codend towed at 4 knots, one was left undisturbed, and one was fished 10 

times with two gangs of four Newhaven (spring-tooth) dredges. Both gears reduced the 

abundance of most species, and resulted in significant changes in the benthic community 

between fished and unfished waylines. There were no significant differences between the two 

fished waylines, even though they were fished by the different gear, which suggests that the 

disturbance caused by either gear had similar effects on the benthic community.

Bradshaw et al. (2001) conducting controlled scallop dredging experiments in a 2 km2 closed 

area near the Isle of Man, in the Irish Sea, that was closed to commercial fishing by towed gear 

in 1989. The entire area adjacent to and inside the closed area had been heavily dredged for 50 

years prior to the closure. Two experimental plots inside the closed area were dredged every two 

months or so for 5 years using two sets of four spring-loaded Newhaven-type scallop dredges 

towed 10 times along each line. In addition, three plots located outside the closed area are 

exposed to commercial scallop dredging. Grab samples were collected twice a year in all seven 

plots. Depth in the study area ranged from about 25 to 40 m and the seabed was a mixture of 

gravel, sand, and mud. Samples collected over a three-year period showed the same trend of 

experimentally dredged plots being more similar to commercially dredged plots than undredged 

plots in the closed area. However, none of these differences were significant, nor were there any 

clear trends for particular species or groups of species. There were also no significant 

differences in total species number or richness between treatments. There was evidence that 

dredging reduces benthic community heterogeneity. Sessile organisms were considered to be 

especially sensitive to dredging disturbance and were analyzed separately. Three years after 

experimental dredging began and 9 years after the area was closed, encrusting bryozoans, 

encrusting sponges, and small ascidians were more common in dredged plots, while upright 

forms such as bryozoans and hydroids were more common in the undredged plots. 

In an earlier paper, Bradshaw et al. (2000) analyzed density estimates of epibenthic animals 

made during diver surveys in the undisturbed portion of the closed area. Many epifaunal species 

increased significantly in abundance between 1989 and 1998, including brittlestars, a spider crab, 

scallops, hermit crabs, and one species of starfish. The most significant changes occurred in the 

5

th, 7th, and 9th years after the area was closed.

Bradshaw et al. (2002) compared recent benthic sample data from 7 sites, located south and west 

of the Isle of Man subject to varying levels of fishing, to historical (from1938-1952; some of 

these data were analyzed by Hill et al. 1999) data collected when scallop dredging in the area 

was still very limited. Fishing disturbance for each site was evaluated in terms of total fishing 

effort of a sample fleet (1981-1993) and its coefficient of variation (greater values indicate a 

more even distribution of fishing disturbance from year to year), the number of years since 

fishing began, and a fishermen’s index of total fishing effort since the start of the fishery. Time 

was a significant factor across all sites and, at two sites where spatial and temporal replicate 

samples were available, the historical samples were distinct from all the recent (1994-1999) 

samples collected at the same sites at different times. Taxa that decreased in abundance between 

the two time periods included species of brittlestars, hydroids, upright and encrusting bryozoans, 

encrusting worms, and barnacles. Taxa that were more abundant in recent samples included 
40

large-bodied tunicates, mobile crustaceans (shrimp, spider crabs and squat lobsters) and robust 

scavengers (whelks, hermit crabs, and starfish). Taxa that became more abundant had, on 

average, more “robust” life-history characteristics than those that decreased in abundance. 

Faunal similarity decreased significantly as the fishermen’s index of effort and the number of 

years since fishing began increased. Similarly, the proportion of species “lost” between the two 

sampling periods increased significantly as the number of years since fishing began increased. 

The increase in total fishing effort, as estimated from fishermen’s logbooks, had no effect. These 

results suggested to the authors that it is the length of time over which fishing occurs, rather than 

absolute levels of effort, which are important in structuring benthic communities. There was no 

clear evidence of a relationship between change in taxonomic diversity and fishing effort, 

although taxonomic distinctness – probably the best indicator of changes in biodiversity –

decreased over time at two of the most heavily fished sites.

Caddy (1973) used a two-man submersible to collect visual, photographic and video 

observations of the effects of 0.8 m wide inshore Alberton toothed dredges in Chaleur Bay, Gulf 

of St. Lawrence. Depth varied from 40 to 50 m and the substrate was sand overlaid by glacial 

gravel, 1-10 cm in diameter, with occasional boulders up to 60 cm across embedded in the 

gravel. A gang of three dredges were attached to a common steel towing bar. The upper and 

lower edges of each dredge mouth were armed with blunt teeth 4 cm long. Tracks left by these 

dredges were shallow with a flat floor. Gravel was sparser inside than outside the track and 

dislodged boulders were commonly observed. Tooth marks were seen over sandy bottom. Spoil 

ridges were left between adjacent dredges and piles of small rocks were seen at intervals along 

the track. 

Table 20. Summary of literature on effects of toothed scallop dredges on habitat with gravel substrate. Bold 

references indicate peer-reviewed journals. Blank cells indicate information was not provided by the reference.

Reference Location Depth Sediment Effects Recovery Comments

Bradshaw et al. 

2000, 2001

Irish Sea 25-40 

m

gravel, sand, and 

mud

dredged plots had 

benthic communities 

more similar to 

commercially dredged 

plots 6-8 years after 

closure, more 

heterogeneous 

communities in 

undredged plots, 

encrusting species more 

abundant in dredged 

plots, upright species 

less abundant

increased 

abundance of 

several 

epifaunal 

species 5-9 

years after 

closure

experimental dredging 

in portion of closed area

Bradshaw et al. 

2002

Irish Sea sand and gravel some taxa less abundant 

in recent samples, 

“robust” taxa more 

abundant; faunal 

differences and 

proportion of “lost” 

species between time 

periods increased 

significantly as number 

of years since fishing 

began increased, no 

effect of increases in 

total effort

compared recent data 

from 7 sites exposed to 

varying amounts of 

fishing effort to data 

collected 50-60 years 

ago, when scallop 

fishing was very limited
41

Table 20. (continued)

Reference Location Depth Sediment Type of Effects Recovery Comments

Caddy 1973 Chaleur Bay, 

Gulf of St. 

Lawrence, 

Canada

40-50 m gravel over sand, 

with cobble and 

boulders

tracks with berms in 

sand, boulders dislodged, 

rocks plowed by dredge

submersible and 

photographic 

observations

Kaiser et al. 1996(a) Irish Sea, 

west of Isle of 

Mann

not given, assume 

gravel (see 

Bradshaw et al. 

2000)

reduced abundance of 

most species

observations 

Veale et al. 2000 Irish Sea 20-67 m coarse sand or 

gravel, often 

overlain with 

pebbles, cobbles 

and dead shell.

decreases in species 

diversity and richness, 

and total number of 

individuals with 

increasing fishing effort 

compared bycatch from 

fishing grounds exposed 

to varying amounts of 

fishing 

Conclusions

Based on results of six studies of toothed scallop dredges on gravel sediments, dredging 

produced tracks in sediments, and disrupted and overturned gravel and boulders. Dredging also 

reduced the abundance of some infauna and epifauna, although some species were less abundant 

in a closed area, while others were more abundant. Many epifauna taxa recovered 5-9 years after 

the area was closed, but not before. Longterm changes in benthic communitites exposed to 

varying degrees of fishing effort could not be related solely to increased fishing activity; some 

sessile epifauna were more abundant in low effort fishing grounds, while others were more 

abundant in high effort grounds.

3. Live Bottom

Effects and Recovery

Hall-Spencer and Moore (2000) examined the effects of scallop dredging in the Clyde Sea, 

Scotland, on living calcareous rhodophytes by conducting single tows at depths of 10-15 m in an 

area that had been commercially dredged for 40 years and at a previously undredged area. A 

gang of three Newhaven dredges with spring-loaded teeth 10 cm long mounted 8 cm apart on a 

horizontal metal bar that was held off the seabed by a rubber roller at each end was used for 

experimental dredging. Immediate effects of dredging were noted and one transect at each site 

was monitored by divers 2-4 times a year over the following 4 years. Video recordings showed 

that the rollers and cha in rings were in contact with the bottom while the dredge teeth projected 

fully into the maerl substratum (10 cm) and disrupted the seabed, creating a cloud of suspended 

sediment. Cobble, rocks and boulders <1 m3 in size were overturned and dragged through the 

sediment. Dredges created 2.5-m wide tracks and erased natural bottom features (e.g., crab pits 

and burrow mounds). Sand and silt was brought to the sediment surface and living maerl was 

buried. Dredge tracks remained visible for 0.5-2.5 years depending on depth and exposure to 

wave action. Most megafauna on or within the top 10 cm of maerl were either caught in the 

dredges or left damaged on the dredge track. Large, fragile organisms (e.g., sea urchins and 

starfish) were usually broken on impact, whereas strong-shelled organisms (e.g., scallops, 

gastropods) usually passed into the dredge intact. Deep-burrowing species escaped dredge 

damage. Predatory species (e.g., whelks, crabs, and brittlestars) rapidly aggregated in the dredge 

track to feed. Species with regular recruitment and rapid growth recovered quickly, as did mobile 

epibenthic species which migrated into test plots soon after dredging. Slow-growing species 

and/or infrequently recruiting sessile organisms remained depleted on test plots at the undredged 
42

site 4 years after dredging occurred. The macrobenthic community at the previously dredged site 

returned to pre-experimental status within 2 years.

Table 21. Summary of literature on effects of toothed scallop dredges on livebottom habitat. Bold references 

indicate peer-reviewed journals. Blank cells indicate information was not provided by the reference.

Reference Location Depth Sediment Effects Recovery Comments

Hall-Spencer & 

Moore 2000

Clyde Sea, 

Scotland

10-15 m live bottom (maerl) plowing of seafloor to 10 

cm, overturned boulders, 

suspended sediment, 

smoothing of bottom 

features and burial of 

living maerl; megafauna 

in top 10 cm caught or 

damaged, aggregation of 

predatory species

tracks visible 

for 0.5-2.5 

years, after 2 

years 

macrobenthos 

at previously 

dredged site 

recovered, 

after 4 years 

some species 

at previously 

undredged 

still depleted 

experimental dredging; 

recovery monitored for 4 

yrs

Conclusions

A single study of the effects of dredging on maerl beds showed that a single tow plowed the 

seafloor, destroyed and buried living maerl, overturned boulders, erased bottom features, and 

suspended sediment. Dredge tracks were visible for 0.5-2.5 years depending on depth and 

exposure to wave action. Biological effects included removal or mortality to infauna and large 

epifauna, and attraction of invertebrate predators and scavengers. The benthic community 

recovered completely at a previously dredged site within 2 years, but some species at a 

previously undredged site still had not recovered after 4 years.

e. Suction Dredges

1. Mud

Effects and Recovery

Hall and Harding (1997) evaluated the effects of suction and tractor dredging on intertidal 

infaunal communities in Auchencairn Bay, on the north side of the Solway Firth, on the west 

coast of Scotland. Sediments there are 60-90% silt/clay in the interior of the bay and 25-60% 

silt/clay in the center and outer parts of the bay. Cockles (Cerastoderma edule) are harvested in 

the bay, but suction dredging was prohibited 4.5 months before experimental dredging began and 

no significant tractor dredging activity was reported. Core samples were collected in control 

plots prior to suction dredging, and in experimental plots immediately after and 1, 4, and 8 weeks 

after dredging. Dredge tracks could not be seen after the first day. Immediately after dredging, 

there was a decrease in total abundance (up to 30%), number of species (up to 50%), and in the 

abundance of 3 of the 5 dominant species. Abundance increased over time with recovery of 

most effects by 8 weeks.

Table 22. Summary of literature on effects of suction dredges on habitat with mud substrate. Bold references 

indicate peer-reviewed journals. Blank cells indicate information was not provided by the reference.

Reference Location Depth Sediment Effects Recovery Comments

Hall & Harding 

1997

Scotland intertidalmud number of infaunal 

species and individuals 

decreased

most species 

recovered 

within 4-8 

weeks 

experimental suction 

dredging 
43

Conclusions

Results of one study showed that suction dredges in intertidal mud habitat resulted in tracks in 

the sediment that disappeared within 1 day, and decreases in the number of species and 

individuals of infauna, which recover within 4-8 weeks. 

2. Sand

Effects and Recovery

Hall et al. (1990) studied the physical and biological effects of suction dredging for razor clams 

(Ensis spp.) in a shallow (7 m) sea loch on the west coast of Scotland. The depth at the study site 

was 7 m and the sediment was fine sand. The study site was unexploited but located near a 

recently-dredged area. Each experimental plot was dredged intensively for approximately 5 

hours in order to simulate commercial fishing activity. Replicate experimental and control plots 

were sampled by divers immediately after dredging and 40 days later. After dredging, the 

experimental plots were crisscrossed by shallow trenches (0.5 m wide and 0.25 m deep) 

interspersed with larger holes (up to 3.5 m wide and 0.6 m deep) that were presumably produced 

when the dredge remained stationary for a brief period. Sediments in the holes and trenches 

were almost fluidized. After 40 days, however, none of these features remained. The number of 

infaunal species and total abundance were reduced immediately after dredging (significantly, for 

individuals), but there were no detectable differences 40 days later. There were no significant 

differences in the abundance of individual species on either sampling occasion. The authors 

concluded that dredging caused a short-term, non-selective reduction in the numbers of all 

infaunal species and that recovery from physical effects was accelerated by a series of winter 

storms and considerable sediment disturbance in the study area.

Effects of suction dredge harvesting of cultivated manila clams (Tapes philippinarum) on a 

muddy sand intertidal flat in southeast England were investigated by Kaiser et al. (1996c). 

Samples of benthic infauna and sediment were collected prior to, 3 hours after, and 7 months 

after harvest in one cultivated plot and in one control location. Immediately after harvest, large 

amounts of fine sand were resuspended by the dredge, exposing the underlying clay, and the total 

number of infaunal species and individuals (e.g., crustaceans and bivalves) were significantly 

reduced. The sediments and benthic community recovered completely within 7 months.

Table 23. Summary of literature on effects of suction dredges on habitat with sand substrate. Bold references 

indicate peer-reviewed journals. Blank cells indicate information was not provided by the reference.

Reference Location Depth Sediment Effects Recovery Comments

Hall et al. (1990) Scotland 7 m fine sand shallow trenches and 

large holes; significant 

reductions in numbers 

and species of infaunal 

organisms 

complete 

recovery of 

physical 

features and 

benthic 

community 

after 40 days

experimental dredging 

Kaiser et al. (1996) SE England intertidal

fine sand resuspension and loss of 

fine sand from sediment 

surface, significant 

reductions in total 

number of infaunal 

species and individuals

complete 

recovery 

within 7 

months

experimental suction 

dredging 
44

Conclusions

Two studies on use of suction dredges in sand habitat concluded that dredging forms trenches 

and large holes in sediment, fluidizes sediments, resuspends fine sediment, and reduces the 

number of infauna species and individuals. Physical and biological habitat features recovered 

within 40 days in a subtidal environment and 7 months in an intertidal environment. 

f. Other Non-Hydraulic Dredges 

1. Submerged Aquatic Vegetation 

Effects and Recovery

Fonseca et al. (1984) examined the effects of small, hand-pulled scallop dredges on eelgrass near 

Beaufort, North Carolina. Two connected 65-cm wide, light-weight dredges were used, each 

weighing 13 kg and with no teeth on the dredge foot. Two study sites were selected, an exposed 

site with compacted sandy sediments with 19.8% silt and clay in the upper 3 cm and 5.2% 

organic matter, and a protected site where sediments were less compact and had a higher silt-clay 

content (22.3%) and lower organic content (2.6%) to a depth of 20 cm. Plots at each site were 

dredged 15 times, 30 times, or not at all. At both sites, the number of eelgrass shoots and 

biomass decreased significantly with increasing dredging. Both shoot number and leaf biomass 

were reduced to zero at the soft-bottom site after 30 dredge pulls. The proportional reduction in 

shoot number was greater at the soft-bottom site, but the hard-bottom site lost more biomass than 

the soft-bottom site because the initial biomass there was higher. The authors concluded that 

intensive scallop dredging for bay scallops, with this gear or with the heavier dredges pulled by 

power boats, has the potential for immediate as well as long-term reduction of eelgrass habitat.

Table 24. Summary of literature on effects of other non-hydraulic dredges on seagrass habitat. Bold references 

indicate peer-reviewed journals. Blank cells indicate information was not provided by the reference.

Reference Location Depth Sediment Effects Recovery Comments

Fonseca et al. 1984 Beaufort, 

North 

Carolina

very 

shallow, 

subtidal

sand with eelgrass significant reduction in 

number of eelgrass shoots 

and biomass with 

increasing dredging 

experimental dredging 

(hand pulled) at two sites

Conclusions

Based on the results of 1 study, repeated use of light-weight bay scallop dredges reduced eelgrass 

biomass in shallow, sandy habitat. 

2. Oyster Reefs and Mussel Beds

Effects and Recovery

Langan (1998) examined the effects of dredge harvesting on an oyster population and its 

associated benthic community in the Piscataqua River, which divides the states of New 

Hampshire and Maine. An oyster bed approximately 18 acres in size is located in the river 

channel and is divided nearly equally by the border between the two states. Maine allows 

commercial harvesting of oysters, but New Hampshire had not for many years prior to the study. 

The dredge used on the Maine side of the river is 30 inches wide, weighs approximately 60 lbs, 

and has blunt, 2-inch teeth and chain mesh bag. No significant differences between the two areas 

were found in the number, species richness, or diversity of epifaunal or infaunal invertebrates. 

Oligochaetes were equally abundant on both sides of the line, polychaete density was slightly 
45

higher in NH, and total crustaceans and total molluscs were more numerous in ME. The size 

distribution of the oysters on the unexploited side of the river was skewed towards older, larger 

individuals. The concentration of suspended sediment 10 m behind the dredge was slightly more 

than double the ambient level (10 mg/l) and dropped off to the ambient level 110 m behind the 

dredge.

Dredging oyster reefs in the Neuse River, North Carolina reduced the mean height of the reefs by 

29 ± 6 cm (Lenihan and Peterson 1998). Unharvested reefs lost only 0-2 cm of height over the 

one week duration of the experiment. The loss of oysters in the estuary during the last 50 years 

or so was attributed to the reduction of reef height by dredging and the effects of bottom water 

hypoxia.

Riemann and Hoffmann (1991) assessed the water column effects of mussel dredging in a 

shallow, eutrophic sound (Limfjord) in Denmark. Suspended particulate matter, oxygen, and 

nutrient (phosphorus and nitrogen) levels were measured at a number of stations throughout the 

water column at a dredged and a control site before dredging, immediately after dredging, and 30 

and 60 minutes later. Maximum water depth was 9 m. The substrate was not described, but 

presumably was a mussel bed. Average suspended particulate matter increased significantly 

immediately following a single, circular, 15-minute dredging event using a 2 m-wide mussel 

dredge. Oxygen decreased steadily, but only slightly, at the dredged site and increased similarly 

at the control site during the sampling period. A large apparent increase in ammonia was 

obscured by large horizontal variations, particularly near the bottom. Changes in other nutrients 

were small. Increases in particulate matter and nutrients (particularly phosphorus) were also 

observed on a day with high wind velocity (15 m/sec) compared to a day with low wind velocity 

(3 m/sec).

Table 25. Summary of literature on effects of other non-hydraulic dredges on oyster reefs and mussel beds. Bold 

references indicate peer-reviewed journals. Blank cells indicate information was not provided by the reference.

Reference Location Depth Sediment Effects Recovery Comments

Langan 1998 Piscataqua 

River, New 

Hampshire 

and Maine

oyster bed no differences in number 

of benthic invertebrates, 

species richness or 

diversity

compared dredged and 

undredged sides of river

Riemann & 

Hoffmann 1991

Denmark 7.5 m -

11 m

mussel bed significant increase in 

suspended particulate 

matter

turbidity 

returned to 

normal within 

1 hour

experimental dredging at 

2 locations

Lenihan & Peterson 

1998

Neuse River, 

North 

Carolina

3 m, 6 m oyster reefs dredging lowered mean 

height of 1-m reefs by 

about 30%

loss of oysters in last 50 

years attributed to 

dredging and hypoxia

Conclusions

Oyster dredging reduced the height of oyster reefs. Mussel dredging increased turbidity, slightly 

reduced dissolved oxygen concentrations in the water column, and caused apparent large 

increases in ammonia.
46

3. Multiple Mobile Gears

In many geographic regions, the same areas within fishing grounds are fished by a number of 

different mobile gears including otter trawls, beam trawls, mechanical dredges and/or hydraulic 

dredges (ICES 1993, DeAlteris et al. 1999, Kaiser 2000). Within these areas, it is difficult to 

differentiate effects on habitat and biota from any single specific gear type, but an opportunity 

exists to examine cumulative effects of multiple gear types. 

a. Sand

Effects and Recovery

A remotely operated vehicle (ROV) was used to compare conditions in and outside the Swans 

Island Conservation Area (depths 30-40 m) in the northern Gulf of Maine, which had been 

closed to mobile fishing gear for 10 years (Auster et al. 1996). Video transects indicated that on 

sand/shell bottom, habitat complexity was provided mostly by sea cucumbers attached to shell 

and other biogenic debris and by depressions created by mobile fauna. Both of these habitat 

features were significantly less common outside the closed area; this was attributed to harvesting 

or bycatch of the structure-providing species.

Side-scan sonar images of Stellwagen Bank in the Gulf of Maine taken in 1993 showed that 

storm-created coarse sand ripples (30-60 cm between crests and 10-20 cm high) with shell-filled 

troughs were disturbed by scallop dredging (Auster et al. 1996). ROV observations on the 

bank’s crest (32-43 m depths) indicated otter trawls and scallop dredges remove aggregations of 

emergent hydroids and disturb benthic microalgal cover. Several shrimp species, which were 

abundant in the hydroid aggregations, were not observed in a swath from which hydroids had 

been removed by fishing gear. Observations in July 1994 showed that an ascidian species 

(which slightly increased bottom complexity) was widely distributed (but not present in otter 

trawl paths) and hydroids were absent.

The southern half of Closed Area II on Georges Bank was sampled 41⁄2 years after it had been 

closed to fishing (Almeida et al. 2000). Preliminary conclusions from sampling paired stations 

just inside and outside the closed area included: 1) species composition, species diversity and 

richness of trawl-caught organisms inside the closed area were similar to those immediately 

outside the area; 2) numbers and biomass of haddock and yellowtail flounder were greater inside; 

3) most other groundfish species had similar abundances inside and outside; some were slightly 

more abundant outside; 4) size distributions of fish and megainvertebrates were similar inside 

and outside, except sea scallops were significantly larger inside; and 5) total organic carbon in 

sediments was generally higher inside, and was related to sediment grain size. From analysis of 

videotapes and still photographs, greater abundance of emergent sponges inside the closed area 

was the only significant difference in microhabitat resources attributable to gear effects. It was 

speculated that the lack of major differences inside and outside the closed area was probably due 

to the area’s sandy habitat type.

Kaiser et al. (2000b) sampled sediment type (with grab samples), and infauna and epifauna (with 

2-m beam trawl and anchor dredge) along the south Devon coast in England: 3 high fishing 

effort areas open to all fishing (otter trawl, beamtrawl, scallop dredge and pots), 2 medium 
47

fishing effort areas open to mobile gear for 6 months out of the year and pots year round, and 1 

low fishing effort area only open to pots. Sediments followed a gradient from fine sand to 

medium sand and coarse-medium sand. Fine sand areas were located at 15-17 m depth. All 

others were located at 53-70 m depth. Within sediment types, there were significant differences 

in epifauna and infauna between areas with high, medium and low fishing effort. In fine sand 

areas, hydroids decreased and scavenging hermit crabs and starfish increased. In medium sand 

areas, large starfishes and tube-dwelling amphipods decreased, while scavenging crabs 

increased. In coarse-medium sand areas, several species of infauna decreased in biomass and 

abundance including hydroids, soft coral and small urchins, while crabs and seastars increased in 

abundance. Areas closed to draggers had higher total biomass, and higher abundances of 

emergent fauna (e.g., soft corals and hydroids) that increased habitat complexity. Areas open to 

draggers were dominated by smaller-bodied fauna and scavenging taxa. The authors concluded 

that removal of epibenthic fauna by fishing had decreased habitat complexity, possibly causing 

the biological community to shift to an alternative stable state. 

In contrast, Hall et al. (1993) sampled benthic macroinfauna (with grabs) from demersal fishing 

grounds in the North Sea (Turbot Bank) using distance from shipwrecks as a proxy for fishing 

intensity. Sediments were characterized as coarse sand at 80 m depth. No significant differences 

were evident, instead species abundance was strongly related to sediment characteristics. 

Table 26. Summary of literature on effects of multiple mobile gear on habitat with sand substrate. Bold references 

indicate peer-reviewed journals. Blank cells indicate information was not provided by the reference.

Reference Location Depth Sediment Type of Effects Recovery Comments

Almeida et al. 

2000

Georges Bank sand size and abundance of 

fish and 

megainvertebrates 

similar inside and outside 

closed area, abundance of 

sponges higher inside

comparison of samples 

inside and outside closed 

area.

Auster et al. 

1996

Gulf of Maine 

(Swans Island)

30-40 m sand-shell reduction in biogenic 

depressions and sea 

cucumbers

ROV and video 

observations

Auster et al. 

1996

Gulf of Maine 

(Stellwagen 

Bank)

20-55 m sand with gravel 

and shell

removal of epibenthic 

fauna and microalgal 

cover

ROV and video 

observations inside and 

outside a closed area

Hall et al. 1993 North Sea 80 m coarse sand no change in macroinfauna

sampled infauna along 

distance from shipwreck 

(proxy for control) within 

demersal fishing grounds

Kaiser et al. 

2000b

England (South 

Devon Coast)

15-17 m fine sand decrease in biomass of 

infauna and emergent 

epifauna, increase in 

abundance of scavengers

compared areas of high, 

medium and low fishing 

intensity 

Kaiser et al. 

2000b

England (South 

Devon Coast)

53-70 m medium sand decrease in biomass of 

infauna and emergent 

epifauna, increase in 

abundance of scavengers

compared areas of high, 

medium and low fishing 

intensity 

Kaiser et al. 

2000b

England (South 

Devon Coast)

53-70 m coarse-medium 

sand

decrease in biomass of 

infauna and emergent 

epifauna, increase in 

abundance of scavengers

compared areas of high, 

medium and low fishing 

intensity 
48

Conclusions

Four studies on the effects of a combination of mobile gears on sand habitats are summarized in 

this report. ROV observations in areas inside and outside fishing grounds showed that fishing 

reduces biogenic depressions, reduction in microalgal cover, and remova l of emergent epifauna. 

One study reports that fishing by a combination of otter trawls, beam trawls, and scallop dredges 

resulted in decreased biomass of infauna and epifauna, and increased abundance of scavengers. 

In contrast, one study using a shipwreck as a “pseudo control” and another that examined an area 

closed to fishing for 4 1⁄2 years found no effects on macrofauna and no effects on species 

composition, diversity or richness of trawl caught organisms.

b. Gravel

Effects and Recovery

In 1994 Collie et al. (2000b, 1997, 1996) sampled two shallow (42-49 m), gravel sites and three 

deep (80-90 m), gravel sites on Georges Bank that had varying histories of disturbance (as 

determined by side-scan sonar, bottom photographs and fishing records) by scallop dredging and 

otter trawling. Only one shallow and one deep site were classified as disturbed, but the other 

shallow site may have been previously fished (it had no boulders large enough to prevent 

fishing), and one of the two deep “undisturbed” sites had evidence of light dredging disturbance. 

Samples of megabenthic organisms taken with a 1 m wide Naturalists’ dredge showed lower 

densities, biomass, species richness and species diversity at the disturbed sites than the 

undisturbed sites (Collie et al. 1997). Small polychaetes, shrimps and brittle stars were among 

the species that were less abundant or absent at the dredged sites. Analysis of videos and still 

photographs (Collie et al. 2000b) revealed the undisturbed sites had significantly higher percent 

cover of the colonial, rock-encrusting polychaete, Filograna implexa, and higher abundance of 

anemones, sponges, sculpins and plant-like animals. This emergent epifauna was considered to 

provide a complex habitat for mobile invertebrates and small fish at the undisturbed sites. 

Although other factors could have contributed to differences in emergent epifauna (e.g., 

sediments were coarser at undisturbed sites and epifauna was more abundant at deep sites), the 

authors concluded that fishing disturbance was the most likely explanation for the reduction in 

complexity and species diversity at the disturbed sites (Collie et al. 2000b). 

An ROV was used to compare conditions in and outside the Swans Island Conservation Area 

(depths 30-40 m) in northern Gulf of Maine, which had been closed to mobile fishing gear for 10 

years (Auster et al. 1996). Video transects indicated that on cobble/shell bottom, habitat 

complexity was provided mostly by emergent epifauna (e.g., hydroids, bryozoans, sponges, 

serpulid worms) and sea cucumbers. These species were less common outside the closed area; 

this was attributed to harvesting or bycatch of the structure-providing species.
49

Table 27. Summary of literature on effects of multiple mobile gear on habitat with gravel substrate. Bold references 

indicate peer-reviewed journals. Blank cells indicate information was not provided by the reference.

Reference Location Depth Sediment Type of Effects Recovery Comments

Collie et al. 1997 Georges Bank 42-49 m, 

80-90 m

gravel pavement decrease in megafauna 

abundance; aggregation 

of predators

compared disturbed and 

undisturbed sites (6 

sites); scallop dredge 

and otter trawl 

Collie et al. 2000b Georges Bank 42-49 m, 

80-90 m

gravel pavement decrease in megafauna 

abundance, decrease in 

cover by emergent 

epifauna

video and photo 

observations of disturbed 

and undisturbed sites (5 

sites); scallop dredge and 

otter trawl

Auster et al. 1996 Gulf of Maine 

(Swans 

Island)

30-40 m cobble-shell reduction in abundance 

and cover by emergent 

epifauna

ROV and video 

observations inside and 

outside area closed to 

mobile gear for 10 years; 

dredge and trawl

Conclusions

According to the studies summarized above, the use of multiple mobile gear on gravel habitat 

results in a reduction in epifauna abundance and cover, similar to effects of individual mobile 

gear on gravel habitats. 

c. Various Sediments

Effects and Recovery

Valentine and Lough (1991) used side scan sonar and a submersible to describe the effects of 

scallop dredges and trawls on sand and gravel bottom habitats on eastern Georges Bank. They 

noted that the most evident signs of disturbance occurred on gravel pavement, where long, low 

mounds of gravel had been formed by trawling and dredging. In some areas the sea bed was 

covered by trawl and dredge tracks. Gravel areas which were unfished (due to the presence of 

large boulders) had a biologically diverse community with abundant attached organisms. 

Conversely, the attached epifaunal community was sparse and the bottom was smoother in areas 

that had been disturbed by dredging and trawling. 

Reise and Schubert (1987), Riesen and Reise (1982), and Reise (1982) compared invertebrate 

surveys in the Wadden Sea of northern Sylt taken between 1869 and 1986. Bottom sediments in 

these areas range from mud to coarse sand and some pebbles. The area is made up of tidal flats, 

shallow subtidal banks, and channels down to a depth of 23 m. Surveys were completed using 

oyster dredges and grabs. During the period of time encompassed by the various surveys, 

abundant oyster reefs were overexploited and seagrass beds were lost to a natural epidemic. 

Furthermore, fishermen have claimed to have deliberately eliminated Sabellaria reefs by towing 

heavy gear across them. The area is now dominated by soft sediments and mussel beds, which 

prior to 1920 were restricted to the shallows. Comparisons show that 28 species (8 associated 

with oyster beds, 8 with Sabelleria, and 7 with seagrasses) have declined in abundance. Twentythree species (half are polychaetes) that were missing or rare in earlier surveys are now common. 

Epifauna were more abundant in the 1920s, and infauna were more abundant in the 1980s. In 

total 59% of all species have shown changes in abundance. These changes have balanced out, so 
50

that total abundance has remained relatively stable. Because of the multiple factors affecting this 

area, changes can not be attributed solely to fishing. 

Side scan sonar and video observations were used to document the cumulative effects of various 

mobile fishing gears used in Bras D’Or Lakes and St. Peters Canal, Nova Scotia (Canadian 

Department of Fisheries and Oceans 1993). Water depths were greater than 10 m, and bottom 

sediments included rich organic mud, clay, pebbly mud, well-sorted sand, gravel and boulders. 

Scallop dredges left 3-4 m wide scars with teeth marks. These scars were seen mostly in gravel 

but also in silt.

Thrush et al. (1998) tested hypotheses regarding trends for benthic fauna in the Hauraki Gulf, 

New Zealand by sampling 18 locations exposed to varying fishing effort. Samples were taken by 

video, sediment cores, and grab or section dredge from areas fished predominantly by otter 

trawls with 480 kg doors and groundrope with 140-150 mm rubber bobbins and steel balls, but 

also by Danish seine and 2-m wide box dredge. Sediments were described as 1- 48% mud and 

depths ranged from 17-35 m. Side scan sonar revealed high incidence of trawl door tracks and 

scallop dredge marks in some areas, which concurred with estimates of fishing effort. After 

accounting for differences of location and sediment, 15-20% of the variability in macrofauna 

community composition was attributed to fishing. Analysis of video transect data showed that 

the density of large epifauna decreased significantly with increasing fishing effort. Analysis of 

core data showed that the density of echinoderms, the polychaete to mollusk ratio, total diversity, 

and species richness all decreased significantly with increasing fishing pressure, while the ratio 

of small to large Echinocardium (heart urchin) increased significantly with increasing fishing 

pressure. Analysis of grab/suction dredge data showed that density of deposit feeders and 

number and species richness of epifauna decreased with increasing fishing pressure, although 

these relationships were not significant. The authors conclude that their results indicate broadscale changes in benthic communities directly related to fishing, and because they were taken 

over a large sampling area, suggest ramifications for the entire ecosystem. 

Table 28. Summary of literature on effects of multiple mobile gear on habitat with mixed substrate. Bold references 

indicate peer-reviewed journals. Blank cells indicate information was not provided by the reference.

Reference Location Depth Sediment Type of Effects Recovery Comments

Canadian 

Department of Fish 

and Ocean 1993

Nova Scotia 

(Bras D'or 

Lakes)

>10 m variety (e.g., 

organic mud, clay, 

pebbly mud)

tracks with berms in 

sediment

side scan sonar 

observations over various 

habitats

Reise and Schubert, 

1987; Riesen and 

Reise 1982; Reise 

1982

Wadden Sea <23 m sediments range 

from mud to coarse 

sand and some 

pebbles

oysters overexploited by 

dredges, Sabelleria reefs 

destroyed by heavy trawl 

gear, decrease in abundance 

of 28 species (molluscs and 

amphipods), 23 new 

species (mostly 

polychaetes)

no 

recovery, 

area now 

dominated 

by mussels

compared various 

surveys conducted 

between 1869 and 1986 ; 

seagrasses lost to natural 

epidemic during same 

period

Thrush et al. 1998 New Zealand 17-35 m variety of substrates 

with 1-48% mud

changes to macrofauna 

composition (# species, # 

individuals, diversity, and 

density of large epifauna 

increased with decreased 

fishing effort)

sampled areas over 

gradient of fishing effort

Valentine and Lough 

1991

Georges Bank sand and gravel tracks in sediments, 

removal of epifauna

side scan sonar and 

submersible observations
51

Conclusions

Because of the differences in gear types and habitat types in the studies summarized above, a 

synthesis of results is not appropriate.

4. Pots and Traps

a. Various Sediments

Effects and Recovery

Eno et al. (2001) observed effects of pots (creels and 3 types of crustacean pots) set in water 

depths from approximately 14-23 m over a wide range of sediment types in Great Britain: mud 

communities with sea pens, limestone slabs covered by sediment, large boulders interspersed 

with coarse sediment, and rock. Observations demonstrated that sea pens were able to recover 

fully from pot impact (left in place for 24-48 hours) within 72-144 hours of the pots being 

removed. Pots remained static on the seafloor, except in cases where insufficient line and large 

swells caused pots to bounce off the bottom. When pots were hauled back along the bottom, a 

track was left in the sediments, but abundances of organisms within that track were not affected. 

The authors did record incidences of detachment of ascidians and sponges and damage to ross 

coral, but it was not clear if these resulted from this study or from previous damage. Authors 

conclude that no short-term effects result from the use of pots, even for sensitive species. The 

study did not examine chronic impacts.

Table 29. Summary of literature on effects of pots on habitat with various substrate. Bold references indicate peerreviewed journals. Blank cells indicate information was not provided by the reference.

Reference Location Depth Sediment Type of Effects Recovery Comments

Eno et al. 2001 Great Britain <23 m mud bending and uprooting of 

sea pens

sea pens reroot in 24-72 

hours

experimental fishing (1 

site) 

Eno et al. 2001 Great Britain <23 m limestone slabs 

covered by 

sediment, coarse 

sediment with 

boulders

bending of sea fans immediate 

after removal 

of pots

experimental fishing 

(1site) with 3 types of 

commercial pots

Eno et al. 2001 Great Britain <23 m rocky substrate abundance of sponges 

increased

experimental fishing (5 

sites) with commercial 

crustacean pots

Conclusions

A study on 3 different habitat types concluded that the use of pots and traps had no lasting effects 

on sea pens, sea fans, or sponges.

b. Coral

Effects and Recovery

Garrison (1997, 1998) observed commercial fish traps in the U.S. Virgin Islands, and found that 

82-86% were set directly upon live substrate (e.g., stony corals, gorgonians, sponges, seagrasses 

or algae/sponge). In south Florida, Taylor and McMichael (1983) observed that preferred 

substrates for wire fish pots are coral reefs, live bottom (coral-sponge), limestone ledges, and 

outcroppings. Also in south Florida, Sutherland et al. (1983) completed a submersible survey of 
52

derelict trap/pots following the closure of the trap fishery in the state. Traps were set either 

singly or in lines, and most were set within 20-45 m of a coral reef and rock ledge. Of 23 

derelict/ghost traps, 15 were on sand or algal flats, 4 were on high profile reef, and 4 were in live 

bottom area.

A total of 2,000 out of 5,000 fish (arrowhead) pots observed by Quandt (1999) were set on coral 

reefs in St. Thomas, U.S. Virgin Islands. These pots resulted in scrapes and breakage to 5% of 

all corals observed and tissue damage to 47% of all gorgonians observed (tissue damage to 20% 

of each gorgonian). Based on the number of pots fished per year and the average area of coral 

reef damaged per pot, Quandt estimated that a total of 104 m2 of coral reef is damaged by wire 

pot fishing per year in the U.S. Virgin Islands. The author discussed indirect effects to 

reproductive and recruitment capabilities if damaged corals suffer infections. 

Appeldoorn et al. (2000) observed wire fish pots (arrowhead pots) set by commercial fishermen 

in La Parguera, Puerto Rico, and recorded sediment type and damage caused by deployment, 

soaking, and rehauling of traps. Of the traps observed, 45% were set on sand or mud and 44% 

were set on hard bottom or reef. Of the habitat types observed under traps, 23% of coral 

colonies, 34% of gorgonian colonies, and 30% of sponges were damaged by deployment. All 

traps deployed on hard bottoms or reef caused at least some damage to corals and gorgonians. 

Additional damage from hauling the traps to the surface occurred for 30% of the traps observed. 

The author estimated that approximately 64.7 m2 of coral, 47.0 m2 of gorgonians, and 4.7 m2 of 

sponges are damaged within La Pargueara per year (total damage of 116.4 m2 with 95% 

confidence limits of 35 to 202 m2). The long-term fate of these individuals was not determined. 

Furthermore, the author found that trap-induced habitat damage was concentrated in certain 

areas, and concluded that there would be a higher potential for repeated damage within those 

areas. This concentration of effort is expected to have greater impacts than if the trap activity 

were spread over the whole shelf. Damage by fishing pots could add important cumulative 

effects on areas that are already experiencing damage from environmental conditions.

Van der Knapp (1993) also recorded injury to staghorn coral, other corals, sponges, and 

gorgonians from commercial traps in Bonaire, Netherlands Antilles. However, the author 

examined recovery times and found that gorgonians recover within a month, and staghorn corals 

begin to regenerate after 35 days. Recovery times are longer, however, if algae begin to grow in 

the damaged areas. The longterm fate of damaged individuals is unknown.

Table 30. Summary of literature on effects of pots and traps on coral reef habitat. Bold references indicate peerreviewed journals. Blank cells indicate information was not provided by the reference.

Reference Location Depth Sediment Type of Effects Recovery Comments

Quandt 1999 U.S. Virgin 

Islands

coral reefs corals, gorgonians, 

sponges damaged

observations of 

commercial fish pots

Appeldoorn et al. 

2000

Puerto Rico corals, gorgonians, 

sponges damaged

observations of 

commercial pots

Van der Knapp 1993 Netherlands 

(Bonaire)

coral reefs corals, gorgonians, 

sponges damaged; 

algal growth in scars

staghorn corals 

begin regeneration 

after 35 days, 

gorgonians recover 

within a month

experimental pot 

fishing 
53

Conclusions

Three papers, 2 observational and 1 experimental, report that the use of pots and traps damages 

corals, gorgonians, and sponges. One of these studies reports recovery of gorgonians within a 

month and the initiation of regeneration to staghorn coral within 35 days. The study does not 

indicate the time needed for complete regeneration.

5. Set Gill Nets – Summary of Available Science

The majority of research concerning impacts of gillnets focuses on effects on populations 

resulting from ghost fishing by lost gear; few studies have examined adverse effects of gillnets 

on habitat. A few studies have noted that, upon retrieval, gillnets can become entangled in hard 

bottom areas, and snag and break coral (Breen 1990, Ohman 1993, Jennings and Polunin 1996, 

Kaiser et al. 1996c, Erzini et al. 1997, ICES 2000). Lost gillnets, in particular, often get caught 

on and damage or cover hard bottoms and reefs. However, these nets are quickly covered by 

encrusting epifauna, and eventually blend into the background habitat (Carr et al. 1985, Cooper 

et al. 1988, Erzini et al. 1997, ICES 2000). Erzini et al. (1997) observed that lost gillnets became 

incorporated into the reef and provided a complex habitat which was attractive to many 

organisms. Carr and Milliken (1998) noted that in the Gulf of Maine, cod reacted to lost gillnets 

as if they were part of the seafloor. Thus, other than damage to coral reefs, effects on habitat by 

gillnets are thought to be minimal (ICES 1991, 1995, Stephan et al. 2000).

6. Set Longline -Summary of Available Science

Very little information exists on the effects of longlining on benthic habitat. The principal 

components of the longline that can produce seabed effects are the anchors or weights, hooks and 

the mainline (ICES 2000). During submersible dives off southeast Alaska, NMFS scientists 

observed the following regarding halibut longline gear (NPFMC 1992): “Setline gear often lies 

slack on the seafloor and meanders considerably along the bottom. During the retrieval process, 

the line sweeps the bottom for considerable distances before lifting off the bottom. It snags on 

whatever objects are in its path, including rocks and corals. Smaller rocks are upended, hard 

corals are broken, and soft corals appear unaffected by the passing line. Invertebrates and other 

light weight objects are dislodged and pass over or under the line. Fish, notably halibut, 

frequently moved the groundline numerous feet along the bottom and up into the water column 

during escape runs disturbing objects in their path. This line motion was noted for distances of 

50 feet or more on either side of the hooked fish.”

D. RECOMMENDATIONS FROM THE LITERATURE

1. Bottom Trawls

The majority of specific recommendations offered in the literature relate to gear design and 

deployment. Bergman and Van Santbrink (2000) recommend that the following management 

measures be considered for the southern North Sea, an area that is subject to considerable beam 

trawling: a significant reduction of trawling effort, development of gears less damaging for 

habitats and fauna, and designation of areas closed to fisheries for species and habitats that 
54

cannot be protected otherwise. Van Marlen (2000) recommends that more effort be put into 

developing electrified beam trawls that use electrical stimulation rather than mechanical 

disturbance to catch fish. While this method requires large investments up front, and could 

possibly require higher repair costs, the huge decrease in resistance of the gear should lower fuel 

costs considerably. A 1999 ICES working group report (ICES 1999) recommends that further 

research and development be completed for wheels used on beam trawls, ways to reduce friction 

or compression forces, and ways to reduce the number of weights on groundropes. Furthermore, 

they recommend a reduction of the sweep contact, possibly through use of semi-pelagic riggings 

and alternatives to mechanical stimulation. 

Other recommendations focus on reducing gear interactions with certain habitat types. 

Lindeboom and de Groot (1998) recommend that the areas impacted by bottom trawls and the 

number of bottom trawlers be restricted from expanding and that the interactions with groups 

working on conservation of ecosystems be strengthened. For specific mitigation measures, they 

recommend: spatial closures, reduction of effort, gear substitution (e.g., static for mobile gear), 

and gear modifications (although this would only moderately reduce impacts). Many authors 

recommend the protection of specific, vulnerable habitats such as seamounts (Koslow and 

Gowlett-Holmes 1998, Probert et al. 1997), seagrasses (Godcharles 1971), and gravel beds with 

associated epifauna (Auster et al. 1996).

2. Dredges

Hydraulic dredges are towed more slowly and cover less ground per haul than most trawls 

(Stewart 1999), but have more area in contact with the bottom, and unlike trawls, are designed to 

penetrate the substrate to remove infaunal invertebrates (Rogers et al. 1998). Scallop dredges are 

towed at approximately 2 times the speed of most trawls, but they are designed to skim along the 

surface of the seafloor. Many authors have voiced concern over the use of hydraulic dredges in 

seagrass habitats because of the extensive damage and slow recovery of grasses within the 

dredge tracks (Manning and Dunnington 1955, Godcharles 1971, Jolley 1972, Chesapeake Bay 

Program 1995, Orth et al. 1998). No recommendations regarding use of dredges in other habitat 

types were offered in the literature.

3. Pots and Traps 

Pots and traps are considered to be less damaging than mobile gear, because they are stationary 

in nature, and thus, come into direct contact with a much smaller area of the seafloor (Stewart 

1999, Eno et al. 2001). Traps affect habitat when they settle to the bottom and when they are 

hauled back to the surface. While soaking, traps and pots with buoy lines of insufficient length 

may bounce or drag along the seafloor during rough seas. This movement will increase the 

amount and areal extent of damage. In many locations, traps are strung together by trotlines or 

longlines. These trotlines may cause further damage during deployment and retrieval by 

catching and shearing organisms if they are dragged along the bottom. Grappling hooks used to 

retrieve pots and traps can also cause damage by scraping the benthos.

Van der Knapp (1993) emphasizes the need for regulations that restrict trap fishing to sand areas 

or coral areas that regenerate completely (e.g., staghorn coral). Quandt (1999) recognized that 
55

regulations were needed to help control habitat impacts from trap fishing, but offered no specific 

recommendations for those regulations.

IV. STATE OF INFORMATION

A. LIMITS OF INFORMATION AND NEED FOR RESEARCH

Ideally, in order to understand the ecosystem effects of fishing on habitat, research is needed that 

uses comparable, replicate fished and non-fished areas at the scale of fishing grounds for specific 

fisheries, and at a time-scale greater than the life span of the longest-lived species (Hall 1994). 

Unfortunately, the time and resources needed to complete this research can be prohibitive. Thus, 

most of the research to date has been limited in scope. Most studies concentrate on a single gear 

type and do not address cumulative effects of all gears used within a given fishing ground. Often 

research projects are simplified by examining effects on a specific habitat type. These small 

scale studies may not be applicable over larger areas (i.e., scale of fishing ground) that consist of 

a mosaic of habitat types. They also do not consider cumulative effects over long periods of 

time. Furthermore, estimates of recovery are often limited to measurements of recovery from a 

single (or limited) disturbance event rather than from ongoing impacts that commonly occur 

from fishing. Typically, the habitats against which recovery is measured have already been 

significantly altered by long-term effects of fishing, leaving an inaccurate picture of recovery 

times. Finally, where information is available on physical or biological effects, the role these 

habitat impacts have on harvested populations, in most cases, is unknown. Even when there is 

good time series information on fish abundance, there is a lack of empirical information on 

linkages between habitat and survival, which would allow modeling and experimentation to 

predict outcomes of various levels of disturbance (Auster and Langton 1999). 

In addition to problems with research approach, questions have been reaised about details of data 

sampling and experimental design. Moran and Stephenson (2000) conclude that net sampling is 

not an accurate method of measuring effects on habitat because it does not indicate the number 

or types of organisms that are damaged or detached, but not caught, by the net. Rogers et al. 

(1999) question the level of sampling needed (e.g., community indices, species abundances) to 

best examine quantifiable effects of exploitation. For example, Sanchez-Jerez and Espla (1996) 

found that community changes due to trawling in Posidonia (neptunegrass) meadows were not 

evident at the phylum and class levels of benthic fauna, but that family and species levels of 

amphipods and isopods showed significant differences, and thus were the best indicators of 

trawling impacts for this geographic area. According to McConnaughey et al. (2000), lumping 

taxa for analytical purposes can mask species effects that are a result of functional processes 

rather than taxonomy. Jennings and Cotter (1999) state that vulnerable species are better 

indicators of fishing effects than community based measures that can be explained by factors 

other than fishing. These types of issues need to be evaluated when designing and interpreting 

studies on effects of fishing gear to habitat. 

In order to better assess the effects of fishing gear we also need a better understanding of the 

distribution of fishing effort by gear type. Analyses of fishing effort have been completed in 

other countries (Rijnsdorp et al. 1998, Greenstreet et al. 1999, Jennings et al. 1999), but for most 
56

United States fisheries we currently have no systematic way of tracking effort at the scale of 

habitat type within a given geographic area. Churchill (1989) attempted to summarize trawling 

effort in the Middle Atlantic Bight off the northeast U.S. using fishing effort data in 30' latitude x 

30' longitude blocks. While areas impacted could be estimated over blocks, a lack of data on the 

extent of the area actually disturbed within each block, especially for static gears, made analysis 

of the impacts to habitat difficult. In an attempt to address this problem, other methods of 

estimating fishing effort have been explored. Authors have used incidence of damage to starfish 

(Kaiser 1996), scars in molluscan growth lines (Witbaard and Klein 1993) and side scan sonar of 

mobile gear tracks (Krost et al. 1990, Friedlander et al. 1999). These methods, however, also 

have limitations. Seastars and molluscs are affected differently by different gear types, and are 

not available over all geographic areas. And, detection of fishing effects by side scan sonar 

surveys depends on the timing of the survey relative to the timing of the fishing impact and the 

recovery time of the sediments. 

Research also needs to evaluate natural impacts (e.g., storms) that occur over large geographic 

scales. In some areas these natural impacts may render local effects of fishing insignificant 

(Stevenson and Confer 1978, Daan 1991). Furthermore, the strength and occurrence of natural 

or non-fishing anthropogenic influences are strong determinants of recovery time (Flint and 

Younk 1983, Hall 1994, DeAlteris et al. 1999). In theory, communities in variable (or high 

energy) environments are capable of recovering more quickly than communities in more stable 

(or low energy) environments and, thus, are more resistant to disturbance (Flint and Younk 1983, 

Collie et al. 2000a). 

Given the MSA mandate to minimize adverse effects of fishing on habitat in order to support 

sustainable fisheries, research is needed to address the limitations of existing information 

discussed above. 

B. MANAGEMENT PHILOSOPHIES

Given the current state of existing information, and the limitations on our ability to gather needed 

information, different philosophies have developed as to how we should manage fishing impacts 

to habitat. Many believe that we should look beyond scientific literature to anecdotal 

information and other “non-scientific” evidence. For example, Pederson and Hall-Arber (1999) 

discuss the extensive information on habitat condition and long-term habitat changes that can be 

gained from fishermen and incorporated into management decisions. 

Under the precautionary approach to management, measures to minimize effects of fishing to 

habitat should be implemented based on the concept that the risk of allowing possibly 

irreversible damage to continue outweighs the short-term economic hardships that might be 

incurred. Many authors support a precautionary or risk averse approach to habitat conservation 

and protection (McAllister and Spiller 1994, Auster and Malatesta 1995, Dayton et al. 1995, 

Auster et al. 1997, Koslow and Gowlett-Holmes 1998, Carr and Milliken 1998, Collie 1998, 

Fogarty and Murawski 1998, Goñi 1998, Mirarchi 1998, Thrush et al. 1998, Auster and Langton 

1999, Hall-Spencer et al. 1999, Langton and Auster 1999, Norse and Watling 1999, Turner et al. 

1999, Auster and Shackell 2000, Frid and Clark 2000, ICES 2000, McConnaughey et al. 2000, 

Auster 2001, NRC 2002). 
57

It has been argued that, although definitive evidence may not be available, studies have shown 

“beyond doubt” that some negative impacts from mobile fishing gear are occurring, and thus, 

that management decisions need to be made without waiting for more scientific evidence 

(Kenchington 1995, Lindeboom and de Groot 1998, Watling and Norse 1998, Gray 2000, NRC 

2002). Kenchington (1995) argues that the burden of proof required in scientific research is not 

appropriate in fisheries management and that we need to take into account the risk that mobile 

fishing gear is significantly reducing fish production by modifying benthic habitats. Dayton et 

al. (1995) state that, while policy makers clearly understand the financial implications of 

reducing fishing effort when no adverse effects are occurring, there is no clear understanding of 

the financial implications of ecosystem effects and loss of resources by continuing to fish when 

impacts have occurred but not been detected. 

A number of authors have recommended the use of closed areas for research and conservation 

(Bergman et al. 1990, Bergman and Hup 1992, Engel and Kvitek 1998, Rumohr 1998, HallSpencer et al. 1999, Auster and Shackell 2000, Ball et al. 2000). Hutchings (1990) recommends 

periodic closures of areas, strip trawling to leave regularly spaced islands of untrawled areas to 

supply recruits for replenishment, and modification of gear to minimize impacts. Carr and 

Milliken (1998) recommend that nations modify gear to target specific species, encourage the 

use of lighter sweeps rather than heavier gears, reduce the amount of sea bottom available to 

mobile gear, and opt for stationary gear over mobile gear. McAllister and Spiller (1994) 

recommend the establishment of nearshore continental shelf and slope protected areas, regular 

monitoring of impacts of different gear types, and a switch to gear types with low habitat impacts 

and low bycatch. Ball et al. (2000) recommend large areas closed to fishing to allow large scale 

experiments, with particular attention to deeper waters at the shelf edge and slope where natural 

disturbance is less common, sediments are highly bioturbated, and faunal assemblages are less 

capable of sustaining disturbance. Auster et al. (1997) recommend a more extensive use of 

closed areas, starting with a specific fishing gear within a geographical region and if existing 

knowledge suggests that negative effects on seafloor habitats are occurring from that gear (even 

if the available information is uncertain or inadequate), then management authorities define the 

habitats likely to be affected by that gear and designate marine protected areas for those habitats. 

Based on a fishermen survey by Fuller and Cameron (1998), fishermen generally approved of 

closing spawning areas during spawning and concurred that fisheries management should occur 

on an ecosystem level including habitat protection. A number of authors also support the use of 

adaptive management, in which fisheries research provides feedback to management decisions 

(Sainsbury et al. 1993, Thrush et al. 1998, Turner et al. 1999). For example, managers could 

implement closed areas and then adjust the size or location of those closed areas as scientific 

research bears new information, and we have a better understanding of effects of fishing to 

ecosystems. 

Kaiser et al. (1999) argue that the magnitude of fishing effects varies greatly relative to the 

background of natural disturbances and that we need to consider subtle differences in habitat 

structure and assemblage composition before we can understand the consequences of fishing. 

Kaiser (1998) reviewed scientific studies on the effects of fishing in the North Sea and concluded 

that oceanic influences have greater ecological effects than localized effects of either 

eutrophication or fishing disturbance. Langton et al. (1996) suggest protection of “essential” 
58

habitats using a decision tree based on scientific information. Messieh et al. (1991) argue that 

we need to study effects on habitat that have the potential of causing widespread and long-term 

changes (e.g., gradual modification to surficial sediments and increased suspended sediment 

loads).

Despite this diversity of management philosophies, the MSA mandates that Councils minimize 

to the extent practicable adverse effects of fishing on EFH. Under National Standard 2 of MSA, 

Councils and the Secretary of Commerce must base conservation and management measures on 

the “best scientific information available.” Under the Administrative Procedures Act, the 

decision to approve a measure must be supported by a record that suggests the measure will 

contribute to the conservation and management of the fishery resource based on analyses and 

conclusions that are neither arbitrary nor capricious.

V. CONCLUSIONS

This document reviews available information on effects of bottom trawls, dredges, pots/traps, set 

gill nets and set longline to mud, sand, gravel, seagrass, coral reef and, in some cases, seamount 

habitats. Despite gaps in existing information (e.g., spatial extent of fishing effort, effects of 

specific gear configurations within specific habitat types, role of natural disturbance, link 

between habitat and fish population abundance) the numerous scientific studies summarized 

herein document physical and community effects of both mobile and static fishing gear to a 

range of habitat types. This document also reviews the various management philosophies 

regarding fishing impacts presented in the literature. These philosophies range from doing 

nothing until more information is available to establishing precautionary systems of closed areas 

to protect habitats and fish populations from uncertain consequences of human impacts. 

For the most part, the information needed for Councils to assess effects of fishing on EFH is 

currently available. This document provides the basis for Councils to conduct fishery-specific 

evaluations of potential adverse effects of fishing on benthic habitats, which along with other 

appropriate information should guide decisions regarding management measures to conserve and 

protect fish habitat.
59

VI. REFERENCES CITED

Almeida, F., L. Arlen, P. Auster, J. Cross, J. Lindholm, J. Link, D. Packer, A, Paulson, R. Reid, 

and P. Valentine. 2000. The effects of marine protected areas on fish and benthic fauna: the 

Georges Bank closed area II example. Poster presented at American Fisheries Society 130th

Annual Meeting, St. Louis, MO, August 20-24, 2000.

Appeldoorn, R.S., M. Nemeth, J. Vasslides, and M. Scharer. 2000. The effect of fish traps on 

benthic habitats off La Parguero, Puerto Rico. Report to the Caribbean Fishery Management 

Council, Hato Rey, Puerto Rico.

Ardizzone, G.D., P. Tucci, A. Somaschini, and A. Bellauscio. 2000. Is bottom trawling partly 

responsible for the regression of Posidonia oceanica meadows in the Mediterranean Sea? 

Pp. 37-46 In M.J. Kaiser and S.J. de Groot. The Effects of Fishing on Non-target Species 

and Habitats. Blackwell Science. 

Auster, P.J. 2001. Defining thresholds for precautionary habitat management actions in a 

fisheries context. North American Journal of Fisheries Management 21:1-9.

Auster, P.J. 1998. A conceptual model of the impacts of fishing gear on the integrity of fish 

habitats. Conservation Biology 12(6):1198-1203.

Auster, P.J. and N.L. Shackell. 2000. Marine protected areas for the temperate and boreal 

Northwest Atlantic: the potential for sustainable fisheries and conservation of biodiversity. 

Northeastern Naturalist 7(4):419-434.

Auster, P.J. and R.J. Malatesta. 1995. Assessing the role of non-extractive reserves for 

enhancing harvested populations in temperate and boreal marine systems. Pp. 82-89 In N. 

Shackell and J.J.M. Willison, eds. Marine Protected Areas and Sustainable Fisheries. 

Science and Management of Protected Areas Association, Wolfville, Nova Scotia. 

Auster, P.J. and R.W. Langton. 1999. The effects of fishing on fish habitat. Pp. 150-187 In L. 

Benaka, ed. Fish habitat: essential fish habitat and rehabilitation. American Fisheries 

Society, Symposium 22, Bethesda, Maryland.

Auster, P.J., L. Watling, and A. Reiser. 1997. Comment: The interface between fisheries 

research and habitat management. North American Journal of Fisheries Management 

17:591-595.

Auster, P.J., R.J. Malatesta, R.W. Langton, L. Watling, P.C. Valentine, C.L.S. Donaldson, E.W. 

Langton, A.N. Shepard, and I.G. Babb. 1996. The impacts of mobile fishing gear on 

seafloor habitats in the Gulf of Maine (northwest Atlantic): implications for conservation of 

fish populations. Reviews in Fisheries Science 4(2):185-202.

Ball, B., B. Munday, and I. Tuck. 2000. Effects of otter trawling on the benthos and 

environment in muddy sediments. Pp. 69-82 In M.J. Kaiser and S.J. de Groot. The Effects 

of Fishing on Non-target Species and Habitats. Blackwell Science.

Ball, B., G. Fox, and B. Munday. 1999. Long and short term consequences of a Nephrops otter 

trawl fishery on the benthos and environment of the Irish Sea. ICES Journal of Marine 

Science.

Barnes, D., K. Chytalo, and S. Hendrickson. 1991. Final Policy and Generic Environmental 

Impact Statement on Management of Shellfish in Uncertified Areas Program. NY 

Department of Environment and Conservation. 79 p. 

Barnette, M.C. 2001. A review of the fishing gear utilized within the Southeast Region and 

their potential impacts on essential fish habitat. NOAA Technical Memorandum NMFS -

SEFSC - 449.
60

Bergman, M.J.N, M. Fonds, M. Hup, and A. Stam. 1990. Direct effects of beam trawl fishing 

on benthic fauna in the North Sea. ICES C.M. 1990/MINI:11.

Bergman, M.J.N., and J.W. Van Santbrink. 2000. Fishing mortality of populations of megafauna 

in sandy sediments. Pp. 49-68 In M.J. Kaiser and S. J. de Groot. The effects of fishing on 

non-target species and habitats. Blackwell Science.

Bergman, M.J.N., and M. Hup. 1992. Direct effects of beam trawling on macrofauna in a sandy 

sediment in the southern North Sea. ICES Journal of Marine Science 49:5-11.

Black, K.P. and G.D. Parry. 1999. Entrainment, dispersal, and settlement of scallop dredge 

sediment plumes: field measurements and numerical modelling. Canadian Journal of 

Fisheries and Aquatic Science 56:2271-2281.

Black, K.P. and G.D. Parry. 1994. Sediment transport rates and sediment disturbance due to 

scallop dredging in Port Phillip Bay. Memoirs of the Queensland Museum 36(2):327-341.

Botsford, L.W., J.C. Castilla, and C.H. Peterson. 1997. The management of fisheries and 

marine ecosystems. Science 277:509-515.

Bradshaw, C., L.O. Veale, A.S. Hill, and A.R. Brand. 2001. The effect of scallop dredging on 

Irish Sea benthos: experiments using a closed area. Hydrobiologia 465:129-138.

Bradshaw, C., L.O. Veale, A.S. Hill, and A.R. Brand. 2000. The effects of scallop dredging on 

gravelly seabed communities. Pp. 83-104 In M.J. Kaiser and S.J. de Groot. The Effects of 

Fishing on Non-target Species and Habitats. Blackwell Science. 

Bradshaw, C., L.O. Veale, and A.R. Brand. 2002. The effect of scallop-dredge disturbance in 

long-term changes in Irish Sea benthic communities: a re-analysis of an historical dataset. 

Journal of Sea Research 47:161-184.

Bradstock, M. and D.P. Grodon. 1983. Coral-like bryozoan growths in Tasman Bay, and their 

protection to conserve commercial fish stocks. New Zealand Journal of Marine and 

Freshwater Research 17:159-163.

Breen, P.A. 1990. A review of ghost fishing by traps and gillnets. Pp. 571-599 In R.S. 

Shomura and M.L. Goldfrey (Editors). Proceedings of the Second International Conference 

on Marine Debris 2-7 April 1989, Honolulu, Hawaii. NOAA Technical Memorandum 

NOAA-TM-NMFS-SWFSC 154.

Bridger, J.P. 1972. Some observations on penetration into the seabed of tickler chains on a 

beam trawl. ICES CM 1972/B:7. Gear and Behavior Committee, 9 p.

Brylinsky, M., J. Gibson, and D.C. Gordon, Jr. 1994. Impacts of flounder trawls on the intertidal 

habitat and community of the Minas Basin, Bay of Fundy. Canadian Journal of Fisheries and 

Aquatic Sciences 51:650-661.

Butcher, T., J. Matthews, J. Gla ister, and G. Hamer. 1981. Study suggests scallop dredges 

causing few problems in Jervis Bay. Australian Fisheries 40:9-12.

Caddy, J.F. 1973. Underwater observations on tracks of dredges and trawls and some effects of 

dredging on a scallop ground. Journal of the Fisheries Research Board of Canada 30:173-

180.

Caddy, J.F. 1968. Underwater observations on scallop (Placopecten magellanicus) behavior and 

drag efficiency. Journal of the Fisheries Research Board of Canada 25(10):2123-2141.

Canadian Department of Fisheries and Ocean. 1993. Seabed disturbances from fishing 

activities. Unpublished Report. Canadian Department of Fisheries and Oceans. ScotiaFundy Region. Industry Services and Native Fisheries Branch. 4 p.
61

Cappo, M., D.M. Alongi, D. Williams, and N. Duke. 1998. A review and synthesis of 

Australian fisheries habitat research. Volume 2: Scoping Review, Issue 4: Effects of 

Harvesting on Biodiversity and Ecosystems. FRDC 95/055.

Carr, H.A. and H. Milliken. 1998. Conservation engineering: Options to minimize fishing’s 

impacts to the sea floor. Pp. 100-103 In E.M. Dorsey and J. Pederson, editors. Effects of 

Fishing Gear on the Sea Floor of New England. Conservation Law Foundation. Boston, 

Massachusetts. 160 pp.

Carr, H.A., E.A. Amaral, A.W. Hulbert, and R. Cooper. 1985. Underwater survey of simulated 

lost demersal and lost commercial gill nets off New England. Pp. 438-477 In R.S. Shomura 

and H.O. Yoshida. Proceedings of the Workshop on the Fate and Impact of Marine Debris, 

26-29 November 1984, Honolulu, Hawaii. NOAA-TM-NMFS-SWFC-54.

Chesapeake Bay Program. 1995. Guidance for protecting submerged aquatic vegetation in 

Chesapeake Bay from physical disruption. Annapolis, Maryland. 28 p.

Churchill, J.H. 1989. The effect of commercial trawling on sediment resuspension and transport 

over the Middle Atlantic Bight continental shelf. Continental Shelf Research 9(9):841-864.

Coen, L.D. 1995. A review of the potential impacts of mechanical harvesting on subtidal and 

intertidal shellfish resources. Unpublished Report. South Carolina Department of Natural 

Resources, Marine Resources Research Institute.

Collie, J.S. 1998. Studies in New England of fishing gear impacts on the sea floor. Pp. 53-62 In 

E.M. Dorsey and J. Pederson, editors. Effect of Fishing Gear on the Sea Floor of New 

England. Conservation Law Foundation. Boston, Massachusetts. 160 p. 

Collie, J.S., S.J. Hall, M.J. Kaiser, and I.R. Poiner. 2000(a). A quantitative analysis of fishing 

impacts on shelf-sea benthos. Journal of Animal Ecology 69:785-798.

Collie, J.S., G.A. Escanero, and P.C. Valentine. 2000(b). Photographic evaluation of the 

impacts of bottom fishing on benthic epifauna. ICES Journal of Marne Science 57:987-1001.

Collie, J.S., G.A. Escanero, and P.C. Valentine. 1997. Effects of bottom fishing on the benthic 

megafauna of Georges Bank. Marine Ecology Progress Series 155:159-172.

Collie, J.S., G.A. Escanero, L. Hunke, and P.C. Valentine. 1996. Scallop dredging on Georges 

Bank: Photographic evaluation of effects on benthic epifauna. International Council for the 

Exploration of the Sea. Mini-Symposium on Ecosystem Effects of Fisheries. ICES CM 

1996/Mini:9. 14 p. 

Cooper, R.A., H.A. Carr, and A.H. Hulvert. 1988. Manned submersible and ROV assessment of

ghost gillnets on Jeffries and Stellwagen Banks, Gulf of Maine. Research Report 88-4. 

NOAA Undersea Research Program. 

Currie, D.R. and G.D. Parry. 1999. Impacts and efficiency of scallop dredging on different soft 

substrates. Canadian Journal of Fisheries and Aquatic Science 56:539-550.

Currie, D.R. and G.D. Parry. 1996. Effects of scallop dredging on a soft sediment community: a 

large-scale experimental study. Marine Ecology Progress Series 134:131-150.

Daan, N. 1991. A theoretical approach to the evaluation of ecosystem effects of fishing in 

respect of North Sea benthos. ICES CM 1991/L:27. 6 p.

Dayton, P.K., S.F. Thrush, M.T. Agardy, and R.J. Hofman. 1995. Environmental effects of 

marine fishing. Aquatic Conservation: Marine and Freshwater Ecosystems 5:205-232.

DeAlteris, J., L. Skrobe, and C. Lipsky. 1999. The significance of seabed disturbance by mobile 

fishing gear relative to natural processes: a case study in Narragansett Bay, Rhode Island. 

Pp. 224-237 In L. Benaka, ed. Fish habitat: essential fish habitat and rehabilitation. 

American Fisheries Society, Symposium 22, Bethesda, Maryland.
62

de Groot, S.J. 1984. The impact of bottom trawling on the benthic fauna of the North Sea. 

Ocean Management 9:177-190.

de Groot, S.J. and J.M. Appledorn. 1971. Some experiments on the influence of the beam trawl 

on the bottom fauna. ICES CM 1971/B:2.

Demestre, M., P. Sanchez, and M.J. Kaiser. 2000. The behavioural response of benthic 

scavengers to otter-trawling disturbance in the Mediterranean. Pp. 121-129 In M.J. Kaiser 

and S.J. de Groot. The Effects of Fishing on Non-target Species and Habitats. Blackwell 

Science.

Drabsch, S.L., J.E. Tanner, and S.D. Connell. 2001. Limited infaunal response to experimental 

trawling in previously untrawled areas. ICES Journal of Marine Science 58:1261-1271.

Drew, S.C., and R.E. Larsen. 1994. Worldwide trawl and dredge study. Unpublished Report. 

Marine Data Systems. Plymouth, Massachusetts. 8p.

Dyekjaer, S.M., J.K. Jensen, and E. Hoffmann. 1995. Mussel dredging and effects on the 

marine environment. ICES CM 1995/E:13. 

Eleftheriou, A. and M.R. Robertson. 1992. The effects of experimental scallop dredging on the 

fauna and physical environment of a shallow sandy community. Netherlands Journal of Sea 

Research 30:289-299.

Engel, J. and R. Kvitek 1998. Effects of otter trawling on a benthic community in Monterey Bay 

National Marine Sanctuary. Conservation Biology 12(6):1204-1214.

Eno, N.C., D.S. MacDonald, J.A.M. Kinnear, S.C. Amos, C.J. Chapman, R.A. Clark, F.P.D. 

Bunker, and C. Munro. 2001. Effects of crustacean traps on benthic fauna. ICES Journal of 

Marine Science 58:11-20.

Erzini, K., C.C. Monteir, J. Ribero, M.N. Santos, M. Gaspar, P. Monteiro, and T.C. Borges. 

1997. An experimental study of gill net and trammel net ‘ghost fishing’ off the Algarve 

(southern Portugal). Marine Ecology Progress Series 158:257-265.

Flint, R.W. and J.A. Younk. 1983. Estuarine benthos: long-term community structure variations, 

Corpus Christi Bay, Texas. Estuaries 6(2):126-141.

Floderus. S. and L. Pihl. 1990. Resuspension in the Kattegat: impact of variation in wind climate 

and fishery. Estuarine, Coastal and Shelf Science 31:487-498.

Fogarty, M.J. and S.A. Murawski. 1998. Large-scale disturbance and the structure of marine 

systems: fishery impacts on Georges Bank. Ecological Applications 8(1):S6-S22, 

Supplement.

Fonds, M. and S. Groenewold. 2000. Food subsidies generated by the beam-trawl fishery in the 

southern North Sea. Pp. 130-150 In M.J. Kaiser and S.J. de Groot. The Effects of Fishing on 

Non-target Species and Habitats. Blackwell Science.

Fonseca, M.S., G.W. Thayer, A.J. Chester, and C. Foltz. 1984. Impact of scallop harvesting on 

eelgrass (Zostera marina) meadows: implications for management. North American Journal 

of Fisheries Management 4:286-293.

Fonteyne, R. 2000. Physical impact of beam trawls on seabed sediments. Pp. 15-36 In M.J. 

Kaiser and S.J. de Groot. The Effects of Fishing on Non-target Species and Habitat. 

Blackwell Science.

Fossa, J.H., P.B. Mortensen, and D.M. Furevik. 2001. The deep water coral Lophelia pertusa in 

Norwegian waters; distribution and fishery impacts. First International Symposium on Deep 

Sea Corals, Halifax, Nova Scotia, 30 July-2 August 2001.
63

Freese, L., P.J. Auster, J. Heifetz, and B.L. Wing. 1999. Effects of trawling on seafloor habitat 

and associated invertebrate taxa in the Gulf of Alaska. Marine Ecology Progress Series 

182:119-126.

Frid, C.L.J. and R.A. Clark 2000. Long-term changes in North Sea benthos: discerning the role 

of fisheries. Pp. 198-216 In M.J. Kaiser and S.J. de Groot. The Effects of Fishing on Nontarget Species and Habitat. Blackwell Science.

Frid, C.L.J. and S.J. Hall. 1999. Inferring changes in North Sea benthos from fish stomach 

analysis. Marine Ecology Progress Series 184:184-188.

Frid, C.L.J., R.A. Clark, and J.A. Hall. 1999. Long-term changes in the benthos on a heavily 

fished ground of the NE coast of England. Marine Ecology Progress Series 188:13-29.

Friedlander, A.M., G.W. Boehlert, M.E. Field, J.E. Mason, J.V. Gardner, and P. Dartnell. 1999. 

Sidescan-sonar mapping of benthic trawl marks on the shelf and slope off Eureka, California. 

Fishery Bulletin 97:786-801.

Fuller, S. and P. Cameron. 1998. Marine benthic seascapes: fishermen’s perspectives. Marine 

Issues Committee Special Publication. Vol. 3. Ecology Action Centre. Halifax, Nova 

Scotia. 64 p.

Futch, C.R. and D.S. Beaumariage. 1965. A report on the bait shrimp fishery of Lee County, 

Florida. Florida Board of Conservation Marine Laboratory Maritime Base, Bayboro Harbor, 

St. Petersburg, Florida. FBCML:65-1.

Garrison, G. 1998. Reef fishes of St. John, U.S. Virgin Islands. In Mac, M.J., P.A. Opler, C.E. 

Puckett Haecker, and P.D. Doran, Eds. Status and Trends of the Nations’ Biological 

Resources. U.S. Department of Interior, U.S. Geological Survey. Washington, DC.

Garrison, G. 1997. St. John, U.S. Virgin Islands fish trap study, 1992-1994. Unpublished 

Report. Biological Resources Division, USGS, Virgin Islands National Park.

Gibbs, P.J., A.J. Collins, and L.C. Collett. 1980. Effect of otter prawn trawling on the 

macrobenthos of a sandy substratum in a New South Wales estuary. Australian Journal of 

Marine and Freshwater Research 31:509-516.

Gilkinson, K., M. Paulin, S. Hurley, and P. Schwinghamer. 1998. Impacts of trawl door 

scouring on infaunal bivalves: results of a physical trawl door model/dense sand interaction. 

Journal of Experimental Marine Biology and Ecology 224:291-312.

Glemarec, M., Y. LeFaou, and F. Cuq. 1996. Long-term changes of seagrass beds in the Glenan 

Archipelago (South Brittany). Oceanologica Acta 20(1):217-227.

Godcharles, M.F. 1971. A study of the effects of a commercial hydraulic clam dredge on benthic 

communities in estuarine areas. State of Florida Department of Natural Resources Marine 

Resources Laboratory Technical Series No. 64.

Goñi, R. 1998. Ecosystem effects of marine fisheries: an overview. Ocean and Coastal 

Management 40(1):37-64.

Gordon, D.C., Jr., P. Schwinghamer, T.W. Rowell, J. Prena, K. Gilkinson, W.P. Vass, and D.L. 

McKeown. 1998. Studies in eastern Canada on the impact of mobile fishing gear on benthic 

habitat and communities. Pp. 63-67 In E.M. Dorsey and J. Pederson, editors. Effect of 

Fishing Gear on the Sea Floor of New England. Conservation Law Foundation. Boston, 

Massachusetts. 160 p.

Gray, J.S. 2000. The measurement of marine species diversity, with an application to the 

benthic fauna of the Norwegian continental shelf. Journal of Experimental Marine Biology 

and Ecology 250(1-2): 23-49.
64

Greene, H.G., M.M. Yoklavich, R.M. Starr, V.M. O’Connell, W.W. Wakefield, D.E. Sullivan, 

J.E. McRea, Jr., and G.M. Cailliet. 1999. A classification scheme for deep seafloor habitats. 

Oceanologica Acta 22(6):663-678.

Greenstreet, S.P.R. and S.J. Hall. 1996. Fishing and groundfish assemblage structure in the 

northwestern North Sea: an analysis of long-term and spatial trends. Journal of Animal 

Ecology 65:577-598.

Greenstreet, S.P.R., F.B. Spence, A.M. Shanks, and J.A. McMillan. 1999. Fishing effects in 

northeast Atlantic shelf seas: patterns in fishing effort, diversity and community structure. II. 

Trends in fishing effort in the North Sea by UK registered vessels landing in Scotland. 

Fisheries Research 40:107-124.

Hall, S.J. 1999. The Effects of Fishing on Marine Ecosystems and Communities. Blackwell 

Science. Oxford, United Kingdom. 274 p.

Hall, S.J. 1994. Physical disturbance and marine benthic communities: life in unconsolidated 

sediments. Oceanography and Marine Biology: An Annual Review 32:179-239.

Hall, S.J. and M.J.C. Harding. 1997. Physical disturbance and marine benthic communities: the 

effects of mechanical harvesting of cockles on non-target benthic infauna. Journal of 

Applied Ecology 34:497-517.

Hall, S.J., M.R. Robertson, D.J. Basford, and S.D. Heaney. 1993. The possible effects of fishing 

disturbance in the northern North Sea: an analysis of spatial patterns in community structure 

around a wreck. Netherlands Journal of Sea Research 31(2):201-208.

Hall, S.J., D.J. Basford, and M.R. Robertson. 1990. The impact of hydraulic dredging for razor 

clams Ensis sp. on an infaunal community. Netherlands Journal of Sea Research 27(1):119-

125.

Hall-Spencer, J.M. and P.G. Moore. 2000. Impact of scallop dredging on maerl grounds. In

Effects of Fishing on Non-Target Species and Habitats: Biological, Conservation, and Socioeconomic Issues (M.J. Kaiser and S.J. de Groot (eds.). Blackwell Science.

Hall-Spencer, J., V. Allain, and J.H. Fossa. 2002. Trawling damage to Northeast Atlantic 

ancient coral reefs. Proceedings Royal Society of London 269:507-511.

Hall-Spencer, J.M., C. Froglia, R.J.A. Atkinson, and P.G. Moore. 1999. The impact of Rapido 

trawling for scallops, Pecten jacobaeus (L.), on the benthos of the Gulf of Venice. ICES 

Journal of Marine Science 56:111-124.

Hansson, M., M. Lindegarth, D. Valentinsson, and M. Ulmestrand. 2000. Effects of shrimptrawling on abundance of benthic macrofauna in Gullmarsfjorden, Sweden. Marine Ecology 

progress Series 198:191-201.

Harris, A.N. and I.R. Poiner. 1991. Changes in species composition of demersal fish fauna of 

Southeast Gulf of Carpentaria, Australia, after 20 years of fishing. Marine Biology 

111(3)503-519.

Hayes, D.F., G.L. Raymond, and T.N. McLellan. 1984. Sediment resuspension from dredging 

activities. Pp. 72-82 In Proceedings of the ASCE Specialty Conference. Dredging ‘84. 

Clearwater, Florida. 

Hayes, M.L. 1983. Active fish capture methods. In Fisheries Techniques. Nielson, L.A. and 

D.L. Johnson, eds. American Fisheries Society, Bethesda, Maryland.

Heiftez, J. 1997. Workshop of the potential effects of fishing gear on benthic habitat. NMFS 

AFSC Processed Report 97-04. 17 p.
65

Hewitt, J.E., S.F. Thrush, V.J. Cummings, and S.J. Turner. 1998. The effect of changing 

sampling scales on our ability to detect effects of large-scale processes on communities. 

Journal of Experimental Marine Biology and Ecology 227(2):251-264. 

High, W.L. 1998. Observations of a scientist/diver on fishing technology and fisheries biology. 

NOAA, NMFS, AFSC Processed Report 98-01. 47 p.

Hill, A.S., L.O. Veale, D. Pennington, S.G. Whyte, A.R. Brand, and R.G. Hartnoll. 1999. 

Changes in Irish Sea benthos: possible effects of 40 years of dredging. Estuarine, Coastal 

and Shelf Science 48(6):739-750.

Hutchings, P. 1990. Review of the effects of trawling on macrobenthic epifaunal communities. 

Australian Journal of Marine and Freshwater Research 41:111-120.

ICES. 2000. Report of the Working Group on Ecosystem Effects of Fishing Activities. ICES 

CM 2000/ACE:2.

ICES. 1999. Report of the Working Group on Fishing Technology and Fish Behavior. ICES, 

Fisheries Technology Committee. ICES CM 1999. 51 p.

ICES. 1995. Report of the Study Group on Ecosystem Effects of Fishing Activities, 

Copenhagen, Denmark, 7-14 April 1992. ICES Cooperative Research Report, Number 200, 

120 pp.

ICES. 1993. Report of the Working Group on Ecosystem Effects of Fishing Activities. 

International Council for the Exploration of the Sea. Working Group on Ecosystem Effects 

of Fishing Activities ICES CM 1993/G:4. 9 p.

ICES. 1992. Report of the Study Group on Ecosystem Effects of Fishing Activities, 

Copenhagen, 7-14 April, 1992. International Council for the Exploration of the Sea. Study 

Group on Ecosystem Effects of Fishing Activities. ICES CM 1992/G:11. 144 p.

ICES. 1991. Report of the study group on ecosystem effects of fishing activities, Copenhagen, 

Denmark, International Council for the Exploration of the Sea. Study Group on Ecosystem 

Effects of Fishing Activities. ICES CM 1991/G:7. 

ICES. 1973. Effects of trawls and dredges on the seabed. ICES, Gear and Behavior Committee. 

ICES CM 1973 /B:2.

Jenning, S., J. Alvsvag, A.J.R. Cotter, S. Ehrich, S.P.R. Greenstreet, A. Jarre-Teichmann, N. 

Mergardt, A.D. Rijnsdorp, and O. Smedstad. 1999. Fishing effects in northeast Atlantic 

shelf seas: patterns in fishing effort, diversity and community structure. III. International 

trawling effort in the North Sea: an analysis of spatial and temporal trends. Fisheries 

Research 40:125-134.

Jennings, S. and A.J.R. Cotter. 1999. Fishing effects in northeast Atlantic shelf seas: patterns in 

fishing effort, diversity and community structure. I. Introduction. Fisheries Research 

40:103-106.

Jennings, S. and M.J. Kaiser. 1998. The effects of fishing on marine ecosystems. Advances in 

Marine Biology 34:201-352.

Jennings, S. and N.V.C. Polunin. 1996. Impacts of fishing on tropical reef ecosystems. Ambio 

25:44-49.

Jolley, J.W., Jr. 1972. Exploratory fishing for the sunray venus clam, Macrocallista nimbosa, in 

northwest Florida. Florida Department of Natural Resources Technical Series No. 67:1-42.

Kaiser, M.J. 2000. The implications of the effects of fishing on non-target species and habitats. 

Pp. 383-392 In M.J. Kaiser and S.J. de Groot. The Effects of Fishing on Non-target Species 

and Habitats. Blackwell Science.
66

Kaiser, M.J. 1998. Significance of bottom-fishing disturbance. Conservation Biology 

12(6):1230-1235.

Kaiser, M.J. 1996. Starfish damage as an indicator of trawling intensity. Marine Ecology 

Progress Series 134:303-307.

Kaiser, M.J. and K. Ramsay. 1997. Opportunistic feeding by dabs within areas of trawl 

disturbance: possible implications for increased survival. Marine Ecology Progress Series 

152:307-310. 

Kaiser, M.J. and B.E. Spencer. 1996a. Behavioural responses of scavengers to beam trawl 

disturbance. Pp. 116-123 In S.P.R. Greenstreet and M.S. Tasker, editors. Aquatic Predators 

and Their Prey. Blackwell Scientific Publications, Oxford. 

Kaiser, M.J. and B.E. Spencer. 1996b. The effects of beam-trawl disturbance on infaunal 

communities in different habitats. Journal of Animal Ecology 65(3):348-358.

Kaiser, M.J. and B.E. Spencer 1994. Fish scavenging behavior in recently trawled areas. Marine 

Ecology Progress Series 112:41-49.

Kaiser, M.J. and B.E. Spencer. 1993. A preliminary assessment of the immediate effects of 

beam trawling on a benthic community in the Irish Sea. ICES CM 1993/B:38. 9 p.

Kaiser, M.J. and B.E. Spencer. 1993. Opportunistic feeding on benthos by fishes after the 

passage of a 4-m beam trawl. ICES CM 1993/G:27. 13 p.

Kaiser, M.J., G. Broad, and S.J. Hall. 2001. Disturbance of intertidal soft-sediment benthic 

communities by cockle hand raking. Journal of Sea Research 45:119-130.

Kaiser, M.J., K. Ramsay, C.A. Richardson, F.E. Spence, and A.R. Brand. 2000a. Chronic 

fishing disturbance has changed shelf sea benthic community structure. Journal of Animal 

Ecology 69: 494-503.

Kaiser, M.J., B.E. Spencer, and P.J. Hart. 2000b. Fishing-Gear Restrictions and Conservation of 

Benthic Habitat Complexity. Conservation Biology 14(5):1512-1525.

Kaiser, M.J., K. Cheney, F.E. Spence, D.B. Edwards, and K. Radford. 1999. Fishing effects in 

northeast Atlantic shelf seas: patterns in fishing effort, diversity and community structure. 

VII. The effects of trawling disturbance on the fauna associated with the tubeheads of 

serpulid worms. Fisheries Research 40:195-205.

Kaiser, M.J., D.B. Edwards, P.J. Armstrong, K. Radford, N.E.L. Lough, R.P. Flatt, and H.D. 

Jones. 1998. Changes in megafaunal benthic communities in different habitats after trawling 

disturbance. ICES Journal of Marine Science 55:353-361.

Kaiser, M.J., A.S. Hill, K. Ramsay, B.E. Spencer, A.R. Brand, L.O. Veale, K. Pruden, E.I.S. 

Rees, B.W. Munday, B. Ball, and S.J. Hawkins. 1996a. Benthic disturbance by fishing gear 

in the Irish Sea: A comparison of beam trawling and scallop dredging. Aquatic 

Conservation: Marine and Freshwater Ecosystems 6(4): 269-285.

Kaiser, M.J., D.B. Edwards, and B.E. Spencer. 1996b. Infaunal community changes as a result 

of commercial clam cultivation and harvesting. Aquatic Living Resources 9:57-63.

Kaiser, M.J., B. Bullimore, P. Newman, K. Lock, and S. Gilbert. 1996c. Catches in ‘ghost 

fishing’ set nets. Marine Ecology Progress Series 145:11-16.

Kenchington, E.L.R., J. Prena, K.D. Gilkinson, D.C. Gordon Jr., K. MacIssac, C. Bourbonnais, 

P.J. Schwinghamer, T.W. Rowell, D.L. McKeown, and W.P. Vass. 2001. Effects of 

experimental otter trawling on the macrofauna of a sandy bottom ecosystem on the Grand 

Banks of Newfoundland. Canadian Journal of Fisheries and Aquatic Science 58:1043-1057.
67

Kenchington, T.J. 1995. A summary of the published evidence relating to habitat modification 

by fish draggers. Pp. 109-116 In The Canadian Maritimes Fishing: Let’s Fix It, An Action 

Plan. SW Nova Scotia Fixed Gear Association. Shelburne, Nova Scotia, Canada.

Koslow, J.A. and K. Gowlett-Holmes. 1998. The seamount fauna off southern Tasmania: 

benthic communities, their conservation and impacts of trawling. Final report to 

Environment Australia and the Fisheries Research Development Corporation. FRDC Project 

95/058.

Koslow, J.A., K. Gowlett-Holmes, J.K. Lowry, T. O'Hara, G.C.B. Poore, and A. Williams. 

2001. Seamount benthic macrofauna off southern Tasmania: Community structure and 

impacts of trawling. Marine Ecology Progress Series 213:111-125.

Kroncke, I. 1995. Long-term changes in North Sea benthos. Senckenbergiana Maritima 26(1-

2):73-80.

Krost, P., M. Bernard, F. Werner, and W. Hukriede. 1990. Otter trawl tracks in Kiel Bay 

(Western Baltic) mapped by side-scan sonar. Meeresforschung 32:344-353.

Kyte, M., P. Averill, and T. Hendershott. 1975. The impact of the hydraulic escalator shellfish 

harvester on an intertidal soft-shell clam flat in the Harraseeket River, Maine. Project 

Completion Report, Maine Dept. Marine Resources, Augusta, ME, 54 p.

Langan, R. 1998. The effect of dredge harvesting on Easter Oysters and the associated benthic 

community. Pp. 108-110 In Effects of Fishing Gear on the Sea Floor of New England. 

Conservation Law Foundation. Boston, Massachusetts. 160 p. 

Langton, R.W. and P.J. Auster. 1999. Marine fishery and habitat interactions: to what extent are 

fisheries and habitat interdependent? Fisheries 24(6):14-21.

Langton, R.W. and W.E. Robinson. 1990. Faunal associations on scallop grounds in the western 

Gulf of Maine. Journal of Experimental Marine Biology and Ecology 144:157-171.

Langton, R.W. and J.R. Uzmann. 1990. A photographic survey of megafauna of the central and 

eastern Gulf of Maine. Fisheries Bulletin 87(4):945-954.

Langton, R.W., R.S. Steneck, V. Gotceitas, F. Juanes, and P. Lawton. 1996. The interface 

between fisheries research and habitat management. North American Journal of Fisheries 

Management 16(1):1-7. 

Langton, R.W., P.J. Auster, and D.C. Schneider. 1995. A spatial and temporal perspective on 

research and management of groundfish in the northwest Atlantic. Reviews in Fisheries 

Science 3(3):201-229.

LaSalle, M.W. 1990. Physical and chemical alterations associated with dredging: An overview. 

Pp1-12 In Effects of Dredging on anadromous Pacific Coast Fishes. Workshop Proceedings, 

Seattle, September 8-9, 1988. Report of Washington Sea Grant Program.

Lenihan, H.S. and C.H. Peterson. 1998. How habitat degradation through fishery disturbance 

enhances impacts of hypoxia on oyster reefs. Ecological Applications 8(1):128-140.

Levin, L.A. 1984. Life history and dispersal patterns in a dense infaunal polychaete assemblage: 

community structure and response to disturbance. Ecology 65(4):1185-1200. 

Lindeboom, H.J., and S.J. de Groot, 1998. Impact II. The effects of different types of fisheries 

on the North Sea and Irish Sea benthic ecosystems. NIOZ Rapport 1998-1. 404 p.

Lindholm, J.B., P.J. Auster, and L.S. Kaufman. 1999. Habitat-mediated survivorship of juvenile 

(0-year) Atlantic cod Gadus morhua. Marine Ecology Progressive Series 180:247-255.

MacKenzie, C.L., Jr. 1982. Compatibility of invertebrate populations and commercial fishing 

for ocean quahogs. North American Journal of Fisheries Management 2:270-275.
68

Maier, P.P., P.H. Wendt, W.A. Roumillat, G.H. Steele, M.V. Levisen, and R. Van Dolah. 1995. 

Effects of subtidal mechanical clam harvesting on tidal creeks. South Carolina Department 

of Natural Resources, Marine Resources Division. Final Report. 38 p.

Manning, J.H. and E.A. Dunnington. 1955. The Maryland soft-shell clam fishery: a preliminary 

investigational report. Proceedings of the National Shellfisheries Association 46:100-110.

Margetts, A.R. and J.P. Bridger. 1971. The effect of a beam trawl on the sea bed. ICES Council 

Meeting. 1971/B:8. 

Mayer, L.M., D.F. Schick, R.H. Findlay, and D.L. Rice. 1991. Effects of commercial dragging 

on sedimentary organic matter. Marine Environmental Research 31:249-261.

McAllister, D.E. and G. Spiller. 1994. Trawling and dredging impacts on fish habitat and 

bycatch. Pp. 1709-1718 In Coastal Zone Canada 1994, Cooperation in the Coastal Zone. 

Conference Proceedings, Volume 4. Coastal Zone Canada Association, Dartmouth, Nova 

Scotia. 

McConnaughey, R.A., K.L. Mier and C.B. Dew. 2000. An examination of chronic trawling on 

soft bottom benthos of the eastern Bering Sea. ICES Journal of marine Science 57:1388-

1400.

Medcof, J.C. and J.F. Caddy. 1971. Underwater observations on the performance of clam 

dredges of three types. ICES CM 1971/B:10.

Messieh, S.N., T.W. Rowel, D.L. Peer, and P.J. Cranford. 1991. The effects of trawling, 

dredging and ocean dumping on the eastern Canadian continental shelf seabed. Continental 

Shelf Research 11(8-10):1237-1263.

Meyer, D.L., M.S. Fonseca, P.L. Murphey, M.W. LaCroix, P.E. Whitfield, D.R. Colby, and 

G.W. Thayer. 1991. Impact of bait shrimp trawling on seagrass beds and fish bycatch in 

Tampa Bay, Florida. Unpublished Report submitted by NMFS, Southeast Fisheries Center, 

Beaufort Laboratory to Florida Department of Natural Resources, Marine Research Institute. 

DNR Contract #C4488. 28 p. 

Meyer, T.L., R.A. Cooper, and K.J. Pecci. 1981. The performance and environmental effects of 

a hydraulic clam dredge. Marine Fisheries Review 43(9):14-22.

Mirarchi, F. 1998. Bottom trawling on soft substrates. Pp. 80-84 In E.M. Dorsey and J. 

Pederson, editors. Effects of Fishing Gear on the Sea Floor on New England. Conservation 

Law Foundation. Boston, Massachusetts. 160 p. 

Moore, D.R., and H.R. Bullis, Jr. 1960. A deep-water coral reef in the Gulf of Mexico. Bulletin 

of Marine Science of the Gulf and Caribbean 10(1):125-128.

Moran, M.J. and P.C. Stephenson. 2000. Effects of otter trawling on macrobenthos and 

management of demersal scalefish fisheries on the continental shelf of north-western 

Australia. ICES Journal of Marine Science 57:510-516.

Murawski, S.A. and F.M. Serchuk. 1989. Environmental effects of offshore dredge fisheries for 

bivalves. ICES CM 1989/K:27. 12 p.

National Research Council. 2002. Effects of Trawling and Dredging on Seafloor Habitat. 

National Academy Press, Washington, DC.

Norse, E.A. and L. Watling. 1999. Impacts of mobile fishing gear: the biodiversity perspective. 

Pp. 31-40 In L. Benaka, ed. Fish habitat: essential fish habitat and rehabilitation. American 

Fisheries Society, Symposium 22, Bethesda, Maryland. 
69

NPFMC. 1992. Final Supplemental Environmental Impact Statement and Regulatory Impact 

Review/Initial Regulatory Flexibility Analysis of Proposed Inshore/Offshore Allocation 

Alternatives (Amendment 18/23) to the Fishery Management Plans for the Groundfish 

Fishery of the Bering Sea and Aleutian Islands and the Gulf of Alaska. North Pacific Fishery 

Management Council.

Ohman, M.C., A. Rajasuriya, and O. Linden. 1993. Human disturbance on coral reefs in Sri 

Lanka: a case study. Ambio 22:474-480.

Orth, R.J., K.A. Moore, D.J. Wilcox, and J.R. Fishman. 1998. Chincoteague Bay, Virginia: 

effectiveness of the SAV sanctuary and revegetation of SAV habitat disturbed by clam 

dredging. Unpublished Report to the Virginia Marine Resources Commission. 6 p + figures.

Overholtz, W.J. and A.V. Tyler. 1985. Long-term responses of the demersal fish assemblages 

of Georges Bank. Fish. Bull. 83(4):507-520.

Pederson, J. and M. Hall-Arber. 1999. Fish habitat: a focus on New England fishermen’s 

perspectives. Pp. 188-211 In L. Benaka, ed. Fish habitat: essential fish habitat and 

rehabilitation. American Fisheries Society, Symposium 22, Bethesda, Maryland. 

Philippart, C.J.M. 1998. Long-term impact of bottom fisheries on several bycatch species of 

demersal fish and benthic invertebrates in the southeastern North Sea. ICES Journal of 

Marine Science 55:342-352.

Pilskaln, C.H., J.H. Churchill, and L.M. Mayer. 1998. Resuspension of sediment by bottom 

trawling in the Gulf of Maine and potential geochemical consequences. Conservation 

Biology 12(6):1223-1229.

Pranovi, F. and O. Giovanardi. 1994. The impact of hydraulic dredging for short-necked clams, 

Tapes spp., on an infaunal community on the lagoon of Venice. Scientia Marina 

58(4):345353.

Pranovi, F., S. Raicevich, G. Franceschini, M.G. Farrace, and O. Govanardi. 2000. Rapido 

trawling in the northern Adriatic Sea: effects on benthic communities in an experimental 

area. ICES Journal of Marine Science 57:517-524.

Prena, J., P. Schwinghamer, T.W. Rowell, D.C. Gordon, Jr., K.D. Gilkinson, W.P. Vass, and 

D.L. McKeown. 1999. Experimental otter trawling on a sandy bottom ecosystem of the 

Grand Banks of Newfoundland: analysis of trawl bycatch and effect on epifauna. Marine 

Ecology Progress Series 181:107-124.

Probert, P.K., D.G. McKnight, and S.L. Grove. 1997. Benthic invertebrate bycatch from a deepwater trawl fishery, Chatham Rise, New Zealand. Aquatic Conservation: Marine and 

Freshwater Ecosystems 7(1):27-40.

Quandt, A. 1999. Assessment of fish trap damage on coral reefs around St. Thomas, USVI. 

Independent Project Report, Univeristy of the Virgin Islands, Spring 1999. 9 p.

Rachor, E. 1990. Changes in sublittoral zoobenthos in the German Bight with regard to 

eutrophication. Netherlands Journal of Sea Research 25(1-2):209-214.

Ramsay, K., M.J. Kaiser, and R.N. Hughes. 1998. Responses of benthic scavengers to fishing 

disturbance by towed gears in different habitats. Journal of Experimental Marine Biology 

and Ecology 224:73-89. 

Ramsay, K., M.J. Kaiser, and R.N. Hughes. 1996. Changes in hermit crab feeding patterns in 

response to trawling disturbance. Marine Ecology Progress Series 144(1-3):63-72.

Reise, K. 1982. Long term changes in the macrobenthic invertebrate fauna of the Wadden Sea: 

Are polychaetes about to take over? Netherlands Journal of Sea Research 16:29-36.
70

Reise, K. and A. Schubert. 1987. Macrobenthic turnover in the subtidal Wadden Sea: the 

Norderaue revisited after 60 years. Helgolander Meeresunters 41:69-82.

Rester, J.K. 2000. Annotated bibliography of fishing impacts on habitat. Gulf States Marine 

Fisheries Commission. Number 73. Ocean Springs, Mississippi. 168 p.

Riemann, B. and E. Hoffmann. 1991. Ecological consequences of dredging and bottom trawling 

in the Limfjord, Denmark. Marine Ecology Progress Series 69:171-178. 

Riesen, W. and K. Reise 1982. Macrobenthos of the subtidal Wadden Sea: revisited after 55 

years. Helgolander Meeresunters 35:409-423. 

Rijnsdorp, A.D. and P.I. Van Leeuwen. 1996. Changes in growth of North Sea plaice since 

1950 in relation to density, eutrophication, beam trawl effort, and temperature. ICES Journal 

of Marine Science 53:1199-1213.

Rijnsdorp, A.D. and B. Vingerhoed. 2001. Feeding of plaice Pleuronectes platessa L. and sole 

Solea solea (L.) in relation to the effects of bottom trawling. Journal of DeepSea Research 

45:219-229.

Rijnsdorp, A.D., A.M. Buys, F. Storbeck, and E.G. Visser. 1998. Micro-scale distribution of 

beam trawl effort in the southern North Sea between 1993 and 1996 in relation to the 

trawling frequency of the sea bed and the impact on benthic organisms. ICES Journal of 

Marine Science 55:403-419.

Rogers, S.I., D. Maxwell, A.D. Rijnsdorp, U. Damm, and W. Vanhee. 1999. Fishing effects in 

northeast Atlantic shelf seas: patterns in fishing effort, diversity and community structure. 

IV. Can comparisons of species diversity be used to assess human impacts on demersal fish 

faunas? Fisheries Research 40:135-152.

Rogers, S.I., M.J. Kaiser, and S. Jennings. 1998. Ecosystem effects of demersal fishing: A 

European perspective. Pp. 68-78 In E.M. Dorsey and J. Pederson, editors. Effect of Fishing 

Gear on the Sea Floor of New England. Conservation Law Foundation. Boston, 

Massachusetts. 160 p.

Ruffin, K.K. 1995. The effects of hydraulic clam dredging on nearshore turbidity and light 

attenuation in Chesapeake Bay, MD. Master’s Thesis. University of Maryland. 79 p.

Rumohr, H. 1998. Information on impact of trawling on benthos in Kiel Bay. Annex to Eighth 

Report of the Benthos Ecology Working Group. ICES CM 1989/L:19. p. 80. 

Rumohr, H. and P. Krost. 1991. Experimental evidence of damage to benthos by bottom 

trawling with special reference to Arctica islandica. Meeresforschung 33(4):340-345.

Sainsbury, K.J. 1988. The ecological basis of multispecies fisheries and management of a 

demersal fishery in tropical Australia. Pp. 349-382 In J.A. Gulland, ed. Fish Population 

Dynamics, 2nd edition. John Wiley and Sons, London.

Sainsbury, K.J. 1987. Assessment and management of the demersal fishery on the continental 

shelf of Northwestern Australia. Pp. 465-503 In JJ. Polovina and S. Ralston, ed. Tropical 

snappers and groupers: biology and fisheries management. Westview Press, Boulder, 

Colorado.

Sainsbury, K.J., R.A. Campbell, R. Lindholm, and A.W. Whitelaw. 1994. Experimental 

management of an Australian multispecies fishery: examining the possibility of trawlinduced habitat modification. Pp. 107-112 In E.K. Pikitch, D.D. Huppert, and M.P. 

Sissenwine, ed. Global Trends: Fisheries Management. American Fisheries Society, 

Symposium 20, Bethesda, Maryland.
71

Sainsbury, K.J., R.A. Campbell, and A.W. Whitelaw. 1993. Effects of trawling on the marine 

habitat on the north west shelf of Australia and implications for sustainable fisheries 

management. Pp. 137-145 In D.A. Hancock, ed. Sustainable Fisheries Through Sustaining 

Fish Habitat. Canberra, Australia, Australian Government Publishing Service.

Sanchez, P., M. Demestre, M. Ramon, and M.J. Kaiser. 2000. The impact of otter trawling on 

mud communities in the northwestern Mediterranean. ICES Journal of Marine Science 

57:1352-1358.

Sanchez-Jerez, P. and A.A. Ramos Espla. 1996. Detection of environmental impacts by bottom 

trawling on Posidonia oceanica (L.) Delile meadows: sensitivity of fish and 

macroinvertebrate communities. Journal of Aquatic Ecosystem Health 5(4):239-253.

Schoellhamer, D.H. 1996. Anthropogenic sediment resuspension mechanisms in a shallow 

microtidal estuary. Estuarine, Coastal and Shelf Science 45(5):533-548.

Schratzberger, M., T.A. Dinmore, and S. Jennings. 2002. Impacts of trawling on the diversity, 

biomass and structure of meiofauna assemblages. Marine Biology 140:83-93.

Schwinghamer, P., D.C. Gordon, Jr., T.W. Rowell, J. Prena, D.L. McKeown, G. Sonnichsen, and 

J.Y. Guigne. 1998. Effects of experimental otter trawling on surficial sediment properties of 

a sandy-bottom ecosystem of the Grand Banks of Newfoundland. Conservation Biology 

12(6):1215-1222.

Smith, E.M., L.L. Stewart, M. S. Alexander, L.A. Gunn, M.W. Johnson, R.F. Sampson, Jr., 

M.M. Blake, P.T. Howell, R.E. MacLeod, D.G. Simpson, W.H. Webb, P.J. Auster, N.K. 

Bender, K.Bucholz, J. Crawford, and T.J. Visel. 1985. Study of lobster fisheries in the 

Connecticut waters of Long Island Sound with special reference to the effects of trawling on 

lobsters. Department of Environmental Protection, Division of Conservation & Preservation, 

Bureau of Fisheries, Marine Fisheries Program.

Stephan, C.D., R.L. Peuser, and M.S. Fonseca. 2000. Evaluating fishing gear impacts to 

submerged aquatic vegetation and determining mitigation strategies. ASMFC Habitat 

Management Series #5. 38 p.

Stevenson, J.C. and N.M. Confer. 1978. Summary of available information on Chesapeake Bay 

submerged vegetation. FWS/OBS - 78/66. 

Stewart, P.A.M. 1999. Gear modification as a management tool to limit ecosystem effects of 

fishing. ICES/SCOR Symposium, Ecosystem Effects of Fishing, April 1999, St. John’s, 

Newfoundland. 20 p.

Sutherland, D.L., G.L. Beardsley, and R.S. Jones. 1983. Results of a survey of the South Florida 

fish-trap fishing grounds using a manned submersible. Northeast Gulf Science 6(2):179-183.

Tabb, D.C. 1958. Report on the bait shrimp fishery of Biscayne Bay, Miami, Florida. Florida 

State Board of Conservation, Marine Lab, University of Miami. 16 p.

Tarr, M. 1977. Some effects of hydraulic clam harvesting on water quality in Kilisut Harbor, 

Port Susan, and Agate Pass, Washington. State of Washington, Dept. Fisheries, Progr. Rep. 

22, 82 p.

Taylor, R.G. and R.H. McMichael, Jr. 1983. The wire fish-trap fisheries in Monroe and Collier 

Counties, Florida. Florida Marine Research Publication. No. 39. 19 p.

Thompson, G. 1993. Impacts of trawling on the seabed and benthic community. Appendix F. 

Amendment 24, Bering Sea/Aleutian Islands Groundfish Fishery Management Plan. 5 p.
72

Thrush, S.F., J.E. Hewitt, V.J. Cummings, P.K. Dayton, M. Cryer, S.J. Turner, G.A. Funnell, 

R.G. Budd, C.J. Milcurn, and M.R. Wilkinson. 1998. Disturbance of the marine benthic 

habitat by commercial fishing: impacts at the scale of the fishery. Ecological Applications 

8(3):866-879.

Thrush, S.F., J.E. Hewitt, V.J. Cummings, and P.K. Dayton. 1995. The impact of habitat 

disturbance by scallop dredging on marine benthic communities: What can be predicted from 

the results of experiments? Marine Ecology Progress Series 129(1-3):141-150.

Tilmant, J.T. 1979. Observations on the impact of shrimp roller frame trawls operated over 

hardbottom communities in Biscayne Bay, Florida. National Park Service Report Series No. 

P-553. 23 p.

Tuck, I.D., N. Bailey, M. Harding, G. Sangster, T. Howell, N. Graham, and M. Breen 2000. The 

impact of water jet dredging for razor clams, Ensis spp., in a shallow sandy subtidal 

environment. Journal of Sea Research 43:65-81.

Tuck, I.D., S.J. Hall, M.R. Robertson, E. Armstrong, and D.J. Basford. 1998. Effects of 

physical trawling disturbance in a previously unfished sheltered Scottish sea loch. Marine 

Ecology Progress Series 162:227-242.

Turner, S.J., S.F. Thrush, J.E. Hewitt, V.J. Cummings, and G. Funnell. 1999. Fishing impacts 

and the degradation or loss of habitat structure. Fisheries Management and Ecology 6:401-

420.

Valentine, P. C. and R.G. Lough. 1991. The influence of geological and oceanographic 

environmental factors on the abundance and distribution of fisheries resources of the 

northeastern United States continental shelf: The seafloor environment and the fishery of 

eastern Georges Bank. Open File Report 91-439, US Geol. Surv. 25 p.

Van der Knapp, M. 1993. Physical damage to corals caused by trap fishing on reefs of Bonaire, 

Netherlands Antilles. Environmental Conservation 20(3):265-267.

Van Dolah, R.F., P.H. Wendt, and N. Nicholson. 1987. Effects of a research trawl on a hardbottom assemblage of sponges and corals. Fisheries Research 5:39-54.

Van Marlen, B. 2000. Technical modifications to reduce the by-catches and impacts of bottom 

fishing gears. Pp. 198-216 In M.J. Kaiser and S.J. de Groot. The Effects of Fishing on Nontarget Species and Habitats. Blackwell Science.

Veale, L.O., A.S. Hill, S.J. Hawkins, and A.R. Brand. 2000. Effects of long-term physical 

disturbance by commercial scallop fishing on subtidal epifaunal assemblages and habitats. 

Marine Biology 137(2):325-337.

Watling, L. and E. A. Norse. 1998. Disturbance of the seabed by mobile fishing gear: a 

comparison to forest clearcutting. Conservation Biology 12(6):1180-1197.

Watling, L., R.H. Findlay, L.M. Mayer and D. Schick. 2001. Impact of a scallop drag on the 

sediment chemistry, microbiota, and faunal assemblages of a shallow subtidal marine benthic 

community. Journal of Sea Research 46:309-324.

Wion, D.A. and R.A. McConnaughey. 2000. Mobile fishing gear effects on benthic habitats: A 

bibliography. U.S. Department of Commerce, NOAA Technical Memorandum NMFSAFSC-116. 163 p.

Witbaard, R. and R. Klein. 1993. A method to estimate the bottom trawl intensity 

independently from fisheries itself by using internal molluscan growth lines ICES CM 

1993/K:16. 8 p.