The extent and effects of fishing on the seabed depend on gear design, access to fishing areas, and fishing effort. Three management tools for mitigating the effects of fishing on seafloor habitats correspond directly to those variables: modification of gear design or type, establishment of closed areas, and reductions of fishing effort (National Marine Fisheries Service, 1997). Management generally will warrant some combination of these measures. Because the social, economic, and regulatory context in which fishing occurs also influences the nature and extent of seafloor impacts, it is important to consider the opportunities for and constraints of particular management actions and their potential ecological as well as socioeconomic consequences.
Given the diversity of habitats, gear types, and interactions between them, and given the variety of social, economic, and regulatory contexts in which interactions occur, no single management solution will address all situations in the different regions and fisheries where use of mobile bottom gear affects the seafloor. Gear modifications often are more acceptable to a fishing community when they have fewer practical, social, or economic consequences. However, changes in gear tend only to diminish, not eliminate, seafloor impacts. Closed areas offer the advantage of eliminating the impacts caused by trawling and at particular sites, but closures also displace effort, potentially increasing fishing pressure elsewhere and causing economic and social problems in nearby coastal communities. Reduction of fishing effort can reduce the aggregated effects on seafloor habitat by decreasing the frequency and area of disturbance, but effort reduction could be more difficult or costly from a human dimensions perspective. When the fishing capacity of the fleet is higher than necessary to harvest the allowable catch (overcapacity), as with the western groundfish fishery (Pacific Fishery Management Council, 2000), gear modification and area closures might be insufficient to mitigate seafloor habitat disturbance. Hence, in fisheries where overcapacity is a problem, effort reduction, in conjunction with area closures or gear restrictions, will be required both to sustain fisheries and to reduce seafloor impacts.
Each of these management tools is discussed in turn in this chapter. Some of the opportunities for and constraints to their use following from practical, social, and economic considerations are examined, and the potential ecological and human consequences of their implementation are discussed. Selected case studies are used to illustrate the application of management tools in various situations.
Gear modifications include changes in gear design, deployment, and type. Changes in gear design include alterations to existing gear, for example, by raising footropes on bottom trawls to reduce contact with the seafloor. Changes in gear deployment that could mitigate seafloor impacts include modifications in towing speed or duration. Changes in gear type include prohibition of some gears and reallocation to alternatives that cause less damage to seafloor habitats.
As described in Chapter 2, trawls and dredges have been developed and modified to enable fishing in less
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Effects of Trawling and Dredging on Seafloor Habitat 6 Management Options The extent and effects of fishing on the seabed depend on gear design, access to fishing areas, and fishing effort. Three management tools for mitigating the effects of fishing on seafloor habitats correspond directly to those variables: modification of gear design or type, establishment of closed areas, and reductions of fishing effort (National Marine Fisheries Service, 1997). Management generally will warrant some combination of these measures. Because the social, economic, and regulatory context in which fishing occurs also influences the nature and extent of seafloor impacts, it is important to consider the opportunities for and constraints of particular management actions and their potential ecological as well as socioeconomic consequences. Given the diversity of habitats, gear types, and interactions between them, and given the variety of social, economic, and regulatory contexts in which interactions occur, no single management solution will address all situations in the different regions and fisheries where use of mobile bottom gear affects the seafloor. Gear modifications often are more acceptable to a fishing community when they have fewer practical, social, or economic consequences. However, changes in gear tend only to diminish, not eliminate, seafloor impacts. Closed areas offer the advantage of eliminating the impacts caused by trawling and at particular sites, but closures also displace effort, potentially increasing fishing pressure elsewhere and causing economic and social problems in nearby coastal communities. Reduction of fishing effort can reduce the aggregated effects on seafloor habitat by decreasing the frequency and area of disturbance, but effort reduction could be more difficult or costly from a human dimensions perspective. When the fishing capacity of the fleet is higher than necessary to harvest the allowable catch (overcapacity), as with the western groundfish fishery (Pacific Fishery Management Council, 2000), gear modification and area closures might be insufficient to mitigate seafloor habitat disturbance. Hence, in fisheries where overcapacity is a problem, effort reduction, in conjunction with area closures or gear restrictions, will be required both to sustain fisheries and to reduce seafloor impacts. Each of these management tools is discussed in turn in this chapter. Some of the opportunities for and constraints to their use following from practical, social, and economic considerations are examined, and the potential ecological and human consequences of their implementation are discussed. Selected case studies are used to illustrate the application of management tools in various situations. GEAR MODIFICATIONS Gear modifications include changes in gear design, deployment, and type. Changes in gear design include alterations to existing gear, for example, by raising footropes on bottom trawls to reduce contact with the seafloor. Changes in gear deployment that could mitigate seafloor impacts include modifications in towing speed or duration. Changes in gear type include prohibition of some gears and reallocation to alternatives that cause less damage to seafloor habitats. As described in Chapter 2, trawls and dredges have been developed and modified to enable fishing in less
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Effects of Trawling and Dredging on Seafloor Habitat accessible, but often particularly valuable, habitats. In the North Irish Sea off the Isle of Man, for example, scallop vessels began fishing rougher areas of the seabed when fixed tooth-bar dredges were replaced with Newhaven spring-tooth dredges, introduced in 1972, coupled with a reduction in dredge size and an increase in the number of dredges fished in a spread (Brand, 2000; Mason, 1983). In the Northwest Atlantic and elsewhere, the development of rockhopper gear with 24 inch rollers allowed trawl vessels to drag through rough bottom types. Before those innovations, the costs associated with the higher frequency of gear loss or damage prevented most fishermen from fishing in these areas and generally limited the scope (if not the magnitude) of seafloor impacts. Most gear modifications have been motivated by economics. Especially in areas where stocks have declined or where demand has surpassed local supply, the drive to catch more fish has created an incentive to modify gear to fish more efficiently or to access previously unfished sites. In other cases, economic, regulatory, and other incentives have encouraged gear modifications to promote conservation and increase marketable catch. In some instances, the prospect of limited fishing opportunities because of unacceptable bycatch rates has prompted technological innovations toward gear that generates less bycatch and reduces seafloor contact. The Alaskan pollock fishery (Box 6.1) provides a case study of an incentive-based gear innovation that was driven by a need to reduce bycatch. Gear modifications or innovations come from within and outside the fishing industry. In the case of the Alaska pollock fishery, the fishermen were given the incentive to reduce bycatch, but they also were given Box 6.1 Case Study: Gear Modifications in the Alaskan Pollock Fishery The walleye pollock (Theragra chalcogramma) fishery of the eastern Bering Sea is one of the largest in the world. In 2000, 1.1million metric tons of pollock was captured. Pollock occur on the sea bottom and midwater up to the surface, and most catches are taken at 50–300 m. The fishery is managed with total allowable catch (TAC) for the target species, constrained by bycatch limits for several pelagic and demersal species. In 1990, concerns about bycatch and seafloor habitats affected by this large fishery led the North Pacific Fishery Management Council to apportion 88 percent of TAC to the pelagic trawl fishery and 12 percent to the nonpelagic trawl fishery (North Pacific Fishery Management Council, 1999). For practical purposes, nonpelagic trawl gear is defined as trawl gear that results in the vessel having 20 or more crabs (Chionecetes bairdi, C. opilio, and Paralithodes camstschaticus) larger than 1.5 inches carapace width on board at any time. Crabs were chosen as the standard because they live only on the seabed and they provide proof that the trawl has been in contact with the bottom. By the mid-1990s, most vessels participating in the pollock fishery had voluntarily switched to pelagic trawls. Prohibited species bycatch limits provided the incentives: If the limits were exceeded as recorded by onboard observers, premature fishery closures would take effect before the pollock TAC was taken. Even though nonpelagic trawls accounted for only 2 percent of the pollock catch in 1996, they were nearly one-third of the halibut bycatch and about one-half of the crab bycatch. One year later, out of continuing concerns about bycatch and the effects of trawl gear on the seafloor, the Alaska Marine Conservation Council proposed that the North Pacific Fishery Management Council ban all bottom trawling for pollock. In response, the North Pacific Fishery Management Council prepared an amendment to the Bering Sea and Aleutians Islands groundfish fishery management plan (North Pacific Fishery Management Council, 1999). In November 1999, with broad industry and public support, the North Pacific Fishery Management Council banned bottom trawl gear use in the Bering Sea pollock fishery. The fishery now attains TAC specifications with modest bycatch rates. Although this gear was modified to reduce bycatch, it is postulated to have had the secondary effect of diminishing the impact on seafloor habitat. However, these trawls may be frequently fished in contact with the seafloor, especially in shallow water (<50 fathoms). To confirm that this gear has reduced seafloor impacts, the extent of bottom contact and disturbance should be quantified. If the trawls never touch the bottom, the pelagic trawl definition could be set at zero crab tolerance. Because typical pelagic trawls have large mesh webbing in the lower section of the net and are affixed to chain footropes, bycatch enumerated by onboard observers might substantially underestimate the number of demersal fish and invertebrates that are affected because they fall through the large mesh panels instead of being captured by this gear.
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Effects of Trawling and Dredging on Seafloor Habitat the latitude to develop technology and practices to achieve that goal. Their direct involvement in the process facilitated practical and acceptable changes. In contrast, specific gear modifications to reduce bycatch and exclude turtles from trawls in the Gulf of Mexico and the Southeast were imposed by state and federal agencies. Initially, these measures were strongly resisted by the industry, in part because of their impracticality, but also because they told fishermen how to fish, and thereby dismissed a key area of fishermen’s knowledge and expertise. Another fundamental constraint to gear modifications could be a lack of awareness or public recognition of a particular kind of gear, and the potential benefits of modifying its design or deployment to mitigate those effects. Visual presentations of how gear alters the seafloor can be instructive, both in making fishermen and others aware of the problem and in stimulating discussion about potential gear modifications. The development and testing of fishing gear technology is expensive and time-consuming. In some cases, it is difficult for fishermen to experiment with new gear designs, especially if they participate in highly competitive, open-access fisheries. However, other opportunities for innovation can be created. One way would be to establish a limited experimental fishery in which gear could be tested without loss of fishing opportunity. This approach was used to develop and conduct at-sea trials of the raised footrope trawl in the New England silver hake fishery. Another mechanism is to study gear–habitat interactions, funded by landings taxes or flat assessments (like the California Salmon Stamp), or by tax credits given to industry for sponsored gear research. Finally, academic, government, and commercial research facilities for testing and computer modeling of new gear designs can provide further opportunities for the development of modifications. Collaborations among gear technologists, fishermen, and net manufacturers have been successful in addressing concerns about gear selectivity. Gear modification will not be an appropriate solution to bottom habitat damage in all cases, however, either because it fails to diminish damage or because it is physically, socially, or economically impractical. Some species (e.g., scallops, flatfish) can only be captured by mobile bottom-contact gear. Where gear modifications are technologically feasible, social and economic considerations can prevent their adoption. As with other management measures, gear modifications entail several costs. Those include not only the financial costs of modifying the gear, but also those associated with learning how to use the gear effectively and with the possibility of reduced catch efficiency. In addition, although some modifications may improve the quality of the catch, others result in reductions in either quality or quantity that are unacceptable to fishermen, fish buyers, and consumers. Some otter trawls, for example, are designed to cause a cloud of sediment that herds fish into the trawl path (Smolowitz, 1998). Gear modifications that reduce habitat disturbance are likely to reduce catch rates, and therefore would be unacceptable to most fishery participants. Requirements to use less efficient gear to protect habitat could lead to more intensive fishing effort, thereby offsetting the benefits. CLOSED AREAS Closed areas encompass regions of the seafloor where mobile bottom-contact gear is not allowed, either permanently or temporarily. The recent National Research Council report, Marine Protected Areas: Tools for Sustaining Ocean Ecosystems (National Research Council, 2001), defines several types of closed areas, differentiated by their goals and the degree of protection sought. The report defines marine protected areas (MPAs) as discrete geographic areas that have been designated to conserve and enhance marine resources through an integrated plan that includes restrictions on some activities. Marine reserves are MPAs in which some or all biological resources are protected from removal or disturbance. Marine reserves include fishery reserves, which preclude fishing for some or all species to protect critical habitat, rebuild stocks, and protect against overfishing, and ecological reserves, zones that protect all living marine resources from removal or disturbance other than for research purposes to evaluate reserve effectiveness. As spatially based management tools, MPAs are consistent with the concepts of essential fish habitat and habitat areas of particular concern (HAPC). As stated in the interim final rule, HAPC can be designated based on one or more of the following criteria: 1) the importance of the ecological function provided by the habitat, 2) the extent to which the habitat is sensitive to human-induced environmental degradation, 3) whether and to what extent development activities are or will stress the habitat type, and 4) the rarity of the habitat type. The recent Tortugas Ecological
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Effects of Trawling and Dredging on Seafloor Habitat Reserve and other MPAs along the coast of the United States were established in response to many of these concerns. Interest has been growing in the potential role of MPAs in fishery and broader marine resource management, and there has been a proliferation of efforts to establish them within and outside the United States. To date, most closed areas were implemented to reduce fishing mortality, at least within the reserve, rather than to protect habitat, per se. Enhanced public awareness of the adverse effects of mobile bottom gear on seafloor habitats, however, has increased interest in, and the use of, marine reserves to protect bottom habitats from these effects (National Research Council, 2001). Direct evidence of the structure and complexity of some habitats can enhance recognition of their vulnerability to mobile bottom fishing gear and engender support for area closures to protect them. For instance, photographic documentation of red tree corals (Primnoa willeyi and P. resedaeformis) and associated long-lived Sebastes species and other fishes led to broad public support for the creation of the Sitka Pinnacles Marine Reserve in the eastern Gulf of Alaska (O’Connell et al., 1998). Only pelagic troll gear for salmon is allowed in this reserve. However, MPAs raise important social and economic issues that warrant careful consideration. One potential negative effect of closed areas is crowding in the areas that remain open to fishing. Although overcrowding might not be problematic from a habitat perspective if vessels are displaced into less-sensitive habitats, it can still have negative social and economic consequences. Displacement of fishing effort can lead to incursions into other fishermen’s or other resource users’ (e.g., recreational users’) territory, creating social conflict both on the fishing grounds and at the docks or market. Informal territorial use rights in fisheries (LeVieil, 1987) and other spacing conventions have been widely documented, especially in fixed gear fisheries (e.g., Maine lobster fishery, Acheson, 1975, 1988; Alaska golden king crab [Lithodes aequispinus] fishery, Herrmann et al., 1998), but also in such mobile gear fisheries as the cod trawl fisheries off Newfoundland (Durrenberger and Palsson, 1987). Furthermore, closures could have economic costs both for those who have been displaced and for those who work the areas that remain open. Moreover, if there is a large displacement of effort, intensified fishing in open areas can result in ecological damage, including overfishing of other stocks. These concerns suggest that area closures should be combined with effort reduction, gear modification, or both, to reduce potential ecological disturbance, although the social and economic consequences of the combined measures would need to be assessed. Other social consequences of closed areas include loss of access and increased costs and risk, if fishermen must travel to more distant or more dangerous fishing grounds. Enforcement is an extremely important consideration determining the efficacy of closed areas. Closures are much more likely to be successful when they have the support of the fishing industry; the cooperation of affected users is essential to ensuring compliance. Adequate funding for enforcement operations also is important. New technologies, such as satellite transponders and satellite-mounted synthetic aperture radar (for viewing vessels through clouds and at night), can be effective enforcement tools. Georges Bank provides a good example of the use of closed areas for fishery management (Box 6.2). Initially there was great opposition, but over time, this management tool has become accepted by most fishermen as benefits have accrued from improved stocks and higher catch rates for some species. But even as fishermen hail the economic benefits of better catches outside the closed areas, some are pressing for a partial reopening to obtain even higher catches. Rotational area closures, a variant of marine reserves, have been implemented to afford some protection to seafloor habitats while not permanently closing access. Rotational closures also can be more consistent with some fishing patterns. In some fisheries (e.g., scallop dredge fisheries), fishermen are known to “give areas a rest,” rotating their effort among locations to adapt to spatial and temporal variations in resources. The New England Fishery Management Council is currently considering an amendment that would include rotational area closures in the management plan for the scallop fishery (New England Fishery Management Council, 2002). Because rotational closures allow periodic fishing, they are inappropriate for highly structured seafloor habitats with long-lived attached species. But they could be viable for more energetic, sandy habitats inhabited by short-lived species. In applying rotational closures, schedules for closing and opening areas should be tied to recovery time. In shallow areas with frequent storms, the recovery time might be very short, as the fauna and flora have adapted to natural disturbance. Rotational closures, based on regular monitoring, fit within an adaptive management framework.
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Effects of Trawling and Dredging on Seafloor Habitat Box 6.2 Case Study: Closed Areas on Georges Bank In response to the collapse of the principal groundfish species—cod, haddock, and yellowtail flounder—the Secretary of Commerce took emergency action in December 1994 by initiating year-round closure of two areas on Georges Bank and one in southern New England (Figures B.4 and B.5). These areas, totaling 17,000 km2, were closed to all bottom-fishing gear capable of catching groundfish, and they have remained closed except for partial and temporary openings for scallop dredging in 1999 and 2000 (Murawski et al., 2000). During the same period, fishing effort was reduced by half for most of the mobilegear fleets, and complementary regulations were implemented on the Canadian side of Georges Bank. It appears that the implementation of those management measures has allowed scallop and some groundfish stocks to rebuild substantially. Standardized surveys conducted by the National Marine Fisheries Service show much higher densities of groundfish and scallops inside the closed areas. The degree of protection afforded is related to the proportion of the stock contained in the areas and the fraction of the year they reside in the area. The closed areas have been most successful in the conservation of the more sedentary demersal fishes and sea scallops. Haddock and yellowtail flounder have recovered to an abundance last observed in the 1970s; between 1994 and 1998, scallop biomass increased 14-fold in the closed areas (Murawski et al., 2000). The recovery of cod has been slower because of the lack of strong recruitment. The area closures, combined with effort reductions in the fishery, have reduced fishing mortality on the principal groundfish stocks, and have protected the seafloor habitat from the physical effects of bottom fishing. Current studies are comparing the benthic communities inside and outside of the closed areas. Particularly in the northern part of Closed Area II, there has been a rapid increase in epifauna on gravel sediments. In 1998, the New England Fishery Management Council designated part of the closed area as an HAPC on the basis of the occurrence of juvenile groundfish on gravel–cobble sediment. The success of these management measures is largely attributable to the closure of areas with the highest groundfish and scallop catch rates. Simultaneous effort reduction measures (fewer days fished) helped reduce the consequences of displaced effort. Some boats switched to different fisheries, although they bear higher costs because of increased effort in other areas or fisheries. The current fishing effort is concentrated around the edges of the closed areas, which suggests that they are acting as sources for the surrounding areas. In the future, the boundaries of the closed areas could be refined to enhance larval production and protect nursery areas, spawning concentrations, and migration corridors (Murawski et al., 2000). EFFORT REDUCTION Fishery managers often strive to reduce effort as a way to eliminate biological or economic overfishing. Recruitment overfishing occurs when spawning stock biomass is reduced so much that future recruitment is compromised. Growth overfishing occurs when fish are caught before they grow large enough to achieve maximum yield per recruit, but without decline in recruitment levels (Gulland, 1983). Economic overfishing occurs when excess fishing effort causes a fishery to produce no positive economic rent, that is, when the total costs of extraction equal or exceed the revenue provided by the fishery (Clark, 1976). In addition to reducing the ecological and socioeconomic impacts of overfishing, effort reduction can lessen the effects of trawling and dredging on the seafloor. Effort can be reduced through seasonal closures, license limitations, quotas, vessel buyback programs, or trip limits. Often they are used in combination, as when limited entry is combined with a fishery quota to guard against excessive effort by those who remain in the fishery. The establishment of some form of rights-based fishery management program (e.g., individual fishing quotas) is one approach for meaningful and permanent reduction of fishing effort (National Research Council, 1999). Figure 6.1 illustrates the relationship between fishing effort and seafloor habitat disturbance from mobile bottom-contact gear. As effort increases, so does habitat damage until all epibenthic structure and associated biota have been removed. At that point, the curve levels off because maximum habitat damage has occurred. At high effort levels, reductions will decrease damage marginally at first, and benefits will increase as effort declines further. The amount of fishing effort at which maximum habitat damage occurs (Figure 6.1, B) depends
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Effects of Trawling and Dredging on Seafloor Habitat FIGURE 6.1 Schematic of the relationship between fishing effort and habitat damage. When effort corresponds to A, a change in effort will change the degree of habitat damage. At B, damage is at its maximum and increased effort does not increase damage, bur reduced effort decreases damage. At C, small adjustments in effort neither increase nor decrease habitat damage. MHD refers to maximum habitat damage. on habitat type and the amount of natural disturbance. If the effort level is high (Figure 6.1, C), it could be impractical to decrease effort to the extent that habitat will begin to recover. Effort reductions can decrease effects in sensitive areas if they result in a smaller area being swept by fishing gear. As noted in Chapter 3, the need or desire to increase catches has led to increases in effort and expansion into new, and sometimes more sensitive, habitats. Effort reduction could slow or arrest this process; decrease the incentive to develop new, more intrusive gear; and limit or reduce the spatial extent of trawling and dredging and hence their disturbance of seafloor habitat. As stocks recover, the fishing fleet is likely to concentrate in high-density areas, thus decreasing the total area of seafloor disturbed by fishing. There are important practical, social, and economic considerations that must attend effort reduction strategies. Reductions in effort usually result in immediate short-term losses of income, employment, and lifestyle for at least some fishery participants, even if they hold the promise of longer term benefits to fishermen, resources, and habitat. Those consequences raise questions about equity, manifested in the allocation of costs and benefits that society and policymakers will need to address. Moreover, if initial measures, such as trip limits, fail to conserve fish stocks, social and economic consequences could be exacerbated by later, more substantial effort reductions. Those could include limited-entry programs that substantially cut the number of fishery participants and the aggregate fishing capacity. On the West Coast, years of increasingly strict effort controls in the face of declining groundfish fish populations were unsuccessful in matching capacity with the level of the resource. After the declaration of the West Coast groundfish disaster in February 1999, the Pacific Fishery Management Council’s Scientific and Statistical Committee determined that only 27–41 percent of the trawl fleet’s current capacity was needed to catch its allocation (Pacific Fishery Management Council, 2000). The Council is now considering how to eliminate excess capacity in the fishery to reduce effort, with the expected benefit that less effort also will diminish seafloor disturbance. Practical, social, and economic considerations warrant attention not only in the context of the fishery in question, but also in the broader context of regional fisheries. Participants displaced from a trawl fishery might move into other fisheries, possibly causing further ecological, economic, and social problems. Ideally, decisions to reduce fishing effort, as with all proposed major changes in fishery management systems, should be informed by analyses of the full suite of short- and long-term benefits and costs. A case study of the Browns Bank scallop fishery (Box 6.3) provides an example of a technological solution to achieve effort reduction that also reduces the effects of fishing gear on the seafloor. The same quota was caught and less area of bottom was affected with the multibeam technology (1999) than without it (1998). However, there are caveats to the universality of this approach. First, success hinges on the implementation of TAC that is set as a sustainable fraction of scallop biomass. In the absence of TAC, fishing fleets could use the technology to deplete fishery resources more efficiently. Second, the technology successfully identifies the densest aggregations of scallops, but it is not known whether those high catch rates can be sustained over the long-term. Third, such industry– government collaborations are exemplary, but in such cases the resultant data could be proprietary, leading to policy or legal issues concerning data access by other potential users. Finally, scallops predominate on gravel rather than sand substrate, and more concern exists about scallop dredge effects on hard than on soft bottoms. It has yet to be demonstrated or quantified
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Effects of Trawling and Dredging on Seafloor Habitat Box 6.3 Case Study: Fishing Effort Controls in the Browns Bank Scallop Fishery The Canadian scallop dredge fishery on Browns Bank on the western Scotian Shelf northeast of Georges Bank provides an example of a technological approach to reducing the total amount of seafloor swept by mobile bottom-contact gear through de facto effort controls (Kostylev et al., in press; Manson and Todd, 2000). The fishery is important locally, accounting for approximately one-third of the region’s shellfish catch. Since the 1970s, fishing has been prosecuted on different portions of the bank, with inconsistent success. The stock abundance is estimated from assessment surveys, stratified largely by the distribution of the commercial fishing effort. Recently, this fishery has been managed on the basis of an enterprise allocation system, in which each of seven companies receives a share of the annual TAC (Department of Fisheries and Oceans Canada, 2000). A recent collaboration among the Department of Fisheries and Oceans, the Geological Survey of Canada Atlantic, and the fishing industry is exploring the application of geosciences to the fishery. The project’s objectives include documenting the relationships among scallops and substrate, optimizing fishing practices, and adopting sustainable fishery management through increased knowledge. The project has entailed intensive data collection from multibeam bathymetry, high-resolution seismic reflection, sidescan sonar, extensive bottom sampling, video, and photographic surveys. Recently, a scallop-catch sampling program was added to the research. The research demonstrates that scallops are strongly associated with gravel lag deposits, which the multibeam data easily distinguishes from sandy bottom. There is a highly significant relationship between backscatter intensity and scallop survey catches that could be incorporated into improved stock assessments. Although the industry’s prime motivation initially was to improve efficiency, other benefits have accrued, as evidenced by the following tabular comparison of fishery attributes from 1998, when multibeam maps were not used, and from 1999, when multibeam maps were applied during the fishery. 1998 1999 Scallop quota, kg 13,640 13,640 Time on bottom, hr 162 43 Distance towed, km 1176 311 Time lost, hr 15 0 Value of lost gear $10,000 0 Fuel used, L 72,697 17,545 Application of the technology resulted in a 73 percent reduction in both the duration of bottom contact time and in the area of habitat affected, a 75 percent reduction in fuel use, and an elimination of gear loss and lost fishing time. The implication is that habitat disturbance can be substantially reduced if information about the relationship between the substrate type and scallop abundance is used to target fishing effort to the most productive scallop grounds. that overall ecological damage is reduced when effort is reduced but concentrated on gravel bottoms. The amount of damage caused by mobile bottom-contact gear depends on the frequency of repeated trawling (or dredging) and the recovery time of affected fauna. Whether it is better to spread the effort or concentrate it into a few, heavily affected areas is an important, but complex, question. Notwithstanding those qualifiers, the Browns Bank scallop habitat project is an excellent example of a collaborative and technological approach to meet management goals for seafloor habitats. CONCLUSION Three fishery management tools can be used to mitigate the effects of trawls and dredges on seafloor habitats, fishing effort reduction, modification of gear design or gear type, and area closures. Three fishery management tools, fishing effort reductions, modifications of gear design or gear type, and establishment of areas closed to fishing, are used to mitigate the effects of mobile bottom-contact gear on seafloor habitats.
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Effects of Trawling and Dredging on Seafloor Habitat Effort reduction is the cornerstone of managing the effects of fishing, including, but not limited to, the effects on habitat. However, effort reduction alone is insufficient to address all circumstances in which fishing gear disturbs bottom habitat. The success of fishing effort reduction depends on the resilience and recovery potential of the habitat. Each of the other management tools generally requires effort reduction to achieve maximum benefit. Gear modifications will be most useful for finfish species that can be caught with gear that does not rely on disturbing the bottom to catch the fish. This could include shifts to a different gear type, such as long lines or fish traps, but the social and economic consequences of such reallocation must be recognized and addressed. Also, the overall ecological benefits of using another, and often less efficient, type of gear, can be reduced if there is a subsequent increase in fishing effort or if there is significantly higher bycatch with the alternative gear. Closed areas are necessary to protect a range of representative habitats. Closures are particularly useful for protecting areas with emergent epifauna (e.g., corals, bryozoans, hydroids, sponges) that are vulnerable to even low levels of fishing effort. As evidenced by the case of Georges Bank (Box 6.2), damage to emergent epifauna is recoverable after areas are closed. In general, area closures will need to be paired with effort reductions to offset the effects of displaced effort in the open fishing grounds. It is unlikely that any one measure can resolve all seafloor habitat issues. Rather, some combination of options will often be most effective. The choice, utility, and limitations of a particular combination of the three measures to control fishing effects on seafloor habitats in a specific situation depends on the current regulatory setting, social and economic characteristics of the fishery and its participants, available habitat types, and the specific fishery management goals and objectives. Ideally, the choice of the particular mix of the three tools for any one case should be informed by analyses of the full suite of benefits and costs over a reasonable period. As demonstrated by the case studies, creative solutions can be found to lessen the effects of fishing on seafloor habitats while maintaining viable, long-term commercial fisheries. In fact, the two are inextricably connected.