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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