Science Advisory Report 2006/025

Impacts of Trawl Gears and Scallop Dredges on Benthic Habitats, Populations and Communities

Summary

• Mobile bottom-contact fishing gears do have impacts on benthic populations, communities, and habitats.  The effects are not uniform, but depend on at least:
• the specific features of the seafloor habitats, including the natural disturbance regime;
• the species present;
• the type of gear used, the methods and timing of deployment of the gear, and the frequency with which a site is impacted by specific gears; and
• the history of human activities, especially past fishing, in the area of concern.
• The nature of many of the dependencies referenced above are described in the advice
• Application of measures to reduce impacts of mobile bottom-contacting gears requires case specific analyses and planning; there are no universally appropriate fixes.  However, the documented effects of mobile bottom-contacting gears on seafloor populations, communities, and habitats are consistent enough with well-established ecological theory, and across studies, that cautious extrapolation of information across sites is legitimate.  Case-specific research programmes are not required to develop options for case-specific applications of these generalisations.
• Circumstances are discussed under which general spatial management, closed areas, gear modifications, and effort reductions could provide some mitigation of the effects of mobile bottom-contacting gears on benthic habitats, populations, and communities.
• “Frontier areas” (areas without histories of fishing by bottom-contacting gears) require special considerations in managing the risks posed by mobile bottom-contacting gears.  Several of these special considerations are discussed.
• In the application of precaution for managing the ecosystem effects of any human activity, the capacity of ecosystem components to recover from perturbations is an important consideration.  Several considerations in this context are discussed, as are related issues of more general risk management relative to fisheries using bottom-contacting mobile gears.
• A number of gaps in knowledge and necessary scientific studies are discussed.

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