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Effects of Trawling and Dredging on Seafloor Habitat
Box 1.1Statement of Task
This study will be the first in a series that will evaluate available data related to the physical and biological effects of fishing on marine habitats and ecosystems. This first study will 1) summarize and evaluate existing knowledge on the effects of bottom trawling on the structure of seafloor habitats and the abundance, productivity, and diversity of bottom-dwelling species in relation to gear type and trawling method, frequency of trawling, bottom type, species, and other important characteristics; 2) summarize and evaluate knowledge about changes in seafloor habitats with trawling and cessation of trawling; 3) summarize and evaluate research on the indirect effects of bottom trawling on non-seafloor species; 4) recommend how existing information could be used more effectively in managing trawl fisheries; and 5) recommend research needed to improve understanding of the effects of bottom trawling on seafloor habitats.
Research Council’s Division on Earth and Life Sciences to undertake a series of studies to examine the effects of various fishing practices and to make recommendations for action that could reduce or mitigate effects. This first report addresses the specific effects of bottom trawling on seafloor habitats, as described in the statement of task (Box 1.1). In deliberations at its first meeting on the topic, the committee decided to address the effects of both trawls and dredges, because these are the two major types of bottom-tending mobile gear used in U.S. fisheries.
STUDY APPROACH AND REPORT ORGANIZATION
This report summarizes the literature on the effects of bottom trawling on habitats and discusses management tools that can be applied to mitigate them. Inshore and offshore areas are considered, although there is more emphasis on offshore regions because of the greater amount of information generally available for federally managed waters. The Caribbean and West Pacific regions are not discussed because they have no major trawl or dredge fisheries. The regulatory framework provided by provisions of the SFA is introduced below. Chapter 2 describes different types of mobile bottomtending gear used in trawl and dredge fisheries. Chapter 3 summarizes research findings on the direct and indirect effects of trawling and dredging and it reviews the literature on the postdisturbance recovery of habitat and biota. Chapter 4 describes what is known about the seafloor habitats and about the regional distribution and frequency of trawling and dredging activities. Appendix B presents maps and more detailed descriptions of the distribution and frequency of trawling in U.S. waters. Ecological risk assessment methods are presented in Chapter 5, and management options for reducing the damage caused by trawling and dredging are presented in Chapter 6. In Chapter 7, the committee presents its conclusions and recommends topics for research. Appendix A lists committee and staff members. Appendix C gives a brief explanation of mapping tools.
EFH provisions of the Sustainable Fisheries Act (1996) gave resource managers a new tool to address degradation and loss of fish habitat. The final rule published by the National Marine Fisheries Service (NMFS) (2002) defines EFH as follows:
. . . those waters and substrate necessary to fish for spawning, breeding, feeding, or growth to maturity. For the purpose of interpreting the definition of essential fish habitat: “Waters” include aquatic areas and their associated physical, chemical, and biological properties that are used by fish and may include aquatic areas historically used by fish where appropriate; “substrate” includes sediment, hard bottom, structures underlying the waters, and associated biological communities; “necessary” means the habitat required to support a sustainable fishery and the managed species’ contribution to a healthy ecosystem; and “spawning, breeding, feeding, or growth to maturity” cover a species full life cycle.
The act requires fishery management plans to describe and identify EFH, minimize to the extent practicable adverse effects on EFH caused by fishing, and identify other actions to encourage habitat conservation and enhancement. EFH must be designated for each life stage of the more than 700 federally managed species. Additionally, NMFS must provide conservation recommendations to all federal or state agencies on actions that adversely affect EFH. Federal agencies must respond within 30 days to recommendations, although the recommendations are nonbinding. Hence, the SFA made habitat conservation a mandate under federal fisheries management.