Shifting gears: assessing collateral impacts of fishing methods in US waters

the deployment of excessive levels of fishing effort – is one of the most pressing problems for fisheries around the world (Pauly et al. 2002; Myers and Worm 2003). While attempts to address this problem continue at a single-species level, an ecosystem-based approach to fisheries management is necessary to understand the overall impacts of fishing (Dayton et al. 1995; Pitcher and Pauly 1998). In addition to changing the trophic structure of marine ecosystems (eg fishing down food webs, as described by Pauly et al. 1998), there is growing evidence that collateral impacts, such as bycatch and habitat damage, have occurred in many fisheries (Watling and Norse 1998; AMCC 2001; POC 2003). The term “bycatch,” as used here, refers to incidental catch of fish, other vertebrates, and invertebrates not targeted by the fishing gear, and subsequently discarded alive, injured, or dead (Figure 1). The term includes “economic bycatch” (species discarded because they are of little or no economic value), “regulatory bycatch” (marketable species discarded because of management regulations, such as size limits, allocations, and seasons) and “collateral mortality” (species killed in encounters with fishing gear, though not necessarily brought on board the vessel). Habitat damage includes damage to living seafloor structures (eg corals, sponges, seagrasses) as well as alterations to the geologic structures (eg boulders, cobbles, gravel, sand, mud) that serve as nursery areas, refuges, and homes for fish and organisms living in, on, or near the seafloor. A number of measures have been implemented in the US to address the collateral impacts of fishing. For example, a mandatory observer program places government representatives on board fishing vessels to collect data and observe practices in several fisheries, including, among many others, the Alaska cod (Gadus macrocephalus) bottom trawl fishery, which has 30% observer coverage (AMCC 2000) and the California swordfish (Xiphias gladius) drift net fishery, which has 14% observer coverage (Rasmussen and Holts 2001). In some cases, gears are modified to reduce bycatch, as with the turtle excluder devices (TEDs) inserted into shrimp trawls to reduce catch of turtles, and the streamer lines used on longline boats to reduce catch of seabirds. The banning of bottom trawls throughout the 1.5 million mi of the Western Pacific Fishery Management Council (Anon 2002) and the closing of the groundfish fishery on Georges Bank in New England (Collie et al. 1997) have also reduced habitat damage, although this was not explicitly the reason these measures were put in place. However, much more could be done to systematically and consistently address the collateral impacts of major fishing gears operated in US waters. One novel approach, called the “damage schedule”, merges existing information about collateral impacts of ten commercial fishing gears with the pertinent knowledge and judgments of fishers, managers, and scientists to compare levels of impacts 517