Foraging ecology of pinnipeds has been the subject of scientific investigations for many years because pinnipeds are often perceived as being in competition with human fisheries. Examples of pinniped-fishery interactions during the last century exist in various locations throughout the world. Seal and sea lion populations in the northeast Pacific rely on groundfish, herring, salmon and squid as major components of their diet (Lowry & Frost 1985). These same stocks are also large components of commercial fishery operations. Grey seals in Britain have been implicated in a number of detrimental fishery interactions ranging from predation on free swimming and net-pen salmon to more indirect effects of driving fish away from nets and increasing the presence of codworm in the Atlantic cod (Harwood & Greenwood 1985). However, pinniped-fishery interactions must also be examined with some perspective. During the late nineteenth and early twentieth centuries, many pinniped stocks throughout the world were hunted to a small fraction of their former population levels (Beddington & Mare 1985) for both fur and to reduce fishery interactions. From early in the twentieth century until passage of the federal Marine Mammal Protection Act of 1972 (MMPA), Washington State had an active pinniped control unit and bounty program for the removal of pinniped species. Significant conservation efforts in the last century and passage of laws such as the MMPA have allowed many pinniped populations to rebound; however many remain critically low (VanBlaricom et al. 2001).
In recent years, the west coast of the United States has seen the emergence of a new category of pinniped-fishery interactions. Since the passage of the MMPA, populations of California sea lions (Zalophus californianus) and Pacific harbor seals (Phoca vitulina richardsii) have experienced dramatic increases throughout the West Coast, and may be at their highest levels in several centuries (NMFS SAR 2001). Increases in pinniped populations have coincided with dramatic decreases of many marine and anadromous fish populations (WDF et al. 1993). A number of these populations have declined to a point where they have been listed, or are under consideration for listing, as endangered or threatened under the federal Endangered Species Act (ESA) of 1973 as amended. There has been a growing concern throughout the West Coast that pinnipeds, while not likely the cause of any decline in salmonids, have the potential to affect the recovery of many threatened and endangered salmonid stocks (NMFS 1999).
