The need for international cooperation to reduce competition among salmon for a common pool of prey resources in the North Pacific Ocean
Randall M. Peterman*1, Carrie A. Holt1,2, and Murray R. Rutherford1
1School of Resource and Environmental Management, Simon Fraser University, Burnaby,
BC V5A 1S6, Canada (Email: peterman@sfu.ca; Tel: 778 782-4683; Fax 778 782-4968)
2Present address: Fisheries and Oceans Canada, Pacific Biological Station, 3190 Hammond Bay Rd., Nanaimo, BC V9T 6N7, Canada
Many populations of Pacific salmon (Oncorhynchus spp.) show long-term decreases in age-specific body size, which reduce the economic value of catches and fecundity of spawners. Several hypotheses have been proposed to explain these trends, including deteriorating environmental conditions, size-selective fishing, and density-dependent growth associated with the large increases in pink (O. gorbuscha) and chum (O. keta) salmon abundance in the North Pacific Ocean. The density-dependent hypothesis related to competition for food has the greatest support, based on overlapping geographic distributions of pink, chum, and sockeye salmon (O. nerka) populations, their stomach contents, and analyses of scale-growth patterns and abundances. Some sockeye populations have also suffered reduced productivity (adult recruits produced per spawner), in addition to reduced growth, when present with high abundances of competitors, particularly pink salmon populations that vary dramatically in abundance between even- and odd-years. Hatchery-released pink and chum salmon constitute a substantial and growing portion of total wild plus enhanced salmon in the North Pacific Ocean, and plans exist to dramatically expand hatchery releases in the future. Such plans are worrisome, given the importance of density-dependent processes on the high seas that reduce body size of both hatchery-origin and wild salmon and in some cases, productivity of wild salmon stocks. Therefore, it is important that salmon-producing nations begin serious discussions on how to deal with this "common-pool resource" problem caused by competition for prey in the North Pacific. We recommend that such discussions be coordinated by the North Pacific Anadromous Fish Commission (NPAFC) after appropriate amendments are made to its mandate. The objective would be to develop strategies and incentives for cooperation among salmon-producing nations. The ultimate goal would be to take collective action to prevent further increases in competition among salmon from different nations or even reduce it. In an analogous situation over 20 years ago, the NPAFC reduced exploitation of salmon in the North Pacific Ocean by banning directed fishing on salmon in waters beyond territorial limits. However, there is currently no analogous measure to deal with the next lower trophic level, i.e., to restrict the "harvest" of a common pool of North Pacific prey by salmon populations from different nations. Many precedents exist worldwide for creating appropriate incentives to sustainably use such limited common-pool resources. Among other actions, such incentives include sharing of benefits and side-payments to change the incentive structure. Action on this problem of multi-national grazing of salmon food is long overdue.