Publications

The possible effects and management implications of climate variability/change on pinniped-salmonid interactions at low population levels of salmonids

Citation

Morimoto, G.E. 2001. The possible effects and management implications of climate variability/change on pinniped-salmonid interactions at low population levels of salmonids. MMA thesis, School of Marine Affairs, University of Washington, Seattle.


Abstract

The decline of certain salmonid runs on the West Coast of the United States has resulted in the listing of several runs, or Evolutionarily significant Units (USUs) of salmonids under the Endangered Species Act of 1973 (ESA;16 U.S.C. 1531 ET SEQ.) as “threatened” or “endangered.” There are a number of different factors that are thought to have caused the decline of salmonid runs, but the focus of this thesis is on the morality of salmonids associated with pinniped predation in certain “bottleneck” locations.

While literature does exist on pinniped-salmonid interactions, comprehensive literature is limited. This thesis is intended to be an exploratory “first cut” using a climate “lens” to probe these issues.

Information is brought together form three broad areas of study: climate variability/change, pinnipeds, and salmonids. In certain areas during El Niño events, pinniped predation on salmonids is thought to increase. This is a particular problem, when a severely depleted salmonid stock is exposed to increased pinniped predations pressure. Under the current management scheme, pinnipeds may be lethally removed from an area only after intensive study has been conducted. The time lag needed to complete sufficient study in some cases could allow irreparable harm to salmonids to occur.

The pinnipeds that prey upon the salmonid stocks discussed herein are protected under the Marine Mammal Protection Act of 1972 (MMPA; 16 U.S.C. 1361 et seq.). Congress did not envision in the passage of the MMPA and ESA that a protected marine mammal population would disadvantage an ESA listed species. In biological and societal terms it seems clear that the latter species should receive preference. However, this relationship is not made explicit in either piece of legislation.