The possible effects of climate variability/change on pinniped-salmonid interactions at low population levels of salmonids: Management implications for salmonid recovery

Gina E. Morimoto

Chairperson of the Supervisory Committee:
Douglas P. DeMaster, Affiliate Associate Professor
David L. Fluharty,
School of Marine Affairs

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 (ESUs) of salmonids under the Endangered Species Act of 1973 (ESA) 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 mortality of salmonids associated with pinniped predation in certain “bottleneck” locations.

The pinnipeds that predate on the salmonid stocks discussed herein are protected under the Marine Mammal Protection Act of 1972 (MMPA).  Congress did not envision in the passage of the MMPA and ESA that a protected marine mammal population could disadvantage an ESA listed species.  It seems clear that the latter species should receive preference.  However, this relationship was never made explicit in either piece of legislation.

While literature does exist on pinniped-salmonid interactions, comprehensive literature is limited.  This thesis is intended to be exploratory, in that it is a “first cut” at this issue and not intended to solve all associated questions.

Information is brought together from three broad areas of study: climate variability/change, pinnipeds, and salmonids.  A number of approaches are taken to understand the relationship between these areas.  Climate events (e.g., El Niño, La Niña, Pacific Decadal Oscillation, anthropogenic climate change) are examined.  The effects of El Niño events on pinnipeds and salmonids are described.  Studies of pinniped predation on salmonids are reported.  Managers and fishermen are interviewed to understand real world processes.

A policy analysis is conducted using NMFS’s recommendations to Congress (NMFS, 1999), interviews with managers and fishermen, knowledge of life history characteristics of pinnipeds and salmonids, and intense climate events.  I recommend that Congress adopt a policy alternative that is: flexible; incorporates (and is consistent with) salmonid conservation or recovery plans; considers pinniped population trends and impacts of pinnipeds on the ecosystem before authorizing lethal removal; develops safe and effective non-lethal deterrents; and implements site-specific management for pinnipeds while incorporating climate events.

Two main elements are made apparent in this thesis: 1) El Niño events can force opportunistic predators (i.e., pinnipeds) to change their diet composition, as well as change species distribution (i.e., Pacific whiting, red pelagic crab); 2) even at low consumption levels on very small ESUs (i.e., Lake Washington winter-run steelhead), predation can lead to extinction.