254 



DRAFT 



"However, almost 13 percent of the stomach contents of California sea 

 lions taken in the Columbia River area in 1982 was salmon;. . . (Beach et 

 al. 1985)" 



The report does not acknowledge that these samples were collected in an area where, 

 and most often when, giilnet fisheries for salmon where taking place. There is no 

 question that sea lions (and seals) prey on salmon in gillnets in this area. The resulting 

 analysis of sea lion diets from such collections cannot be applied to sea lion numbers 

 statewide to estimate salmon consumption over a broad geographic area because of the 

 influence of this fishery on the diet of these species. The report notes that Jameson and 

 Kenyon (1977) and Roffe and Mate (1985) showed that salmon made up a small part of 

 sea lion diets and that predation had negligible impacts on Rogue River salmonid 

 populations. It would also be invalid to use these studies to imply that sea lion 

 predation has no affect on salmon numbers anywhere in the Northwest. 



'Based on the above data, it would seem reasonable to assume that 

 salmon could comprise... ocean commercial fishery in 1990. ' 



The calculations and consumption estimates presented in the report are not arrived at by 

 defensible scientific methods. Because of the numerous assumptions and variables 

 involved, the results presented are highly questionable and probably very inaccurate. 

 For example, it is inappropriate to use predation estimates from a single study in 

 British Columbia and broadly apply them to pinnipeds in completely different 

 geographic areas where behavioral, biological, environmental and other factors 

 affecting both predator and prey populations (including relative abundances) may be 

 very different. Site specific studies are required to make valid estimates of this type. 



The calculations of salmonid loss to marine mammal predation are also affected by 

 assumptions concerning salmonid (prey) availability. It cannot be assumed that salmon 

 are available to every predator every day of the year (or every day that a pinniped is in 

 Oregon waters). Nor can it be assumed that pinnipeds would selectively consume 

 salmon when other more abundant, more easily caught and consumed prey are available 

 (particularly for harbor seals). Many of the calculations in this report are based on the 

 assumption that salmon are available to marine mammals 365 days of the year: 

 estimated predation losses, therefore, likely over-estimate actual losses greatly. 



Other Marine Mammals ^pages 110-11 H 



This discussion mentions that several other marine mammal species have been known 

 to consume salmonids at some time, but provides no information of the relevance of 

 this fact to the decline of Oregon's wild salmonids. Of some 34 marine mammal 

 species that occur in the northeastern Pacific, 10 have been known to consume salmon 

 at some time (Fiscus 1980). In Oregon, less than five of these species have salmonids 

 in their diets with any frequency. Three of those are the pinnipeds discussed 

 previously. In geneial, marine mammals as a group are thought to have negligible 

 effects on free-swimming salmon in the open ocean (Fiscus 1980). 



Killer whales are known to consume seals and sea lions, but the report only briefly 

 mentions this fact. Certain groups of Orca are known to specialize on pinniped as 



A-48 



