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Fishery Bulletin 100(3) 



Salmon in the harbor seal diet 



Harbor seals consumed several species and sizes of salmon 

 throughout our study, but frequency was greatest during 

 spring. Size of otoliths recovered indicated that most of 

 these fish were juvenile chinook and that adult salmon 

 were consumed to a lesser extent, primarily during fall. 

 Fryer ( 1998) reported no difference in mean fork lengths of 

 adult spring-summer O. tshawytscha with scars from pin- 

 nipeds and those without scars at the Bonneville Dam and 

 observed a greater percentage offish with scars earlier in 

 the year, although these findings do not necessarily con- 

 tradict data from our study. Scarred fish represent failed 

 predation and perhaps harbor seals attempted to capture 

 fish beyond their ability when spring run-off results in 



greater water turbidity. In addition, part of the discrep- 

 ancy may be due to the classification of "adult" salmon. 

 For our purposes, we categorized all fish with estimated 

 lengths greater than outgoing migrants (30 to 35 cm 

 depending on the species) as "adults." The mean lengths of 

 scarred spring-summer O. tshawytscha from 1994 to 1996 

 (75.9 to 79.3 cm standard length) were greater than the 

 mean length of "adult" fish estimated from prey remains 

 (73.4 cm mean standard length). 



Riemer and Brown (1997) also examined all skeletal 

 structures; however, their results summarized data for 

 four years and 154 samples collected on eight dates. 

 Riemer and Brown (1997) reported salmon FO as great 

 as 39% for a single sampling date but found no salmonid 

 remains in scats collected during February and March. 



