626 



Fishery Bulletin 88(4), 1990 



year and month (Table 8). The only comparison which 

 showed non-significant variation by year or month was 

 the monthly variation in euphausiid occurrences for 

 juvenile chinook salmon. Three prey categories did not 

 show significant variation (P>0.05) when analyzed by 

 area. Comparisons by area showed less significant 

 variation than by year and month for both coho and 

 chinook salmon juveniles for most of the major prey 

 categories (Table 8). 



Examination of inshore-offshore variations in major 

 prey composition for four cruises (two each for coho 

 and chinook salmon) showed generally few significant 

 variations by occurrence for the dominant prey cate- 

 gories (Table 9). Although the species and life-history- 

 stage composition of the prey was different in inshore 

 and offshore collections (i.e., more Sebnstes and En- 

 graulis larvae offshore, and more iuvenile Atnmodyteti, 

 Clupea, and Hemilepidotus inshore), all cross-shelf 

 variations in total fish occurrences were not significant 

 (P>U. 05). The most significant differences were for 

 decapod larvae, and were due to higher occurrences 

 oi Cancer spp. megalopae in chinook salmon stomachs 

 inshore in May 1982 and lower occurrences in coho 

 salmon stomachs inshore in June 1984. 



Discussion 



Overall food habits 



This study represents the first detailed description of 

 the diets of several species of sympatric juvenile salmon 



Table 9 



Results of the chi-square analysis analyzing inshore-offshore 

 variations for major prey categories of juvenile coho and 

 chinook salmon off Oregon and Washington. All significances 

 are at 2 degrees of freedom. 



Prey 

 category 



Coho salmon 



Chinook salmon 



May 81 June 84 May 82 June 85 



Fishes 

 Euphausiids 

 Decapods 

 Amphipods 



3.86 n.s. 

 3.14 n.s. 

 3.83 n.s. 

 3.14 n.s. 



5.82 n.s. 



2.66 n.s. 

 15.07*** 

 15.88*** 



1.34 n.s. 1.40 n.s. 



1.82 n.s. 9.76** 



9.00* 1.82 n.s. 



3.23 n.s. 0.41 n.s. 



*P<0.05, **P<0.01, ***P<0.001, n.s. P>0.05 



in coastal marine waters off Washington and Oregon. 

 Despite generally low diet overlaps at the lowest tax- 

 onomic levels, there were some similarities in the major 

 prey groups consumed by the salmon species. Juvenile 

 chinook salmon were primarily piscivorous, consuming 

 a variety of larval and juvenile fishes. The diet of coho 

 salmon consisted of both fishes and large zooplanktonic 

 crustaceans, such as euphausiids, crab megalopae, and 

 hyperiid amphipods. Chum and sockeye salmon diets 

 were more diverse than the diets of coho and chinook 

 salmon, with fishes, small crustaceans (euphausiid fur- 

 cilia and juveniles, crab larvae, and copepods), and 

 chaetognaths being important prey. 



Our findings are consistent with what is known of 

 the marine food habits of juvenile salmon off Wash- 

 ington and Oregon and British Columbia. Juvenile 

 chinook salmon tend to be more piscivorous than 

 juvenile coho for the same-sized predator (Healey 1978, 

 1980; Peterson et al. 1982; Emmett et al. 1986). Coho 

 collected dm'ing this study, however, consumed a larger 

 overall mean length of fish prey relative to predator 

 length (Brodeur In press). Juvenile northern anchovy, 

 Pacific sand lance, and rockfishes were the dominant 

 fish species eaten off Washington and Oregon (Peter- 

 son et al. 1982, Emmett et al. 1986), and herring and 

 Pacific sand lance were the main fish species consumed 

 off British Columbia (Healey 1978, 1980). Many of 

 these prey fish species tend to be heavily pigmented 

 and are often associated with the neustonic layer in 

 coastal waters (Brodeur et al. 1987b, Shenker 1988, 

 Brodeur 1989). 



Macrozooplankton, such as euphausiids, hyperiid am- 

 phipods, and crab larvae, are also readily consumed by 

 these juvenile salmon. These macrozooplankton prey 

 may be easily detected due to their large size or darkly- 

 pigmented eyes (Peterson et al. 1982) and occur in large 

 aggregations near the surface (Brodeur et al. 1987b, 

 Shenker 1988). Terrestrial insects, which may be blown 



