Brodeur and Pearcy: Trophic relations of juvenile salmon off Oregon and Washington 



623 



/ MONTH 



^M SEPTEMBER (n • 132) 

 iZD JULY-AUGUST (n • 98) 



JUNE (n . 300) 



MAY (n • 265) 



"./ ^/ 



FISH EUPH DECA. PTER AMPH COPE CEPH OTHER 

 PREY CATEGORY 



AREA 



cm OREGON (n - IS-l) 

 ^^ COLUMBIA (n - 478) 

 ^M WASHINGTON (n • 163) 



^3^ 



■/- / 



FISH EUPH DECA PTER. AMPH. COPE. CEPH. OTHER 

 PREY CATEGORY 



Figure 4 



Juvenile chinook salmon diets by month and area for the major prey 

 categories as a percent of total IRI, Sample sizes (no, of fish with 

 food) for each subset are given in the legend. All figures include data 

 collected off Washington and Oregon. 1980-85, 



There were few consistent patterns observed among 

 the invertebrate taxa consumed between the different 

 areas (Fig. 4). Hyperiid amphipods were rarely found 

 in chinook salmon stomachs collected off Washington 

 as opposed to the other regions. The large numbers of 

 decapod larvae eaten off the Columbia River were 

 mainly C. oregonensis and C. magister larvae. 



Chum salmon 



General food habits Of the 109 chum salmon stom- 

 achs examined, lUl (92.6%) contained food; however, 

 overall mean stomach fullness (2.4) and digestion (2.1) 

 were low. The diet was dominated by zooplanktonic 

 crustaceans, particularly euphausiids, calanoid cope- 

 pods, and hyperiid amphipods (Appendix Table 2). 

 Euphausiids (mostly juveniles', pacifirn and T. spini- 

 fera) accounted for over 54% of the total weight and 

 47% of the total IRI for all cruises combined. A tax- 

 onomically diverse array of hyperiids, copepods. and 

 decapod larvae were also consumed. These taxa fre- 

 quently occurred in the stomachs and were important 

 numerically, but were of lesser importance gravi- 

 metrically. Chaetognaths and larvae and juveniles of 

 several fish species were the dominant non-crustacean 

 prey (Appendix Table 2). 



Temporal variations Chum salmon diets varied con- 

 siderably during the 5 years examined (Table 4). Some 



