FISHERY BULLETIN: VOL. 80, NO. 4 



Table 6.— Sampling data and percent of total numbers of major prey items found in juvenile coho stomachs off the Oregon coast 

 (only at those stations where six or more juvenile coho were taken). Includes only those prey taxa comprising 2% or more of the total 

 number of prey items. 



Pi is the proportion of the ith taxa (based on num- 

 bers of individual prey) in a stomach (Whittaker 

 1960), and PSI between a pair of stations is calcu- 

 lated by summing the smaller (minimum) P/s 

 for all food items. Similarity was generally low 

 (<50%) among stations. Only 6 of the 45 possible 

 pairings showed similarities >66% (stations 2-3, 

 2-12, 2-29, 3-29, 10-27, and 28-39), and only two 

 pairs had a similarity >75% (2-29 and 28-39). 



Some of this variability among stations may be 

 related to the geographical regions sampled. For 

 example, the numerical percentage of euphausi- 

 ids averaged 45.5% for coho caught near the 

 Columbia River plume (stations 1-22) compared 

 with 17.4% off the central Oregon coast (stations 

 27-39, Table 6). Fishes occurred in the diets at all 

 stations and made up 14% of the total prey num- 

 bers in the Columbia River area, whereas they 

 were a significant part of coho diets at only one of 

 four stations off Newport. Amphipods occurred 

 more frequently in the stomach contents off 

 Newport, averaging 63.6% of the total number, 

 compared with 20.1% in coho from the Columbia 

 River plume. The copepod, Calanus cristatus, 

 and pteropod, Limacina helicina, were impor- 

 tant components of the diets of only those juvenile 

 coho caught off the central Oregon coast. An 

 additional component of among-station variabil- 

 ity may be attributed to differences in diet be- 

 tween inshore and offshore stations. Coho taken 

 within 12 km of shore contained a greater pro- 

 portion of fishes at two of three stations, while 

 those captured offshore contained more euphau- 

 siids. 



Chinook Salmon 



Thirty taxa were identified from the stomachs 

 of juvenile chinook. Major prey items were juve- 

 nile euphausiids (T. spinifera), hyperiid amphi- 

 pods (mostly Hyperoche medusarum), pinnother- 

 id crab larvae, and various fishes (Table 3). The 

 most frequently identified fishes were flatfish 

 and Pacific sand lance larvae, both occurring in 

 31% of the stomachs. Juvenile scorpaenids were 

 third, occurring in only 7% of the stomachs. 



Chinook salmon with stomachs full of fresh 

 food {n = 42) were studied to test the hypothesis 

 that weight of euphausiids and weight of fish 

 prey in stomachs were independent, using the 

 same procedure as with coho. The x 2 from the 

 contingency table (Table 7) was significant at the 

 0.07 level. Hence there is a tendency for chinook 

 to eat either euphausiids or fishes, but this in- 

 verse relationship is not as strong as for juvenile 

 coho salmon. The weight of stomach contents in- 

 creased with size of juvenile chinook salmon. The 

 slope of the regression (weight of prey = —4.2 + 

 0.032 X length of chinook, over the range of 100- 

 200 mm) was significantly different from zero 

 (r = 0.66, P<0.05). 



Table 7.— Contingency table comparing 

 weight of fish and euphausiid prey found in 

 the stomachs of 42 juvenile chinook salmon. 



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