JUDKJSS aad nOOSGEBiz FOtLECCT CONTEXTS OF Sergfita timiEt 



numbers designated "day-net" comprise a set 

 of nine samples of from 3 to 10 shrimp each and 

 collected by nets that were towed exclusively be- 

 tween sunrise and sunset. "Twilight-net" col- 

 lection numbers represent three samples collec- 

 ted by nets which were sr*:^ >"v towed at sunset 

 or sunrise. Collection n.: designated '*fish 



stomachs" represent 10 samples of 2 to 24 shrimp 

 taken from stomachs of albacore. The albacore 

 were taken during daylight hours by trolling 

 lines; exact times of capture were not available 

 for five of the si)ecimens. 



Included in statistical analyses were all classes 

 of food occurring in 10% or more of any of the 

 sets of night-net, day-net, and fish samples. Cal- 

 anoid genera occurring in 10% or more of any 

 of the sets of samples were considered separately. 

 The small number of twilight-net samples was 

 not included in statistical comparisons of the 

 sampling categories, but the details of this set 

 are given in Table 2. Overall mean? (no. prey 

 foregut) and frequencies (*■>) were calculated 

 for the three sets of samples that were compared. 

 In addition, means were calculated for each 

 night-net, day-net, and fish sample. The Mann- 

 Whitney f '-Test, a test designed to estimate the 

 significance of differences in median values of 

 two samples was used to compare median sam- 

 ple means between day- and night-net samples 

 and between combined day- and night-net sam- 

 ples and fish samples. 



RESLTTS 



Ingested items inc t euphausiids, ostra- 

 cods, amphipods, ch£.e: _ . ths, and fish scales, 

 but the principal identif t ::>mponents in aU 

 sampling categories were aduit calanoid cope- 

 pods (Table 2). The composition of foregut 

 contents from different geographical regions 

 (North Pacific Subarctic, Xorth Pacific Drift, 

 and the Califomia Current) were very similar 

 and hence were not considered separately. The 

 diversity of calanoids was much greater in aU 

 categories of net samples than in fish samples: 

 42 species were identified in net samples, but 

 only 7 were found in fish samples. 



Foregut contents varied widely in the extent 

 of maceration by digestion and mastication. 



219 



