FISHERY BULLETIN: VOL. 82, NO. 2 



between and 50 m in the northwestern Pacific 

 were usually highest in near-surface depths by 

 day and below 10 m at night. Euphausiids were an 

 important food taxa only in salmon caught below 

 10 m during the day. Since average stomach full- 

 ness indices were higher during the day than the 

 night, Machidori concluded that light was neces- 

 sary for salmon to feed. Takagi (1971) reported 

 that surface longlines and gill nets caught salmon 

 during morning and evening, but during the night 

 salmon were caught in gill nets but not by 

 longlines. These observations indicate reduced 

 feeding activity of salmon at night. 



Shimazaki and Mishima (1969) concluded from 

 diel trends in the feeding of maturing pink and 

 chum salmon at two locations in the Sea of 

 Okhotsk that feeding activity was high in the 

 evening before and after sunset and low in day- 

 time. They found peak stomach fullness values 

 after sunset. In three of four instances these peak 

 values were the first values after sunset, and may 

 have been the result of crepuscular feeding. In one 

 instance involving pink salmon, however, stomach 

 fullness increased from 1917-2040 h to a peak at 

 2119-2245 h, indicating active feeding at night. 

 Amphipods, squids, and fishes were the dominant 

 food on a wet weight basis. 



Additionally, Ueno et al. (1969) found that pink 

 and chum salmon had full stomachs during the 

 late afternoon as well as after dark in waters off 

 Kamchatka. Suzuki (1970) compared the volume 

 of food in stomachs of chum salmon caught in gill 

 nets off the Kamchatka Peninsula during night 

 (2100-2330 h) and morning daylight hours (0330- 

 0610 h) and concluded that no major differences 

 existed. He found that myctophid fishes always 

 comprised a larger percentage of the stomach con- 

 tents during the morning and pteropods usually 

 comprised a larger percentage at night. 



Thus the above studies plus our own clearly 

 document that salmon are capable of feeding dur- 

 ing both day and night periods in oceanic waters. 

 Their feeding behavior is flexible and variable, 

 permitting opportunistic exploitation of a profit- 

 able food resource regardless of when it is en- 

 countered. 



ACKNOWLEDGMENTS 



We heartily thank all the crew and cadets of the 

 Oshoro Maru who worked throughout the 24-h 

 period of this study and made the research possi- 

 ble. The research was supported in part by grants 

 from the Sea Grant College Program (No. 



NA81AA-D-00086, Project No. R/OPF-17) and the 

 National Science Foundation (INT80-00665/R- 

 XMB0102). 



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