'10' '12' '14' '16' '18' '20' 

 HOUR OF THE DAY (PDT) 



Figure 1. -Average catch of albacore per boat for each hour of 

 the day from 0500 to 2200 for 3 mo in 1969 and for 20 July-2 

 August 1970. The numbers for hours of the day refer to the time 

 at the beginning of the interval. 



heterogeneity of catches for all four of the data 

 sets are significant (P<0.05), indicating that catch 

 rates were not constant with time but varied 

 throughout the day. Consistent trends for diel 

 periodicity in catches, however, are not apparent. 



Only during 1970 was there an obvious trend for 

 peak catch rates to occur early in the morning and 

 in the evening. These peaks coincided with the 

 local mean times of sunrise and sunset (about 0600 

 and 2100 PDT). 



The separate months of 1969 show a variable 

 pattern with peaks occurring at different times 

 during different months. There is no evidence for 

 a pronounced early morning "bite," except 

 perhaps 0800-0900 in July. Catch raies generally 

 increased with time during the day. Most 1969 

 afternoon catch rates were above the median for 

 each of the 3 mo, but they were not markedly 

 higher in the evening as was found for 1970. 



The catches during 1970 were exceptionally 

 high. Even the lowest 1970 catch rate was higher 

 than any of the peak 1969 catches (Figure 1). The 

 1970 jig-boat season for albacore off Oregon was 

 unusually short (most fish were caught between 22 

 and 29 July) and the fleet was localized in a small 

 area (Pearcy 1973; Keene 1974). For those reasons, 

 the spatiotemporal variability for the 1970 data is 

 probably much less than for the separate months 

 of 1969. 



692 



From our limited data we conclude that albacore 

 feed throughout the day. Catch rates averaged 

 over several weeks do not always indicate morning 

 and evening periods of intense feeding. Obviously 

 this does not preclude the occurrence of morning 

 and/or evening bites in some areas on some days. 



Although stomach fullness and catch rates are 

 both related to feeding behavior, they may provide 

 different results on feeding periodicity because of 

 the influence of such factors as changes in depth 

 distributions, vulnerability to fishing methods, 

 and the times required for accumulation and 

 digestion of food in the fish's stomach. For 

 example, the especially high rates of capture of 

 albacore on surface jigs during sunrise-sunset 

 periods of 1970 may be related to the vertical 

 migration of Pacific saury, Cololabis saira, their 

 major prey during this time (Pearcy 1973). Saury 

 migrate to surface waters at sunset and descend 

 into deeper waters at sunrise (Hotta and Odate 

 1956; Hughes and Gill 1970). Relatively low catch 

 rates during the day may therefore be the result of 

 either albacore pursuing saury into deeper water 

 where albacore are less vulnerable to surface lures 

 or to reduced feeding activity. 



Acknowledgments 



We thank the albacore fishermen who made this 

 study possible. This research was part of the 

 Oregon State University Sea Grant Program, 

 supported by NOAA Office of Sea Grant, Depart- 

 ment of Commerce under Grant No. 04-5-158-2. 



Literature Cited 



Dragovich, a. 



1970. The food of sitipjack and yellowfin tunas in the 

 Atlantic Ocean. Fish. Bull., U.S. 68:445-460. 

 Hotta, H., and K. Odate. 



1956. The food and feeding habits of the saury, Cololabis 

 saira. [In Jap., Engl, abstr.] Bull. Tohoku Reg. Fish. Res. 

 Lab. 7:60-69. 

 Hughes, S. E., and C. D. Gill. 



1970. Saury is promising 'new' fish on west coast. Natl. 

 Fisherman 50(12): 12C-14C. 

 Iverson, R.T. B. 



1962. Food of albacore tuna, Thunnus germo (Lacepede), in 

 the central and northeastern Pacific. U.S. Fish Wildl. 

 Serv., Fish. Bull. 62:459-481. 

 Keene, D. 



1974. Tactics of Pacific northwest albacore fishermen-1968, 

 1969, 1970. Ph.D. Thesis, Oregon State Univ., Corvallis, 

 93 p. 

 Magnuson, J. J. 



1969. Digestion and food consumption by skipjack tuna 

 (Katsuwonus pelamis). Trans. Am. Fish. Soc. 

 98:379-392. 



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