FISHERY BULLETIN: VOL. 71, NO. 3 



Table 4. — Catch of steelhead trout and catch per gill net and longline set by research vessels of the Fish- 

 eries Agency of Japan, 1955-?7 and 1962-67 (no information available for 1958-61). 



'Effort and gear for 1955-57 from Fisheries Agency of Japan (1956-58). Catch for 1955 and 1957 from personal 

 communication, Fisheries Agency of Japan; for 1956 from Fisheries Agency of Japan (1957). 

 2 Data from Fisheries Agency of Japan ( 1962- 1967). 



The longline fishing by the Canadians in 

 1961 and subsequent years covered most of the 

 Gulf of Alaska and the eastern North Pacific 

 Ocean east of long. 170 °W and north of lat. 

 42 °N. Fishing effort was well dispersed over 

 this area in all years except 1961, when it was 

 concentrated near Kodiak Island. The period 

 of operation extended from early spring to mid- 

 summer in 4 of 7 yr and from early winter to 

 midspring in 3 of 7 yr. From one to four ves- 

 sels were assigned to the investigations. 



The Canadian longline catches in the Gulf 

 of Alaska and eastern North Pacific averaged 

 one steelhead trout per set over the 7-yr 

 period, 1961-67 (Table 5). The annual catch 

 varied from a high of 1.75 per set in 1965 to 

 a low of 0.29 per set in 1967. Individual sets 

 yielded up to 41 steelhead trout. Catches of 



Table 5. — Catch of steelhead trout and catch per long- 

 line set by research vessels of the Fisheries Research 

 Board of Canada, 1961-67. 



from 5 to 20 steelhead trout per set were not 

 uncommon. The ratio of steelhead trout to 

 salmon in longline catches averaged 1:54 for 

 all years (Table 1). 



AGE, LENGTH, AND WEIGHT 



OF STEELHEAD TROUT 



CAUGHT AT SEA 



The age, length, and weight of steelhead 

 trout caught at sea by research vessels of 

 NMFS in 1955-67 are shown in Table 6. 



Age 



Age determinations were made from pro- 

 jected images of plastic impressions of scales 

 (Mosher, 1950). Of those collected and 

 examined, 78% or 323 scales had well-defined 

 winter annuli for each year of fresh- and salt- 

 water life. The other 22% were unreadable for 

 age because of regeneration of scale features 

 at some stage in the life history of the fish. 



The formulae of Koo (1962) were followed 

 for designation of age. Briefly described, the 

 number of winters in fresh water is expressed 

 by an appropriate numeral followed by a dot; 

 the number following the dot denotes winters 

 in salt water. Total winters of life ai-e derived 

 by adding the two numerals; for steelhead 

 trout, which spawn in the spring, this sum 

 represents total age. Thus, a 1.2 age steelhead 

 trout that has spent one winter in fresh water 



794 



