16 



salmon, though not numerous, were most 

 abundant in late August in the northern and 

 southern extremes of the sampling area. 



Immature chum salmon (3 years and older) 

 were scarce along long. 176° W., and catches 

 of these older fish indicated no peak of abun- 

 dance by time period or area. Along long. 

 167° W., the older chum salmon were much 

 more abundant than the young; their peak of 

 abundance fell between August 1 and 10; they 

 were in similar abundance throughout the 

 sampling area, except'for slightly lower con- 

 centrations at the very southern stations. 

 Abundance of chum salmon along long. 158 

 W. was similar throughout the sampling pe- 

 riod; greatest numbers occurred 300-360 

 miles offshore (lats. 51°30' N. to 50°30' N.). 



Purse seine and gill net catches of sock- 

 eye salmon did not reflect relative abundance 

 in a similar manner. Catches of chum salm- 

 on indicated little relationship between the 

 two types of gear. 



Studies of Dropouts 



Percentages of salmon caught in a gill net 

 which are not present when the gear is hauled 

 (dropouts) were estimated from periodic in- 

 spection of the nets during normal fishing. 

 The procedure used was to patrol the nets at 

 night from small boats, mark the location of 

 gilled salmon, and determine their presence 

 or absence at later patrols and when gear was 

 hauled. Portable spotlights were used to lo- 

 cate fish in the net. 



Comparisons of relative abundance be- 

 tween the three sampling areas (table) indi- 



Dropout rates were substantial (49 per- 

 cent) when measured over a period of 8-10 



Average Catch of Immature Sockeye and Chum Salmon Per Shackle for Three Areas of the North Pacific Ocean, July -September 1966 



Area (Long . ) 



Sockeye Salmon 



Chum Salmon 



l-Winter-at-Sea 



2- or 3-Winteis-at-Sea 



2 -Year-Old 



3 -Year- and Older 



176°22' W. (Paragon) 



3.53 



1.07 



1.84 



0.58 



167° W. (George B. Kelez) . . . 



2.29 



1.31 



1.09 



3.25 



158° W. (St. Michael) 



1.50 



2.45 



0.98 



2.91 



cated that 1 -winter -at -sea sockeye salmon 

 were most abundant along long. 176° W., and 

 were least abundant along long. 158° W. On 

 the other hand, 2- and 3 -winter -at -sea sock- 

 eye salmon were least abundant near Adak 

 Island and most abundant along long. 158°W. 

 Both the younger and older sockeye salmon 

 had their peak of abundance at similar lati- 

 tudes in the three sampling areas. 



The relative abundance of chum salmon 

 was similar to that of sockeye salmon. The 

 2 -year -old fish were most abundant near 

 Adak Island and least abundant along long. 

 158 W. The older chum salmon were more 

 abundant along long. 158° W. and 167° W., 

 and least abundant along long. 176° W. 



Comparison of Purse Seine and 

 Gill Net Catches 



Comparative fishing was conducted with 

 gill nets (vessel Paragon), and purse seines 

 (vessel Storm, Fisheries Research Institute) 

 to determine if the two forms of gear simi- 

 larly reflected the relative abundance of 

 salmon. Gill nets were fished at night and 

 purse seines during the day in the same area. 



hours. After 2-2|^ hours, dropout rates were 

 about 22 percent. The loss rate was 4 per- 

 cent after one-half hour. Salmon known to be 

 in the nets at least 2^ hours continued to drop 

 out. The loss is attributed to escape, falling 

 out of the nets, or to predation. 



By J. R. Dunn, 



Fishery Biologist (Research), 

 BCF Biological Laboratory, 

 Seattle, Wash. 98102 



Note: See Commercial Fisheries Review , July 1966 pp. 40-41. 



Alaska Fisheries Explorations 

 and Gear Development 



R/V "SABLEFISH" CONTINUES 

 GEAR STUDIES ON SHRIMP TRAWLS 



The BCF chartered R/V Sablefish has 

 completed phase two of the shrimp try-net 

 experiment in Tutka Bay. Three try -nets 

 were sampled. The results indicate a definite 

 possibility of developing a selectively fishing 



