Forecasts of Sockeye Salmon Runs 



A system to estimate the numbers of sockeye salmon which 

 will return to Bristol Bay each year is one of our primary 

 goals. Both industry and management will benefit if the 

 number of fish that will arrive 6 months to a year later 

 can be predicted with reasonable accuracy. Such forecasts 

 reduce costs of the U.S. salmon industry largely because 

 the canning operations can be planned more effectively. 

 The Alaska Department of Fish and Game also needs the 

 forecasts when it sets regulations designed to utilize sockeye 

 salmon runs fully and to assure the optimum number of 

 spawners on the spawning grounds. 



Predictions of sockeye salmon runs to Bristol Bay have 

 been made by U.S. scientists since the late 1950's. The fore- 

 casts were based on counts of spawners and downstream 

 migrants, surveys of distribution and abundance of salmon 

 in the ocean, age composition (of fish at sea and in spawning 

 streams), and estimates of the catches and fishing eflforts 

 of the Japanese vessels. Made in November each year, the 

 forecasts are not yet highly reliable. We hope that our goal 

 of accurate estimates may he reached when more information 

 is available on the distribution and abundance of salmon in 

 relation to the ocean envii'onment. 



Our biometricians have developed a method to predict 

 the size of the run of Bristol Bay sockeye salmon 1 to 3 weeks 

 before the fishing season. It is a complicated system that 

 requires an adjustment for variations in the Jaiianese fishing 

 effort and an estimate of the percentage of fish that have 

 lived 2 years in the ocean. The new method is under eval- 

 uation. 



Effects of Fishing 



The response of fish populations to fishing is modified 

 by the harvesting techniques and by the environment. To 

 measure these responses, biologists have conducted fishing 



gear experiments in the ocean and controlled population 

 studies in the laboratory. 



Fish caught by gill nets but not enmeshed in the nets 

 when they are brought aboard a vessel are called "dropouts. " 

 The effects of the loss of salmon from gill nets may have 

 an important bearing on the management of fisheries. After 

 escaping the nets, the salmon may die, be less able to evade 

 enemies, or be more susceptible to disease than salmon never 

 meshed in nets. Dead salmon also may drop out. The lost 

 fish contribute nothing to man's food supply nor to the re- 

 production of stocks. 



Experiments in 1966-67 on the high seas to measure 

 dropout rates yielded interesting results. The gill nets set 

 by research vessels were patrolled at night by small boats. 

 Mo.st of the time this work was difficult in a tossing boat 

 and in darkness penetrated only by portable spotlights. Dur- 

 ing each ixitrol, the locations of gilled salmon were marked 

 with colored pins, and the presence of salmon was noted 

 on later patrols or when the nets were hauled. 



Total dropouts ranged from about 11 percent (for fishing 

 periods up to 1 hour) to as high as 64 percent (for periods 

 up to 10 hours). Losses varied according to mesh size; 

 losses were larger in shorter periods (21/^ hours or less) 

 in large-mesh nets and for longer periods (5-10 hours) in 

 small-mesh nets. 



Additional dropout experiments were carried out in 1966- 

 68 at our Bowman Bay Marine Station on Puget Sound, 

 Wash. (fig. 14). Up to 45 percent of the sockeye salmon 

 escaped after being caught by gill nets, and 79 percent of 

 these fish were dead within 20 days. All live fish that were 

 removed from the nets died within 20 days, but only 1/10 

 of the fish not exposed to gill nets died. Thus, in a fishery, 

 for every 1,000 fish enmeshed in a gillnet, 550 might have 

 been landed and an additional 450 might have been landed 

 if they had not dropped out. Of the 450 dropouts, only 94 

 might have lived to reach inshore fisheries. 



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