FISHERY BULLETIN: VOL. 71, NO. 3 



ing a problem of net-injured salmon in the 

 streams of Hokkaido Island, Japan. He also 

 reported that up to 5% of the salmon in some 

 streams in 1960 were gill net-marked. 



These net-marked or injured salmon that are 

 observed in coastal waters or in river systems 

 are, of course, only the surviving salmon that 

 have encountered and escaped either a high- 

 seas or an inshore gill net fishery. The loss or 

 dropout of salmon from high-seas gill nets has 

 been recognized as a potentially serious loss to 

 the resource by scientists of all nations con- 

 cerned; however, neither the rates of fish drop- 

 ping from the nets nor the number which perish 

 are known. Doi (1962), in experiments on the 

 high seas, estimated the rate of dropouts from 

 examination of the catch in gill nets at 30-min 

 intervals. He concluded that the rate of drop- 

 outs is a function of the time the fish are in the 

 nets; that is, dropouts increase with time in the 

 net. In Doi's experiments, dropout rates ranged 

 up to 55% for coho salmon, O. kisutch, and 47% 

 for sockeye salmon after periods of 5V2 h. 

 Miyazaki and Taketomi (1963, as cited by 

 Konda, 1966) estimated a 20% loss of pink sal- 

 mon, 0. gorbuscha, from gill nets. Semko 

 (1964), in discussing the irrationality of a high- 

 seas salmon fishery, stated that a large mortality 

 is inflicted in salmon by the drift nets and that 

 the loss may amount to 30% of the catch. Konda 

 (1966), while commenting on the loss of salmon 

 from gill nets during hauling, stated that the 

 ratio of live to dead fish is closely related to the 

 length of time needed to haul the net. He 

 further stated ". . . not only when hauling in the 

 set, but even while setting the gillnet, no small 

 number of fish will leave the net after having 

 once been gilled, ..." and ". . . as is well 

 known, the gillnet is effective for high seas sal- 

 mon fishing, however, it is always accompanied 

 with a large loss of resources." Ishida et al. 

 (1969) found salmon dropout rates of 4.2 to 

 24.1% in four experiments in the Okhotsk Sea. 

 Thus, there is recognition of loss of resources 

 due to dropouts during the drift of gill nets 

 and due to fallouts during hauling of the fishing 

 gear. 



Because of the possible deleterious effects 

 on U.S. salmon stocks by the Japanese high- 

 seas gill net fishery, the former Seattle Bio- 



logical Laboratory of the Bureau of Commer- 

 cial Fisheries (now National Marine Fisheries 

 Service) undertook studies on the loss of salmon 

 owing to a gill net fishery in 1964. 



Progress on these studies has been reported 

 in Annual Reports of the International North 

 Pacific Fisheries Commission (French, 1966; 

 French, Craddock, and Dunn, 1967; French, 

 Craddock, Bakkala, Dunn, and Thorson. 1967; 

 French et al.. 1969, 1970, 1971). Progress on 

 determining the fate of salmon which escape 

 from gill nets has been reported by Thompson, 

 Hunter, and Patten (1971); by Hunter, Patten, 

 and Thompson (1972); and by Thompson and 

 Hunter (1972)2. 



Reported here are the results of 6 yr of 

 experiments to determine: (1) the rate of drop- 

 out; (2) the effect of varying length of fishing 

 time on dropout loss rate; (3) the effect of 

 different types of gill net materials and mesh 

 sizes on dropout rates of maturing and im- 

 mature salmon; and (4) rate of fallouts during 

 hauling operations. Included are estimates of 

 loss of salmon from high-seas and inshore 

 gillnetting. 



In this report we use the term "dropouts" as 

 those salmon that become unmeshed or other- 

 wise escape from drifting gill nets; the term 

 "fallouts" is used to describe those salmon 

 seen to fall from gill nets as the gear is hauled 

 aboard the vessel. 



EXPERIMENTAL METHODS 



Dropout Studies 



Experimental methods used in 1964 and 

 1965 differed from those used in 1966-69. The 

 former methods were based on indirect observa- 

 tions of the fish, whereas, the more recent 

 studies were based on direct observation of the 

 fish. Experimental methods will be described 

 separately below for the indirect and direct 

 methods of observation. 



2 Thompson, R. B., and C. J. Hunter. 1972. Viabil- 

 ity of adult sockeye salmon that disentangle from gill 

 nets. In Investigations by the United States for the 

 International North Pacific Fisheries Commission — 1971, 

 p. 95-105. Northwest Fish. Cent., Natl. Mar. Fish. Serv., 

 NOAA, Seattle, Wash. [Processed.] 



846 



