FRENCH and DUNN: LOSS FROM HIGH-SEAS GILLNETTING 



the resource as associated with an open sea 

 fishery. 



SUMMARY AND CONCLUSIONS 



Studies by U.S. scientists on the loss of sal- 

 mon from gill nets fished on the high seas com- 

 menced in 1964. The indirect methods of 

 determining losses used in 1964 and 1965 

 resulted in the estimates of loss of immature 

 salmon of 32% for periods up to 12.5 h in 1964 

 and an estimated average loss of maturing sal- 

 mon of 27% for a 3-h period in 1965. These 

 losses were attributed to disentanglement and 

 to extraction by predators. 



Direct methods of observation were initiated 

 in 1966. These studies permitted estimates of 

 rate of loss of salmon for periods up to 1, 2V2, 

 and 3 h (and in some years up to 5 h) as well 

 as periods up to 10-11 h. These studies were 

 directed toward both maturing and immature 

 salmon; comparisons were also made between 

 large and small mesh gill nets and between 

 monofilament and multifilament gill nets. 



In the 4 years' experiments, 534 salmon were 

 marked. Overall loss rates for periods up to 11 h 

 was 41%. Loss rates were nearly 6% up to 1 h 

 and 14% up to 2V2 h, and it was shown that 

 losses continued with time in the net. 



Losses from small mesh (64- and 83-mm) 

 multifilament nets, which capture mainly the 

 small age .1 immature salmon, were similar to 

 losses from large mesh nets (45% vs. 41% ). Loss 

 rates from the small mesh nets were similar to 

 those of large mesh multifilament nets for 

 periods up to 1 h (5 and 6% , respectively) and 

 greater than the losses in large mesh multi- 

 filament nets for periods up to 2V2 h (21 and 7% , 

 respectively). 



Comparisons of the loss rates of large mesh 

 (98-, 114-, and 133-mm) multifilament nets as 

 opposed to large mesh (114- and 133-mm) mono- 

 filament nets indicated that for periods up to 11 

 h, loss rates from the multifilament nets 

 exceeded the monofilament nets (41% vs. 33% ), 

 although the difference was not statistically 

 significant. 



The loss rates of primarily immature salmon 

 in the summers of 1966 and 1967 were com- 

 pared with the catches of primarily maturing 



salmon in the spring of 1968 and 1969. Loss 

 rates for the immatures for the three time 

 periods (1, 2V2, and 11 h) were 9, 17, and 46% ; 

 for maturing salmon the loss rates for the three 

 time periods were 0, 4, and 20%. 



It was not possible to determine accurately 

 species during the process of marking the loca- 

 tions of fish in the nets. It was concluded that 

 dropout rates would be applicable to those 

 species which make up the bulk of the catches 

 (sockeye and chum salmon made up over 70% of 

 the catch during these experiments). 



The losses were attributed to both disen- 

 tanglement (dropout) and to extraction by 

 predators. Attempts at differentiating between 

 losses due to dropout and losses due to preda- 

 tion were not entirely conclusive. Estimates of 

 the loss of salmon due only to dropout was about 

 12% , although the data from which this esti- 

 mate was derived are limited. It was concluded 

 that the estimates of losses from gill nets based 

 on research vessel data apply equally to the 

 Japanese mothership fishery because of simil- 

 arity of fishing methods, gill net construction, 

 and susceptibility to predation. 



Weather (wind and sea state) was expected 

 to influence gill net loss, but the available data 

 failed to demonstrate any relation, primarily 

 because the experiments were generally con- 

 ducted in comparatively calm weather. 



Direct observation of the loss of maturing 

 salmon from gill nets was extended to an in- 

 shore fishery (Puget Sound) in August 1967. 

 No losses were recorded for periods up to 3 h. 

 Subsequent studies by the Department of 

 Fisheries, State of Washington, also failed to 

 demonstrate significant losses, suggesting that 

 losses from gill net fisheries were mainly 

 related to high-seas fishing. 



Additional losses in high-seas gillnetting 

 were attributed to fallouts, those salmon lost 

 while hauling the nets aboard the vessel. 

 Examination of U.S. research vessel catches 

 from 1965 to 1970 indicated that fallouts 

 amounted to about 1.4% of the total number of 

 salmon landed. There was relatively little dif- 

 ference in percentage of fallouts by size of ves- 

 sel. Although the number of fallouts did not 

 form a substantial part of the total number of 

 salmon landed, if the percentage loss was 



873 



