FISHERY BULLETIN: VOL. 71, NO. 3 



Abegglen (1955) studied the survival and spawn- 

 ing of sockeye salmon marked by gill nets in the 

 Karluk Lagoon (Alaska). In experiments on 

 maturing salmon entering Karluk River, fish 

 were induced to enter gill nets, tagged, and 

 recovered at upriver weirs or on the spawning 

 grounds. Nelson and Abegglen estimated that 

 from 10 to 20% of the gill net-marked fish 

 escaping commercial gill nets die because of 

 injuries inflicted by the webbing. 



More conclusive evidence of high mortality 

 of salmon which escape from gill nets in salt 

 water comes from controlled experiments in 

 1968 and 1970. These experiments indicated 

 that an average of 73% of the dropouts died in 6 

 days compared with 10% for control fish (Thomp- 

 son and Hunter, see footnote 2). 



Recoveries in inshore areas of gill net- 

 caught salmon which had been tagged and 

 released at sea have been far fewer than 

 recoveries of gill net-caught fish tagged in 

 rivers or estuaries. For example, from 1952 to 

 1957, Japanese scientists tagged 6,155 salmon 

 that had been captured in gill nets on the high 

 seas; only 26 (0.4%) were recovered (Fisheries 

 Agency of Japan, 1959). In another example, 

 U.S. scientists tagged 378 salmon captured with 

 gill nets on the high seas, and none were 

 recovered. At the same time as these experi- 

 ments, salmon were captured by longlines and 

 purse seines and were tagged and released; 

 recoveries amounted to 7.3% . From inshore tag- 

 ging during these same series of experiments 

 (fish were captured in gill nets and tagged 

 primarily in Bristol Bay, east of long. 165 °W), 

 recoveries were 6.9%, whereas recoveries from 

 fish captured with longline and purse seines 

 averaged 29% (Lander et al.. 1967). The poor 

 recovery of tagged salmon led Japanese, Cana- 

 dian, and United States scientists to abandon 

 gill nets as a means of capturing salmon for 

 tagging experiments. 



There is evidence, on the other hand, that 

 recoveries of salmon captured in gill nets and 

 tagged in fresh water may be relatively high. 

 Salmon captured in gill nets at Hells Gate 

 (Fraser River, B.C.) were tagged in 1939 and 

 1940; upstream recoveries were 40% in 1939 

 and 31% in 1940 (Thompson, 1945). 



If we assume similar care in handling fish 



for offshore and inshore experiments and 

 assume that the fish were in the nets for 

 approximately equal time periods, these exam- 

 ples illustrate that salmon upon i-eaching 

 estuaries and fresh water are likely to be much 

 hardier than their offshore counterparts and 

 apparently are much more able to survive the 

 effects of gillnetting. 



From the evidence of tagging experiments 

 and from studies on the viability of salmon 

 escaping gill nets, we concluded that the survi- 

 val of salmon escaping gill nets on the high 

 seas is relatively low. Furthermore, we may 

 assume that losses of salmon due to predation 

 result in 100% mortality of the extracted fish. 

 Therefore, the potential loss of salmon and 

 waste of the resource due to dropouts and 

 predation amount to large numbers of salmon. 



Japan engages in a major high-seas gill net 

 fishery for Pacific salmon in the North Pacific 

 Ocean and Bering Sea. The Japanese mother- 

 ship fishing area, governed by agreements 

 with Canada and the United States (Inter- 

 national North Pacific Fisheries Convention) 

 and with the USSR (International Convention 

 for Northwest Pacific Fisheries), lies west of 

 long. 175 °W and extends generally from lat. 

 46° to 60°N (International North Pacific 

 Fisheries Commission, 1968). In addition, a 

 land-based gill net fishery for salmon is pur- 

 sued by Japan in areas of the North Pacific 

 Ocean south of the mothership fishing area 

 (Figure 7). 



Fukuhara (1971) analyzed the Japanese 

 mothership fishery, the details of which follow. 

 The fishing effort of the fleet since 1961 has 

 numbered 11 motherships and 369 catcher 

 boats, fishing between 5 and 7.5 million tans" 

 (cumulative effort) of nylon gill nets during a 

 season. West of long. 170 °E, the maximum 

 allowable number of tans per boat is 264 and 

 330 east of that longitude. On a given day, 

 therefore, the fleet is capable of fishing 4,900 

 to 6,100 km of gill nets, depending on its east- 

 west distribution. Two sizes of mesh are used, 

 121 mm and 130 mm, stretched measure. The 

 ratio of large mesh to small mesh must be 6:4 

 west of long. 170°25'E and may be 4:6 east of 



^ A tan is approximately 50 m long. 



870 



