salmon were transferred from hatcheries to salt-water ponds 

 where they were handled, tagged, and chased to exhaustion. 



Biochemists found the blood lactate concentrations of 

 maturing sockeye salmon after stress were below concen- 

 trations that accompanied high mortalities of maturing coho 

 and Chinook salmon caught by troll gear in investigations 

 by other scientists. The adult sockeye and immature chinook 

 salmon did not die within several hours after subjection to 

 stress, although their blood lactate increased. The immature 

 chinooks did not suffer delayed mortality; the maturing 

 sockeyes began dying after 2 days, however, possibly be- 

 cause of additional stress induced by shipboard handling. 



Although actual mortalities are unknown, the number 

 of salmon lost from dropping out of, and from predation in, 

 gill nets in a fishery on the scale of the Japanese mother- 

 ship operations could be tremendous. If more information is 

 obtained about the secondary effects on salmon of being 

 held and escaping from gill nets and if mortality could be 

 measured accurately, management of the fisheries and the 

 accuracy of forecasts could be improved. 



Fisheries in Miniature 



Not all investigations on the effects of fishing are done 

 at sea. One project studies populations in the miniature 

 world of the laboratory aquarium. Although not directly 

 related to salmon, these experiments will jirovide knowledge 

 that can be applied to all types of fisheries. The studies 

 eliminate extraneous conditions such as weather and ocean 

 currents that affect commercially fished populations and ob- 

 scure the relations between populations and fishing. Fishing 

 is simulated by selective removal of fish from aquaria. 



One experiment with guppies and swordtails measured 

 the effect of fishing on competing poinilations. The max- 

 imum sustainable yield was achieved when each species was 

 fished at a rate of 10 percent per brood interval. The more 

 vigorous reproduction and growth of guppies than of the 

 swordtails eventually caused the disappearance of sword- 

 tails from the control population. 



Two experiments with tilapia, a tropical pond food fish, 

 are in progress. One is designed to determine the effect 

 of space on the relation of catch to fishing. The other ex- 

 amines the genetic eflfects of selective fishing. 



Ocean Growth and Mortality 



One approach toward finding the potential yield from 

 a salmon population is to evaluate their growth and mor- 

 tality in the ocean. In 1964, laboratory biologists assessed 

 the long-term growth of sockeye salmon from western Alaska; 

 in 1968 they completed the investigations of seasonal (May- 

 Seirtember) and long-term (between age groups) growth 

 of chum salmon at sea. 



The analysis of growth in chum salmon was based on 

 body lengths and patterns of scale growth of fish caught by 

 gill nets in the North Pacific Ocean and Bering Sea during 

 195.5-56. Chum salmon of Asian origin were smaller and 

 grew at a faster rate than those of North American origin, 

 which suggested a shorter growing season for Asian stocks. 

 Maturing and immature fish of the same age and stock grew 

 at about the same rate. Growth was considerable from the 

 time maturing fish left offshore areas until they arrived in 

 coastal waters. Estimates of growth rates in the year be- 

 fore maturity of chum salmon that spent 3 years in the ocean 

 (those most vulnerable to the oceanic fishery) indicated 

 increases of population weight that considerably exceeded 

 reasonable estimates of mortality. In other words a greater 

 yield can be obtained from a coastal rather than an oceanic 

 fishery. 



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