FISHERY BULLETIN: VOL. 70, NO. 1 



nevertheless was considerably higher than for 

 any of the age 1 smolts. 



In the absence of knowledge of survival rates 

 for the more northern populations of coho salm- 

 on, an examination of the effect of increased 

 freshwater residence on sockeye salmon, the 

 dominant species of salmon in the Karluk system, 

 is of value. Sockeye salmon juveniles at Karluk 

 Lake have long been known to reside in the lake 

 a year or more longer than do sockeye salmon 

 in other areas (Gilbert and Rich, 1927) . In most 

 Alaska systems, sockeye salmon smolts migrate 

 at the beginning of their second or third year of 

 life, but at Karluk Lake most sockeye salmon 

 smolts migrate at the beginning of their third 

 or fourth years. Possibly the factor (s) respon- 

 sible for the 1-year holdover of juvenile sockeye 

 salmon in the lake may also be responsible for 

 the holdover of juvenile coho salmon. 



Freshwater sui'vival of sockeye salmon at Kar- 

 luk Lake is extremely poor, but marine survival 

 is good. During the late 1920's and early 1930's, 

 freshwater survival was less than 1 % and ocean 

 survival was about 21% (Barnaby, 1944). In 

 recent years, freshwater survival has dropped 

 to less than 0.5% and ocean survival has in- 

 creased to about 40%.' Ricker (1962) modi- 

 fied Barnaby's data by applying a marking mor- 

 tality factor derived from his Cultus Lake studies 

 and determined that the older, larger smolts have 

 greater marine survival and that Barnaby's ori- 

 ginal estimate of 21% survival was too low. 

 Average marine survival by freshwater age for 

 the years 1926 and 1929-33 were as follows: age 

 1 smolts, 18.3%; age 2, 27.4%; age 3, 34.2%,, 

 and age 4, 33.3%. Ricker attributed the high 

 ocean survival to the large size of the smolts 

 when they entered salt water. The larger size 

 of the sockeye salmon smolts at the time of sea- 

 ward migration, however, is offset by a greater 

 total freshwater mortality due to their prolonged 

 stay in the lake. 



I have shown that in the more northern lat- 

 itudes coho salmon usually reside a minimum of 

 one extra year in fresh water before they migrate 



' Unpublished data on file at National Marine Fish- 

 eries Service Auke Bay Fisheries Laboratory, Auke Bav. 

 Ala.ska 99821. 



to sea. Generally, a longer period of freshwater 

 residence will result in greater freshwater mor- 

 tality but lower marine mortality because the 

 fish are larger when they enter the ocean. Most 

 likely, as with Karluk Lake juvenile sockeye 

 salmon, an extra year in the lake for juvenile 

 coho salmon probably results in a greater total 

 freshwater mortality. Total marine mortality, 

 however, may be less for coho salmon than for 

 sockeye salmon because the coho salmon gener- 

 ally spend less time at sea before returning to 

 spawn (12 to 18 months rather than 24 to 30 

 months). 



SUMMARY AND CONCLUSIONS 



Both the freshwater and total ages of adult 

 coho salmon increase from southern to northern 

 latitudes. In California, the southern portion 

 of the coho salmon's range, fish of ages 32 and 22 

 are in the majority, but in the northern areas, 

 ages 43 and 32 predominate. Karluk coho salmon, 

 however, are unique, in that although age 43 fish 

 are still the primary age class, the age 32 fish are 

 replaced by age 54, so that age 54 fish account 

 for 42% of the run. In no other North Amer- 

 ican or Asiatic coho salmon stock for which in- 

 formation is available is such a large percentage 

 of the run composed of 54 fish. 



The increase in total age of coho salmon from 

 south to north is associated with the increased 

 time the juveniles spend in fresh water. The 

 small numbers of age 54 fish in several Alaska 

 stocks may represent juveniles that live in lakes 

 rather than rivers. 



Fecundity generally increases from south to 

 north, and Karluk coho salmon are the most 

 fecund of any North American stock and closely 

 parallel the highly fecund Asiatic stocks from 

 the Kamchatka Peninsula. In Karluk coho 

 salmon, there is a relation between number of 

 eggs and length but no relation between egg 

 size and length or egg size and fecundity. Egg 

 counts are significantly higher in the right ovary 

 than in the left. 



Coho salmon smolts generally migrate after 

 the ice breaks up and the water warms. In North 

 America, the migration is earlier in southern 

 latitudes than northern ones. The coho salmon 



92 



