Comparative catches and food habits of dolly varden and arctic charrs, Salvelinus malma and S. alpinus, at Karluk, Alaska, in 1939–1941

Synopsis

For many years the seriousness of the predations of dolly varden (Salvelinus malma) upon the eggs, alevins and juveniles of Pacific salmons (Oncorhynchus) has been a controversial subject. Over $ 300,000 was spent in Western Alaska from 1920 to 1941 for bounties on dolly varden in the belief that they were serious salmon predators. The writter undertook this study because of an intense desire to evaluate the need and justification for such a bounty system. The incidental examination of stomach contents of charrs which were captured for tagging or for tag recovery purposes from Karluk Lake and Karluk River on Kodiak Island, Alaska, and from Shelikof Strait and Uyak Bay during the summer months of 1939, 1940 and 1941 presented an excellent opportunity to pursue such a project. Stomachs were collected and contents analyzed from 1,992 arctic charr (Salvelinus alpinus) and 2,565 dolly varden charr (Salvelinus malma), taken by beach seine, gill net, fyke net, hook and line and by weir trap from Karluk Lake; from 956 dolly varden taken by seine and weir trap from the Karluk River; and from 462 dolly varden taken by beach seine and commercial salmon traps in Uyak Bay. Among the more than 5,000 charr stomachs examined, only 42 were found to contain salmon smolts, parr or alevin. Examination of 500 stomachs taken from dolly varden charr captured in the lower Karluk River at the height of the red salmon (Oncorhynchus nerka) smolt migration in May of 1939 revealed very little evidence of predation on the smolts in fresh water. There was some evidence that this relationship may have changed after the migrating charr had become adjusted to salt water, although the examination of 460 stomachs of dolly varden captured in salt water revealed nothing particularly incriminating in its role as a salmon predator. The fact that the downstream migration of the dolly varden reached its peak before that of the red salmon smolts was considered significant. Examination of the 4,500 charr stomachs at Karluk Lake in the months from April through September led to the discovery that two distinct species of charrs were present, one, the dolly varden, primarily stream-inhabiting and anadromous, and the other, the arctic charr, primarily lake-inhabiting and nonanadromous. Although red salmon eggs constituted 32% of the total volume of food ingested by both species of charr at Karluk Lake, there was considerable evidence that they were consumed in salvage or scavenger feeding, and there was practically no evidence that they were consumed as a result of predatory feeding. Only five, or one-tenth of one percent, of the thousands of charr stomachs examined at Karluk Lake contained red salmon parr or alevin.

A summary of the contrasts in the feeding and migratory habits and physical characteristics of Salvelinus malma and Salvelinus alpinus led to the conclusion that alpinus was a more serious potential salmon predator than malma at Karluk Lake. In view of the fact that alpinus was seldom reached by the predator-control program whereas malma was being systematically destroyed only because it was more easily captured due to its migratory tendencies, it was recommended that the predator control program be terminated in Karluk waters.