VAN CLEVE and BEVAN: DECLINE OF KARLUK SALMON RUNS 



the weir in recent years. Moreover, Bell's fish 

 ladder was only tried on the eastern end of the 

 weir and the numbers of fry and small finger- 

 lings injured and blocked by the rest of the weir 

 were not studied. 



The blocking action of such a weir to fry is 

 confirmed by M. C. Bell (1972) who finds that the 

 maximum darting speed of small salmonids is 

 about equal to 1 ft/s per inch of length. This 

 speed can be maintained for only a few seconds. 

 The 28- to 72-mm fry and fingerlings observed 

 by Walker in the Karluk River would be able 

 to dart through maximum velocities of 1.1 ft/s 

 for the smaller fish to 1.9 ft/s for the small fin- 

 gerlings Walker found moving upstream in the 

 Karluk River between late July and September. 

 These velocities correspond to a drop in water 

 level of V4 to 1 V2 inches through the weir pickets 

 which are smaller drops than could be expected 

 when the weir is clean. Passage through the 

 weir would be impossible if only a few dead 

 spawned-out fish rested against the weir pickets. 



Predation has been a favorite explanation 

 for the decline of sockeye salmon runs. Rounse- 

 fell (1958: 142) discussed efforts to control pred- 

 ators in the Karluk system: 



At Karluk the destruction of predators was confined 

 to attempting to destroy large numbers of Dolly Varden 

 charrs by seining or trapping at the salmon-counting 

 weir during their annual downstream migration in May 

 and June. In the 21 years from 1922 to 1942 the annual 

 reports of the Alaska Division mention the destruction 

 of Dolly Vardens during 15 years. During the 9 years in 

 which the numbers destroyed are recorded they vary 

 from 3,000 to 81,500. The work was hampered by high 

 water and by the desire to avoid harming the down- 

 stream sockeye migrants. These migrants commence 

 their seaward migration soon after that of the Dolly 

 Vardens and there is considerable overlap. 



DeLacy and Morton (1943) have shown that many 

 Dolly Vardens are found in the tributaries of Karluk 

 Lake during the season when those that have migrated 

 downstream are at sea, so it is obvious that not all the 

 Dolly Vardens were subject to capture at the weir. 



Evaluation of the predacity of Dolly Varden 

 in the Karluk system led DeLacy (1941) and 

 DeLacy and Morton (1943) to the conclusion 

 that they are not a significant consumer of sock- 

 eye salmon fry or smolts. The relationship de- 

 scribed by Rounsefell and by Delacy and Mor- 

 ton is complicated by the pre.sence of two species 

 of char described by the latter two authors in 



Karluk Lake. The presence of the two sjDecies is 

 discussed in a later paper by McPhail (1961). 

 The arctic char are described as lake dwellers 

 while the Dolly Varden are anadromous. While 

 DeLacy and later DeLacy and Morton did not 

 find large numbers of sockeye salmon young in 

 the char stomachs they examined, they sampled 

 only at the weir, which was located then at the 

 lower end of the Karluk River, and in Karluk 

 Lake above its outlet. As in most studies of char 

 predation. this inve.stigation was carried out as 

 a personal effort by DeLacy and Morton in addi- 

 tion to their primary duties concerned with the 

 study of the sockeye salmon. It is not surprising 

 therefore that sampling of stomach contents in 

 their programs was designed to interfere as 

 little as possible with the sockeye salmon work 

 rather than to provide a complete picture of 

 the char feeding habits. 



Roos (1959) also indicated that Dolly Varden 

 are not serious predators of sockeye salmon in 

 the Chignik .system since he found only an aver- 

 age of 0.1 sockeye salmon per stomach in 5,050 

 Dolly Varden stomachs examined. However, he 

 did find that 31.1% of the Dolly Varden taken in 

 swift water below the outlet of Chignik Lake 

 were feeding on sockeye salmon. Moreover John 

 Rogers and John Wells in 1970 encountered a 

 school of Dolly Varden in the Black River above 

 Chignik Lake that were feeding on sockeye 

 salmon fry as they emerged from the gravel and 

 dropped out of the Chiaktuak Creek. Roos had 

 not sampled in that location. On the other hand 

 no char were seen at that .same location and 

 under comparable circumstances in 1971 (Rogers 

 and Wells, pers. comm., 1972). 



Large losses suffered by migrating sockeye 

 salmon smolts to Arctic char are reported by 

 Rogers (1972) in the Wood River system where 

 the char .school at the lower ends of each con- 

 necting river in the system and feed on the 

 smolts as they move downstream. A loss of at 

 least 4,000,000 smolts was estimated in 1971 

 in Lake Aleknagik alone and a total loss to char 

 of 27% of the total number of smolts ])roduced in 

 the Wood River system was estimated. 



The relationship found between Arctic char, 

 Dolly Varden, and sockeye salmon varies widely 

 in different locations and times of sampling. 

 Ricker (1941) found that Dollv Varden were 



643 



