SUMMARY 



Three lakes in the Kitoi Bay area of Alaska 

 were studied to determine how removal of 

 resident fish affects the production of sockeye 

 introduced after removal. Ruth Lake was 

 treated with rotenone in 1955; Little Kitoi 

 and Midarnn Lakes, untreated, served as con- 

 trol lakes. Little Kitoi and Midarm Lakes 

 contain populations of Dolly Varden, stickle- 

 backs, and sculpins; Little Kitoi Lake also 

 maintains populations of sockeye, coho, and 

 a few pink salmon. After Ruth Lake was 

 treated, sockeye fry were introduced in 1956 

 into Ruth and Midarm Lakes. Because of sub- 

 sequent limited availability of salmon fry, 

 Midarm Lake was not stocked again, Ruth 

 Lake was planted with sockeye fry each year 

 in 1956-60 and in 1963. 



Fresh-water survival of the fry introduced 

 into Ruth Lake was considerably greater than 

 the survival of fry in Midarm Lake and nnost 

 probably in Little Kitoi Lake. The survival 

 of the single brood year from fry to smolt 

 for Midarm Lake was 3.6 percent; the aver- 

 age for four brood years in Ruth Lake was 

 17.9 percent; and the estimated average for 

 Little Kitoi Lake was 9.7 percent. A 30- 

 percent egg-to-fry survival in Little Kitoi 

 Lake is assumed for comparisons between 

 Little Kitoi Lake and the other two. 



Survival and growth were considerably 

 greater in the treated lake. The optinnum 

 nunnber of snnolts was produced from a fry 

 stock of about 12,400 per surface hectare in 

 both Little Kitoi and Ruth Lakes. 



The average survival of fry to the smolt 

 stage in Ruth Lake was considerably higher 

 than survival of fry introduced into other 

 sockeye lakes that maintained populations of 

 predator and competing fishes. 



The length of time of fresh-water residence 

 of sockeye and the percentage survival appear 

 to be correlated negatively with density of 

 fry, although environmental conditions such 

 as temperature and ice cover probably exert 

 considerable influence during certain years. 

 Survival and growth of fry in both Ruth and 

 Little Kitoi Lakes were also affected by the 

 annount of recruitment; survival rates and 

 average lengths of smolts decreased with in- 

 creased fry density. Growth of sockeye fry 

 introduced into treated Ruth Lake was con- 

 siderably greater than growth of fry in un- 

 treated Midarm and Little Kitoi Lakes. The 

 average length of smolts for the 1955-59 

 brood years for Ruth Lake was 104 mm., but 

 for Little Kitoi Lake it was only 70 mm. The 

 average length of smolts for the single brood 

 year in Midarm Lake was 83 mm. From 

 limited plankton studies it appears that, prior 

 to treatment, Ruth Lake maintained plankton 

 populations of about the same magnitude as 

 did Little Kitoi Lake. Since treatment in 1955, 



the plankton population has increased more 

 than tenfold. Removal of resident fishes by 

 the treatment of Ruth Lake is held to be 

 responsible for the higher survival and growth 

 of introduced fry in this lake than of intro- 

 duced fry in Midarm Lake and of natural fry 

 in Little Kitoi Lake. 



ACKNOWLEDGMENTS 



The following members of the staff of 

 Alaska Department of Fish and Game took 

 part in planning the investigation and collect- 

 ing data: Richard C. Dugdale, Quentin A. 

 Edson, Ahron Gibor, Daniel L. Gittings, James 

 A. Gohr, Richard A. Marriott, Mark Meyer, 

 Robert R. Parker, William L. Sheridan, Wil- 

 liam A. Smoker, Robert E. Vincent, John 

 Winther, and Gil Ziemer. In addition, many 

 seasonal aids contributed to the collection of 

 data. 



LITERATURE CITED 



BARNABY, JOSEPH T. 



1944. Fluctuations in abundance of red 

 salmon, Oncorhynchus nerka (Walbaum), 

 of the Karluk River, Alaska. Fish 

 Wildl. Serv., Fish. Bull. 50: 237-295. 

 BRETT, J. R., and J. A. McCONNELL. 



1950. Lakelse Lake sockeye survival. J. 

 Fish. Res, Bd. Can. 8(2): 103-110. 

 CAPPS, STEPHEN R. 



1937. Kodiak and adjacent islands, Alaska. 



U.S. Geol. Surv.Bull.880-C,p, 111-184. 



FISHERIES RESEARCH BOARD OF CANADA. 



1956. Biological Station, Nanaimo, B.C. Its 

 Annu, Rep., 1955: 77-109. 



1957. Biological Station, Nanainno, B.C. Its 

 Annu. Rep., 1956-57: 81-110. 



1958. Biological Station, Nanaimo, B.C. Its 

 Annu. Rep., 1957-58: 87-114. 



FOERSTER, R. EARLE. 



1925. Studies in the ecology of the sockeye 

 salmon ( Oncorhynchus nerka) at Cultus 

 Lake, British Columbia. Contrib. Can. 

 Biol., NewSer. 2(16): 335-422. 



1934. An investigation of the life history and 

 propagation of the sockeye salmon 

 ( Oncorhynchus nerka) at Cultus Lake, 

 British Colunnbia. Contrib, Can. Biol., 

 New Ser. 8(27): 347-355. 



1936. The return from the sea of sockeye 

 salmon ( Oncorhynchus nerka ) with spe- 

 cial reference to percentage survival, 

 sex proportions and progress of migra- 

 tion. J. Fish. Res. Bd. Can. 3(1): 26-42. 



1938a. An investigation of the relative effi- 

 ciencies of natural and artificial propa- 

 gation of sockeye salmon ( Oncorhynchus 

 nerka ) at Cultus Lake, British Colum- 

 bia. J. Fish. Res. Bd. Can. 4(3): 151- 

 161. 



17 



