GENERAL DISTRIBUTION AND ABUNDANCE 

 OF ALL FISH SPECIES 



Although the principal subject of this study was 

 juvenile sockeye salmon, data were collected on all 

 species of fish encountered because of probable in- 

 teractions among the species. Earlier work (Johnson, 

 1956) had indicated that juvenile sockeye salmon were 

 readily available to tow nets in summer in the pelagic 

 portion of the freshwater rearing areas and our effort 

 was concentrated on this gear and habitat. We sam- 

 pled with other gear in other habitats, however, to 

 learn more of the biology of all the species present. 



The greatest effort with all types of gear was in 1962; 

 the results for that year are summarized in Table 3 to 

 give a general picture of the distribution and relative 

 abundance of all species. The table shows the percent 

 frequency of occurrence of each species in collections 

 made with each type of gear and its contribution to the 

 total catch as percent of the total number of fish cap- 

 tured by each gear in each lake. The data are known to 

 be biased in at least three ways: (1) most of the sam- 

 pling was done from 15 July to 1 September, and 

 marked seasonal changes in distribution are known to 

 occur for many species; (2) each type of gear has its 

 peculiar abilities to catch the various species; and (3) 

 the distribution of fishing effort varied between areas 

 in regard to type of gear, amount of effort, and season. 

 Because of these biases, detailed discussion of the dis- 

 tribution of all species is not warranted and the abun- 

 dance in relation to juvenile sockeye salmon will be 

 treated in detail only for those species consistently and 

 abundantly captured in the pelagic areas in tow nets — 

 threesprine and ninespine sticklebacks and pond 

 smelt. 



Five species offish were clearly predominant in the 

 collections — sockeye salmon, threespine and nine- 

 spine sticklebacks, pygmy whitefish, and pond smelt 

 (Table 3). The most widely distributed and, in general, 

 the most abundant species was the sockeye salmon. 

 Juvenile sockeye salmon were taken with all appropri- 

 ate gear and in all major lakes of the system. The 

 distribution of threespine and ninespine sticklebacks 

 approximated that of the sockeye salmon and in a few 

 areas the sticklebacks were more abundant than 

 juvenile salmon (e.g.. West End and Northwest 

 Basin). The other two species that occurred abun- 

 dantly in some collections, pygmy whitefish and pond 

 smelt, were each abundant in some basins, but were 

 never abundant together. The pond smelt was abun- 

 dant only in tow net catches in Coville Lake and the 

 pygmy whitefish only in trawl and seine catches in 

 Brooks Lake and parts of South Bay. 



None of the many other species were ever abundant 

 in the collections. Some, such as the coho salmon 

 (most gear) and the Arctic lamprey (tow nets and fyke 

 nets), were collected in many locations, whereas 

 others, such as the burbot and least cisco, were col- 

 lected in only a few locations. Local concentrations of 



some predators coincide in time and place with migra- 

 tions of juvenile sockeye salmon, for instance the lake 

 trout and Arctic char at the outlet of Coville Lake and 

 Arctic char and northern pike in parts of Grosvenor 

 River. Intensive study of each species is needed to 

 determine its abundance and role in the ecology of the 

 system. 



ABUNDANCE OF JUVENILE 

 SOCKEYE SALMON 



The tow netting to determine abundance of juvenile 

 sockeye salmon was largely exploratory in 1961 when 

 some areas and depths were sampled frequently and 

 others not at all. From 1962 to 1964, however, the 

 sampling was done systematically by season, area, and 

 depth. 



Although it has never been firmly established, the 

 assumption that changes in the abundance of juvenile 

 sockeye salmon in tow net catches reflect actual 

 changes in their abundance has proved to be a work- 

 able hypothesis. The work of Pella ( 1968), who used a 

 recording echo sounder in conjunction with tow net- 

 ting, showed that tow netting is at least a good index of 

 relative abundance of sockeye salmon in the area 

 being sampled. The validity of tow net sampling for 

 measuring the abundance of juvenile sockeye salmon 

 was further substantiated in the present study: catches 

 declined in the lake from which fish were migrating 

 (Coville Lake) and increased in the lake to which they 

 migrated (Iliuk Arm). 



Assessment of the abundance of fish in the pelagic 

 areas of the lakes is based on tow net data from sam- 

 pling mainly at night. Night sampling with tow nets 

 proved to be successful in western Alaska (Burgner et 

 al., 1969), although workers in British Columbia found 

 it best to sample with tow nets only during the transi- 

 tional period from dusk to darkness (Johnson, 1956; 

 Ruggles, 1966). Echograms and the results of concur- 

 rent tow netting by Pella (1968) in a lake in western 

 Alaska demonstrate that juvenile sockeye salmon re- 

 main dispersed at night near the surface in pelagic 

 areas of lakes. I found no consistent differences in the 

 rate of catch of juvenile sockeye salmon in tow nets 

 during different parts of the night in the Naknek sys- 

 tem. Some of the tow net data from Iliuk Arm were 

 collected in daylight because the water was so opaque 

 that sampling was apparently as effective in daylight as 

 in darkness. 



The average catch per tow for four tows — two sur- 

 face and two deep — was used as the standard unit of 

 measure of abundance. The relative abundance in the 

 two depths frequently varied between lakes within a 

 year and between years within a lake. When unequal 

 numbers of tows were made at the two depths, the 

 averages for the two depths were averaged to give 

 equal significance to each depth. The only exception 

 to the use of this standard was for sampling in area 

 N-l, which was too shallow for deep tows. 



In 1964 to compare the fishing capabilities of the two 



