DISTRIBUTION, FOOD, AND FEEDING OF THE THREESPINE 



STICKLEBACK, GASTEROSTEUS ACULEATUS, IN GREAT 



CENTRAL LAKE, VANCOUVER ISLAND, WITH COMMENTS ON 



COMPETITION FOR FOOD WITH JUVENILE SOCKEYE SALMON, 



ONCORHYNCHUS NERKA 



J. I. Manzer' 



ABSTRACT 



The distribution, relative abundance, and food of the threespine stickleback, Gasterosteus aculeatus, 

 was studied in Great Central Lake on Vancouver Island, B.C., in 1970 and 1971 as part of a 

 multidisciplinary study on the production of sockeye salmon, Oncorhynchus nerka, following controlled 

 additions of inorganic nutrients (1970-73 inclusive) to an oligotrophic sockeye nursery lake. Stickleback 

 appeared along shore in relatively low numbers prior to mid-April and most were between 30 and 59 mm 

 long. Following spawning in June and July, initially stickleback were smaller, but as fish of the year 

 became more available, both the number and average size of stickleback increased. They were absent in 

 the littoral zone by November, but their presence in the pelagic zone in winter could not be established. 

 Over the diel cycle the larger individuals apparently move offshore during the day. The populations in 

 the 2 yr did not differ greatly in size. 



In each of the 2 yr stickleback had a wide but similar diet. They predominantly fed on two cladocerans 

 (Holopediuni gibberum, Bosmina coregoni), two copepods (Epischura nevadensis, Diaptomus 

 oregonensis), and a cyclopoid copepod {Cyclops bicuspidatuf:). Larvae and pupae of the family 

 Chironomidae were also of some importance. Other food items, but of minor importance, included 

 harpacticoid copepods, insects, pelecypods, ostracods, acarids, Araneida, planaria, Odonata, and fish. 

 Variations in diet in relation to season, size and sexual maturity of stickleback, and time of day were 

 observed. The daily ration for stickleback was estimated to be 6.55% of their body weight in July and 

 7.80% in October. 



Stickleback and juvenile sockeye salmon in the littoral zone exhibited considerable dietary overlap, 

 especially during the late spring and summer. However, since sockeye salmon in this zone are relatively 

 few in number, and stickleback do not inhabit the limnetic zone, serious interspecific competition for 

 food in the lake is probably lacking, especially in years of abundant food supply. 



Along the Pacific coast of North America, three- 

 spine stickleback, Gasterosteus aculeatus, here- 

 after referred to as stickleback, occur in many 

 coastal lakes, rivers, and streams ranging from 

 western Alaska to lower California (McPhail and 

 Lindsey 1970). In British Columbia and Alaska, 

 large populations have been reported in some 

 nursery lakes of young sockeye salmon, Onco- 

 rhynchus nerka (Greenbank and Nelson 1959; 

 Ruggles 1965). Separate studies on the food of 

 young sockeye salmon (Ricker 1937; Narver 1970; 

 Barraclough and Robinson 1972) and stickleback 

 (Greenbank and Nelson 1959) in British Columbia 

 and Alaska lakes have generally shown that both 

 species feed mainly on planktonic crustaceans and 

 insects. Rogers (1968) compared the food of both 



'Pacific Biological Station, Department of the Environment, 

 Nanaimo, B.C.. Canada V9R 5K6. 



Manuscript accepted January 1976. 

 FISHERY BULLETIN: VOL. 74, NO. 3, 1976. 



species residing in the same lake in Alaska and, 

 after finding a great similarity in diet, concluded 

 that potential interspecific competition for food 

 exists. Krogius and Krokhin (1956) and Ruggles 

 (1965) studied production of young sockeye salmon 

 in different lakes where the two species were 

 present and observed that sockeye salmon 

 production was inversely related to stickleback 

 abundance. 



In 1969, the Pacific Biological Station of 

 the Department of the Environment, Canada, 

 started a multidisciplinary investigation to deter- 

 mine if the production of juvenile sockeye salmon 

 in Great Central Lake on Vancouver Island, B.C., 

 (Figure 1) would be increased by controlled addi- 

 tions of inorganic nutrients. Approximately 100 

 tons of inorganic nutrients were added from late 

 spring through summer for 4 yr beginning in 1970, 

 usually in 5-ton weekly lots with the ultimate 



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