FISHERY BULLETIN: VOL. 74, NO. 3 



Figure l.-Map of Great Central Lake, British Columbia, 

 showing the location of beach seining (numbers) and mid-water 

 trawling (lines) stations. 



purpose of increasing the food resource for young 

 sockeye salmon without significantly altering 

 water quality. Preliminary results for 1970 when 

 compared with 1969 (untreated year), indicate 

 that primary production was increased without 

 substantially changing the nature of the food 

 chain (Parsons et al. 1970; Parsons et al. 1972). 

 Zooplankton standing stock from May through 

 October was approximately 10 times higher (Le- 

 Brasseur and Kennedy 1972). Young sockeye 

 salmon generally consumed the important zoo- 

 plankters in the lake and underyearling sockeye 

 salmon were 30% heavier in weight (Barraclough 

 and Robinson 1972). Considering the results of 

 earlier studies by other investigators on the food 

 of young sockeye salmon and stickleback, and the 

 uncertainty of the response of the stickleback 

 population to lake enrichment, a study on the 

 biology of stickleback with special emphasis on 

 diet and feeding habits was carried out in 1970 and 

 1971 as part of the overall fertilization experiment 

 in Great Central Lake. This paper reports on the 

 results of studies on distribution, relative abun- 

 dance, and food and feeding of stickleback, and in 

 addition contains comments on stickleback as a 

 competitor of juvenile sockeye salmon for the food 

 resource in the lake. 



DESCRIPTION OF GREAT 

 CENTRAL LAKE 



Great Central Lake is an ultra-oligotrophic lake 

 situated in the central part of Vancouver Island, 

 B.C. The lake is approximately 34 km (21 miles) 

 long, varies between 1 and 2.5 km (0.6 and 1.5 

 miles) in width, and has a surface area of 5,100 

 hectares. The maximum depth is approximately 

 250 m (800 feet). The shoreline varies from gentle 

 sloping beaches to rocky, precipitous ledges. The 

 littoral area in comparison to lake perimeter is 



relatively small and depths of 25 m or more only a 

 few meters from shore are common. Beach cover 

 ranges from small pebbles to rocks and boulders. 

 Water inflow is by two major streams at the west 

 end and several minor streams around the lake, as 

 well as by snow melt in the spring months. The 

 lake is drained at its east end by the Stamp River, 

 which flows approximately 30 km before emptying 

 into the sea at the head of Alberni Inlet. Surface 

 water temperatures in the lake ranged from 4° to 

 21°C in 1970 and from 4° to 24°C in 1971. Minimal 

 temperatures occur in February; maximal tem- 

 peratures in late July. In general warm-up is 

 slower in the western end, but once maximum 

 temperatures are reached in July, surface water 

 cools off at approximately the same rate. In some 

 winters, the lake is ice-covered for varying periods 

 of time, more often at the western end. 



The fish community consists of at least eight 

 species. Young sockeye salmon are by far the most 

 abundant, followed by stickleback. Other species 

 caught in considerably fewer numbers are juvenile 

 coho salmon, 0. kisutch; cutthroat trout, Salmo 

 clarki; rainbow trout, 5. gairdneri: Dolly Varden, 

 Salvelinus malma; prickly sculpin, Cottus asper; 

 pumpkinseed, Lepomis gibbosus; and river lam- 

 prey, Lampetra ayresi. 



TAXONOMY 



Two morphologically different forms of G. 

 aculeatus occur along the Pacific coast of North 

 America: a heavily plated form, trachurus, that is 

 usually marine, and a partially plated freshwater 

 form, leiurus. McPhail and Lindsey (1970) provid- 

 ed nomenclatural and taxonomic details regarding 

 the G. aculeatus complex. Recent studies on 

 isolated freshwater populations indicate consider- 

 able geographic variation with the result that 

 their taxonomic status is of considerable uncer- 

 tainty and interest (Hagen 1967; Narver 1969; 

 Miller and Hubbs 1969; Hagen and McPhail 1970; 

 Hagen and Gilbertson 1972). Hagen and Gilbert- 

 son (1972) consider that at least three plate morphs 

 are present in permanent freshwater populations 

 of Gasterosteus, namely low plated (3-7), partially 

 plated (8-29), and fully plated (30-35). 



The stickleback morph in Great Central Lake 

 was identified from samples collected prior to the 

 spawning season at four stations (3, 5, 13, and 14, 

 see Figure 1) located along the length of the lake. 

 The individual samples contained from 14 to 20 



648 



