MANZER: DISTRIBUTION AND FOOD OF STICKLEBACK 



stickleback. The length of the stickleback in the 

 combined samples ranged from 45 to 79 mm. 

 Lateral plates along the left side and caudal keel 

 were counted, using a probe and binocular micro- 

 scope. Since all individuals in the samples exceeded 

 30 mm in length, plate formation was considered 

 complete (Hagen and Gilbertson 1972). Analysis of 

 variance revealed no significant difference in plate 

 counts between stations (F = 3.15; df = 3, 66; 

 P>0.05). The mean plate count for the combined 

 samples was 25.17. Considering plate counts, it can 

 be concluded that the stickleback population in 

 Great Central Lake is a freshwater population 

 more representative of the trachiiriis than the 

 leiuru>i form. 



Descriptid)! 



Gentle slope, gravel bottom 

 Gentle slope, rocks and boulders 

 Rock slope, sharp dropoff 



Station 



1, 4, 5, 9, 10, 14 

 6, 12, 15, 16, 17. 18 

 2,3, 7. 8, II, 13, 19 



Information on the winter distribution of stick- 

 leback was obtained from purse seining operations 

 carried out on 18 February and from mid-water 

 trawling on 23 and 24 March in the pelagic zone, 

 using a mid-water trawl routinely employed to 

 catch age-0 sockeye salmon in the lake (Barra- 

 clough and Robinson 1972). Ice cover restricted 

 fishing to the eastern one-half of the lake. 



Results 



DISTRIBUTION AND 

 RELATIVE ABUNDANCE 



Methods 



Distribution and estimates of relative abun- 

 dance of stickleback were determined from 

 catches made with a purse seine used as such in 

 mid-lake waters or as a beach seine along the 

 shoreline, in 1970 and 1971. A description of the 

 gear and its operation as a beach seine was 

 provided by Manzer (1971). The net sampled an 

 area between 450 and 550 m-, or approximately 10 

 m of shoreline. 



The field program in 1970 was carried out over 

 eight surveys between 22 April and 27 November. 

 Some purse seining and sighting were carried out 

 in the early season but most eff'ort was devoted to 

 beach seining along shore. Here 18 different loca- 

 tions representing typical but different shoreline 

 habitats were fished between 0830 and 1730 h 

 (Pacific daylight time). Eleven of these stations 

 were established as key stations. Coverage was 

 more complete between late June and late August 

 when surveys were conducted at 2-wk intervals. 

 The fishing program in 1971 was essentially the 

 same as in 1970. Five secondary stations sampled 

 in 1970 were deleted and one new station was 

 added to provide better coverage of the lake. 

 Seven surveys were carried out between 18 Feb- 

 ruary and 30 November, approximately at month- 

 ly intervals beginning in May. Fishing was con- 

 ducted between 0630 and 1830 h. No fishing was 

 done in September in either 1970 or 1971. The 

 beach seining stations are shown in Figure 1 and 

 grouped by character below, the stations in bold- 

 face being key stations. 



Sighting surveys, purse seining, and beach 

 seining were conducted in the eastern part of the 

 lake in April and June 1970. The purpose of these 

 operations was to determine the distribution of 

 stickleback in proximity to the shoreline. It was 

 considered that the results of these operations 

 would be applicable to the lake as a whole. Stick- 

 leback were readily observed in varying numbers 

 close to shore apparently moving at random and 

 feeding in waters from less than 1 foot (0.3 m) to 

 several feet (ca. 2 m) deep. They were rarely seen in 

 offshore waters. This general pattern of distribu- 

 tion was confirmed by purse seine and beach seine 

 catches. Eight "blind" (i.e., uncorroborated by 

 sightings) purse seine sets in the limnetic zone 

 yielded three stickleback. The net was considered 

 effective to a depth of 3-4 m. In contrast, 16 beach 

 seine sets at shore areas ranging from shallow 

 beaches to precipitous slopes yielded stickleback 

 on all but three occasions. As many as 350 stick- 

 leback were caught in a single set. Their virtual 

 absence in offshore waters was indicated by the 

 results of townetting for young sockeye salmon in 

 the lake. A total of 480 tows made during 1969-73 

 in the limnetic zone of the lake at various depths 

 (0-60 m) with trawl nets with mouth openings of 

 approximately 18 m- and 4 m- yielded 21 stickle- 

 back (D.G. Robinson pers. commun.). From the.se 

 operations it is concluded that stickleback were 

 primarily concentrated close to shore. 



Catches of stickleback by beach seining opera- 

 tions are given in Table 1 by survey and location. 

 Catches in each year ranged from zero or a few fish 

 to estimates of 2,500. In 1970, 105 sets were made 

 and 10,727 stickleback were caught. Twenty-one 

 sets failed to catch stickleback. In 1971, 89 sets 

 were made and 10,806 stickleback were caught. Of 



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