MANZER: DISTRIBUTION AND FOOD OF STICKLEBACK 



80 



60 



40- 



20 



X 



80 



60- 



40- 



20 



OCTOBER 1970 



(12) 



-MAXIMUM LENGTH 



- +2 S.E OF MEAN 

 -MEAN LENGTH 



-2 S.E OF MEAN 



- MINIMUM LENGTH 

 (251- SAMPLE SIZE 



(25) 



(22) 



I 1 1 1 1 1 1 r- 



JULY 1971 



n r'(25) 



n(l6) , 



(22) 



(19) 



0700 



1300 1900 



HOUR 



0100 



Figure 3.-Diel changes in the length of threespine stickleback 

 as indicated by paired catches at station 1, October 1970 and July 

 1971. Open bars = length range; solid bars = ±2 SE of mean; 

 dash = mean length. Site A = left bar, site B = right bar. 



the catches in the 2 yr averaged out, the mean 

 catch for surveys in 1971 was consistently higher 

 than that for the same period in 1970. The dif- 

 ference between yearly mean catches was only 

 20%, suggesting that the stickleback populations 

 in the 2 yr were approximately similar in size. 



Discussion 



Seasonal changes in abundance and distribution 

 have been described for several lake populations of 

 threespine stickleback. Greenbank and Nelson 

 (1959), on the basis of beach seine catches, reported 

 that in Bare and Karluk lakes, Alaska, from late 

 May into September stickleback in varying 

 numbers essentially inhabited shallow waters. A 

 few were sighted on the surface of Karluk Lake at 

 a considerable distance from shore, and some were 

 caught by fyke nets at depths of 30 and 80 feet 

 (approximately 9 and 25 m) but not in sets at 126 or 

 200 feet (approximately 39 and 61 m). Ruggles 

 (1965), while studying juvenile sockeye salmon in 

 Lake Owikeno, B.C., observed that during April to 



October, stickleback were most abundant in areas 

 suitable for spawning and were taken in two 

 netting operations in midlake surface waters in 

 considerable numbers. Stickleback fry were 

 caught throughout the spring to fall seasons but 

 largest catches were made in the spring. In some 

 years, a secondary increase in abundance occurred 

 in the fall. In Lake Aleknagik, Alaska, Rogers et 

 al. (1963), and Rogers (1968) using beach seines, 

 trawls, and tow nets, observed stickleback in the 

 spring and early summer to inhabit mainly the 

 littoral area. By midsummer, fish of age I and II 

 became pelagic while age and III tended to 

 remain inshore. Observations on stickleback dis- 

 tribution, movement, or numbers during the late 

 fall and winter are lacking for these lakes, pre- 

 sumably because of ice cover. Markovtsev (1972), 

 however, in Lake Dalnee from January through 

 August observed that stickleback are present over 

 winter in the pelagic zone and the population 

 started moving from the pelagic to the littoral 

 zone about May and resumed pelagic residence in 

 the summer. 



The seasonal occurrence of threespine stick- 

 leback in Great Central Lake is generally similar 

 to those described for other lake populations along 

 the Pacific coast, but their distribution during 

 summer appears to be somewhat diff"erent. In 

 other lakes, beginning in midsummer, some stick- 

 leback leave the littoral area to inhabit pelagic 

 waters; those in Great Central Lake remain rela- 

 tively close to or along the shore throughout lake 

 residence. The reason for this apparent difference 

 in distribution patterns is not known although it 

 seems unlikely that it is the result of diff'erent 

 fishing gears and methods employed by various 

 investigators. The distribution patterns in the 

 different lakes may be related to lake bathymetry. 

 By camparison with other lakes studied Great 

 Central Lake has relatively little littoral area. 

 Expanses of water exceeding 25 m or more in 

 depth only a few meters from shore are common. 

 This bathymetric feature may provide stickleback 

 with a food supply close to shore thus making it 

 unnecessary for them to move into offshore feed- 

 ing areas. 



The virtual absence of stickleback in the pelagic 

 zone in Great Central Lake does not conflict with 

 the documented onshore-offshore movements of 

 larger individuals during midsummer and fall. 

 Offshore movement during the day and corre- 

 sponding onshore movements at night were 

 reported for marine threespine stickleback in the 



653 



