binckspotted sticklebnrk ( Gastzer osteus w heat 1 a nd 1 ) from the threespine 

 stickleback (G. ac uleatus ) . Thus, the imi)lngenient percent specJes 

 composition of both species was based on samples collected since October 

 1981. The blackspotted stickleback was rarely found in trawls at MNPS, 

 while the threespine stickleback was occasionally found in trawls from 

 JC and NR (Tables 1 and 3). Sticklebacks were absent or infrequently 

 found in plankton and seine programs. Even though sticklebacks ranked 

 fifth in seines, they accounted for less than 1% of the total abundance 

 (Table 1). Of all impinged threespine stickleback, 90% occurred from 

 November through April. Blackspotted stickleback was present in 

 impingement samples during a much shorter season; over 90% occurred in 

 March and April (Table 4). The length frequency distributions of both 

 species taken from impingement samples were dominated by mature 

 individuals. The length distribution of blackspotted stickleback had a 

 narrow peak from 40-50 mm, while the distribution of threespine 

 stickleback, the larger of the two species, had a broader peak (50-60 

 mm) (Fig. 8). 



10 



15 



20 



^ 25 



g 30 

 3 35 



40 

 5 45 

 M 50 

 oj 55 

 ►J 60 



65 



70 



75 



Z3 



200 400 600 

 FREQUENCY 



800 



' I I' 



200 400 600 800 1000 



FREQUENCY 



Figure 8. Length frequency of G. wheatlandi (left) and G. aculeatus 



(right) in impingement collections from October 1981 through 

 September 1983. 



To describe changes in log-transformed abundance of sticklebacks, 

 harmonic regression models of weekly catch data from impingement 

 programs were developed. The two species were combined for constructing 

 these models. Impingement catch was described as a function of 



20 



