FISHERY BULLETIN: VOL. 71, NO. 4 



mer inshore migrations of ninespine stickle- 

 backs in Crooked Lake, Ind. 



The shoal areas where sticklebacks concen- 

 trated in the summer were represented by 

 stations 2 and 3 (Figure 1). Station 2 included 

 a sandy beach, approximately 2 miles long, 

 at Presque Isle Bay, Stockton Island, which 

 gradually deepened and merged with the soft 

 bottom muds of the deeper areas. In summer 

 sticklebacks congregated in large numbers on 

 the beach in V2 to 2 fathoms of water. The 

 fish could easily be seen by eye and were 

 evenly distributed over the bottom throughout 

 the entire beach area. Station 3, along the 

 south shore of Oak Island, was characterized 

 by a sandy shelf about V4 mile wide parallel- 

 ing the shore which gradually deepened to 8 

 fathoms. The bottom then dropped steeply to 

 12 fathoms. This steep slope was covered with 

 a dense growth of Nitella sp. The summer con- 

 centration of sticklebacks occurred in this 

 vegetation. No fish could be seen over the 

 sandy shelf, and no fish were caught unless 

 the net was recovered with mats of Nitella sp. 

 clinging to it. 



Dryer (1966), Anderson and Smith (1971), and 

 field observations by the senior author of this 

 paper indicate that smelt, slimy sculpins, lake 

 trout under 28-cm TL, and trout-perch, Percop- 

 sis omiscomaycus (Walbaum), had food habits 

 similar to the stickleback and were apparently 

 abundant enough to be potential competitors 

 with the stickleback. Rank correlation coef- 

 ficients (rj were obtained between the aver- 

 age number of sticklebacks caught per 1-mile 

 trawl tow (CPE) and the CPE of these potential 

 competitors in 100 trout index tows. The CPE's 

 were ranked for each species, ties being 

 given the mean rank, and r^ values were deter- 

 mined by the formula presented by Snedecor 

 (1956). The 100 tows were randomly selected 

 from all (322) trout index tows made at stations 

 86, 75, 44, 24, and 12 from 1965 to 1968. The 

 significant relationships were those for juvenile 

 smelt, trout-perch, and slimy sculpins (Table 10). 

 Sticklebacks inhabited different areas than 

 juvenile smelt and trout-perch, and stickle- 

 backs and sculpins inhabited the same areas, 

 at least during spring and fall. The results of 

 the correlations do not preclude significant 



Table 10. — Rank correlation coefficients (is) between 

 stickleback CPE and CPE's of other species in 100 ran- 

 domly selected index trawl tows in the Apostle Islands, 

 1965-68. 



Species 



rs 



Juvenile lake trout to 1 1 inches 



Smelt adults 



Smelt juveniles 



Slimy sculpin 



Trout-perch 



-0.077 

 + 0.073 

 -0.461** 

 + 0.568** 

 -0.360** 



'Significant at 0.01 level (98 degrees of freedom). 



relationships at other times of the year or 

 other places, nor do they consider possible ef- 

 fects of differences in availability to the gear. 

 Further discussion of these correlations will be 

 presented in the section on food habits. 



RELATIVE ABUNDANCE 



Dryer (1966) reported that the ninespine 

 stickleback was the most abundant species in 

 578 Apostle Islands experimental trawl tows 

 from 1958 through 1963. The average CPE of 

 stickleback during this period was 51.8. Smelt 

 ranked second (CPE = 40.4), and slimy sculpin, 

 Cottus cog)iatus Richardson, were third (CPE 

 = 22.3). Lake trout CPE was 6.8. 



Over the 1965-68 period, 322 trout index 

 tows were made, and the relative rank of stickle- 

 backs, smelt, and slimy sculpins was unchanged 

 from the 1958-63 period (Table 11). The CPE's 

 were 61.1, 50.3, and 17.7, respectively. The catch 

 statistics of the two time periods show slight 

 increases for sticklebacks, smelt, and lake trout. 

 Further comparison is meaningless however, 

 because sampling allocations between index 

 stations used in the two time periods were 

 not identical, and extreme between-tow variation 

 was observed. Table 11 does not include data 

 from stations 2 and 3 because they were not 

 used by BCF as trout index trawl stations. 



To sample the shallow inshore area of station 

 2, where sticklebacks congregated in midsum- 

 mer, V4 mile tows were made with the small 

 outboard trawl. The wingspread opening of the 

 trawl was determined by measuring the width 

 of the trawl path on the bottom as indicated by 

 ground-rope disturbance immediately after the 



1048 



