a percentage of the catch by weight. The catches 

 were dominated by alewife and chubs — over 

 95.O % — followed by smelt, yellow perch, and lake 

 trout. The other eight species listed according 

 to descending abundance made up less than 1.0% 

 of the total catch. 



The availability and vulnerability of alewife at 

 the time of this study probably accounted for 

 their dominance in the catches. Reigle (1969) 

 found that during the April to June period, ale- 

 wives were found at all depth zones and dom- 

 inated the zone when present. With the excep- 

 tion of chubs, test results showed that the dom- 

 inance pattern of all species did not change sig- 

 nificantly, whether using the standard trawl or 

 the electrictal trawl with power on or power off 

 for arrays 1 and 3. Chubs did, however, show 

 a significant increase in percent of total kilo- 

 grams caught with array 2. 



Length-Frequency Distribution. — The length-fre- 

 quency of the alewife, chubs, and yellow perch 

 with and without power are presented in Figures 

 3 through 11. Also presented with the figures 

 are the results of statistical evaluations of the 

 difference between two mean lengths. Overall, 

 when all length data for alewife are combined, 

 the mean length for power on drags was 

 165.7 mm compared with 163.1 mm for power 



120 130 140 150 160 170 180 190 200 210 



TOTAL FISH LENGTH (MM) 



Figure 3. — Alewife length-frequency distribution with 

 electrode array 1. Solid line, power on (N = 146; 

 mean = 170.2) ; dashed line, power off (N = 139; 

 mean = 166.7). z test for difference between the two 

 sample means at 0.05 level of probability: calculated 

 Z = 1.86, tabular Z = 1.96; not significant. 



80 90 100 110 120 130 140 150 160 170 160 190 200 210 220 230 

 TOTAL FISH LENGTH (MM) 



Figure 4. — Alewife length-frequency distribution with 

 electrode array 2. Solid line, power on (N = 77; 

 mean = 174.5) ; dashed line, power off (N = 77; 

 mean = 166.5). Z test for difference between the two 

 sample means at 0.05 level of probability: calculated 

 Z = 0.38, tabular Z — 1.96; not significant. 



120 130 140 I! 

 TOTAL FISH LENGTH (MM) 



60 190 200 210 220 



Figure 5. — Alewife length-frequency distribution with 

 electrode array 3. Solid line, power on (N = 144; 

 mean = 155.3); dashed line, power off (N = 128; 

 mean = 156.6) . Z test for difference between the two 

 sample means at 0.05 level of probability: calculated 

 Z = 189, tabular Z = 1.96; not significant. 



off drags, a 2.0% increase in mean length with 

 power on (Figure 6). Length selectivity be- 

 tween the arrays was not significantly different 

 (Figures 3 through 6). 



For chubs, the overall mean length for power 

 on drags was 250.7 mm compared with 245.7 mm 

 for power off drags, a 2.0% increase in mean 

 length with power on (Figure 10). Length se- 

 lectivity was only significant for fish taken with 

 arrays 1 and 2 with power on (Figures 7 and 8) . 



For yellow perch, the highest mean length of 

 195.9 mm was obtained with array 2 with power 

 on (Figure 11). This was 2.5% greater than 

 the mean length of 191.0 mm obtained with 

 power off. No length data was obtained for 



