258 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



viduals of an age group did not differ in condition 

 from tlie shorter, slower-growing fish of the same 

 group. 



The conclusion concerning the independence of 

 growth rate and condition disagrees with Van 

 Oosten's (1937) observation that the slower-grow- 

 ing individuals of the Lake Superior longjaw 

 {Leucichthys zenithicus) were in the better condi- 

 tion. The same author (Van Oosten 1938) 

 found, however, that growth rate and condition 

 were not correlated in the Lake Erie sheepshead 

 (Aplodinotus (jrunniens) . 

 Effect of type of gear on determining value of K 



The study of condition in the preceding sections 

 was confined entirely to data from collections 

 taken by trap and pound nets. Gill-net samples 

 were excluded because of the effect of the selective 

 action of that gear on the determination of K. 

 The extent to which gill-net selection affects the 

 determination of the value of the coefficient of 

 condition may be seen from the data of table 35 

 which show the average K for each centimeter- 

 length interval of the Lake Erie yellow perch 

 taken from trap and gill nets in the same month 

 and calendar year. Only five series were available 

 for comparisons. The consistency with which the 

 value of K was greater for fish caught in gill nets 

 than in trap nets each month leaves little doubt 

 that gill nets capture relatively heavier yellow 

 perch than do impounding nets. In no single 

 month did yellow perch taken in trap nets have 



average coefficients of condition as great as thosp 

 of fish taken in gill nets. 



The unweighted averages given in the two 

 columns at the extreme right of table 35 give 

 further information on the general influence of the 

 type of net on the value of K. These averages 

 were computed only for those lengths that were 

 represented in the samples in all the months for 

 which comparisons are given. An examination 

 reveals that fish taken in gill nets had consistently 

 higher average values of K. The averages also 

 reveal a difference between gill- and trap-net 

 samples with respect to the variation of K with 

 length. Except for the relatively high figures at 

 141 to 150 mm. and 161 to 170 mm., the values of 

 K tended to be constant at all lengths in the trap- 

 net samples. The cause of the high values of K in 

 these shorter fish taken in impounding nets has 

 been discussed previously (p. 256). The nearly 

 constant value of K over the interval 171 to 220 

 mm. is proljably descriptive of true condition in 

 the population. In the gill-net samples, on the 

 contraiy, K decreased consistently with each 

 increase in length over the entire interval of 171 to 

 240 mm. In other words, the gill nets selected 

 the heavier short fish and the slenderer long fish. 

 At lengths below 171 mm. the captures of perch 

 by gill nets were probably in large measure 

 "accidents," that is, the fish were tangled in the 

 meshes by their fins or the marginal bones of the 

 mouth. The selective action of gill nets with 



Table 35. — Effect of type of gear on determination of the coefficient of condition (K) in Lake Erie yellow perch 



[Number of specimens in parentheses] 



' Unweighted mean, computed only for length intervals that were represented in all samples. 

 ' Unweighted mean. 



