YELLOW PERCH OF LAKE ERIE 



221 



mining the length of fish with a girth equal to the 

 circumference of the largest meshes found in the 

 lifting pot of the nets. Since the largest meshes of 

 the impounding nets from which the yellow-perch 

 samples were taken were approximately 2}: inches 

 (stretched measm-e), no fish with a girth in excess 

 of about 5 inches should be expected to escape from 

 the net. Forty-two perch with an average girth of 

 5 inches (range, 4.72 to 5.28 inches) had an average 

 total length of 7.9 inches. 



Examination of the length-frequency distribu- 

 tions of the age groups (table 19) shows that only 

 the larger of group I were retained because they 

 were too large to escape. About one-fourth of the 

 yellow perch in age group II were as short as the 

 theoretical maximum size of escape; only a few of 

 the group-Ill fish and none in age groups IV and V 

 were shorter than 7.9 inches. 



It is not possible to make precise estimates of the 

 extent to which the reliability of the samples of the 

 different age groups was affected by the selective 

 action of the gear. However, group-I samples were 

 unquestionably composed of individuals with the 

 most rapid growth. Group-II samples were 

 affected much less severely. Beyond age group II, 

 gear selection probably had no significant effect on 

 the reliability of the samples. It may be concluded, 

 then, that inadequate sampling traceable to gear 

 selectivity was an important factor in the dis- 

 crepancies between the lengths calculated from 

 group-I yellow perch and from older fish, and was 

 a contributing factor in discrepancies between the 

 lengths calculated from group II and from older 

 fish. Discrepancies among age groups older than 

 group II cannot be attributed to the selective 

 action of the nets. 



The selective action of the impounding nets 

 serves also as the basis for the differential destruc- 

 tion, correlated with growth rate, that brings about 

 an exaggeration of the discrepancies between the 

 calculated growth histories of yellow perch of 

 different ages. Capture in a commercial net ex- 

 poses illegal-sized perch * to a serious risk of de- 

 struction in the fishery since a significant propor- 

 tion ° of the undersized yellow perch are dead when 

 the nets are lifted. With a fishery as intensive as 



' Since the legal siie for yellow perch (8H inches total length) Is well above 

 the marimum length of escape, the question of differential destruction de- 

 pendent on gear selectivity concerns only the undersized flsh. 



' Dr. John Van Ooston, U. S. Fish and Wildlife Service, found that approxi- 

 mately 14 percent of the undersized yellow perch were dead in Lake Erie trap 

 nets at the time of lifting. 



that in Lake Erie a single individual may be ex- 

 posed to destruction repeatedly. Consequently, 

 a severe mortality of the faster-growing yellow 

 perch of the younger age groups, especiallj' age 

 group I, is certain to occur. It appears, then, that 

 perch of the same year class captured at older ages 

 show relatively slow growth not only because the 

 samples of the younger age groups were composed 

 of the faster-growing fish but also because some of 

 these same fast growers were eliminated from the 

 stock as young fish. 



SEGREGATION CORRELATED WITH SEXUAL 

 MATURITY 



Any segregation of the yellow-perch population 

 according to maturity would be in effect a segre- 

 gation according to size also, since the proportion 

 of mature individuals increased rapidly mth in- 

 crease La length (table 36), and it was the larger 

 fish in the j'ounger age groups that were mature. 

 It will be shown later that the only evidence of a 

 segregation of yellow perch according to maturity 

 was found during the spawTiing season when the 

 samples consisted almost entirely of mature fish — 

 97 percent of the yellow perch in samples taken 

 April 11 and 13, 1932, were mature. 



A comparison of the percentage of mature radi- 

 viduals at different lengths (table 36) with the 

 length-frequency distribution of the age groups 

 (table 19) provides an indication of the extent to 

 which segregation on the basis of maturity may 

 affect the samples of each age. It is seen in table 

 36 that a majority of the males reached maturity 

 at 6)2 inches but that most of the females were not 

 mature until thej' had passed 8)2 inches. It is 

 apparent from table 19 that of the males only 

 group I would be affected by a segregation on the 

 basis of maturity. Such segregation, however, 

 would practically eliminate the group-I females, 

 seriously affect those in age group II, and to a 

 lesser degree disturb age group III. Because the 

 data in tables 19 and 36 were largely from fish 

 taken in the fall, the remarks concerning each age 

 group may be expected to apply equally well to the 

 next-older group in the next spawning season, 

 since little if any intervening growth would occur. 

 Thus, in the spawning season a segregation on the 

 basis of sexual maturity would affect some of the 

 males and practically all of the females in group II, 

 a few of the males and many of the females in group 

 III, and almost none of the fish in group 1\ and 



