YELLOW PERCH IN SAGINAW BAY 



383 



Table 20. — Length-weight relation of Saginaw Bay yellow 

 perch in the different seasons of 1955 



(Number of fish in parenthesesi 



Table 21. — Length-weight relation of yellow perch popula- 

 tions in the different Great Lakes waters 



[Data adapted from publications as follows: Green Bav and Lake Michigan' 

 Hile and Jobes (1942); Lake Erie, Jobes (1952); Saginaw Bay in 1929-30, 

 Hile and Jobes (1941)] 



1 Based on samples of Apr. 18 and May 18. The June 7 sample was ex- 

 cluded because of the lack of records as to the state of gonads in some fish. 

 1 Ripe and spent males and spent females combined; no immature fish. 

 5 Mature fish, sexes combined. 



The differences in weight among the different 

 seasons were so slight that it is not possible to 

 speak of a seasonal trend. Nevertheless, some 

 differences could be detected. The males and 

 spent females of the spawning-run sample, for 

 example, usually were lighter than perch caught 

 June 22 and October 19, and ripe females had 

 a somewhat weaker tendency to be heavier than 

 fish caught later in the year. The fall fish (Octo- 

 ber 19) were a little heavier than the June 22 

 sample for lengths between 5.0 and 7.9 inches, 

 but for larger sizes (8.0 to 10.4 inches) yellow 

 perch tended to be heavier in summer. In his 

 study of the length-weight relation of Lake Erie 

 perch. Jobes (1952) found the fish to be lighter 

 in June than later in the season. He recorded 

 the following coefficients of conditions for differ- 

 ent months: June. 1.80: July. 1.97: August. 1.98: 

 September, 1.92; October, 1.87. No other studies 

 have been made of the seasonal trends of weight 

 in perch in the Great Lakes. 



Comparison with Length-Weight Relation in 1929-30 

 and with other Great Lakes Populations 



Data on the length-weight relation (table 21) 

 of the yellow perch from Green Bay, Lake Michi- 

 gan, Lake Erie, and Saginaw Bay (1929-30) are 

 from records published by Hile and Jobes (1941, 



1942) and Jobes (1952). The table was arranged 

 to facilitate the comparison of weights of fish 

 of the same length in the different Great Lakes 

 populations. The following length-weight equa- 

 tions from which weights were derived will 

 clearly show the different degrees of deviation 

 from the cube relationship between weight and 

 length. 



Lake Erie : 



W = 1.766 X 10- 5 Z 3 ° 15 

 Green Bay: 



W = 0.9319 X 10- 5 Z 3133 

 Lake Michigan: 



W = 5.8405 X 10- 5 Z 2 811 

 Saginaw Bay (1929-30) : 



W = 0.9826 X 10- 5 Z 3 im 

 In all the above equations W = weight in grams 

 and Z = standard length in millimeters. 



The length-weight relations (weights calcu- 

 lated from length-weight equations) of the dif- 

 ferent Great Lakes yellow-perch populations 

 (table 21) did not differ greatly. Most impor- 

 tant differences, perhaps, were in the values of 

 the exponent n which measures the ratio of the 

 instantaneous rates of increase in weight and 

 length. The value of n in the equation for Sagi- 

 naw Bay samples of 1943-55 (3.262) shows the 

 most rapid rate of increase in weight with in- 

 crease in length yet reported for a Great Lakes 

 stock of perch. Thus these Saginaw Bay perch, 

 though substantially lighter than Lake Michigan 

 fish at the shorter lengths, were able to overtake 



