stable), survival from the egg to age-group I is 

 determined as 0.011 percent. This estimate is 

 beset with many uncertainties. It assumes, for 

 example, that the determination of the number of 

 I-group individuals from the ratio of numbers of 

 fish in age-groups I and II in August-November 

 samples was accurate; that year-to-year differ- 

 ences of stock were small enough to justify the 

 pooling of data in the preparation of table 4; 

 that the samples that contributed to table 5 were 

 not unduly biased by gear selection or segregation 

 by size or sex. Even if we granted the survival 

 of 0.011 percent from egg to I-group a wide margin 

 of error, however, the extremely low value still 

 indicates an enormous mortality. 



The extraordinarily low survival of the gizzard 

 shad from eggs to the I-group fish probably results 

 from heavy egg and larval mortality, predation, 

 and (in late fall and early winter) buffeting 

 during storms as well as rapid variations in 

 water temperature. When they become the I- 

 group fish, they are usually too large to be eaten 

 by most predatory fish, but they are susceptible to 

 storms and temperature changes that are greatest 

 in waters relatively close to shore where this age 

 group is usually found. As the shad become older, 

 the survival rates improve, probably because the 

 fish tend to remain in the deeper waters where 

 they are less subjected to climatic disturbances. 



The oldest gizzard shad that I collected from 

 the western end of Lake Erie in 1952-55 were 

 three of age-group VI (seventh year of life). 

 Patriarche (1953) reported X-group gizzard shad 

 from Lake Wappapello, Mo. 



LENGTH-WEIGHT RELATION 



General Relation 



The mathematical relation between length and 

 weight of gizzard shad captured in western Lake 

 Erie in 1952-55 was determined by fitting the 

 equation W=cL n to the average empirical lengths 

 and weights of fish in each 10-mm. length interval. 

 The length-weight relation was investigated for 

 each month in which sufficiently large samples 

 were taken. Between mid- 1952 and mid- 1955 

 there were 25 such monthly samples. At least one 

 equation was determined for each of the 12 months 

 (for some months adequate samples were acquired 

 in each of the 2 or 3 years — hence, two or three 

 equations). For a month having more than one 

 equation, length and weight data were obtained by 



Table 5. — Survival of gizzard shad from one age group to 

 the next higher one 



[The figures in the first column, body of table, obtained from table 4) 



each equation, and from these an average monthly 

 length-weight relation was determined. In like 

 manner a "general" length-weight equation was 

 determined from the data calculated by the 

 monthly equations. The sexes were combined for 

 all monthly equations. The general equation was 

 log W= -4.81765 + 3.07053 log L, where IF is the 

 weight in grams and L is the standard length in 

 millimeters. 



1200 



50 100 150 200 250 300 350 



STANDARD LENGTH (MILLIMETERS) 



Figure 6. — Length-weight relation of gizzard shad in 

 western Lake Erie. The curve is a graph of the general 

 length-weight equation; the data represent the mean 

 empirical values, derived as explained in the text, for the 

 combined collections of 1952-55. 



400 



U.S. FISH AND WILDLIFE SERVICE 



