I9S9 1956 t 01 UER 



Two distinct size groups contributed to catches of croaker in July 

 1961. Individuals in the smaller group were 9. 5 to 16.0 cm. long, with the 

 mode occurring at about 13. 5 cm. They increased in average size through- 

 out the summer and by October were 12.0 to 18. cm. long (mode at 16. 



cm. ). Associated data on sexual maturity 

 showed a preponderance of ripe fish in 4 to 

 17 fathoms between Sand Island Lighthouse, 

 Ala. , and Chandeleur Island Lighthouse, La. , 

 during September -November. Assuming 

 this to be the principal spawning period 

 and drawing also from earlier life history 

 studies conducted in Texas and Louisiana 

 estuaries, it is postulated that the l6-cm, 

 modal group present in October 1961 was 

 the result of spawning in the fall of 1959, 

 and therefore may be identified as the 

 1959 year class. Modal positions for this 

 year class remained relatively constant 

 from January through May, varying only 

 slightly between 16. 5 and 17. 5 cm. Dur- 

 ing this period it was the most important 

 year class contributing to the industrial 

 bottomfish fishery. 



The larger size group evident in 

 July contained individuals ranging from 16. 5 

 to 20. 5 cm. with the mode at 18. cm. These 

 grew at such a rate that by October they 

 ranged in length from 18.0 to 22. cm. , with 

 the mode at 19.0 cna. This group, which in- 

 cluded fish from the 1958 as well as earlier 

 year classes, gradually decreased in density, 

 exhibited little apparent growth, and was 

 characterized in May by a mode of 20. cm. 



In January 1962, a subdominant 

 group of smaller fish with a nnodal length of 

 12. 5 cnn. entered the fishery and is assumed to have been a migrating (estuary 

 to Gulf) as well as faster growing (and hence "selected") segment of the I960 

 year class. 



The 8-cm. modal group appearing in May 1962, can be attributed to 

 the fall spawning in 1961, and henceforth identified as the 1961 year class. 



Assuming that the major modes of the croaker's length frequency 

 distribution indicated successive age groups, it is tentatively concluded that 

 insofar as the croaker is concerned, the industrial bottomfish fishery of the 

 northeastern Gulf depends largely on 1 - and 2-year-old fish. 



5 10 15 20 25 



TOTAL LENGTH IN CENTIMETERS 



Length frequency distributions 

 for Atlantic croaker taken east 

 of the Mississippi Delta, July 

 1961 to May 1962. 



41 



