75 mm., the average was 0.03 ml. in the summer 

 (981 fish) and 0.01 ml. in the fall (162 fish). 



AGE AND GROWTH 



I determined the age of Atlantic croakers by 

 lusing lengtli- frequency data. Fish from the two 

 stations were of similar lengths, except for some 

 segregation by size according to salinity (see next 

 paragraph). Length-frequency data for the sta- 

 tions were, therefore, pooled (fig. 3). The data 

 hidicated that only 18 of 19,107 croakers (less than 

 ).l percent) were in their second year of life. 



Scales may be suitable for age determination of 

 Atlantic croakers from the study area, but this 

 nethod was miacceptable for Lake Pontchartrain 

 isli (Suttkus, 1955). In the Pensacola Estuary, 

 ) of 201 Atlantic croakers had what may have 

 )een an annulus on their scales. The age of fish 



30 

 20 

 10 



30 

 20 

 10 



30 

 20 

 10 



20 



30 



10 



40 



20 



AUGUST 1963 



OCTOBER 1963 

 N = 49 



FEBRUARY 1964 

 N=50 



MAY (EARLY) 1964 

 N=^35 



JUNE 1964 

 N = I^IO 



JULY 1964 

 N = 89l 



- AUGUST 1964 

 N = 847 



SEPTEMBER 1964 

 N = I29 



NOVEMBER 1964 

 N = II4 



JANUARY (EARLY) 1965 

 N = 223 



"T I I I — I — I — I — I — I — I — r~ 

 70 90 110 130 150 170 



10 30 50 



STANDARD LENGTH (MM.) 



as indicated by scales conformed to that indicated 

 by length-frequency data. 



Changes in the size distribution of Atlantic 

 croakers within this estuary occur when the larger 

 fish move to areas of higher salinity. A faster 

 growth rate in more saline waters would accen- 

 tuate this size difference. In June 1964, 620 croak- 

 ers averaged 70 mm. at station IV, and 1,290 aver- 

 aged 76 mm. long at station III ; in collections 8 and 

 12 miles below station III, 283 fish averaged about 

 9-1: mm. Length differences were still apparent in 

 July. Average lengths were 90 mm. at station IV 

 (149 fish), 91 mm. at station III (742 fish), and 

 98 mm. 12 miles below station III (155 fish). 



The average size of Atlantic croakers varied dur- 

 ing the different years (table 6) as a result of dif- 

 ferences in hatching time and growth rate. In 1965, 

 fish arrived in the estuary earlier than in 1964; 



20 

 10 



30 

 20 

 10 



30 

 20 



10 



20 



§20 



S 10 



tr. 



^"20 

 I- 10 



z 



UJ 

 "20 



UJ 10 

 Q. 



30 

 20 

 10 



40 

 20 



60 

 40 

 20 



JANUARY (LATE) 1965 

 N=279 



FEBRUARY 1965 

 N = I57 



MARCH 1965 

 N = I23 



MAY (EARLY) 1965 

 N = 2,269 



MAY (LATE) 1965 

 N = 2^I2 



JUNE 1965 

 N = 3P0I 



AUGUST 1965 

 - N=767 



SEPTEMBER 1965 

 N = 2I 



J. 



T-i — r 



10 30 



A 



DECEMBER 1965 

 N = I3 



T — I — I — I — I — I — I — I — I — I — I — r— 

 50 70 90 no 130 150 170 



STANDARD LENGTH (MM.) 



iQURE 3. — Length-frequency distribution of Atlantic croakers caught in the upper Pensacola Estuar.v at stations III and 



IV. 1963-65. 



JFE HISTORIES OF PINKISH AND ATLANTIC CROAKER 



143 



379-242 O - 70 - 10. 



