WHITE and CHITTENDEN: AGE DETERMINATION OF ATLANTIC CROAKER 



15 



Age I + Fish Captured in March. 

 Age Determined by L/F Method. 



-i — i— i — i — i—i — i — i — i "T " i i VT^-p i ^i i i — r 



> IR-i Back Calculated Length at Age I. 

 o 



-c Age I Fish Captured in October, 

 Age Determined by L/F Method. 



5- 



t — i — i — r 

 70 100 



— i — r 



160 



130 



TOTAL LENGTH (MM 



l — l — I — T 

 190 220 



— I — I — I — i 

 250 280 



FIGURE 9.— Back-calculated length frequencies at age I and 

 length frequencies (L/F) of age I fish in October and age 1+ fish in 

 March. Frequencies are moving averages of three. 



spawning season and/or prolonged time span when 

 the cold-period mark may form. 



HABITAT SEGREGATION 

 BETWEEN AGE GROUPS 



A portion of all croaker age groups apparently 

 utilized bays as feeding grounds during the 

 warmer months, but age I and older fish seemed to 

 occupy different habitat than young-of-the-year. 

 Croaker captured by angling near the oyster reef 

 from June to August were about 200-270 mm in 

 length (Figure 1) and seemed common there. In 

 contrast, trawl-caught bay fish were generally 

 much smaller than 200 mm. Reef and trawl- 

 caught bay individuals were then about age 1 + 

 and age 0, respectively. Many other workers, 

 including Reid (1955), Perret (1966), Nelson 

 (1969), Hansen (1969), Parker (1971), Hoese 

 (1973), and Gallaway and Strawn (1974), have 

 also captured few individuals greater than 200 

 mm by trawling in bays, but they captured 

 many small specimens like we did. Therefore, 

 although capture by angling may have selected 

 larger fish near the reef, the two age-groups seem 

 to segregate by habitat: young-of-the-year occupy 

 soft substrates, and age I and older fish occur near 

 oyster reefs (and similar hard substrates?). This 

 agrees with Harden Jones' (1968) generalization 

 that the feeding grounds of adult fishes are sepa- 

 rate from their spawning grounds and nurseries. 



Age I and older fish seemed to remain near oys- 

 ter reefs until they migrated to sea to spawn. Fish 

 caught near oyster reefs were much larger than 

 those caught by trawling in the Gulf or bays until 

 September-October (Figure 1). Specimens larger 

 than 191 mm were not collected in the Gulf until 

 September, which is about when spawning begins 

 in the northern Gulf (Gunter 1945; Suttkus 1955; 

 present study). Simmons and Hoese (1959) 

 captured fish less than 175 mm long throughout 

 the summer as they migrated to the Gulf, but 

 these workers captured fish similar in size to our 

 reef fish only during September. 



The larger young-of-the-year began moving to 

 sea by late spring or early summer. Trawl-caught 

 fish in the bay were smaller than those in the Gulf 

 during June (Figure 1) when modal length for 

 young-of-the-year was about 120 mm in the bay 

 and about 140 mm in the Gulf. The difference in 

 size between young-of-the-year in the bay and 

 Gulf agrees with Gunter (1945), Haven (1957), 

 and Reid and Hoese (1958) who found a size 

 gradient in estuaries, the smallest young-of-the- 

 year being farthest up the estuary. Haven (1957) 

 and Hoese et al. (1968) suggested that the gradient 

 was due to gradual seaward dispersal of the 

 largestyoung, and Parker (1971) and Franks etal. 

 (1972) suggested that young-of-the-year began 

 moving to sea at about 85-100 mm long. Evidently 

 the Gulf becomes a very important nursery by 

 midspring or early summer, because young 

 croaker compose about 24-29% by number of the 

 fishes found on the white shrimp grounds of the 

 Gulf then (Miller 1965, table 3; Chittenden and 

 McEachran 1976). 



MAXIMUM SIZE AND AGE, LIFE 

 SPAN, AND MORTALITY RATE 



Croaker in the Carolinian Province are typi- 

 cally small and have a short life span and high 

 mortality rate. Most fish we collected were less 

 than 200 mm long and the largest was 357 mm. 

 The largest croaker observed in warm-temperate 

 waters generally have been less than 300 mm 

 (many workers including Hildebrand and Cable 

 1930; Reid 1955; Bearden 1964; Miller 1965; Nel- 

 son 1969; Hansen 1969; Parker 1971; Hoese 1973), 

 although some workers captured fish as large as 

 330-380 mm (Pearson 1929; Gunter 1945; Suttkus 

 1955; Franks et al. 1972; Christmas and Waller 

 1973). Rivas and Roithmayr (1970) found a 668 

 mm specimen, but this is exceptional. 



119 



