AGE DETERMINATION, REPRODUCTION, AND POPULATION DYNAMICS 

 OF THE ATLANTIC CROAKER, MICROPOGONIAS UNDULATUS 12 



Michael L. White and Mark E. Chittenden, Jr. 3 



ABSTRACT 



A validated scale method of age determination is described for the Atlantic croaker, Micropogonias 

 undulatus. Two age-classes were usually observed, but only one was abundant. Mean total lengths 

 were 155-165 mm at age I and 270-280 mm at age II based on three methods of growth estimation. Fish 

 matured near the end of their first year of life when they were about 140-170 mm total length. 

 Spawning occurred from at least September through March but there was a distinct peak about 

 October. Somatic weight-length relationships varied monthly, and changes appeared to be associated 

 with maturation and spawning. Somatic weight reached a maximum in June, and the minimum was 

 observed in March. Maximum somatic weight loss (24%) occurred in March, but no data were obtained 

 from December through February. In estuaries, age croaker apparently occupied soft-substrate 

 habitat and older fish occurred near oyster reefs. Life spans were only 1 or 2 yr, and the total annual 

 mortality rate was 96%. The above life history pattern appears similar for croaker found throughout 

 the Carolinian Province. Contrasts are presented to illustrate differences in the life histories and 

 population dynamics of croaker found north and south of Cape Hatteras, N.C. A parallel is drawn with 

 apparently similar changes in the American shad, A/osa sapidissima, and the suggestion is made that 

 changes in the population dynamics of species that traverse the Cape Hatteras area may represent a 

 general phenomenon. 



The Atlantic croaker, Micropogonias undulatus 

 (Linnaeus), ranges in the western Atlantic from 

 the Gulf of Maine to Argentina (Chao 1976). It is 

 potentially a very important protein source be- 

 cause it is one of the most abundant inshore fishes 

 of the northern Gulf of Mexico (Gunter 1938, 1945; 

 Moore et al. 1970; Franks et al. 1972) and the 

 Atlantic Ocean off the southeastern United States 

 (Haven 1957; Bearden 1964; Anderson 1968). 



Much work has been done on this species. 

 However, many aspects of its life history and 

 population dynamics are not clear; because no 

 reliable method of age determination exists, and 

 reproduction has not been studied intensively. A 

 few early workers, including Welsh and Breder 

 (1924) and Wallace (1940), attempted to age 

 croaker using scales; but criteria for marks were 

 not described and methods were not validated. 

 More recent workers, in general, have not at- 

 tempted to use hard parts to determine croaker 

 age and growth. The scale method is difficult to 

 apply to croaker (Joseph 1972), and this may be 

 related to its migratory habits and extended 



'Based on a thesis submitted by the senior author in partial 

 fulfillment of the requirements for the MS degree, Texas A&M 

 University. 



technical article TA 12419 from the Texas Agricultural 

 Experiment Station. 



department of Wildlife and Fisheries Sciences, Texas A&M 

 University, College Station, TX 77843. 



spawning season (Suttkus 1955). Only Wallace 

 (1940) studied reproduction using a large series of 

 gonads. However, he worked north of Cape 

 Hatteras, N.C. The life history of croaker found 

 north of Cape Hatteras seems quite different from 

 that of individuals in the Carolinian Province. 

 Studies of reproduction in croaker found south of 

 Cape Hatteras have been based on few fish 

 (Gunter 1945; Bearden 1964) or fish less than 200 

 mm long (Hansen 1969). 



This paper describes a validated method of age 

 determination for croaker, their weight-length 

 and girth-length relationships, habitat segrega- 

 tion between age-groups, spawning seasonality, 

 somatic weight variation, growth, maximum size, 

 life span, and total annual mortality rates. Final- 

 ly, it contrasts the life histories of croaker found 

 north and south of Cape Hatteras. Geographically, 

 statements made herein apply to the Carolinian 

 Province and/or more northerly waters. With 

 modifications, particularly ones due to calendar 

 differences in seasons, our findings may also apply 

 in the southern hemisphere; but further work is 

 needed there. 



MATERIALS AND METHODS 



Collections were made from commercial shrimp 

 trawlers during 1974 in the Gulf of Mexico off 



Manuscript accepted June 1976. 



FISHERY BULLETIN: VOL. 75, NO. 1, 1977. 



109 



