REPRODUCTION, MOVEMENTS, AND POPULATION DYNAMICS OF 

 THE SAND SEATROUT, CYNOSCION ARENARIUS''' 



Philip A. Shlossman and Mark E. Chittenden, Jr.^ 



ABSTRACT 



Cynoscion arenarius females mature at 140-180 mm total length as they approach age I. Spawning 

 occurs from early March through September, but concentrates in a distinct spring period ( March-May) 

 and a distinct late summer period (August-September). Spawning occurs in the inshore Gulf of Mexico 

 and coincides with the periodicity of onshore winds and surface currents which probably transport eggs 

 or larvae to estuarine and inshore gulf nurseries. Estuarine nurseries may be most important to late 

 summer spawned groups. The main gulf nursery in the northwestern area is in waters shallower than 

 18 m. Both spawned groups leave estuarine nurseries in fall to overwinter in the gulf. Late summer 

 spawned groups return to estuaries in midspring but reenter the gulf in August to spawn. Fish average 

 210-280 mm total length at age I but some were 300 mm. Predicted sizes of late summer fish were 425 

 mm total length at age II and 574 mm at age III. The largest trawled specimen was 342 mm total length 

 and 99.5'7r were less than 280 mm. No more than three spavmed groups or two year classes occurred at 

 any one time. The typical ma.ximum life span is 1-2 years based on trawl data and possibly as much as 

 2-3 years for other gear. Total annual mortality rate was 99.79'!?^ based on trawling data and appears no 

 lower than 80-90^f if maximum lifespan typically is as great as 3 years. Cynoscion arenarius can be 

 aged using scales. Total weight-total length, girth-total length, and standard length-total length 

 regressions are presented. Temporal isolation of the two spawned groups produced each year suggests 

 they may be separate populations or species. The life history and population dynamics of C. arenarius 

 appear similar to C. regalis along the Atlantic coast south of CapeHatteras, North Carolina. The latter 

 taxon shows zoogeographic change at Cape Hatteras, which needs management consideration. 



The sand seatrout, Cynoscion arenarius (Gins- 

 burg), is endemic to the Gulf of Mexico (gulf) 

 and ranges from southwest Florida ( Roessler 1970) 

 to the Bay of Campeche (Hildebrand 1955). It is 

 one of the most abundant fishes in estuaries and 

 the shallow gulf (Gunter 1945; Christmas and 

 Waller 1973) and is a major component of the in- 

 dustrial fishery landings and shrimp bycatch 

 (Roithmayr 1965; Gutherz et al. 1975). 



The life history of C. arenarius is essentially 

 undescribed despite its abundance. Food habits 

 have been studied (Darnell 1958; Diener et al. 

 1974; Moffett et al. 1979), and general material 

 appears in many faunal studies including Franks 

 et al. (1972), Gallaway and Strawn (1974), and 

 Chittenden and McEachran (1976). Much of this 

 information is misleading, however, because the 

 complex life history of this species has not been 

 recognized. Literature on the possibly conspecific 



'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 16254 from the Texas Agricultural Ex- 

 periment Station. 



^Department of Wildlife and Fisheries Sciences, Texas A&M 

 University, College Station, TX 77843. 



Manuscript accepted June 1981. 



FISHERY BULLETIN: VOL. 79, NO. 4, 1981. 



C. regalis might apply to C. arenarius, but their 

 taxonomic status is still in doubt (Mohsin 1973; 

 Weinstein and Yerger 1976). We have referred to C. 

 arenarius herein as a species separate from C. 

 regalis following Bailey et al. (1970). 



This paper describes spawning seasonality, 

 periodicity, and areas, seasonal distribution 

 and movements, age determination, growth, 

 mortality, and total weight-total length, girth- 

 total length, and standard length-total length re- 

 lations. 



METHODS 



Sand seatrout were collected monthly along a 

 transect in the gulf off Freeport, Tex. (Figure 1), 

 from October 1977 through September 1979 

 aboard a chartered shrimp trawler using twin 10.4 

 m (34-ft) trawls with a 4.4 cm stretched mesh cod 

 end. Collections were made during the day 

 through September 1978; thereafter, a day and a 

 night cruise usually were made each month. Sta- 

 tions were occupied at depths of 4.5, 7, 9, 14-15, 18, 

 22, 27, 37, and 46 m. One or two tows were made at 

 each depth (two tows after October 1978), except 



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