REPRODUCTION, MOVEMENTS, AND POPULATION DYNAMICS OF 

 THE LONGSPINE PORGY, STENOTOMUS CAPRINUS K1 



Paul Geoghegan 3 and Mark E. Chittenden, Jr. 4 



ABSTRACT 



Stenotomus caprinus mature at 90-125 mm TL as they approach age I. Spawning occurs once a year 

 in a discrete period of 50-80 days duration from January through April with peak activity in Febru- 

 ary or March. The male-female sex ratio was 1:1.21 in the spawning period. Spawning occurs in 

 waters deeper than 27 m, and its timing coincides with the periodicity of onshore surface currents in 

 the northern Gulf of Mexico. These currents probably transport eggs and larvae inshore to nursery 

 areas <27 m deep where recruitment occurs. Young-of-the-year gradually disperse as they mature 

 to waters 36-55 m deep where age I and II fish are most abundant. Stenotomus caprinus are most 

 vulnerable to trawling at night. Growth in length is fastest in their first 8 months but slows greatly 

 as they mature and divert energy towards reproduction. Stenotomus caprinus averaged 1 10-135 mm 

 TL at age I, 130-155 mm at age II, and 160 mm at age III. Maximum size is about 200 mm TL and 

 maximum lifespan typically is 2.5-3 years. Total annual mortality rate is 83-99%, butpostspawning 

 survival, mortality rates, and lifespan vary greatly between year classes. Total weight-total length, 

 length-length, and girth-total length relationships are presented. The population dynamics of S. 

 caprinus appear quite different from those of S. ehrysops, and the genus Stenotomus may show zoo- 

 geographic change at Cape Hatteras, N.C. 



Stenotomus caprinus, the longspine porgy, 

 ranges in the Gulf of Mexico (Gulf) from Cam- 

 peche Bank, Mexico, to Apalachee Bay, Fla., 

 (Caldwell 1955) and occurs rarely in the Atlantic 

 to North Carolina (Dawson 5 ). It is very abundant 

 at depths of 40-110 m and is the dominant fish in 

 the brown shrimp community (Hildebrand 1954; 

 Chittenden and McEachran 1976; Chittenden 

 and Moore 1977). Stenotomus caprinus makes up 

 a significant portion of the catch in the industrial 

 fishery of the north central Gulf (Roithmayr 

 1965; Gutherz et al. 1975). 



Despite its abundance, little is known about 

 this species. Its life history is known from gen- 

 eral faunal studies such as Miller (1965), Moore 

 et al. (1970), and Franks et al. (1972), although 

 Henwood et al. (1978) described its food habits. 

 Only Caldwell (1955), Henwood (1975), Henwood 

 et al. (1978), and Dawson (footnote 5) have made 



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

 fulfillment for the M.S. degree, Texas A&M University. 



2 Technical Article 17149 from the Texas Agricultural Ex- 

 periment Station, College Station, TX 77843. 



:i Department of Wildlife and Fisheries Sciences, Texas 

 A&M University, College Station, Tex.; present address: Com- 

 monwealth of Massachusetts, Division of Marine Fisheries, 

 Cat Cove Marine Laboratory, 92 Fort Avenue, Salem, MA 

 01970. 



department of Wildlife and Fisheries Sciences, Texas 

 A&M University. College Station, TX 77843. 



5 Dawson, R. A systematic revision of the sparid genus Ste- 

 notomus. M.S. Thesis in prep., The College of Charleston, 

 Charleston, S.C. 



Manuscript accepted January 1982. 

 FISHERY BULLETIN: VOL. 80. NO. 3, 1982. 



studies specifically directed at 5. caprinus. 



This paper describes maturation and spawn- 

 ing seasonality, movements and spawning areas, 

 growth and sizes at age, mortality and lifespan, 

 merits of age determination by scales and 

 length-frequency analysis, length-length, total 

 weight-total length, and girth-total length rela- 

 tionships for S. caprinus. 



METHODS AND MATERIALS 



Stenotomus caprinus were collected monthly 

 along a transect in the Gulf off Freeport, Tex., 

 (Fig. 1) from October 1977 through March 1980 

 aboard a chartered shrimp trawler using double 

 rigged 10.4 m shrimp trawls with 4.4 cm 

 stretched cod end mesh and a tickler chain. Sta- 

 tions were occupied at depths of 5, 9, 13, 14, 16, 

 22, 24, 27, 36, 47, 55, 64, 73, 82, 86, and 100 m. 

 Collections were made during the day through 

 September 1978; thereafter, a day and night 

 cruise were usually made each month. The 22 m 

 depth range was primarily occupied after Octo- 

 ber 1978, and depths >47 m were first occupied 

 in June 1979. Two tows of 10 min bottom time 

 were made at each depth except that 1 tow was 

 made prior to October 1978, 8-12 tows were made 

 at 14 m, and 24 tows usually were made at 22 m. 



All S. caprinus were separated from the catch, 

 measured for total length, fixed in 10% Forma- 



523 



