459 



Abstract.— We examined 1005 cobia, 

 Rachycentron canadum, from recre- 

 ational catches in the northeastern Gulf 

 of Mexico from 1987 to 1995. Specimens 

 ranged from 325 to 1651 mm fork 

 length (FL); females had a mean FL of 

 1050 mm (f? = 730l and were signifi- 

 cantly larger than males that had a 

 mean FL of 952 mm (n =275). The over- 

 all male to female ratio was 1:2.7. Ages 

 of 565 cobia were estimated from thin- 

 sectioned otoliths (sagittae). Marginal- 

 increment analysis of sagittal otoliths 

 showed a single annual minimum dur- 

 ing June. Male cobia (;i= 170; 52.5-1330 

 mm FL) ranged from age to 9, and 

 females (?i=395; 493-1651 mm FL) 

 ranged from age to 11. The relation- 

 ship of observed fork length and age 

 was described by the von Bertalanffy 

 growth equation for males FL, = 1171( 1- 

 exp [-0.432(/^-1.150l]) and for females 

 FL, = 15551 1-exp [-0:2T2{t +1.25 A)]). 

 Growth in length for both sexes was 

 relatively fast through age 2, after 

 which growth slowed gradually. Esti- 

 mates of the von Bertalanffy growth 

 equation parameters L^, and K were sig- 

 nificantly different for males and fe- 

 males, whereas estimates for ^^ were 

 not significantly different. Sagittal 

 otolith weight was a good predictor of 

 age. The instantaneous rate of total 

 mortality (Z) estimated by catch curve 

 analysis for fully recruited ages 4-8 

 was 0.75. 



Age and growth of cobia, 

 Rachycentron canadum, 

 from the northeastern Gulf of Mexico 



James S. Franks 



Gulf Coast Research Laboratory 

 Institute of Marine Sciences 

 University of Southern Mississippi 

 PO Box 7000 



Ocean Springs, Mississippi 39566-7000 

 E-mail address ifranksg seahorse ims usm edu 



James R. Warren 



Gulf Coast Research Laboratory 

 Institute of Marine Sciences 

 University of Southern Mississippi 

 PO Box 7000 

 Ocean Spnngs, Mississippi 39566-7000 



Michael V. Buchanan 



Mississippi Department of Marine Resources 

 1141 Bayview Avenue. Suite 101 

 Biloxi, Mississippi 39530 



Manuscript accepted 28 August 1998. 

 Fish. Bull. 97:459-471 (1999). 



Cobia. Rachycentron canadum, are 

 large, migi-atory, coastal pelagic fish 

 of the monotypic family Rachy- 

 centridae and are distributed world- 

 wide in tropical and subtropical 

 seas, except for the eastern Pacific 

 (Briggs, 1960; Shaffer and Naka- 

 mura, 1989). In the western Atlan- 

 tic Ocean, cobia occur from Massa- 

 chusetts and Bermuda to Ai-gentina 

 (Briggs, 1958 ) but are most common 

 along the U.S. south Atlantic coast 

 and in the northern Gulf of Mexico 

 (Shaffer and Nakamura, 1989). In 

 the Gulf of Mexico (Gulf), where 

 they range from Key West, Florida, 

 along the entire coast to Campeche, 

 Mexico (Dawson, 1971), R. cana- 

 dum is a highly-prized recreational 

 species and is caught incidentally 

 in several commercial fisheries 

 (Shaffer and Nakamura, 1989). Co- 

 bia landings, recreational and com- 

 mercial combined, from the Gulf 

 and Atlantic averaged one million 

 kilograms (kg) per year during a 

 recent 12-year period ( 1984-95), of 

 which 87% was recreational catch. ^ 



The majority of recreational land- 

 ings of cobia in the United States 

 are from the Gulf (Shaffer and 

 Nakamura, 1989) and averaged 0.5 

 million kg for years 1984-95.^ Rec- 

 reational and commercial cobia 

 regulations enacted in U.S. waters 

 presently consist of a minimum size 

 of 838 mm fork length (33 inches) 

 and daily bag and possession limits 

 of two fish per person.'^ 



In the eastern Gulf, cobia typi- 

 cally migrate from their wintering 

 grounds off south Florida into 



' Gulf of Mexico and South Atlantic Fishery 

 Management Councils. 1996. Report of 

 the mackerel stock assessment panel meet- 

 ing, April 15-18. 1996, Tampa. FL. Gulf 

 Mex. Fish. Manage. Counc, Tampa, FL, 

 and South Atlan. Fish. Manage. Counc, 

 Charleston, SC. 



- Gulf of Mexico and South Atlantic Fishery 

 Management Councils. 1990. Amend- 

 ment No. 5, fishery management plan for 

 the coastal migratory pelagic resources 

 ( mackerels); environmental assessment and 

 supplemental regulatory impact review. 

 Gulf Mex. Fish. Manage. Counc, Tampa, 

 FL, and South Atlantic Fish. Manage. 

 Counc, Charleston, SC. 



