AGE, GROWTH, AND MORTALITY OF GRAY TRIGGERFISH, 

 BALISTES CAPRISCUS, FROM THE NORTHEASTERN 



GULF OF MEXICO 



Allyn G. Johnson and Carl H. Saloman 1 



ABSTRACT 



Age, growth, and mortality of gray triggerfish, Batistes capriscus, from the northeastern Gulf of 

 Mexico were estimated from sections of the first dorsal spine of 1,746 fish. The oldest female was 

 estimated to be 12 years old and the oldest male was 13 years old. The von Bertalanffy growth equa- 

 tions, using weighted means, were as follows: males, l t = 491.9 (1 - e -0.382U- 0.227) > anc j females, 

 l t = 437.5 (1 - e -0.383(<- 0.150)) where / = fork length in millimeters and t = age in years. The 

 mean annual mortality rate as determined by four methods of analyses (based on number of fish at 

 age) ranged from 0.32 to 0.53. The weight-length relationships of gray triggerfish were males, W 

 = 6.71505 x 10" 6 L 3 - 187 , and females, W = 1.3939 x 10" 5 L 3065 , where W = weight in grams and 

 L = fork length in millimeters. 



Exploitation offish from the northeastern Gulf of 

 Mexico by recreational and commercial fisher- 

 men has created a demand for underutilized fish 

 resources. One of the abundant fish resources 

 that is being subjected to exploitation is the gray 

 triggerfish, Balistes capriscus. A dramatic in- 

 crease in demand for this species can be seen in 

 the commercial landings on the west coast of 

 Florida: 7.8 t in 1967 and 26.7 t in 1977 (Anon- 

 ymous 1967, 1977). 



This species is known to occur in the western 

 and eastern Atlantic. In the western Atlantic, its 

 range is from Nova Scotia to Argentina, includ- 

 ing the Gulf of Mexico (Briggs 1958; Moore 1967). 

 In the Gulf of Mexico, the gray triggerfish is a 

 primary reef fish inhabiting the area between 12 

 and 42 m in depth (Smith 1976), except for its 

 first year of life when it is planktonic and associ- 

 ated with Sargassum (Dooley 1972). 



The harvest of the gray triggerfish in the 

 northeastern Gulf of Mexico and its utilization of 

 reef habitats has created a need to know more 

 about the biology of this species, especially age, 

 growth, and mortality. Age and growth of gray 

 triggerfish, using the first dorsal spine, has been 

 reported only for the southwestern coast of Africa 

 (Anonymous 1980; Caveriviere et al. 1981). This 

 paper reports the results of our investigation on 

 age, growth, and mortality, using the first dorsal 



spine of gray triggerfish from the northeastern 

 Gulf of Mexico. 



METHODS AND MATERIALS 



The hook and line fishery for gray triggerfish 

 off Panama City, Fla., was sampled from May 

 1979 to March 1982. During this period, 2,808 fish 

 were sampled and from each the fork length in 

 millimeters and total weight in grams measured 

 and recorded. The sexes of the fish were also 

 recorded when determinable by gross examina- 

 tion of the gonads. First dorsal spines were avail- 

 able from 1,746 of the 2,808 fish in the collection. 

 Total length (TL), standard length (SL), and fork 

 length (FL) were measured in millimeters from 

 100 fish to develop length conversion formulas. 



The first dorsal spines were processed for 

 examination as follows: 1) removing the first 5 

 mm of spine shaft above the condyle with a 

 Dremel 2 tool; 2) placing the shaft section on a 

 mounting tag using Lakeside No. 70c thermo- 

 plastic cement and sectioning the shaft using the 

 method described by Berry et al. (1977); 3) re- 

 moving three 0.18 mm thick serial sections from 

 the cement with 50% isopropanol; and 4) mount- 

 ing the clean sections in 209c Piccolyte cement 

 (20% Piccolyte, 809c xylenes) on glass slides. 



Spine cross sections were examined and mea- 

 sured using a closed-circuit television using a 50 



'Southeast Fisheries Center Panama City Laboratory, Na- 

 tional Marine Fisheries Service, NOAA, 3500 Delwood Beach 

 Road, Panama City, FL 32407-7499. 



Manuscript accepted February 1984. 

 FISHERY BULLETIN: VOL. 82. NO. 3, 1984. 



2 Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



485 



