FISHERY BULLETIN: VOL. 82, NO. 3 



all fish W = 2.146 x 10 5 L 2 " 2 , r = 0.96, 

 n = 175. 



Conversions between different length measures 

 were linear and expressed as follows: 



FL vs. TL: FL = 29.704 + 0.774 TL, r = 

 0.97, n = 100, 



FL vs. SL: FL = 22.823 + 1.171 SL, r = 

 0.99, n = 100, 



TL vs. SL: TL = 9.666 + 1.446 SL, r = 

 0.96, n = 100. 



Estimates of mortality (a, s, and i) varied 

 slightly between estimation methods (Table 8). 

 Full recruitment to the fishery was considered to 

 be at 3 yr for both sexes. Estimates of a were 

 between 0.32 and 0.53 with i between 0.39 and 

 0.75 (Table 8). 



TABLE 8. — Estimated annual mortality (a), annual 

 survival (s), and instantaneous mortality (i) by esti- 

 mation technique for gray triggerfish from the north- 

 eastern Gulf of Mexico, 1979-82. 



DISCUSSION 



The variation in length at age and overlays of 

 length ranges between ages found in gray trig- 

 gerfish is not unusual in fish from southeastern 

 U.S. waters. Many species such as king mackerel, 

 Scomberomorus cavalla; Spanish mackerel, S. 

 maculatus; red grouper, Epinephelus morio; sail- 

 fish, Istiophorus platypterus ; and black sea bass, 

 Centropristis striata, have large variations in size 

 within age groups (Beaumariage 1973; Powell 

 1975; Moe 1969; Jolley 1977; Waltz et al. 1979). 



Our gray triggerfish growth rates are similar 

 to growth information from the Gulf of Mexico, 

 but not information from Africa. Beaumariage 



(1969) reported growth rates for three tagged fish 

 (250, 270, and 332 mm TL) from the northeastern 

 Gulf of Mexico. His fish grew at a rate of 187.2, 

 153.6, and 51.6 mm/yr. If one considers Beaumar- 

 iage's fish to be 2, 2, and 3 yr old, respectively, 

 then his growth increments are similar to ours 

 (Table 7). Gray triggerfish age and growth have 

 been reported from southwestern Africa (Ivory 

 Coast-Ghana-Togo area) by Anonymous (1980). 

 We took the information in Anonymous' figure 

 11 and converted it to mean length at capture 

 per age which gave the following approximate 

 values: age I, 148 mm; age II, 203 mm; values are 

 about 100 mm less than ours for each age (Table 

 7). Caveriviere et al. (1981) provided comprehen- 

 sive information on the age and growth of gray 

 triggerfish off Senegal and the Ivory Coast. Two 

 hypotheses with regard to band formation were 

 suggested: A) one band per year, and B) two bands 

 per year. The sizes (FL) at age (in years) for 

 Senegal fish by hypotheses were age I, 153 mm 

 for hypothesis A, 90 mm for B; age II, 231 mm for 

 A, 170 mm for B; age III, 285 mm for A, 238 mm 

 for B; age IV, 322 mm for A, 290 mm for B; age V, 

 348 mm for A, 324 mm for B. Sizes at age of our 

 Gulf of Mexico fishes (Table 7) were larger after 

 the first year than predicted by both of the above 

 hypotheses for Senegal fish. The sizes at age for 

 Ivory Coast fish were smaller than both the 

 Senegal and the Gulf of Mexico fish using the 

 hypothesis of one band formed per year. These 

 differences may be the result of different envi- 

 ronments, biology, methods of capture, or aging. 

 Anonymous (1980) suggested that the African 

 fish have a seasonal offshore migration to avoid 

 the cold coastal water (during the third quarter of 

 the year) which is the result of upwelling. Gulf of 

 Mexico fish are not known to have migratory 

 habits, and thus might not be subject to the 

 energy expense such movements incur. More in- 

 formation on the life histories and environments 

 of these groups of gray triggerfish is needed to 

 explain the observed variations. 



The K values (growth coefficient) of gray trig- 

 gerfish varied between 0.382 and 0.383. These 

 values were similar to, but higher (about 0.1) 

 than, those reported for other demersal marine 

 fish from the southeastern United States (see 

 Manooch 1982 and Pauly 1978 for a listing of 

 values). The K values estimated for gray trigger- 

 fish may be high because of the low asymptotic 

 lengths that were found. Additional investigation 

 of the larger and older fish is needed to evaluate 

 the growth coefficients of this species. The esti- 



490 



