Hood and Johnson: Life history of Rhomboplttes aurorubens 



837 



to interpret. Barber ( 1989) reported that otolith- 

 based ages were on average three years greater 

 than scale-based ages for GOM vermihon snap- 

 per, although he did not directly compare otoliths 

 and scales from the same fish. Our maximum age 

 was less than the 26 years reported by Barber 

 ( 1989). His older ages are surprising because he 

 used whole otoliths to estimate age. Grimes 

 (1978) noted that one disadvantage to aging ver- 

 milion snapper by using whole otoliths is that 

 rings are difficult to interpret in fish older than 

 age 7. Although we did not compare whole 

 otoliths to sectioned otoliths of vermilion snap- 

 per, for gag (Mycteroperca microlepis), annuli at 

 the edge of the otolith are more readily observed 

 in sectioned otoliths than in whole otoliths 

 (Collins et al., 1987; Hood and Schlieder, 1992). 



Empirical mean lengths and predicted lengths 

 at age were less for our vermilion snapper than 

 for snapper from the western GOM (Table 4; 

 Fig. 9). At age 1, the mean length of fish from 

 our study (211 mm TL) is similar to that offish 

 from studies by Zastrow ( 1984; 207 mm TL) and 

 Nelson (1988; 207 mm TL); however, by age 4, 

 the mean length in our study (253 mm TL) is at 

 least 100 mm less than mean lengths in their stud- 

 ies (353 and 357 mm TL , respectively; Fig. 9). If 

 scale-based ages underestimate actual age, then 

 mean length at age and gi'owth rates will be over- 

 estimated (Beamish and McFarlane, 1987). How- 

 ever, because scales generally give good estimates 

 of age for younger fish and because the mean 

 length of our fish at age 1 is similar to lengths given 

 by Zastrow ( 1984) and Nelson ( 1988). differences in 

 length could reflect differences in growth as opposed 

 to bias from aging structures. 



Our estimates of empirical mean lengths and pre- 

 dicted lengths at age, which were lower than those 

 estimates for vermilion snapper from the western 

 GOM. could also be the product of changes in fishing 

 pressure. Schirripa"* summarized GOM landings data 

 and noted that annual commercial and recreational 

 landings have increased 3- to 4-fold from the mid- 

 1970s to the early 1990s. If larger fish are more vul- 

 nerable to capture, then faster-growing fish within 

 an age class will be selectively removed from the 

 population. The result of this type of selection will 

 be a depression of mean size at age for older age 

 classes and an underestimation of the biologically 

 realistic L„ (Pitcher and Hart, 1982). This pattern 

 was noted by Zhao et al. (1997) for vermilion snap- 

 per in the SAB. Their estimates of growth based on 

 ages from sectioned otoliths for 1979-81 were simi- 

 lar to growth estimates (scale-based ages ) by Grimes 

 (1978) from the mid-1970s, when fishing pressure 



was low. Zhao et al.'s (1997) estimates of size at age 

 and of L . then decreased over time. Estimates of L„ 

 dropped from 629 mm TL (1979-81) to 365 (1982- 

 84) and 333 mm TL (1985-93) (Table 4). They could 

 not attribute declines in size at age or L^ to gear 

 selectivity, sampling regime, depth, or latitude and 

 concluded their observed changes were due to selec- 

 tive fishing for faster-growing individuals within all 

 age classes. 



Similar decreases in observed lengths at age have 

 been reported for red porgy, a species often found in 

 the same habitats as vermilion snapper (Grimes et 

 al., 1982; Barans and Henry, 1984; Chester et al., 

 1984; Sedberry and Van Dolah, 1984; Nelson, 1988) 

 and sought by the same fisheries (Grimes et al, 1982; 

 Nelson, 1988; Collins and Sedberry, 1991). Average 

 total length of GOM red porgy reported by Hood and 

 Johnson" at age 6 years was 348 mm and was over 



Hood, P. B.. and A, K. Johnson. 1997. Age. growth, mortal- 

 ity, and reproduction of red porgy iPagrus pagrus) from the east- 

 ern Gulf of Mexico. Florida Marine Research Institute. Florida 

 Department of Environmental Protection, 100 Eighth Avenue 

 S.E.. St. Petersburg. Florida. Manuscript in prep. 



