Hood and Johnson: Life history of Rhombophtes aurorubens 



829 



ing, and 5) the estimated number of age- 1 fish in the 

 population was declining. Goodyear and Schimpa'^ also 

 noted that large differences in estimates of length-at- 

 age and estimates of fecundity made it difficult to as- 

 sess confidently conditions of the stock by using stan- 

 dard assessment models. 



Existing age and growth data for this species in 

 the GOM are inadequate and dated. Zastrow ( 1984) 

 and Nelson (1988) used scales to age GOM vermil- 

 ion snapper collected in the early 1980s. The maxi- 

 mum age reported was 7 years. However, using scales 

 to determine age has proven to be problematic. Stud- 

 ies in the SAB have shown that as age increases, the 

 readability of the scales decreases (Grimes, 1978; 

 Collins and Pinckney, 1988). Barber (1989) used 

 whole otoliths and scales to age GOM fish and was 

 able to count up to 18 rings in scales and 26 rings in 

 whole otoliths. Although he did not directly compare 

 ages from both structures, his scale- and otolith- 

 based estimates of length at age and growth were 

 very different. In addition, his attempt to validate 

 whole-otolith-based ages was unsuccessful. 



Growth of vermilion snapper may be affected by 

 changes in fishing. Zhao et al. ( 1997) found that mean 

 and predicted sizes-at-age of SAB fish had declined 

 between 1979 and 1993 and associated this change 

 with size-selective fishing. They suggested that fish- 

 ing is removing faster-growing fish from the popula- 

 tion and may have genetic or physiological conse- 

 quences in the life history of this species. 



Information on the reproductive biology of vermil- 

 ion snapper in the GOM is limited. Sex ratio appears 

 to be dependent on location. Sex ratios from the GOM 

 and Puerto Rico are approximately 1:1 (Boardman 

 and Weiler, 1979; Zastrow, 1984; Collins''') although 

 Nelson (1988) reported that males outnumbered fe- 

 males 1.2:1. In the SAB, females consistently out- 

 numbered males, and sex ratios ranged from 1.6:1 

 to 1.7:1 (Grimes and Huntsman, 1980; Collins and 

 Pinckney, 1988; Cuellar et al., 1996; Zhao and 

 McGovern, 1997). Nelson (1988) examined spawn- 

 ing period, fecundity, and sex ratios offish caught in 

 the western GOM. His results were similar to find- 

 ings reported for the SAB (Grimes and Huntsman, 

 1980; Cuellar et al., 1996). In both regions, spawn- 

 ing occurs during the summer and early fall. Nelson 

 (1988) estimated that vermilion snapper batch fe- 

 cundities in the GOM range from 61,600 to 392,000 

 eggs. Fecundity has been found to have a positive 

 relationship with fish size (Grimes and Huntsman, 

 1980; Nelson, 1988; Cuellar et al., 1996). Vermilion 



■' Collins, A. 1997. Southeast Fisheries Science Center, Natl. 

 Mar. Fish. Serv., 3.500 Delwood Beach Road., Panama City, FL 

 32407. Personal commun. 



snapper are thought to spawn in aggregations. 

 Boardman and Weiler ( 1979) and Grimes and Hunts- 

 man ( 1980) found large numbers offish in the same 

 reproductive state in single collections. 



Basic life-history information is needed to prop- 

 erly assess vermilion snapper stocks in the GOM. 

 Accurate ages are needed to develop age-length keys, 

 develop growth models, and estimate total mortal- 

 ity. In addition, the annual periodicity of ring depo- 

 sition in otoliths has not been validated in the GOM. 

 With the increasing reliance on estimates of spawn- 

 ing-potential ratios to describe a stock's condition, 

 information on maturation schedules, sex ratios, and 

 size-specific fecundities are also needed. The purpose 

 of this study was to accurately age eastern GOM ver- 

 milion snapper to develop age-length keys, develop 

 growth models, construct catch curves for deriving 

 estimates of total mortality, and to describe the re- 

 productive biology of this species. 



Methods 



Eastern GOM vermilion snapper were sampled from 

 October 1995 to September 1996. Samples were ob- 

 tained from headboat fishermen, commercial catches, 

 and a Florida Department of Environmental Protec- 

 tion trawl survey. Total length (TL). fork length (FL), 

 and standard length (SL) were measured to the near- 

 est millimeter. Whole weight or gutted weight (or 

 both) were measured to the nearest gram. The rela- 

 tionships between lengths and logjo-transformed to- 

 tal lengths and weights were determined by least- 

 squares regression (SAS Institute, Inc., 1985). Male 

 and female regression lines of logjg-transformed to- 

 tal lengths and weights were compared by using 

 analysis of covariance (Snedecor and Cochran, 1971). 

 Thin sections of sagittae (hereafter referred to gen- 

 erally as otoliths) were used to determine the ages 

 offish. Otoliths were removed and stored dry in cul- 

 ture wells. The left otolith was serially sectioned 

 across its anterior-posterior midpoint at 0.5-mm in- 

 tervals by making a transverse cut with an Isomet 

 diamond saw. Mounted sections were placed on a 

 black field, illuminated with reflected light, and ex- 

 amined with a binocular dissecting microscope. The 

 magnified images of otolith sections were transmit- 

 ted by means of video camera to a video monitor and 

 were analyzed with a computer-driven data-acquisition 

 software package (Optimas Corp., 1996). The number 

 of opaque zones and the radial measurements from the 

 core to the last opaque band and to the edge of the 

 otolith (otolith radius. Fig. 1) were recorded. Marginal 

 increments were measured as the distance between the 

 last opaque band and the edge of the otolith. 



