216 



Fishery Bulletin 98(1) 



of two specimens in the process of changing from 

 female to male is conclusive evidence that snowy 

 grouper are protogynous hermaphrodites. Moore and 

 Labisky ( 1984 ) reported males as young as age 6 and 

 some males with evidence of recent sex change. It is 

 likely that we collected only two transitional speci- 

 mens because sex change occurs after a female fin- 

 ishes spawning, during months when sample sizes 

 in our study were small. Sex change in other grouper 

 species, gag for example, occurs primarily during the 

 first two to three months after the spawning season 

 (McGovern et al., 1998), before males and females 

 become spatially separated (Coleman et al., 1996). 



Our findings on age at maturity and spawning 

 season are in general agreement with the results of 

 Moore and Labisky ( 1984) for snowy grouper in the 

 Florida Keys. They found that the smallest mature 

 female and largest immature female were age 3 and 

 age 5, respectively, whereas the smallest mature 

 female from 1980 to 1985 in our study was also age 3, 

 but small percentages (<10'7f ) of the age 7-9 females 

 were immature (Table 9). Females and males in the 

 Florida Keys were in spawning condition from April 

 through July, although no mature fish were sam- 

 pled in other months (Moore and Labisky, 1984). 

 We found that females off the Carolinas spawn from 

 April through September — possibly longer owing to 

 small sample sizes in October through March. 



The capture of 1160 specimens, some of which were 

 assessed macroscopically as spawning, in four trawl 

 collections on the exploratory squid cruise in June 

 1978 suggests that snowy grouper may form spawning 

 aggregations. Estimates of density would have been 

 much higher than 13.5-79.5 kg/ha calculated from 

 the trawl data if the fish were caught in only a small 

 part of the area sampled during tows of 7.4-18.5 km. 

 Dodrill and Epperly (1995) reported that the initial 

 density of exploitable snowy grouper on a 2700-m-^ 

 virgin reef off North Carolina was 11 kg/m^. 



Depth distribution 



Fishery-independent data collected over several years 

 and with various gear types show that fish length 

 is positively correlated with water depth (Fig. 11). 

 Longlines, Kali poles, and snapper reels were the pri- 

 mary gear types deployed in waters >150 m and the 

 waters <100 m were sampled primarily with chev- 

 ron traps. Chevron traps are not known to be selec- 

 tive for snowy grouper <600 mm. Dodrill et al. ( 1993 ) 

 speculated that the low abundance of adults in shal- 

 low waters may in part reflect years of intensive fish- 

 ing pressure in 40-120 m depths and only relative 

 recent fishing activity at depths >183 m off North 

 Carolina. Alternatively, we propose that snowy grou- 



per may migrate to deeper water toward the end of 

 the juvenile stage. 



Fish length and water depth data from the com- 

 mercial fisheries ( Figs. 13 and 14 ) concurred with the 

 positive correlation noted in the Florida Keys (Moore 

 and Labisky, 1984) and off Georgia and South Car- 

 olina (Low and Ulrich, 1983), although depth data 

 from fishermen may be less accurate than fishery- 

 independent data. We found small juveniles in shal- 

 low water, a finding that agrees with the results 

 of Moore and Labisky ( 1984) and with observations 

 from submersible dives that documented juvenile 

 snowy grouper (<300 mm) between 46 and 91m, but 

 not in deeper waters (Parker^). 



Accurate assessment of population parameters re- 

 quires knowledge of juvenile and adult distributions 

 of snowy gi'ouper as well as characteristics of the fish- 

 ery. The snapper reel fishery catches a greater pro- 

 portion of younger age classes than does the longline 

 fishery because fishing efforts are generally restricted 

 to areas <100 m in depth (Figs. 13 and 14). The long- 

 line fishery presently catches a greater proportion 

 of older age classes than does the snapper reel fish- 

 ery because regulations established by the SAFMC 

 restrict longlines to waters deeper than 91 m. 



Conclusions 



As other investigators have suggested, rebuilding 

 grouper populations may require a novel approach 

 such as long-teiTH area closures or individual trans- 

 ferable quotas (Epperly and Dodrill, 1995; Coleman 

 et al., 1996). At present, the regulations enacted 

 to rebuild the snowy grouper population include an 

 annual quota of 245,082 kg, with a trip limit of 1134 

 kg (SAFMC, 1993). Traditional management mea- 

 sures such as minimum size limits will not be effective 

 because snowy grouper experience fatal embolisms 

 while being brought to the surface from deep waters 

 (Matheson and Huntsman, 1984). Future research 

 should focus on improving our understanding of repro- 

 ductive pattern (e.g. spawning behavior, spatial and 

 temporal aspects of distribution) and include a thor- 

 ough assessment of sex ratio and an updated assess- 

 ment of population age structure. 



Acknowledgments 



We thank F. Rhode, J. Francesconi, and other assisting 

 members of the North Carolina Department of Health, 



'^Parker, R., Jr. 1997. National Marine Fisheries Service, 101 

 Pivers Island Rd., Beaufort, NC, 28516. Personal commun. 



