Wyanski et al : Growth, population age structure, and aspects of the reproductive biology of Epinephelus niveatus 



213 



at age of specimens caught with longlines 

 and snapper reels has increased notice- 

 ably since the 1980s (Table 3), which 

 could be a density-dependent population 

 response to a decrease in competition for 

 resources, 2) 81'a^ of the specimens caught 

 with longlines were ages 1-6, the major- 

 ity (Se*^ ) of which were immature females 

 ( Tables 4 and 9 ), 3 ) the percentage of males 

 appears to have decreased significantly, 

 from T^f to 237^ in the 1970s and 1980s 

 to 19c in the 1990s (Table 7), 4) spawning 

 stock ratio for the snowy grouper popula- 

 tion in the South Atlantic Bight was 0.15 

 in the most recent assessment (SAFMC, 

 1993) — below the 0.30 level which means 

 that the SAFMC considers the stock over- 

 fished, and 5 ) mean length offish landed in 

 the longline fishery has steadily decreased 

 from 65 to 80 cm in the early 1980s to 

 50-60 cm in the mid-1990s (Figs. 13 and 

 15; see also Low, 1998). 



Snowy grouper are susceptible to rapid 

 depletion in a localized area through fish- 

 ing efforts. A study on a previously unexploited deep 

 reef off North Carolina found that fishing can remove 

 3% of the reef population daily (Epperly and Dodrill, 

 1995). In less than three months, the catch per unit 

 of effort and mean size of snowy grouper at that reef 

 were reduced to levels comparable to other exploited 

 sites. The mean size of snowy grouper landed in 

 North and South Carolina during most of the 1990s 

 (Figs. 13 and 15) is comparable to the size Epperly 

 and Dodrill (1995) reported for exploited sites. 



The increase in size at age over a ten-year period 

 for fish from both gear types is noteworthy because 

 this trend has been documented in populations that 

 had experienced moderate to high levels of fishing 

 mortality. Increases in size at age have been noted 

 for silver hake ( Helser and Almeida, 1997 ) and Atlan- 

 tic halibut (Haug and Tjemsland, 1986) in the north 

 Atlantic and several reef fish species (gag, red grou- 

 per, and red porgy) off the southeast coast of the 

 United States and in the Gulf of Mexico (Johnson 

 et al., 1993; Johnson and Collins, 1994; Harris and 

 McGovern, 1997; Goodyear and Schirripa'^). In our 

 study, the increase in size at age may represent den- 

 sity-dependent growth in response to an increase 

 in fishing mortality (Rothschild, 1986). Decreases in 

 the abundance (Low, 1998) of co-occurring species on 

 a similar trophic level, such as gi'ay tilefish (Caulo- 

 latilus microps) and tilefish (Lopholatilus chamaele- 

 onticeps), also may reduce competition for food and 

 shelter in deepwater habitats. Snowy grouper and 

 gi-ay tilefish feed on macroinvertebrates, particularly 



1997 



Year 



Figure 13 



Mean length (±SE) of snowy grouper landed in South 

 Carolina in the longline and snapper reel fisheries. Data 

 were collected through the Trip Interview Program (TIPl 

 at the South Carolina Department of Natural Resources. 

 Sample sizes ranged from 22 to 851. 



crabs (Brachyura), and fishes closely associated with 

 the substrate (Ross, 1982; Dodrill et al., 1993). 



Density-dependent increases in gi-owth rate gener- 

 ally indicate that a population or community is heav- 



