586 



Fishery Bulletin 97(3), 1999 



the Aransas Estuary. Site-specific mortality rates in 

 1994 ranged from 0.129 to 0.141 and no significant 

 difference was detected between sites (ANCOVA, 

 slopes, P=0.741); however, in 1995 mortality rates 

 were significantly lower in ABl (0.129) than in AB2 

 (0.193) (ANCOVA, slopes, P=<0.001). 



1994 



30 



29 



1995 



10 



30 



29 



Date 



Figure 3 



Mean density (sites pooled i per sampling trip of postset- 

 tlement red drum collected from the Aransas Estuary in 

 1994 and 1995. Two size classes of postsettlement red drum 

 (<10 mm SL, >10 mm SLi are shown. 



Cohort-specific mortality rates were estimated for 

 the 1995 year class (Fig. 7). Instantaneous mortal- 

 ity coefficients for 10-d cohorts ranged from 0.106 

 (10.1%/d) to 0.265 (23.3%/d) and a significant tem- 

 poral trend was detected (ANCOVA, slopes, P=0.004). 

 Mortality rates were lowest for midseason cohorts 

 (C, D) and highest for early and late cohorts (B, E), 

 and individuals from the last cohort (E) experienced 

 the greatest mortality. Stage-specific mortality rates 

 (10-20 mm, 12 d) ranged from 1.272 to 1.524 (71.9- 

 78.2%) for midseason cohorts and 2.316 and 3.180 

 (90.1-95.8%) for early and late-season cohorts. 



G:Z Index 



Recruitment potential of different cohorts was evalu- 

 ated by comparing G:Z ratios and temporal varia- 

 tion was observed (Fig. 8). The ratio of G.Z was high- 

 est for mid-season cohorts; 1.305 ( cohort C) and 1.565 

 (cohort D). In contrast, G:Z ratios of early and late- 

 season cohorts (B, E) were <1, suggesting that these 

 cohorts were losing biomass. Moreover, annual esti- 

 mates of G.Z were calculated and ratios were >1 in 

 both 1994 and 1995. Site-specific variation was also 

 observed and, apart from site AB2 in 1995, G:Z ra- 

 tios were always >1 (Table 1). 



Discussion 



Otolith-derived estimates of age indicate that red 

 drum enter estuarine seagrass meadows after a short 

 pelagic interval. Peak densities were observed for 

 individuals 8-9 mm (20-24 d), suggesting that re- 

 cruitment to seagrass meadows follows a planktonic 

 period of approximately 20 d. In support of this find- 

 ing, studies examining red drum during the plank- 

 tonic phase have shown that the upper size range of 

 red drum larvae in pelagic environments is 6-8 mm 

 (Peters and McMichael, 1987; Comyns et al., 1989; 

 Holt et al., 1989). In addition, Peters and McMichael 

 (1987) sampled demersal habitats in Tampa Bay, 

 Florida, and reported that red drum were first de- 

 tected at 8 mm. Consequently, red drum appear to 

 move from pelagic to demersal habitats (i.e. settle- 

 ment) at approximately 8 mm. 



Once in seagrass meadows, length- and weight- 

 specific growth of red drum increases rapidly with 

 increasing size (exponential relationships). Length- 

 specific growth rates of new settlers (20-40 d) in the 

 Aransas Estuary averaged 0.58 and 0.62 mm/d in 

 1994 and 1995, respectively. Growth estimates in the 

 Aransas Estuary are similar to rates reported by 

 Peters and McMichael ( 1987 ) for red drum in Tampa 

 Bay, Florida (0.58 mm/d). With size-at-age equations 



