581 



Abstract.— Patterns of growth and 

 mortality were examined for post- 

 settlement red drum, Sciaenops ocel- 

 latits. inhabiting seagrass meadows in 

 the Aransas Estuary, Texas. Age and 

 growth rates of larvae and early juve- 

 niles were estimated in 1994 and 1995 

 by using daily increments in otoliths. 

 Otolith-derived estimates of age indi- 

 cated that individuals spend approxi- 

 mately 20 d in the pelagic environment 

 before entering demersal habitats (i.e. 

 before settlement). Instantaneous 

 growth coefficients (g) of red drum 

 ranged from 0.049 (4.8'7f/d) in 1994 to 

 O.OSKS.C^f/diin 1995. Site-specific dif- 

 ferences in growth were also examined 

 and a significant site effect was de- 

 tected in 1994; however, no site effect 

 was observed in 1995. Interannual and 

 cohort-specific ( 10-d cohorts ) mortality 

 rates were estimated from declines in 

 log^, abundance (abundance-at-age 

 plots), and results indicated that mor- 

 tality during the early postsettlement 

 period was substantial. Instantaneous 

 mortality coefficients (Z) were similar 

 between years (0.134 IVI.S^Ud] in 1994; 

 0. 139 1 13.0'7f /dl in 1995 ), and no signifi- 

 cant interannual effect was observed. 

 Conversely, cohort-specific mortality 

 rates ranged widely (0.106-0. 265 1 10.1- 

 23.3'-^/d] ) and losses were lowest for 

 midseason cohorts. Recruitment poten- 

 tial {G:Z ratio) was highest for mid- 

 season cohorts (1.30-1.56) and lowest 

 for early and late-season cohorts (<1). 

 Although G:Z ratios varied over spatial 

 and temporal scales, ratios were >1 in 

 1994 and 1995, suggesting that both 

 year classes experienced favorable 

 nursery conditions. 



Spatial and temporal variability in growth, 

 mortality, and recruitment potential of 

 postsettlement red drum, Sciaenops ocellatus, 

 in a subtropical estuary* 



Jay R. Rooker 

 Scott A. Holt 

 G. Joan Holt 



Lee A. Fuiman 



Marine Science Institute 



The University of Texas at Austin 



750 Channelview Drive 



Port Aransas, Texas 78373 



Present address (for J R Rooker) Department of Marine Biology 



Texas A&M University 



5007 Avenue U 



Galveston, Texas 77551 

 E-mail address (for J R Rool^er) rookeriiatamug lamu edu 



Manuscript accepted 27 August 1998. 

 Fish. Bull. 97:581-590 (1999). 



Survival during the lai-val and ju- 

 venile stages of marine fishes is 

 highly variable and plays a critical 

 role in determining recruitment 

 potential (Gushing, 1975; Houde, 

 1987). Early life survival is a func- 

 tion of both gi-owth and mortality, 

 and it is clear that these mecha- 

 nisms act in concert to determine 

 an individual's probability of sur- 

 vival (Houde, 1996). Individuals 

 experiencing rapid growth will 

 spend less time in vulnerable size 

 ranges (reduced stage duration) and 

 achieve a larger body size at a given 

 age, thus enhancing their ability to 

 detect and escape predators (Bailey 

 and Houde, 1989; Fuiman and 

 Magurran, 1994), Consequently, 

 recruitment success or failure is 

 closely linked to variation in growth 

 and mortality during the early life 

 stage. 



Much of our current understand- 

 ing of early life growth and mortal- 

 ity is based on information derived 

 from the examination of otolith mi- 

 crostructures. The daily deposition 

 of growth increments on otoliths has 

 been demonstrated for many ma- 

 rine teleosts and provides a means 



of estimating age, growth rate, and 

 hatching date (see reviews by 

 Campana and Neilson, 1985; Jones, 

 1986). Moreover, knowledge of a 

 population's age structure can be 

 combined with density data (abun- 

 dance-at-age relationships) to esti- 

 mate mortality rates. Thus, funda- 

 mental demographic parameters 

 can be obtained through otolith 

 analysis, and these data are essen- 

 tial for determining the causes and 

 consequences of differential survival. 

 Red drum {Sciaenops ocellatus) 

 inhabit subtropical and temperate 

 waters in the Western Atlantic and 

 support important commercial and 

 recreational fisheries throughout 

 the coastal waters of the Gulf of 

 Mexico (Swingle, 1990; NOAA, 

 1991 ). Red drum spawn in the early 

 fall in offshore waters and areas 

 near tidal inlets, and tidal currents 

 transport larvae through passes 

 and into estuarine nursery habitats 

 (Holt et al., 1989; Comyns et al,, 

 1991). Individuals settle into sea- 



* Contribution 1060 of Marine Science 

 Institute, The University of Texas at Aus- 

 tin, Port Aransas, TX 78373. 



