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Fishery Bulletin 97(3), 1999 



grass and marsh-edge habitats following a 

 fairly short pelagic interval and remain in 

 these habitats during the juvenile stage (Baltz 

 et al., 1993; Rooker and Holt, 1997; Rooker et 

 al., 1998b). 



Although much effort has been directed to- 

 ward the management of red drum stocks, re- 

 search on growth and survival during early 

 life has received limited attention. As a result, 

 ihe aim of this study was to examine spatial 

 and temporal patterns of growth and mortal- 

 ity during the postsettlement period. Specific 

 objectives of this research were to estimate 

 annual variation in growth and mortality, to 

 estimate cohort- and site-specific mortality 

 rates, and to determine the recruitment po- 

 tential of different cohorts. 



Materials and methods 



Field collections 



Red drum were collected from two shoal grass 

 [Halodule ivrightii) meadows in the Aransas 

 Estuary, Texas (Aransas Bay 1 and 2 [ABl, 

 AB2]; Fig. 1), during the annual settlement 

 period (August-December). Collections were 

 taken over a two-year period (1994-951 with 

 an epibenthic sled measuring 0.75(w)x0.5(h) 

 m, equipped with a 505-)am mesh conical 

 plankton net. Triplicate 20-m sled tows were 

 taken every week at each site in 1994. A more 

 comprehensive sampling strategy was em- 

 ployed in 1995 in order to evaluate cohort-specific 

 variation in natural mortality. Ten 20-m sled tows 

 were taken every 3-4 d at each site during the en- 

 tire 1995 settlement season. Red drum larvae and 

 juveniles were preserved in 70% ethanol immediately 

 after capture. Environmental data collected at each 

 site included depth, salinity, and water temperature. 



Laboratory procedures 



Removal and processing of otoliths (lapilli) followed 

 the procedures described by Rooker and Holt ( 1997). 

 Otolith radius, increment count, and increment 

 widths were measured on a straight line from the 

 core to the posterior edge using an image analysis 

 system (Optimas, Bioscan). Because otolith growth 

 is allometric (Campana and Neil'son, 1985), all mea- 

 surements were taken in the same field. Daily deposi- 

 tion of increments was validated in our laboratory by 

 chemically marking the otoliths of known-age red drum 

 with alizarin complexone (S.A. Holt, unpubl. data). 



irsA- 



27 'SO' 



47 06' 



Figure 1 



Location of shoal grass (Halodule wrightii) sampling stations 

 (ABl and AB2) in the Aransas Estuary. Texas. 



Age was determined by enumerating growth in- 

 crements from the core to the margin of the otolith. 

 Inner increments (proximal to the core) on lapilli 

 were often difficult to enumerate. Thus, in order to 

 accurately determine the age of wild red drum, a re- 

 lationship between age and otolith radius from labo- 

 ratory-reared red drum was developed and used to 

 predict the number of growth increments at various 

 distances from the core ( Rooker and Holt, 1997 1. Age 

 was determined by adding the predicted age from 

 the unreadable section (correction factor from age- 

 radius relationship) to the increment count (number 

 of increments from first identifiable increment to 

 edge of the lapillus). Correction factors generally 

 accounted for less than 25% of the actual age esti- 

 mate, and the relative size of the correction did not 

 differ between years. Both the left and right lapilli 

 were examined and estimates of age and growth were 

 derived by averaging readings from both otoliths. On 

 average, age differences between otoliths were small 

 (CV=3.6%: range 0-14%). For some individuals 



