545 



Abstract— Patterns of distribution 

 and growth were examined for young- 

 of-the-year (YOY) greater amberjack 

 {Seriola dumerili) associated with 

 pelagic Sargassum in the NW Gulf 

 of Mexico. Seriola dumerili were col- 

 lected off Galveston, Texas, from May 

 to July over a two-year period (2000 

 and 20011 in both inshore (<15 nauti- 

 cal miles [nmijl and offshore zones 

 (15-70 nmi). Relative abundance of 

 YOY S. dumerili (32-210 mm stan- 

 dard length) from purse-seine col- 

 lections peaked in May and June, 

 and abundance was highest in the 

 offshore zone. Ages of S. dumerili 

 ranged from 39 to 150 days and hatch- 

 ing-date analysis indicated that the 

 majority of spawning events occurred 

 from February to April. Average daily 

 growth rates of YOY S. dumerili for 

 2000 and 2001 were 1.65 mm/d and 

 2.00 mm/d. respectively. Intra-annual 

 differences in growth were observed; 

 the late-season I April I cohort expe- 

 rienced the fastest growth in both 

 years. In addition, growth was signifi- 

 cantly higher for S. dumerili collected 

 from the offshore zone. Mortality was 

 approximated by using catch-curve 

 analysis, and the predicted instan- 

 taneous mortality rate (Z) of YOY S. 

 dumerili was 0.0045 (0.45%/d). 



Distribution, age, and growth of young-of-the-year 

 greater amberjack {Seriola dumerili) 

 associated with pelagic Sargassum 



R. J. David Wells 

 Jay R. Rooker 



Texas A&M University 



Department ol Marine Biology 



5007 Avenue U 



Galveston, Texas 77551 



Present address (lor R. J, D Wells): Coastal Fisheries Institute 



Louisiana State University 

 Baton Rouge, Louisiana 70803 



E-mail address (for R J D Wells) rwells4@lsu.edu 



Manuscript submitted 9 December 2002 

 to Scientific Editor's Office. 



Manuscript approved for publication 

 2 March 2004 by the Scientific Editor. 



Fish. Bull. 102:545-554 (2004). 



Recruitment of marine fishes is highly 

 variable and closely linked to early 

 life events (Houde, 1996; Cole, 1999). 

 Early life survival is dependent upon 

 several biological and environmen- 

 tal factors including spawning time, 

 prey availability, predation pres- 

 sure, growth, and physical transport 

 mechanisms (Bricelj, 1993; Schnack 

 et al., 1998). Recruitment success 

 is commonly assessed by examining 

 patterns of relative abundance (Sano, 

 1997), whereas estimates of growth 

 and mortality are commonly used to 

 index recruitment potential (Rilling 

 and Houde, 1999; Rooker et al., 1999). 

 Early life growth and mortality are 

 linked because fishes with high growth 

 rates often exhibit decreased size-spe- 

 cific predator vulnerability (Meekan 

 and Fortier, 1996). As a result, esti- 

 mates of juvenile abundance, growth, 

 and mortality provide insight into 

 patterns of nursery habitat quality 

 and thus may be used to delineate 

 essential fish habitat (EFH) (Pihl et 

 al., 2000; Sullivan et al, 2000). 



Greater amberjack ( Seriola dumer- 

 ili) is a reef-associated species with 

 a circumglobal distribution in sub- 

 tropical and temperate waters (Ma- 

 nooch and Potts, 1997a). In the Gulf 

 of Mexico, S. dumerili is the largest 

 carangid and supports important 

 recreational and commercial fisher- 

 ies (Thompson et al., 1999). Owing 

 to increased fishing effort and land- 

 ings, S. dumerili in the Gulf are cur- 

 rently assessed as overfished (NOAA, 



2000). Consequently, detailed life his- 

 tory information is needed to effec- 

 tively guide fishery management of 

 this valuable resource. To date, avail- 

 able life history data on S. dumerili 

 have almost entirely been based on 

 assessments of subadults and adults 

 (Manooch and Potts, 1997a, 1997b; 

 Thompson et al. 1 ). Despite the impor- 

 tance of early life processes, data on 

 juvenile or young-of-the-year (YOY) 

 S. dumerili are limited to qualitative 

 surveys of pelagic Sar-gassum (Bor- 

 tone et al., 1977; Settle, 1993). 



The National Marine Fisheries Ser- 

 vice has recently designated Sargas- 

 sum as essential fish habitat (EFH) 

 of several coastal migratory species 

 including S. dumerili (NOAA, 1996). 

 In response, the goal of this study 

 was to examine the distribution and 

 growth of S. dumerili associated with 

 pelagic Sargassum mats in the NW 

 Gulf of Mexico. Specifically, objectives 

 of this research were to quantify spa- 

 tial and temporal patterns of habitat 

 use by S. dumerili and to determine 

 age, hatching-date, growth, and mor- 

 tality of S. dumerili by using otolith- 

 based techniques. 



Thompson, B. A., C. A. Wilson, J. H. 

 Render, M. Beasley, and C. Cauthron. 

 1992. Age, growth, and reproductive 

 biology of greater amberjack and cobia 

 from Louisiana waters. Final report 

 NA90AA-H-MF722, 77 p. Marine Fish- 

 eries Initiative (MARFIN) program. 

 National Marine Fisheries Service, 

 NOAA, St. Petersburg, FL. 



