Walsh et al Juvenile fish assemblages on the southeast United States continental shelf 



271 



studies have found that some fish species select spe- 

 cific sediment characteristics or biogenic structures 

 (Stoner and Abookire. 2002; Diaz et al., 2003; Stoner 

 and Titgen, 2003). and spatial patterns in these habitat 

 characteristics may cause spatial patterns in juvenile 

 fish distribution. We did not stratify sampling by sedi- 

 ment characteristics or biogenic structures and thus we 

 could draw no conclusion regarding the role of habitat 

 characteristics in influencing juvenile fish di.stribution 

 on the Georgia shelf 



No along-shelf spatial patterns were found in the 

 juvenile fish community on the continental shelf off 

 the Georgia coast; however, the along-shelf dimension 

 sampled (-60 km) was relatively small compared to the 

 along-shelf dimension of the southeast U.S. continental 

 shelf ecosystem (-1000 km). Consistent patterns in 

 along-shelf gradients in oceanographic features (Atkin- 

 son et al., 1985; Lee et al., 1991) and adult fish commu- 

 nities (Chester et al., 1984; Wenner and Sedberry, 1989) 

 exist on the southeast U.S. shelf, but over larger along- 

 shelf dimensions than sampled in the present study 

 (200-400 km). Consistent patterns of juvenile use of 

 along-shelf habitat over smaller dimensions (-100 km) 

 have been reported for other shelf ecosystems (north- 

 west U.S.; Norcross et al., 1997; Abookire and Norcross, 

 1998; northeast U.S.: Steves et al., 2000; Sullivan et 

 al., 2000), but the relation to along-shelf environmen- 

 tal and habitat characteristics is unclear. Along-shelf 

 patterns in juvenile fish distribution on unconsolidated 

 sediments may occur on the southeast U.S. shelf, but 

 at dimensions larger than 60-100 km. 



Seasonal patterns in settlement and postsettlement 

 movement both defined and blurred classification of 

 juvenile fish assemblages on the Georgia shelf Many of 

 the resident shelf species were consistently collected in 

 the same cross-shelf regions (i.e., inner and mid-shelf: 

 Ophidian selenops, Prionotus carolinus. Dactyloscopus 

 moorei, Stenotomus sp., and Serranicithis piimilio; outer- 

 shelf; Symphu)-us minor, Serranus phoebe, Centropristis 

 ocyurus, and Bothus lunatus), and the consistent collec- 

 tion of these species helped form a definition of juvenile 

 assemblages. Other resident species shifted juvenile 

 assemblages (e.g., Diplectriim formosum, Monacanthus 

 hispidus, Bothus robinsi, Otophidium omostigmum, and 

 Bothus ocellatus), possibly because of seasonal changes 

 in settlement patterns or ontogenetic postsettlement 

 movements, with the result that some classifications 

 were blurred. Four scieanid species, present during the 

 spring, summer, and fall as larvae (Marancik et al., 

 2005), were collected during the fall as juveniles and 

 contributed to defining the fall inner-shelf (Larimus 

 fasciatus and Menticirrhus americanus) and mid-shelf 

 {Cynosion nothus and C. reg^a/is) juvenile assemblages. 

 These species may shift settlement or juvenile habitat 

 (or both) between estuaries and the coastal ocean; this 

 shift has been shown to occur off the coast of New 

 Jersey (Able et al., 2003; Neuman and Able, 2003). 

 Further, a number of species in the ecosystem spawn on 

 the shelf yet use estuarine habitats as juvenile nurser- 

 ies (Warlen and Burke, 1990; Able and Fahay, 1998). 



In our study, settlement stage L. xanthurus, Brevoortia 

 tyrannus, and Lagodon rhomboides were collected on 

 the shelf, and contributed to the definition of the inner- 

 and mid-shelf assemblages. Some individuals of these 

 estuarine-dependent species may not settle directly 

 into estuarine habitats as has been demonstrated for 

 Centropristis striata off the coast of New Jersey (Able 

 and Fahay, 1998). 



Only a few reef-associated species collected during 

 the study used unconsolidated sediments consistently. 

 Centropristis ocyurus, Diplectrum formosum, and Steno- 

 tomus sp. were the most common reef fishes collected 

 on unconsolidated sediments, and made up >1% of the 

 total catch (Appendix). Other less frequently occur- 

 ring juveniles of important reef-associated species that 

 were collected were Centropristis striata, Epinephelus 

 niveatus, Pristigenys alta, Priacanthus arenatus, and 

 Lutjanus analis. 



Reef-associated species were collected across the en- 

 tire shelf. Centropristis ocyurus and Stenotomus sp. 

 were commonly collected on the outer-, inner-, and mid- 

 shelves, respectively (Table 2, Appendix). Centropristis 

 striata, which uses habitats in estuaries and coastal 

 regions as juveniles (Able and Fahay, 1998), was col- 

 lected on the inner- and mid-shelf in the spring and 

 summer, during periods of high settlement (Able and 

 Hales, 1997). The presence of many reef-associated 

 species at the deeper (50 m) stations (Table 4) may in- 

 dicate greater use of offshore unconsolidated sediments 

 by reef-associated species or that sampling was done 

 in an area closer to rocky-reefs. Several species of the 

 South Atlantic Fishery Management Council snapper- 

 grouper complex have been reported to use a variety of 

 nonreef habitats as newly settled juveniles, including 

 unconsolidated sediments on the shelf (Lindeman et 

 al., 2000). Many coral reef fish also use several types of 

 nearshore nonreef habitat as juveniles (de la Moriniere 

 et al., 2002; Nagelkerken and van der Velde, 2002). 

 These nonreef habitats are assumed to be important 

 nursery habitats; however, strong evidence of movement 

 from juvenile to adult habitats has been documented 

 only for a few reef-associated fishes (Gillanders et al., 

 2003). The fact that reef-associated species also use 

 unconsolidated sediments indicates there is an inter- 

 dependence between reef habitats and unconsolidated 

 sediments; yet the function of each habitat remains 

 unquantified. 



In addition to reef species, a number of commercially 

 and recreationally important demersal species used 

 unconsolidated sediments on the shelf off Georgia as 

 juvenile habitat. Juvenile Cynoscion nothus, C. regalis 

 and Menticirrhus americanus were collected on the in- 

 ner- and mid-shelves in the fall, and settlement-size 

 Leiostomus xanthurus were collected in the winter. 

 However, small noncommercial demersal species were 

 the most abundant juveniles collected during beam 

 trawl sampling. 



Much of the southeast U.S. continental shelf is im- 

 pacted by trawl fisheries that can adversely impact 

 unconsolidated sediments (Barnette^). Current manage- 



