SPECIES ASSOCIATIONS AND DAY-NIGHT VARIABILITY OF 

 TRAWL-CAUGHT FISHES FROM THE INSHORE SPONGE-CORAL 



HABITAT, SOUTH ATLANTIC BIGHT 1 



Charles A. Wenner 2 



ABSTRACT 



Biomass, species composition, diversity, and community structure of demersal fishes were studied during 

 the spring of 1978 in the sponge- coral habitat of the South Atlantic Bight. These results were compared with 

 sampling at an open-shelf site. Otter trawl catch rates were an order of magnitude higher in the sponge-coral 

 habitat than at the open-shelf site. Density and biomass estimates in the sponge-coral habitat averaged 384 

 individuals/ha and 31.0 kg/ha, respectively, whereas at the open-shelf site they averaged 57 individuals/ha 

 and 3.2 kg/ha. In sponge-coral habitat samples, 101 species of demersal teleosts were taken. The Sparidae 

 accounted for the greatest number of species (9), as well as 599c of the total number and 487r of the weight of 

 demersal teleosts. Species diversity was highest in night-trawl tows in the sponge-coral habitat. Species 

 associations, described by numerical classification, showed major differences in faunal assemblages be- 

 tween reef and open-shelf sites and between day and night samples. 



Struhsaker (1969) presented a generalized habitat 

 classification based on substrate type and species 

 composition in a summary of demersal fish resources 

 off the southeastern United States (Fig. 1). The 

 open-shelf habitat extends offshore from 18 m(10fm 

 (fathoms)) to about 55 m (30 fm) and is characterized 

 by a sandy bottom and relatively stable hydrographic 

 conditions due to the moderating influence of the 

 Gulf Stream (Struhsaker 1969; Mathews and Pashuk 

 1977). The ichthyofauna of the open shelf are 

 relatively diverse but have a low biomass (Wenner et 

 al. 1979a, b, c). Abundant teleostean families are the 

 Sparidae, Synodontidae, Serranidae, Bothidae, and 

 Triglidae (Wenner et al. 1979a). 



The sponge-coral habitat (= Struhsaker s [1969] 

 "live bottom") is composed of isolated areas within 

 the open-shelf habitat. These locales have a hard 

 substrate composed of a carbonate, shell, and quartz 

 sand conglomerate which is either exposed or 

 covered with a thin veneer of sand to a depth of 8 cm 

 or less (Powles and Barans 1980). This substrate pro- 

 vides suitable sites for the growth of dense stands of 

 attached invertebrates (sponges, corals, echino- 

 derms, tunicates, hydroids, and bryozoans) and 

 algae. A recent classification divides the sponge- 

 coral habitat into estuarine and nearshore sites (< 18 

 m[<10 fm]), intermediate sites (18-55 m [10-30 fm]), 



1 Contribution No. 148, South Carolina Marine Resources Research 

 Institute; MARMAP Contribution No. 200; Contribution No. 82- 

 32P, Southeast Fisheries Center, National Marine Fisheries Ser- 

 vice, NOAA, Pascagoula, Miss. 



2 Marine Resources Research Institute, South Carolina Wildlife and 

 Marine Resources Department, P.O. Box 12559, Charleston, SC 

 29412. 



and offshore sites (55-183 m [30-100 fm]) (Miller and 

 Richards 1979). 



The most productive areas in the South Atlantic 

 Bight, in terms of fish diversity and biomass, are the 

 hard-bottom areas (Struhsaker 1969; Huntsman and 

 Manooch 1978; Miller and Richards 1979; Powles 

 and Barans 1980). The purposes of this report are to 

 present distribution, relative abundance, and spe- 

 cies composition of trawl-caught fishes from inshore 

 and intermediate reefs sampled during the late 

 spring of 1978 and to comment on the suitability of 

 otter trawl gear for stock assessment of commercial 

 finfish in this habitat. 



Manuscript accepted November 1982. 

 FISHERY BULLETIN: VOL. 81, NO. 3, 1983. 



FIGURE 1.— South Atlantic Bight habitat types as defined by 

 Struhsaker (1969). 



537 



