Parker et al.: Reef fish abundance, composition, and habitat use 



795 



(97 transects over 21 hours vs. 51 point 

 counts over 17 hours), 15 more species 

 were observed off North Carolina. The 

 major difference appears to be that 

 more temperate species usually associ- 

 ated with inshore environments (i.e. 

 inshore lizardfish, toadfish, rock sea 

 bass, pigfish, pearly razorfish, and 

 Spanish mackerel) were present at 

 GRNMS, whereas more tropical species 

 (i.e. red grouper, harlequin bass, wrasse 

 bass, white grunt, knobbed porgy, and 

 queen angelfish) were seen at the North 

 Carolina location. The warm waters of 

 the Gulf Stream provide a mechanism 

 for recruitment and survival of many 

 tropical species (Briggs, 1974). GRNMS 

 is 12 km closer to shore and 8 m shal- 

 lower than the North Carolina site. 

 More importantly, although the position 

 of the Gulf Stream varies across the con- 

 tinental shelf, it generally follows the 200-m 

 isobath which is much farther offshore from 

 GRNMS ( 105 km) than from the North Caro- 

 lina site (40 km). 



The diversity of species collected is partly 

 a reflection of the sampling method. Our ob- 

 servations on species abundance agree only 

 partially with results obtained by trawling. 

 The 10 most abundant and common species 

 observed in this study (Table 3 ) included four 

 (tomtate, black sea bass, cubbyu, and 

 longspine porgy) of the most abundant spe- 

 cies caught by trawling over hardbottom 

 similar to GRNMS off the southeastern U.S. 

 coast (Wenner, 1983; Sedberry and Van 

 Dolah, 1984; Table 4). Size, form, and behav- 

 ior of three of the other six species may pre- 

 clude their capture by trawls. Two of the 

 three most abundant species (round scad and 

 slippery dick) are small and fusiform and can 

 pass through the meshes of most trawls. Slip- 

 pery dick and belted sandfish usually live 

 close to the bottom where they are protected 

 from trawls by the substrate. Round scad 

 have been seen swimming freely in and out 

 of the mouth of trawls towed up to 3.5 knots 

 (Workman 7 ). A major source of unmeasured 

 error in many visual assessments is observer 

 error in sighting, identifying, counting, and 

 recording. In a prior study of ledge fishes at 

 GRNMS, 10 divers operating in pairs per- 



Workman, I. NOAA, NMFS, Mississippi Laboratory, 

 Pascagoula, MS 39567. Personal commun., January 

 1994. 



0.0 



2 3 



SUMMER 1985 



am 



m r^TH nl rl 



M 



lH 



354S43433444S54551 1 1223222231 1 1 



H 

 DC 

 < 



55524334 



1 -LEDGE 



2 - DENSE LIVE-BOTTOM 



3 - MODERATE LIVE-BOTTOM 



4 - SPARSE LIVE-BOTTOM 



5 - SAND 



Figure 5 



Dendrograms of cluster analyses of sites referenced by habitat 

 type for each of four surveys conducted in Gray's Reef National 

 Marine Sanctuary. Note that dissimilarity axes differ in scale. 



