NOTES 



THE RELATIONSHIP BETWEEN TILEFISH, 



LOPHOLATILUS CHAMAELEONTICEPS, 



ABUNDANCE AND SEDIMENT COMPOSITION 



OFF GEORGIA 



Elucidation of the relationship between physico- 

 chemical factors and fish abundance has long been of 

 interest to fisheries biologists. For example, water 

 temperature frequently exerts a strong influence on 

 the abundance of many pelagic marine fishes (Rado- 

 vich 1961; Laurs et al. 1977; Barkley et al. 1978; 

 Moyle and Cech 1982), and this effect has been noted 

 also for freshwater species (Magnuson et al. 1979; 

 Moyle and Cech 1982). For benthic marine fishes, 

 however, substrate composition may be a more im- 

 portant factor affecting fish abundance and distribu- 

 tion. Associations between abundance and substrate 

 composition have been noted for a diverse group of 

 fishes: agonids, bothids, cottids, pleuronectids, scor- 

 paenids, and steichaeids (Day and Pearcy 1968; 

 Powell and Schwartz 1977; Marliave 1977; Barton 

 1982). Where detectable, however, these associa- 

 tions vary substantially in intensity. This is probably 

 due to the fact that many physicochemical factors 

 are intercorrelated and most fishes probably respond 

 to intercorrelated suites of variables rather than to 

 single factors alone. 



In this note we quantify the relationship between 

 catch rate of a demersal species, the tilefish, Lopho- 

 latilus chamaeleonticeps, and substrate composition. 

 This species is commercially exploited throughout 

 most of its range (Grimes et al. 1980; Low et al. 

 1983; Turner et al. 1983), although, prior to this 

 study, tilefish resident to the continental slope off 

 Georgia appeared to have been subjected to minimal 

 exploitation (D. Harrington'). The elucidation of a 

 substrate-abundance relationship for tilefish should 

 aid in the management and harvest of this species. 



Methods 



A total of 19 bottom longline sets and 19 sediment 

 samples were obtained during daylight hours, be- 

 tween 5 May and 22 November 1982. Fourteen long- 

 line sets, each comprising 1.6 km of line, and 12 sedi- 

 ment samples (Table 1) were obtained from the RV 

 Georgia Bulldog (University of Georgia Sea Grant 

 Program vessel). Five sets(X ± 1 SD length = 0.31 



± 0.09 km) and seven sediment samples were col- 

 lected aboard the RV Delaware II (National Marine 

 Fisheries Service vessel). At least one of the authors 

 was present during collections. 



Bottom longlining on the Georgia Bulldog was con- 

 ducted using snap-on gangions (~ 0.5 m in length) 

 spaced about 4 m apart, along a 6.3 mm diameter 

 galvanized aircraft cable groundline. Gangions were 

 equipped with 4/0 or 5/0 circle hooks and baited with 

 either fish or squid. A similar system was employed 

 on the Delaware II except that a much shorter 

 groundline of 6.3 mm diameter hardlaid nylon was 

 used (Table 1), with hook sizes ranging from 3/0 to 

 8/0. 



Substrate Analysis 



Substrate samples were collected with a 25 x 30 

 X 37.5 cm box dredge suspended from a power 

 winch. The dredge was lowered to the bottom and 

 then dragged across the substrate (typically for < 5 

 min). After retrieval, 1.2-2.0 kg of sediment were 

 removed from the dredge and stored in plastic bags. 

 It is assumed that these samples accurately reflect 

 the composition of surface sediments. 



Sediment samples varied in their proximity to 

 longline sets. Fourteen samples were taken at the 

 end of longline sets. Of the remaining five samples, 

 one was taken from the midpoint of a set, three were 

 taken alongside sets within a distance of 0.2 km, and 

 one was taken alongside a set at a distance of 0.6 km. 

 The general area sampled (see Table 1 for loran C 

 coordinates) has a relatively homogenous, low-relief 

 bottom topography, and large variations in substrate 

 composition probably do not occur over short 

 distances (V. J. Henry^). 



To determine the fraction of each sample compos- 

 ed of sand and silt-clay, a known amount of sediment 

 (i.e., enough to yield a dry weight of between 60 and 

 100 g) was dried in a forced-air oven at 98°C until a 

 constant weight was reached. The sample was then 

 moistened with water which contained ~ 2 g of 

 Calgon^ as a dispersant, and washed through a sieve 

 which retained particles > 0.0625 mm (4^) (U.S. 

 standard seive #230). Sediments retained by the 

 sieve were then oven-dried to a constant weight to 



'D. Harrington, University of Georgia Marine Extension Service, 

 Brunswick, GA 31523, pers. commun. 1983. 



^V. J. Henry, Dept. of Geology, Georgia State University, Atlan- 

 ta, GA 30303, pers. commun. 1983. 



^Reference to trade names does not imply endorsement by the Na- 

 tional Marine Fisheries Service, NOAA. 



FISHERY BULLETIN: VOL. 83, NO. 3, 1985. 



443 



