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Fishery Bulletin 91(4), 1993 



sandy areas, may be the result of trophic links through 

 reef-asssociated fishes, such as vermilion snapper, with 

 other ecotopes on the shelf. 



While an important component of regional reef eco- 

 systems and fisheries, vermilion snapper and demer- 

 sal-feeding fishes, such as red porgy (Pagrus pagrus) 

 are being overfished (Low et al., 1985; Collins and 

 Sedberry, 1991). As a result of this increased fishing 

 pressure, vermilion snapper has increased in abun- 

 dance relative to P. pagrus and other overexploited 

 reef fishes off the southeastern United States, and the 

 importance of its functional role in reef ecosystems 

 may have changed. Increased fishing pressure since 

 the late 1970 s has also apparently caused a concomi- 

 tant decrease in mean length and a decrease in size at 

 maturity of vermilion snapper (Collins and Pinckney, 

 1988; Collins and Sedberry, 1991). If small vermilion 

 snapper consume different prey than do large vermil- 

 ion snapper and if average fish size is decreasing in 

 the region, the trophic structure of reefs may be 

 affected. 



The objectives of this study were to describe the 

 feeding habits of vermilion snapper and to evaluate its 

 relative dependence on hard-bottom benthos, sand- 

 bottom infauna, demersal zooplankton (Alldredge 

 and King, 1977, 1985; Porter and Porter, 1977), 

 holozooplankton (Cahoon and Tronzo, 1992) and nek- 

 ton as food. An additional purpose was to describe 

 differences in feeding habits with size. 



Methods 



Stomachs from vermilion snapper were collected dur- 

 ing six cruises in 1980 and 1981 from 11 reef stations 

 off South Carolina and Georgia. Stations were located 

 in each of three depth zones representing the inner 

 shelf ( 16-22 m depth, three stations), middle shelf 

 (23-37 m depth, four stations) and outer shelf (46- 

 69 m depth, four stations). Delineation of depth zones 

 was based on distribution of fish assemblages as noted 

 in previous studies and on community analysis of 

 catches in the present study (Struhsaker, 1969; Miller 

 and Richards, 1980; Sedberry and Van Dolah, 1984). 

 Fishes were collected primarily with a roller-rigged 

 40/54 high rise trawl (Hillier, 1974); a few were cap- 

 tured with traps or hook-and-line. Sampling was con- 

 ducted during the day and at night on hard-bottom 

 reef habitat that was mapped for each station by means 

 of underwater television. Detailed descriptions of sta- 

 tion locations and fish sampling techniques have been 

 described elsewhere (Sedberry and Van Dolah, 1984; 

 Wenneretal., 1984). 



Standard lengths (SL in mm) were measured at sea. 

 Stomachs were removed, individually labeled, and fixed 



in 10% seawater-formalin. Because of limited space 

 and very large catches, only those stomachs that ap- 

 peared to contain ingesta were preserved. No attempt 

 was made in the field to determine the percentage of 

 stomachs with food. Small (<50 mm SL) vermilion snap- 

 per were preserved whole and dissected in the labora- 

 tory. Fixed stomachs and small individuals were 

 washed in tap water and transferred to 50% isopropyl 

 alcohol. 



Contents of individual stomachs were sorted by taxa 

 and counted. Volume displacement of food items was 

 measured in a graduated cylinder or estimated by us- 

 ing a lxl mm grid (Windell, 1971). The relative con- 

 tribution of food items to the diet was determined by 

 using three methods: 



percent frequency occurrence, F= 



number of stomachs 

 with prey taxon 



number of stomachs 

 with food 



percent numerical abundance, N-- 



percent volume displacement, V- 



number of individuals 

 of prey taxon 



total number of 

 prey items 



volume displacement 

 of prey taxon 



total volume of 

 all prey items 



100 



X 100 



100 



These values are presented only for those prey species 

 that occurred with a frequency of at least one percent 

 or that made up at least one percent of the total num- 

 ber or volume of prey. Values of F, N, and V were also 

 calculated for higher prey taxa, for stomachs pooled by 

 50-mm intervals of SL of vermilion snapper. The chi- 

 square statistic (Tyler, 1979) was used to test for sig- 

 nificance (0.05 level) of feeding heterogeneity between 

 predator size classes. 



To determine selection of prey type and predator 

 feeding habitat, stomach samples were compared to 

 samples from the potential prey environment by using 

 Ivlev's index of electivity (Ivlev, 1961), calculated as 



E 



-P, 



r , + P, 



where: E = electivity for the ;th potential prey species; 

 r, = percent by number of species i in the diet; and p, = 

 percent by number of species i in samples from the 

 environment. Electivity values range from -1 to +1. 

 Negative values imply that the species is avoided, not 

 preferred, only incidentally ingested, or unavailable to 

 the predator. Positive values imply that the predator 

 prefers the prey species or that it is feeding on prey 

 species that occur in a different habitat than that 

 sampled by the prey sampler. A value near zero im- 



