Goldman et al.; Feeding habits of Pagrus pagrus and Batistes capriscus 
321 
CCA1 
Figure 3 
Biplot determined with canonical correspondence analysis (CCA) for the diet 
of red porgy (Pagrus pagrus) captured in the South Atlantic Bight from 2009 
through 2011. Arrows represent significant explanatory factors, and dots rep- 
resent prey types. The canonical axes represent linear combinations of the 4 
explanatory variables (i.e., fish length, latitude of capture, season, and depth). 
made up less than 1% of prey consumed at the north- 
ern latitudes (33-34°N). 
The quantity of decapods in the diet of red porgy 
increased with increasing length (Fig. 4D), whereas 
smaller fish (<420 mm TL) consumed more barnacles 
and bivalves than their larger counterparts. 
Feeding strategy According to the Amundsen graphical 
method, the feeding strategy of the red porgy popula- 
tion is generalized (points cluster lower on the y-axis 
of the graph) (Fig. 5), and therefore most prey types 
are eaten on occasion. Xanthid crabs were consumed 
by individual red porgy that were concentrating on this 
prey type as indicated by the point on the top left of 
the graph. The predator population had a broad niche 
width because most of the points are located along or 
below the diagonal from the upper left to the bottom 
right of the graph. A few prey items were eaten oc- 
casionally by most individuals, and these items are 
represented by the points on the bottom right of the 
graph (Fig. 5). 
Gray triggerfish 
Description of general diet Gut contents were collected 
from 82 gray triggerfish that ranged in size from 304 
to 595 mm TL. Gray triggerfish had a diverse diet, com- 
posed of 131 different prey taxa that were combined 
into 19 broader taxonomic groups: gastropods, amphi- 
pods, decapods, unidentified crustaceans, polychaetes, 
bivalves, bryozoans, barnacles, bony fishes, echinoderms, 
tunicates, miscellaneous items (e.g., fish scales, fora- 
minifera, and Sargassum spp.), stomatopods, isopods, 
cnidarians, ostracods, cephalopods, copepods, and un- 
identified mollusks. Barnacles, gastropods, and decapods 
were the main prey of gray triggerfish, accounting for 
29%, 11%, and 11% of the diet by weight, respectively 
(Fig. 6). Although most gastropods were unidentified, 
13 species were pelagic pteropods (group Thecosomata); 
cavolinid pteropods (40%) were the most frequently con- 
sumed pelagic pteropods. Unidentified shrimps were the 
most frequently consumed decapod (30%). Although am- 
phipods were consumed by 63% of predators, this taxon 
accounted for only 0.5% of the diet by weight and 10% 
by number. Other species consumed frequently included 
unidentified crustaceans (59%), polychaetes (46%), bi- 
valves (46%), and bryozoans (43%); however, these spe- 
cies contributed little by weight. 
Ontogenetic, temporal, and spatial changes in diet We 
determined that 15% of the total variability in the 
diet data could be explained by the CCA. The first and 
second canonical axes accounted for 41% and 36% of 
the constrained variation, respectively. Latitude and 
season were the most important explanatory variables 
(P<0.001), followed by depth and length (P<0.05) (Fig. 7). 
