326 
Fishery Bulletin 114(3) 
Frequency of occurrence (%) 
Figure 9 
Graph of the feeding strategy for gray triggerfish {Bati- 
stes capriscus), captured from 2009 through 2011 in the 
South Atlantic Bight. The graph was developed by us- 
ing the Amundsen graphical method. Each dot repre- 
sents a different prey species. 
Another reason for seasonal variation in diet could 
be the reproductive behavior of gray triggerfish. They 
spawn from April through September and peak spawn- 
ing occurs from May through August (Kelly, 2014). Dur- 
ing this time, they are found at deeper depths, and it 
is possible that their feeding behavior could change be- 
cause they are nest guarders. Gray triggerfish caught 
on the outer shelf consumed more gastropods (primar- 
ily pteropods) than the gray triggerfish captured on 
the inner shelf Pteropod distribution patterns remain 
poorly described (Bednarsek et ah, 2012), but it has 
been reported that their distribution and migration 
vary seasonally (Dadon and de Cidre, 1992; Parra- 
Flores and Gasca, 2009). 
Latitude was a highly significant explanatory factor 
in defining the diet for gray triggerfish, and there were 
changes in diet with fish length that might also have 
influenced our results. Small fish consumed more poly- 
chaetes and decapods, and large fish consumed more 
barnacles and bivalves (the opposite was true with 
red porgy). Decapod prey consumed by gray triggerfish 
were often smaller crab species or crustaceans in lar- 
val stages (i.e., crabs, shrimps, and lobsters). Gastropod 
consumption increased with predator size. 
The percentages of explained variation found in this 
study are comparable to those in similar studies of diet 
composition (Jaworski and Ragnarsson, 2006; Latour et 
ah, 2008). Although a relatively small proportion of the 
total variation is explained by the CCA, a small propor- 
tion is expected because the percentage-explained iner- 
tia (variance) for ecological data is typically low (<10%) 
(ter Braak and Verdonschot, 1995). 
Some prey of gray triggerfish and red porgy have 
diel vertical migrations (at least 32 taxa) (Boltovskoy, 
1973; Alldredge and King, 1980; Hopkins et ah, 1994; 
Angel and Pugh, 2000). Pteropods, for example, exhibit 
diurnal vertical migrations along the depth range of 
0-100 m. During the day, pteropods move to deeper 
waters but migrate to the surface at night (Angel and 
Pugh, 2000). They tend to concentrate in the upper lay- 
ers during the night to feed and avoid predators (Hays, 
2003). Gray triggerfish are rarely caught at night dur- 
ing cruises of the Marine Resources Monitoring, As- 
sessment, and Prediction program (senior author, per- 
sonal observ.), and they have been previously described 
as diurnal predators (Randall, 1968). It is possible that 
these fish are not caught on the bottom at night be- 
cause this species migrates into the water column, fol- 
lowing pelagic prey. Many fish species migrate in a diel 
pattern, both vertically (Narver, 1970; Blaxter, 1973; 
Begg, 1976) and horizontally (Baumann and Kitchell, 
1974; Hobson, 1974; Bohl, 1979; Krumme, 2009), fol- 
lowing prey migrations (Ahlbeck et ah, 2012). Although 
gray triggerfish are highly reef associated, they also 
rely on migrating pelagic species as food sources. Other 
studies of reef fishes have reported trophic connections 
that are primarily dependent on these vertically mi- 
grating food webs (Weaver and Sedberry, 2001; Gold- 
man and Sedberry, 2010). 
Although competition between species was not a 
focus of our research, other studies have had results 
worth discussing in the context of our work. Johnson 
(1977) suggested that when %F exceeds 25% between 
2 or more predators, competition is likely. In contrast, 
Pianka (1976) stated that competition for identical re- 
sources is only likely if resources are in short supply. 
Red porgy and gray triggerfish do share many of the 
same prey (e.g., decapods, gastropods, bivalves, bryozo- 
ans, echinoderms, polychaetes, and bony fishes), and, if 
food resources become scarce, then such scarcity could 
lead to competition. Possible causes for a short supply 
could be prey consumption by invasive lionfishes, ocean 
acidification, or other anthropogenic effects (e.g., fish- 
ing). In this study, we did not examine food availability, 
nor did we observe anything that indicated evidence of 
food scarcity. 
Ocean acidification is of particular concern for gray 
triggerfish because a large part of its diet is composed 
of pelagic pteropods. Ocean acidification causes shell 
dissolution in pteropods and some benthic inverte- 
brates that are CaCOs-secreting organisms (Doney et 
ah, 2009). Calcified structures provide protection from 
predators; therefore, pteropods would be adversely af- 
fected by the rising atmospheric CO 2 levels caused by 
human fossil fuel combustion and deforestation (Doney 
et ah, 2009), and adverse effects on pteropods would, in 
turn, have serious effects on populations of gray trig- 
gerfish. This study is far more comprehensive than pre- 
vious studies have been and covers a large geographic 
area, providing a baseline study that can be used to 
monitor potential dietary shifts that result from cli- 
mate change. 
The temporal and geographic differences in prey for 
red porgy and gray triggerfish highlight the need to 
incorporate information on fish food habits into ecosys- 
tem models. Many of the prey species consumed by fish 
