Drymon et al Factors that affect the distribution of sharks throughout the northern Gulf of Mexico 
377 
Figure 5 
Results of the co-inertia analyses on (A) small- and (B) large-scale shark and environmental data from the north- 
ern Gulf of Mexico during 2006-09. Small-scale total inertia is 0.22, and axes 1 and 2 supported 99.17% of this 
structure. Large-scale total inertia is 0.20, and axes 1 and 2 supported 97.32% of this structure. The scale is shown 
in ovals at top of each panel. Arrows and dotted lines represent environmental variables. Filled circles and full 
lines represent shark species. Cbio=crustacean biomass, Chl-a=chlorophyll-a, DO=dissolved oxygen, Fbio=fish bio- 
mass, Sal=salinity, Temp=temperature. 
robust tool. Examination of the results for total inertia 
indicates that analyses at both small and large scales 
were equally useful for identification of patterns be- 
tween sharks and explanatory variables. However, the 
RV coefficients indicate that explanatory variables were 
better correlated with shark abundances at the small 
scale (RV=0.65) than at the large scale (RV=0.42). Giv- 
en 1) the unique coupling of bottom-longline data sets 
collected through the use of identical methods across 
the same temporal scale and 2) the similarity in shark 
size and catch between the surveys at 2 spatial scales, 
our data are particularly well suited to COIA. Our re- 
sults indicate that the factors affecting the distribution 
of sharks in the Gulf of Mexico are species specific but 
relatively well conserved across spatial scales. 
The factors that affect the distribution of Blacktip 
Shark were similar at small and large scales, and the 
distribution of this species was best explained by crus- 
tacean biomass at both scales. However, it is unlikely 
that Blacktip Shark responded to crustaceans as po- 
tential prey. Although previous studies of feeding hab- 
its of Blacktip Shark in the northern Gulf of Mexico 
(Hoffmayer and Parsons, 2003; Barry et al., 2008) and 
Florida (Heupel and Hueter, 2002) have identified crus- 
tacean components, these same studies have revealed 
that Blacktip Sharks prey predominately on teleosts. 
That Blacktip Shark distributions may not be influ- 
enced by the distribution of their preferred prey is 
not surprising. In an acoustic telemetry study in Terra 
Ceia Bay, Florida, no correlation was found between 
juvenile Blacktip Shark and their prey (Heupel and 
Hueter, 2002). After examination of the influence of 
prey abundance on the distribution of sharks (includ- 
ing Blacktip Shark) at 2 spatial scales, Torres et al. 
(2006) showed no correlation between shark catch and 
teleost abundance at individual sampling locations, al- 
though a correlation was shown between shark catch 
and teleost abundance within a region. The strong rela- 
tionship observed in our study between Blacktip Shark 
and crustacean biomass at both spatial scales indicates 
that perhaps the underlying mechanism that most in- 
fluences the distribution of this species correlates with 
crustacean biomass. 
Distribution of Atlantic Sharpnose Shark was best 
explained by chl-a concentration, a pattern that, like 
the one seen for Blacktip Shark, was independent of 
scale. However, although Blacktip Shark may have 
been influenced by factors other than prey, Atlantic 
Sharpnose Shark may have been indirectly responding 
to available prey as indicated by the observed relation- 
ship with concentration of chl-a. The contrast between 
Blacktip Shark and Atlantic Sharpnose Shark may il- 
lustrate basic differences in the ecology of these 2 spe- 
cies. As adults, Blacktip Sharks are a larger, more mo- 
