Baumgartner et al.: Cetacean habitats in the northern Gulf of Mexico 
231 
Table 5 
Results for univariate % 2 , Mann-Whitney, and Monte Carlo tests. Values of 0.0000 for P indicate P < 0.0001. 
X 2 test 
Mann-Whitney 
Monte Carlo 
n 
* 2 
df 
P 
U P 
P 
Bottlenose dolphin 
Depth 
89 
57.6 
11 
0.0000 
— 
Depth gradient 
89 
23.1 
11 
0.0174 
0.7474 
Surface temperature 
57 
26.8 
9 
0.0015 
0.0224 
Surface temperature standard deviation 
30 
17.3 
4 
0.0017 
0.0018 
Depth of 15°C isotherm 
39 
6.0 
6 
0.4184 
0.4909 
Surface chlorophyll 
57 
12.2 
9 
0.1999 
0.4095 
Zooplankton biomass 
40 
1.9 
6 
0.9268 
0.9720 
Risso’s dolphin 
Depth 
67 
53.9 
12 
0.0000 
— 
Depth gradient 
67 
57.4 
12 
0.0000 
0.0000 
Surface temperature 
39 
9.9 
6 
0.1296 
0.1527 
Surface temperature standard deviation 
14 
1.69 0.0456 
Depth of 15°C isotherm 
52 
16.3 
9 
0.0603 
0.0971 
Surface chlorophyll 
49 
9.2 
8 
0.3232 
0.3227 
Zooplankton biomass 
44 
7.3 
7 
0.3970 
0.7056 
Kogia spp. 
Depth 
56 
42.6 
9 
0.0000 
— 
Depth gradient 
56 
20.4 
9 
0.0155 
0.0690 
Surface temperature 
28 
4.8 
4 
0.3038 
0.3540 
Surface temperature standard deviation 
18 
1.98 0.0238 
Depth of 15°C isotherm 
47 
7.2 
8 
0.5125 
0.5371 
Surface chlorophyll 
46 
3.4 
7 
0.8441 
0.8560 
Zooplankton biomass 
35 
31.6 
5 
0.0000 
0.0014 
Pantropical spotted dolphin 
Depth 
107 
50.6 
11 
0.0000 
— 
Depth gradient 
107 
25.1 
11 
0.0088 
0.0687 
Surface temperature 
62 
13.5 
11 
0.2614 
0.3616 
Surface temperature standard deviation 
31 
7.5 
4 
0.1096 
0.1148 
Depth of 15°C isotherm 
99 
19.1 
11 
0.0593 
0.0748 
Surface chlorophyll 
102 
20.6 
11 
0.0380 
0.0985 
Zooplankton biomass 
57 
16.4 
9 
0.0588 
0.3522 
Sperm whale 
Depth 
43 
14.5 
7 
0.0431 
— 
Depth gradient 
43 
13.7 
7 
0.0566 
0.0965 
Surface temperature 
14 
0.27 0.3921 
Surface temperature standard deviation 
11 
1.14 0.1268 
Depth of 15°C isotherm 
34 
11.0 
5 
0.0508 
0.0388 
Surface chlorophyll 
39 
11.5 
6 
0.0741 
0.0749 
Zooplankton biomass 
26 
3.5 
4 
0.4729 
0.7053 
indicates P < 0.05. 
indicates P < 0.01. 
that the distribution with respect to depth gradient was 
not an artifact of the depth distribution (P<0.0001). The 
distribution with respect to surface temperature variabil- 
ity was significantly different from the effort (P<0.05; 
Table 5) and surface temperature variability at Risso’s 
dolphin sightings was generally higher than the effort 
(Fig. 5D). The sighting rate distribution with respect to 
depth was modal about the upper continental slope (Fig. 
8A), whereas group sighting rates increased with increas- 
ing depth gradient (Fig. 8B). 
