Miller and Baltz: Seasonal trends and foraging habitat of Tursiops truncatus 
81 
labile t 
Seasonal frequency of number of sightings, number of individuals seen (based on minimum group size), and number of sightings 
during which foraging behavior was observed for bottlenose dolphins ( Tursiops truncatus ) in northern Gulf of Mexico bays from 
June 1999 until May 2002. 
Winter 
Spring 
Summer 
Fall 
Total 
Number of observations 
68 
60 
71 
70 
269 
Minimum number of individuals 
327 
422 
595 
550 
1894 
Number of foraging observations 
18 
24 
21 
25 
88 
Table 2 
Overall and seasonal means for environmental conditions used by bottlenose dolphins (Tursiops truncatus) in the Barataria 
Bay study area measured from June 1999 to May 2002. Significant seasonal differences (P<0.025) in least-square means 
(±1 standard error [SE] ) are indicated by different superscripted letters reading across each row. 
Variable 
Winter 
Spring 
Summer 
Fall 
Overall mean 
Temperature (°C) 
13.96 ±0.45 a 
23.00 ±0.47 b 
30.12 ±0.44 c 
25.99 ±0.44 d 
23.37 ±0.43 
Dissolved oxygen (mg/L) 
11.58 ±0.28 a 
9.07 ±0.27 b 
6.99 ±0.30 c 
7.90 ±0.29 c 
8.98 ±0.19 
Salinity (psu) 
24.15 ±0.51 a 
21.99 ±0.54 b 
20.84 ±0.50 b 
24.06 ±0.50 a 
22.77 ±0.27 
Turbidity (NTU) 
14.15 ±0.87 a 
13.50 ±0.92 a 
11.19 ±0.85 ab 
9.76 ±0.85 b 
12.08 ±0.45 
Distance from shore (m) 
69.04 ±12.78 
111.42 ±13.61 
91.73 ±12.51 
70.14 ±12.60 
84.77 ±6.47 
Depth (m) 
2.82 ±0.23 
2.54 ±0.25 
2.33 ±0.23 
2.72 ±0.23 
2.60 ±0.12 
in summer and fall and increased significantly in spring 
and again in winter. Mean salinity values fell into two 
general groupings; fall-winter salinities were higher 
than those for summer-spring. Turbidity levels were less 
distinct seasonally. Although the highest turbidity levels 
seen in winter and spring were significantly different 
from those seen in fall, levels seen in summer were not 
significantly different from either. The MANOVA did not 
reveal any seasonal differences in distance from shore 
or water depth. 
Spatial and seasonal environmental variation in the 
study area was considerable, and many of the variables 
were strongly correlated. The FA included all survey 
observations and resolved the six environmental vari- 
ables into three orthogonal factors that explained 71% 
of the variation in the data (Table 3). Each of the six 
environmental variables loaded heavily on at least 
one factor. Factor 1 accounted for 30% of the varia- 
tion and loaded heavily on temperature and dissolved 
oxygen. The signs of these loadings were opposite and 
represented an inverse seasonal relationship. Factors 
2 and 3 each accounted for an approximate additional 
20% of the variation. Factor 2 loaded strongly and posi- 
tively on both salinity and turbidity and did not reflect 
the negative relationship expected over larger salinity 
gradients. Strong positive loadings for the two spatial 
variables of distance from shore and depth were evident 
Table 3 
Rotated factor loadings of environmental variables mea- 
sured at observation sites of bottlenose dolphins (Tur- 
siops truncatus) in lower Barataria and Caminada bays, 
Louisiana, from June 1999 until May 2002. Magnitude 
and signs of factor loadings indicate strength and direc- 
tion of the influence of each variable on a factor. Figures 
in bold indicate the most important variable for the given 
factor. The variances explained by the Eigen value for 
each factor are expressed as absolute, proportional, and 
cumulative values. 
Environmental variable 
1 
Factors 
2 
3 
Temperature (°C) 
-0.88 
-0.36 
-0.01 
Dissolved oxygen (mg/L) 
0.94 
-0.16 
-0.04 
Salinity (psu) 
0.02 
0.82 
0.16 
Turbidity (NTU) 
0.06 
0.67 
-0.19 
Distance from shore (m) 
-0.23 
-0.05 
0.70 
Depth (m) 
0.21 
0.01 
0.81 
Variance explained 
1.85 
1.20 
1.18 
Proportion 
0.31 
0.20 
0.20 
Cumulative proportion 
0.31 
0.51 
0.71 
