79 
Environmental characterization 
of seasonal trends and foraging habitat 
of bottlenose dolphins ( Tursiops truncatus ) 
in northern Gulf of Mexico bays 
Email address for contact author: cara.miller@flinders.edu.au 
Department of Oceanography and Coastal Sciences 
Louisiana State University 
Baton Rouge, Louisiana 70803 
Present address: School of Biological Sciences 
Flinders University 
G.P.O. Box 2100 
Adelaide 5001 South Australia, Australia 
Abstract — A description of the forag- 
ing habitat of a cetacean species is 
critical for conservation and effective 
management. We used a fine-scale 
microhabitat approach to examine 
patterns in bottlenose dolphin ( Tur- 
siops truncatus) foraging distribution 
in relation to dissolved oxygen, tur- 
bidity, salinity, water depth, water 
temperature, and distance from shore 
measurements in a highly turbid estu- 
ary on the northern Gulf of Mexico. In 
general, environmental variation in 
the Barataria Basin marine environ- 
ment comprises three primary axes of 
variability (i.e. , factors: temperature 
and dissolved oxygen, salinity and 
turbidity, and distance and depth) 
that represent seasonal, spatial-sea- 
sonal, and spatial scales, respectively. 
Foraging sites were differentiated 
from nonforaging sites by significant 
differences among group size, tem- 
perature, turbidity, and season. Habi- 
tat selection analysis on individual 
variables indicated that foraging was 
more frequently observed in waters 
4-6 m deep, 200-500 m from shore, 
and at salinity values of around 20 
psu. This fine-scale and multivariate 
approach represents a useful method 
of exploring the complexity, grada- 
tion, and detail of the relationships 
between environmental variables and 
the foraging distribution patterns of 
bottlenose dolphin. 
Manuscript submitted 20 October 2008. 
Manuscript accepted 29 October 2009. 
Fish. Bull. 108:79-86 (2009). 
The views and opinions expressed or 
implied in this article are those of the 
author (or authors) and do not necessarily 
reflect the position of the National Marine 
Fisheries Service, NOAA. 
Cara E. Miller (contact author) 
Donald M. Baltz 
Identifying bottlenose dolphin (Tur- 
siops truncatus) foraging habitat is 
critical for effective species conserva- 
tion. However, simply describing for- 
aging habitat as a geographic location 
or habitat type may be inadequate and 
incomplete given the heterogenous 
and variable nature of marine envi- 
ronments (Miller and Cribb, 2009). 
Therefore, measuring and quantify- 
ing the environmental variables that 
characterize bottlenose dolphin forag- 
ing habitat provides a more power- 
ful and flexible tool for implementing 
management strategies. 
For the well-studied bottlenose dol- 
phin (Tursiops spp.), investigations 
into foraging habitat have been un- 
dertaken with a range of approaches 
in a wide variety of locations. In some 
instances, general habitat type and 
oceanographic features have been re- 
lated to congregations of bottlenose 
dolphin prey by observations of in- 
creased rates of feeding, notably in 
estuarine areas (Ballance, 1992) and 
at interfaces between open ocean and 
protected estuaries, seagrass beds, 
and mangrove shorelines (Grigg and 
Markowitz, 1997; Harzen, 1998). 
Gregory and Rowden (2001) have ob- 
served feeding activity in association 
with tidal movement. Hastie et al. 
(2004) correlated surface feeding be- 
havior with submarine habitat char- 
acteristics, and Bailey and Thompson 
(2006) used modeling techniques to 
further quantify and investigate these 
relationships. Others have investigat- 
ed the frequency of feeding behavior 
in relation to group size (Shane et al., 
1986; Gregory and Rowden, 2001) and 
Campbell et al. (2002) suggested that 
larger groups are more effective and 
efficient in searching for food by using 
cooperative feeding tactics. Numerous 
other studies have noted similar rela- 
tionships between seasonal environ- 
mental patterns and the frequency of 
bottlenose dolphin sightings (Wilson 
et al., 1997; Stockin et al., 2006), but 
environmental variables relating to 
this seasonality have not always been 
quantified. 
The objective of our research was to 
investigate the differences in environ- 
mental habitat between foraging and 
nonforaging locations of bottlenose 
dolphins within an inshore bay of the 
Northern Gulf of Mexico (Waring et 
al., 2007). In addition, the marine 
environment of the study site was 
characterized on a seasonal basis. 
The fine-scale approach we employed 
measured a suite of environmental 
variables and allowed us to discern 
more spatially explicit patterns of 
habitat use by bottlenose dolphins. 
Methods 
Study area 
This study was conducted in Barataria 
Basin, an estuary along the northern 
