Angler interactions with bottlenose dolphins at the South Sunshine

Begging behavior by the common bottlenose dolphin
(Tursiops truncatus) near Savannah, Georgia:
prevalence, spatial distribution, and social structure
Robin Perrtree and Tara Cox
Marine Sciences Program, Savannah State University
Abstract
Results - Prevalence
Illegal feeding of cetaceans, especially the common bottlenose dolphin (Tursiops truncatus), has led to begging
behavior in many areas worldwide. This behavior involves risks to both humans and dolphins that could lead to
injury, illness, or even death. In addition, anthropogenic food sources can lead to changes in social structure
within a population. The purpose of this study was to quantify begging behavior, examine spatial variables that
may influence the distribution of begging, and examine the social structure of dolphins with respect to begging in
the waters around Savannah, Georgia, USA. Surveys were conducted throughout inshore waterways in
summer 2009 and 2010. We observed begging on 64% of survey days and in 22% of sightings. A multivariate
linear analysis (Mantel test) indicated that beg sightings per km were significantly related to sightings per km
(ρ = 0.898, p < 0.001), mean dolphin group size (ρ = 0.162, p = 0.047), path distance to fishing piers (ρ = 0.087,
p = 0.038), and space (ρ = 0.057, p = 0.037); whereas, all other variables (e.g., boat densities and distance to
shrimp docks, dolphin tour docks, marinas, and boat ramps) were not significantly correlated to beg sightings
per km. Social analyses indicated a well differentiated society; however, there was no clear division between
begging and non-begging individuals. Community division by modularity resulted in 5 social clusters, 4 of which
contained both beggars and non-beggars. Begging dolphins were mixed throughout the social network,
indicating a potential risk of further spread of the behavior through social learning. When compared to other
areas with illegal feeding issues, Savannah had the highest rates of begging behavior. The exceptionally high
rate and wide spatial and social distribution indicate begging could cause significant problems for the animals
near Savannah. In addition, there was no correlation between human usage areas and begging locations;
rather, where there were dolphins, there was begging. Finally, in contrast to other locations worldwide, there
was no social segregation related to these human-dolphin interactions.
% Days
% Sightings
Individuals
03Jul09 Photo by R. Perrtree under permit #14219
03Jul09 Photo by S. Bowen under permit #14219
Begging Definition
• Head-up surfacing with chin out of the water within 10 m of a boat, oriented
towards the boat (left)
• OR surfacing within 2 m of a boat with ventral side towards boat (right)
% Catalog
Area (km2)
Distance (km)
Savannah, Sarasota,
GA
FL
64%
26%
22%
4%
59
24
20%
14%
230
84
6.8
Panama
City, FL
Cockburn
Sound, Australia
13%
14
16%
3.4
(Samuels and Bejder, 2004; Finn et al., 2008; Powell and Wells, 2011)
Results - Social Structure
Results - Spatial Distribution
• The Savannah catalog contains 108 individuals with ≥ 6 sightings each;
42 (39%) confirmed beggars, 55 (51%) confirmed non-beggars, and 11 (10%)
unassigned individuals.
• There was structure found within the Savannah dolphin catalog.
• Estimate of “Social Differentiation” = 0.89
• Community division by modularity identified 5 Social Clusters with a modularity
of 0.303.
• 4 of the social clusters (22-27 dolphins each) contained both confirmed
beggars and confirmed non-beggars.
• 1 social cluster contained only 2 dolphins, both of which were confirmed
beggars.
• See poster by C. Kovacs (58:12) for additional information about these social
clusters and shrimp trawler interactions.
Introduction
In other study areas worldwide:
Prevalence
• Rates of human-dolphin interactions vary between 3-26% (Finn et al., 2008; Powell and Wells, 2011)
Spatial Distribution
• Spatial distribution of human-interaction behaviors are often associated with human usage
areas such as boat ramps (Samuels and Bejder, 2004), fishing piers and bridges (Powell and Wells,
2011), slow speed zones (Cunningham-Smith et al., 2006)
• Human-interactions are often confined to small areas
• Panama City, FL - interaction area < 3.4 km2 (Samuels and Bejder, 2004)
• Sarasota, FL
- 6.8 km stretch of ICW (Cunningham-Smith et al., 2006)
Social Structure
• Segregation based on human-interactions (i.e., shrimp trawlers; Chilvers and Corkeron, 2001)
• Dolphins and boats were both distributed throughout the entire study area.
Both were found in lower densities in the Wassaw National Wildlife refuge (red
box).
Objectives
• Assess the prevalence of begging behavior by bottlenose dolphins
in Savannah, Georgia.
• Examine spatial variables that may influence begging behavior by
bottlenose dolphins in Savannah, Georgia.
• Examine the social structure of bottlenose dolphins in Savannah,
Georgia with respect to begging.
Methods
Surveys along set transects
• April through August 2009 and 2010
• All boats passed were recorded
• Detailed sighting data recorded for each
group of dolphins encountered
Prevalence of Begging
• Percent of days with begging observed
• Percent of sightings with begging observed
Panama City, FL
Sarasota, FL
Social Analysis
• Conducted in SocProg 2.4 Compiled
• All non-calf individuals with 6 or more
sightings were included in analysis
Spatial Analysis
• 1 km grid cells
• Standardized by total distance on effort in
each grid cell
• Partial Mantel test
• Spatial distribution of humandolphin interaction areas in
Panama City and Sarasota, FL
are indicated to scale; begging
was observed in Savannah
over a much larger area than in
Panama City, FL and distances
between begging locations
were much greater than in
Sarasota, FL.
• Begging was observed in 40% of the 1 km cells with sightings near Savannah
(52 of 131), including in the Wassaw National Wildlife Refuge (red box), where
there was little boat traffic.
All Maps Created by RP
• Projection: UTM 17N, NAD 1983
• Basemap: USGS National Hydrography
Dataset
• Land based points plotted by RP
• Transects created by RP
Prevalence
• Begging was found at a rate in Savannah several times higher than
any other known area worldwide. By all metrics (% days, %
sightings, % catalog, area, and distance) the Savannah area has the
worst begging problem in the world.
Spatial Distribution
• Begging was found over a wide spatial scale and the strongest
spatial trend found was with dolphin sightings per km.
• There was little correlation between begging and human usage
areas or boat traffic. This was surprising since the distribution of
human-interaction behaviors elsewhere has been shown to be
related to areas of high human use.
Social Structure
• Although there was social differentiation detected, beggars and nonbeggars were found together in 4 of the 5 social clusters.
• Social structure was NOT influenced by begging.
• Instead, social structure may be influenced by spatial use of
individual dolphins or associations with shrimp trawlers (see poster
by C. Kovacs, 58:12).
Map of study area including
transects used for surveys and
all land-based human usage
points.
Red box indicates the Wassaw
National Wildlife Refuge, an
area with very low boat traffic.
Conclusions
• The high rate and wide distribution of begging behavior could
indicate a high risk of injury or death and reduced reproductive
success for the Savannah dolphins.
• Path diagrams of Mantel test results, with
arrows indicating significant correlations of
each variable to space and to beg sightings
per km given spatial autocorrelation and
inter-correlation of all other variables shown.
• There were no significant correlations of Euclidean distances to beg sightings
per km given space and the other Euclidean distance variables (not shown).
Acknowledgements
• Research supported by NOAA Office of Education’s Educational Partnership Program, Environmental
Entrepreneurship Program, award # NA05OAR4811017.
• Fellowship support from EDGE (Enhancing Diversity in Geosciences Education through Coastal Research in
Port City) NSF award GEO-0194680.
• Thanks to the SSUDS Lab graduate students, technicians, interns, and volunteers.
• Photographs and data were collected in accordance with the Marine Mammal Protection Act under NMFS
Letter of Confirmation number 14219 issued to Dr. T. Cox.
Begging behavior by the common bottlenose dolphin
(Tursiops truncatus) near Savannah, Georgia:
prevalence, spatial distribution, and social structure
Robin Perrtree and Tara Cox
Marine Sciences Program, Savannah State University
[email protected]
Literature Cited
Chilvers, B.L. and P.J. Corkeron. 2001. Trawling and bottlenose dolphins' social structure.
Proceedings: Biological Sciences 268:1901-1905.
Cunningham-Smith, P., D.E. Colbert, R.S. Wells, and T. Speakman. 2006. Evaluation of human
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involving common bottlenose dolphins (Tursiops truncatus) in Sarasota Bay, Florida.
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