COMPARISON OF BOTTLENOSE DOLPHIN, TURSIOPS TRUNCATUS, HOT SPOTS ACROSS
TRANSECT AND OPPORTUNISTIC SURVEY METHODS
Shauna M.
1Department
1
McBride
and Jessica S.
2
Taylor
of Psychology, University of Southern Mississippi and 2Outer Banks Center for Dolphin Research
Abstract
One major challenge in marine mammal research is comparing studies using different survey methods and understanding how these different methods can influence results. The objective of this
project was to analyze dolphin habitat utilization patterns in Roanoke Sound, North Carolina and to examine how results vary between data collected via transect surveys and those collected by
opportunistic surveys. Transect surveys were conducted by the Outer Banks Center for Dolphin Research from 2009 to 2013. Opportunistic surveys were conducted aboard the Nags Head Dolphin
Watch from 2009 to 2013. Sighting data was recorded in the same way aboard both platforms. Dolphin group clustering patterns were analyzed separately across transect data and opportunistic
data using the Hot Spot Analysis (Getis-Ord Gi* statistic) within ArcGIS. Hot spot analyses were conducted for groups exhibiting feed, mill, social, and travel activity states to determine how the
habitat was being utilized. Preliminary results indicate some overlap in hot spots between transect sightings and opportunistic sightings, but not all hot spots were consistent across survey methods.
Only feed and travel hot spots were compared across transect data and opportunistic data due to insufficient sample size for mill and social sightings. Results show some overlap of feed and travel
hot spots between transect sightings and opportunistic sightings. Based on results, transect data provides a more accurate representation of dolphin distribution in the survey area due to control of
survey effort. Opportunistic data can still provide valuable information on what behaviors occur most frequently and how those behaviors are distributed throughout the survey area. Together, these
two survey methods can complement each other in order to better understand dolphin distribution and habitat utilization patterns within a given area.
Introduction
• Research on marine mammals has been conducted using a variety
of survey methods to collect data.
• Understanding how survey methods can influence results is
important in order to compare results across studies.
Study Objective
• The objective for this study is to compare habitat utilization results
using data collected via transect surveys and those collected by
opportunistic surveys in Roanoke Sound, North Carolina.
Study Area
• Roanoke Sound is located in the northern Outer Banks and
provides a seasonal habitat for bottlenose dolphins from late spring
to early fall (Taylor et al. 2014; Waring et al. 2013).
• This body of water separates Roanoke Island from Nags Head and
drains freshwater from Albemarle Sound to Oregon Inlet.
• The area ranges from 1 to 4 feet deep near shore and the central
channel ranges from approximately 4 to 16 feet deep.
Results
Results
• Survey effort is listed in Table 1 (Feed and probable feed groups
were consolidated into one behavior category).
Table 1. Survey effort for survey methods.
Transect
Surveys
29
Groups
72
Feed Groups
35
Mill Groups
2
Social Groups
11
Travel Groups
51
Opportunistic
486
1120
632
112
314
787
• There were 4 transect hot spots in the middle and lower channel.
• There were 7 opportunistic hot spots in the middle channel.
• Two transect hot spots overlapped with opportunistic hot spots.
Figure 2. Hot spot results for transect and opportunistic groups.
Figure 1. Survey area with transect and opportunistic sightings.
Discussion
• Transect sample size for mill and social behaviors was insufficient to
analyze so only feed and travel behaviors were compared.
• There were 4 transect feeding hot spots in the channel.
• There were 7 opportunistic feeding hot spots in the channel.
• One transect feeding hot spot overlapped with an opportunistic
feeding hot spot in the middle channel.
Methods
• Transect surveys were conducted by the Outer Banks Center for
Dolphin Research from 2009 to 2013.
• Survey effort was controlled in ArcGIS 10.1 by dividing the
number of groups within a 1 km2 grid cell by the overall transect
mileage within that grid cell (groups/km).
• Opportunistic surveys were conducted aboard the Nags Head
Dolphin Watch during the same period.
• Survey effort was not controlled due to lack of track log.
• Researchers recorded date, location, time, group size, group
behavior, and environmental data.
• Behavior definitions are adapted from Urian and Wells (1996) which
include feed, probable feed, mill, social, and travel.
• The Hot Spot Analysis (Getis-Ord Gi*) tool in ArcGIS 10.1 was
applied to determine frequently utilized areas called hot spots for
transect data and opportunistic data separately.
• Hot spot analyses were conducted for each behavior and compared
across both survey methods.
• There were 4 transect traveling hot spots in the channel.
• There were 7 opportunistic traveling hot spots in the channel.
• Two transect travel hot spots overlapped with opportunistic hot
spots in the middle channel.
Figure 3. Feeding hot spots for transect and opportunistic groups.
• Results show that the middle and lower parts of Roanoke Sound,
specifically the channel, are frequently utilized by dolphins for
feeding and traveling.
• These areas are located in close proximity to Oregon Inlet which
provides access between inshore estuaries and the Atlantic Ocean
for traveling dolphins.
• The narrow part of the channel may act as a bottleneck to capture
prey for foraging dolphins (Wilson, Thompson, and Hammond 1997).
• Transect and opportunistic analyses did not always detect the same
hot spots; however, some overlap suggests that there is some
reliability in results across the two survey methods.
• Transect analyses detected fewer hot spots compared to
opportunistic analyses, but small transect sample size may be a
partial contributor to this result.
Conclusions
• Both survey methods can complement each other to analyze
different aspects of dolphin distribution and habitat utilization.
• Transect data is able to control for survey effort and provide a more
accurate representation of dolphin distribution.
• Opportunistic data can offer increased sample sizes and insight on
how behavior is distributed across the habitat.
Acknowledgements
The authors would like to thank the interns and volunteers that helped collect and process data for the Outer
Banks Center for Dolphin Research. We would also like to thank the Nags Head Dolphin Watch for serving as a
platform for opportunistic data collection and Jeff Adams for assistance with FinBase. Funding for transect field
research was provided by the Outer Banks Center for Dolphin Research through fundraisers, a grant from the North
Carolina Community Foundation, and private donations. Transect survey data was collected under NOAA Permit #s
LOC-13416 and LOC-17988 awarded to J. Taylor.
Literature Cited
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