COMPARISON OF BOTTLENOSE DOLPHIN, TURSIOPS TRUNCATUS, HOT SPOTS ACROSS

TRANSECT AND OPPORTUNISTIC SURVEY METHODS Shauna M. McBride1 and Jessica S. Taylor2

1Department 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 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.

Figure 1. Survey area with transect and opportunistic sightings.

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.

Results

• 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.

Results

• Survey effort is listed in Table 1 (Feed and probable feed groups

were consolidated into one behavior category).

• 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.

• 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.

Figure 3. Feeding hot spots for transect and opportunistic groups.

Table 1. Survey effort for survey methods.

Transect Opportunistic

Surveys 29 486

Groups 72 1120

Feed Groups 35 632

Mill Groups 2 112

Social Groups 11 314

Travel Groups 51 787

Discussion

• 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.

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

Taylor, J., L. Hart, H. Krumsick, and J. Adams. 2014. Preliminary examination of skin lesions on bottlenose dolphins

(Tursiops truncatus) in the Outer Banks, NC. Poster presentation at the Southeast and Mid-Atlantic Marine Mammal

Symposium, 28-30 March 2014, University of North Carolina Wilmington, Wilmington, NC.

Urian, K. W. and Wells, R. 1996. Bottlenose dolphin photo-identification workshop: March 21-22, 1996, Charleston,

South Carolina. Final Report to the National Marine Fisheries Service, Charleston Laboratory, Contract No.

40EUNF500587, National Marine Fisheries Service, Charleston, SC. NOAA Tech. Mem. NMFS-SEFSC-393, 92p.

Waring, G. T., Josephson, E., Maze-Foley, K., and P. E. Rosel, eds. 2013. U.S. Atlantic and Gulf of Mexico Marine

Mammal Stock Assessment-2103. NOAA Tech. Memo NMFS-NE-228, Woods Hole, MA. 475 pp.

Wilson, B., Thompson, P. M., and Hammond, P. S. 1997. Habitat use by bottlenose dolphins: Seasonal distribution

and stratified movement patterns in the Moray Firth, Scotland. Journal of Applied Ecology 34:1365-1374.

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.

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.