Bottlenose dolphin (Tursiops truncatus) stock structure within the estuaries

of southern Georgia, U.S.A. Brian C. Balmer 1,2, Lori H. Schwacke 3, Randall S. Wells 1, Jeff D. Adams 4, R. Clay George 5, Suzanne M. Lane 3, William A. McLellan 2,

Patricia E. Rosel 6, Kate Sparks 5, Todd Speakman 3, and D. Ann Pabst 2 1 Chicago Zoological Society, c/o: Mote Marine Laboratory, 1600 Ken Thompson Parkway, Sarasota, FL, 34236 USA; 2 University of North Carolina Wilmington, Department of Biology and Marine Biology, 601 South College Road, Wilmington, NC, 28403 USA; 3 National Oceanic and Atmospheric Administration, National Centers for Coastal Ocean Science, Hollings Marine Laboratory, 331 Fort Johnson Road, Charleston, SC, 29412 USA; 4 National Oceanic and Atmospheric Administration, National Marine Fisheries

Service, 1315 East-West Highway, Silver Spring, MD, 20901 USA; 5 Georgia Department of Natural Resources, Nongame Conservation Section, One Conservation Way, Brunswick, GA 31520 USA; 6 National Oceanic and Atmospheric Administration, National

Marine Fisheries Service, Southeast Fisheries Science Center, 646 Cajundome Boulevard, Lafayette, LA 70506 USA

Correspondence: bbalmer@mote.org

Bottlenose dolphins within southern Georgia, U.S.A. estuaries have been exposed to extremely high

levels of persistent organic pollutants. Dolphins in this region have the highest polychlorinated biphenyl

levels recorded for any marine mammal and these levels are related to the distance from a Superfund

point-source in the Turtle/Brunswick River Estuary (TBRE). Little previous information is available about

dolphin population structure in this region. This study provides baseline data on abundance, site-fidelity,

and habitat use of dolphins across two adjacent field sites defined as the Brunswick field site, which

included the TBRE, and the Sapelo field site, which included the Sapelo Island National Estuarine

Research Reserve. The Sapelo field site is relatively undeveloped and was selected for comparison to

the more contaminated TBRE. Despite similar survey areas, total dolphin abundance, calculated using

capture-recapture techniques, and dolphin density, measured as the total number of dolphins per

kilometer, were higher in the Sapelo field site, in almost every season surveyed, than in the Brunswick

field site. Dolphins also utilized habitat differently between the two sites. Dolphin densities were similar

across tributary sizes in the Brunswick field site, while dolphin density increased with larger tributary size

in the Sapelo field site. Within both field sites, there were seasonal fluctuations in abundance, with

highest numbers observed in summer and fall. The majority of dolphins sighted during these peaks had

low site-fidelity, and were sighted within larger tributaries, suggesting that these individuals may be

visitors to the region. During seasons with lower abundance, most dolphins had moderate to high site-

fidelity and were sighted across all tributary sizes, suggesting that these individuals may be estuarine

residents. The results of this study provide insight into the appropriate survey effort required in future

stock assessments in other estuaries along the U.S. Atlantic and Gulf of Mexico coasts.

Abstract

Bottlenose dolphins within southern Georgia estuaries are exposed to

extremely high levels of persistent organic pollutants (POPs) from four

Superfund sites (Pulster et al., 2009)

Dolphins in this region have the highest polychlorinated biphenyl

levels (PCBs) for any marine mammal (Balmer et al., 2011)

Dolphin PCB concentrations related to distances sampled from

Superfund site (Balmer et al., 2011)

Dolphin stock structure in this region is poorly unknown

Introduction

To provide baseline data on abundance, site-fidelity, and habitat use of

dolphins across two adjacent field sites in Georgia (Fig. 1):

1) Brunswick field site- TBRE and surrounding waters

2) Sapelo field site- Sapelo Island National Estuarine Research

Reserve (SINERR) and surrounding waters

Research Goals

Methods Seasonal abundance

Vessel-based photo-identification surveys conducted each

season for 2 years (2008-2009)

Capture-recapture techniques and robust design models

utilized to estimate abundance (Pine et al., 2003)

Site-fidelity

All individuals grouped into statistically defined bins based

upon total number of photo-identification sightings (Balmer et al., 2008)

LOW (1-6 sights)

Habitat use

Strahler Stream Order (SSO)- quantitative technique used to

classify habitat based upon the number of upstream

tributaries (Fig. 2a)

Dolphin density- Total number of dolphins sighted per

kilometer of survey effort, within each SSO (Fig. 2b)

Two-way ANOVA including SSO and field site as factors

performed in JMP 7.0 (SAS Institute Inc., Cary, North Carolina, USA)

Dolphin abundance in Sapelo higher in almost every season

than Brunswick (Fig. 3)

Dolphin density in larger tributaries (SSO 3 and 4) three to

four times higher in Sapelo than Brunswick (Fig. 5)

Number of factors that may be contributing to differences:

Carrying capacity- variations in productivity and prey species

abundance may contribute to differences in dolphin abundance

and density (Young and Phillips 2002)

• Land Use

Smooth cordgrass (Spartina alterniflora)- most significant primary

producer within salt marsh estuary (Schelske and Odum 1961)

Development of salt marsh into industrial sites may reduce

productivity in Brunswick field site

• Contaminants

POP contamination negatively affects reproduction and nursery

habitat in dolphin prey species (Rogers et al., 1984, Thomas 1989)

High PCB levels from Superfund sites may be influencing the

survival and recruitment of fish utilizing the Brunswick field site

Lower dolphin densities in the larger Brunswick tributaries

(Fig. 5), as compared to those in Sapelo, may be due to

decreased numbers of dolphin prey in the Turtle River and St.

Simons Sound, which are adjacent to the Superfund sites

Localized stressors- impact dolphin demographic parameters,

such as birth and survival rates, which may result in abundance

differences between field sites

• Vessel Activity

Brunswick field site- includes the city of Brunswick, which is the

sixth-busiest automobile port along the U.S. east coast, four

Superfund sites, and other industrial influences (EPA 2007, Morris 2007)

Sapelo field site- includes the SINEER, which is relatively

undeveloped, and experiences less vessel disturbance (Owen and White 2005)

Lower dolphin abundance in Brunswick may be a result of

increased vessel activity as seen in other regions of the world,

such as Shark Bay, Australia (Bejder et al., 2006)

• Contaminants

Extremely high levels of PCBs have been identified as potential

stressors to marine mammals (reviewed in Schwacke et al., 2002)

High PCB levels in Brunswick female dolphins may promote an

increased risk for reproductive failure (Balmer et al., 2011)

Reproductive effects associated with a PCB point-source in

Brunswick could be contributing to the differences in dolphin

abundance between field sites

Conclusions

Figure 2. (a) SSO schematic representation and

(b) example in the study area.

a. b.

Results

Acknowledgements

Figure 1. Southern Georgia study area (SGA).

Figure 3. Dolphin total

abundance and 95%

confidence interval (CI)

for each season in the

Brunswick and Sapelo

field sites.

Figure 4. Frequency of

individual dolphins sighted

by site-fidelity classification

and year in the Brunswick

and Sapelo field sites.

Figure 5. Dolphins per

kilometer of survey effort

within the Brunswick and

Sapelo field sites, by SSO

classification. Note: Pairwise comparisons for field

site/SSO interaction were made using

Tukey’s HSD test. Points that share

same letter are not significantly different

from each other.

This research was funded by NOAA’s Ocean and Human Health Initiative and NOAA’s Marine Mammal Health and Stranding Response Program

and conducted under Scientific Research Permit Number 932-1905/MA-009526 issued by NOAA Fisheries and IACUC permit numbers HQ-2009-

001 and UNCW 2007-016. Additional support was also provided by the Chicago Zoological Society, University of North Carolina Wilmington,

Georgia Department of Natural Resources, North Carolina Protect Wild Dolphins license plate. and the Dolphin Project. We would like to thank F.

Scharf for statistical analysis assistance; E. Zolman, P. Clarke, and B. Danielson for logistical and field efforts; and the Sapelo Island National

Estuarine Research Reserve, and particularly D. Hurley, for support of this research and logistical assistance.

MOD. (7-12 sights) HIGH (13-18 sights)

Future research Carrying Capacity

• Land use- investigate land use classifications and determine primary

productivity rates

• Contaminants- identify POP levels of dolphin prey species and

systematic dolphin prey sampling

Localized Stressors

• Vessel Activity- perform focal follows to identify different levels of

human activity/interactions

• Contaminants- continued photo-identification surveys to determine

dolphin survivorship