Comparison of abundance and habitat usage for common bottlenose dolphins between sites exposed to differential anthropogenic stressors within the estuaries of southern Georgia, U.S.A

Abstract

The health of common bottlenose dolphins (Tursiops truncatus) within southern Georgia estuaries is of particular concern due to high levels of anthropogenic contaminants in their tissues. Dolphins in this region have the highest polychlorinated biphenyl (PCB) concentrations recorded for any marine mammal and these concentrations correlate to distance from a Superfund point‐source in the Turtle/Brunswick River Estuary (TBRE). Currently, little is known about the population structure of dolphins in this region. This study identifies and compares baseline data on abundance, habitat use, site‐fidelity, and ranging patterns of dolphins across two adjacent field sites; Brunswick, including the TBRE, and Sapelo, including the Sapelo Island National Estuarine Research Reserve. Sapelo is relatively undeveloped and was selected for comparison to the more contaminated TBRE. Dolphin densities increased with tributary size in both sites but dolphin density and total abundance were significantly higher in Sapelo than in Brunswick. Anthropogenic stressors within the TBRE may be an important factor contributing to the differences in abundance, density, and habitat use observed in this study.

Site fidelity, residency, and abundance of bottlenose dolphins (Tursiopssp.) in Adelaide's coastal waters, South Australia

“…Balmer et al . () suggested that depending on the length of time spent within the study area, these defined groups may use the habitat differently. Differences in habitat use among resident and transient individuals are also likely to occur along the Adelaide metropolitan coast, as individuals use different areas within the study site and for different periods of time.…”

“…, Balmer et al . ). Such data provide the basis for management decisions in environmental impact assessments, species conservation assessments, protected area design, conservation and research investment, and management intervention.…”

Fractal analysis provides new insights into the complexity of marine mammal behavior: A review, two methods, their application to diving and surfacing patterns, and their relevance to marine mammal welfare assessment

“…These activities are a potential source of both acute and chronic stress, in both offshore and inshore waters ( e.g ., Balmer et al . , Rossman et al . , Baş et al .…”

Integrating multiple techniques to identify stock boundaries of common bottlenose dolphins (Tursiops truncatus)

“…However, photo‐identification surveys provide additional data that cannot be obtained through telemetry alone and can be conducted without health assessments, which are not possible for many studies. For example, photo‐identification surveys in the SGA began in 2004 and have generated long‐term data on seasonal abundance, habitat use, and identification of different stocks using the region (Balmer et al ., ). Comparisons of individuals sighted within the SGA with photo‐identification catalogues along the east coast of the USA would reduce limitations associated with extended ranging patterns outside of the study area, at a cost for additional analysis time.…”

“…However, the geographic delineations of many of these stocks overlap and apportioning abundance or mortality for a specific stock in the face of overlapping stocks is particularly difficult. There have been several studies in the south‐eastern USA that have provided insight into the geographic boundaries for common bottlenose dolphin stocks (Wells, ; Wells and Scott, ; Zolman, ; Balmer et al ., , ; Speakman et al ., ; Tyson et al ., ). These studies have often required multi‐year, capture–recapture, photo‐identification surveys and tissue sampling for genetic analysis to identify stock boundaries and estimate abundance.…”