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. 2017 Dec;63(6):693-701.
doi: 10.1093/cz/zox049. Epub 2017 Aug 16.

Effects of study area size on home range estimates of common bottlenose dolphins Tursiops truncatus

Samantha R Nekolny  1 , Matthew Denny  2 , George Biedenbach  2 , Elisabeth M Howells  3 , Marilyn Mazzoil  3 , Wendy N Durden  4 , Lydia Moreland  4 , J David Lambert  1 , Quincy A Gibson  1
Affiliations

Effects of study area size on home range estimates of common bottlenose dolphins Tursiops truncatus

Samantha R Nekolny et al. Curr Zool. 2017 Dec.

Abstract

Knowledge of an animal's home range is a crucial component in making informed management decisions. However, many home range studies are limited by study area size, and therefore may underestimate the size of the home range. In many cases, individuals have been shown to travel outside of the study area and utilize a larger area than estimated by the study design. In this study, data collected by multiple research groups studying bottlenose dolphins on the east coast of Florida were combined to determine how home range estimates increased with increasing study area size. Home range analyses utilized photo-identification data collected from 6 study areas throughout the St Johns River (SJR; Jacksonville, FL, USA) and adjacent waterways, extending a total of 253 km to the southern end of Mosquito Lagoon in the Indian River Lagoon Estuarine System. Univariate kernel density estimates (KDEs) were computed for individuals with 10 or more sightings (n = 20). Kernels were calculated for the primary study area (SJR) first, then additional kernels were calculated by combining the SJR and the next adjacent waterway; this continued in an additive fashion until all study areas were included. The 95% and 50% KDEs calculated for the SJR alone ranged from 21 to 35 km and 4 to 19 km, respectively. The 95% and 50% KDEs calculated for all combined study areas ranged from 116 to 217 km and 9 to 70 km, respectively. This study illustrates the degree to which home range may be underestimated by the use of limited study areas and demonstrates the benefits of conducting collaborative science.

Keywords: bottlenose dolphin; core area; home range; kernel analysis.

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Figures

Figure 1.
Figure 1.
The 6 adjacent estuarine study areas: St Johns River (SJR), the Intracoastal Waterway (ICW) south through Duval County (DUV), the ICW south through St John’s county (SJC), the ICW south through Flagler county (FL), the ICW south to New Smyrna Beach (NSB), and south through the Mosquito Lagoon (ML).
Figure 2.
Figure 2.
Map of the intersection between the SJR and the ICW south through DUV study areas, showing the location of the truncated SJR midline. The midline truncated at the SJR and DUV intersection is displayed by the arrow. Stars represent the start and end points of the SJR survey route.
Figure 3.
Figure 3.
Univariate kernel density estimates for the distribution of sighting distances for bottlenose dolphins using the full 253 km study area. Three different bandwidth selection methods are shown: Sheather–Jones plug-in (SJPI), simple normal reference (SNR), and Silverman’s rule of thumb (SROT). SNR was selected for all analyses.
Figure 4.
Figure 4.
Mean 95% KDEs with increasing study area size for dolphins sighted ≥10 times. Error bars display the 95% confidence interval.
Figure 5.
Figure 5.
Mean 50% KDEs with increasing study area size for dolphins sighted ≥10 times. Error bars display the 95% confidence interval.
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