Sex specific differences in the ranging patterns of Indo-Pacific bottlenose dolphins in southwest Australia

Abstract

The analysis of ranging patterns is important to the understanding of species ecology, population dynamics and social and genetic structure. Ranging patterns are influenced by social systems, predation risk, foraging strategies and resource availability. Bottlenose dolphins display a high degree of variability in population structure among different geographic locations. In this study, we investigated differences in ranging patterns between adult male and female Indo-Pacific bottlenose dolphins (Tursiops aduncus) in a temperate environment in Bunbury, Western Australia. To achieve this, we conducted systematic boat-based surveys (n>530) along pre-determined transect lines throughout the 540 km2 study area. Photo-identification data were collected year-round over six consecutive years (2007-2013). More than 1280 dolphin groups were encountered, where over 440 dolphins were catalogued by distinctive fin markings and sex was determined for 55 males and 140 females through genetic analysis or visual observations. A sensitivity analysis was carried out to determine the minimum number of sightings required to most accurately portray range size. Results from minimum convex polygons and fixed kernel estimators revealed that adult males had larger ranges than females and several key areas for females were highlighted. We hypothesize that adult males range further in search for potential mates and that female range patterns are affected by ecological parameters, such as, availability of resources and protection from predators. The key areas identified may be of interest for conservation and management purposes