Abundance estimates and habitat preferences of bottlenose dolphins reveal the importance of two gulfs in South Australia

Kerstin Bilgmann,Luciana M. Möller,Lauren Holmes,Guido J. Parra,Katharina J. Peters,Ian D. Jonsen

doi:10.1038/s41598-019-44310-3

Kerstin Bilgmann, Luciana M. Möller + Show 4 more

Open Access

https://doi.org/10.1038/s41598-019-44310-3

Copy DOI

Abstract

Informed conservation management of marine mammals requires an understanding of population size and habitat preferences. In Australia, such data are needed for the assessment and mitigation of anthropogenic impacts, including fisheries interactions, coastal zone developments, oil and gas exploration and mining activities. Here, we present large-scale estimates of abundance, density and habitat preferences of southern Australian bottlenose dolphins (Tursiops sp.) over an area of 42,438km2 within two gulfs of South Australia. Using double-observer platform aerial surveys over four strata and mark-recapture distance sampling analyses, we estimated 3,493 (CV = 0.21; 95%CI = 2,327-5,244) dolphins in summer/autumn, and 3,213 (CV = 0.20; 95%CI = 2,151-4,801) in winter/spring of 2011. Bottlenose dolphin abundance and density was higher in gulf waters across both seasons (0.09-0.24 dolphins/km2) compared to adjacent shelf waters (0.004–0.04 dolphins/km2). The high densities of bottlenose dolphins in the two gulfs highlight the importance of these gulfs as a habitat for the species. Habitat modelling associated bottlenose dolphins with shallow waters, flat seafloor topography, and higher sea surface temperatures (SSTs) in summer/autumn and lower SSTs in winter/spring. Spatial predictions showed high dolphin densities in northern and coastal gulf sections. Distributional data should inform management strategies, marine park planning and environmental assessments of potential anthropogenic threats to this protected species.

Highlights

A quarter of all large mammal species are threatened with extinction and an additional 800+ species are classified as ‘data deficient’[1]
For the winter/spring survey, the MRDS model with best fit was a DS model with a hazard rate key function scaled with the covariates glare and cloud cover; and a MR model specified with perpendicular distance (Supplementary Table S1b)
The lowest bottlenose dolphin density was estimated for central South Australian shelf waters, with very low numbers for the winter/spring survey and no dolphins observed in shelf waters during the summer/autumn survey (Table 2)

Summary

Introduction

A quarter of all large mammal species are threatened with extinction and an additional 800+ species are classified as ‘data deficient’[1]. The recently described southern Australian bottlenose dolphin ( named Burrunan dolphin; Tursiops australis)[14] occurs in coastal waters of southern Australia, including South Australia[14,15,16] This species is currently not widely recognized as a separate species by the marine mammal scientific community[17,18]. Based on previous population genetic studies of coastal bottlenose dolphins in southern Australian waters, a total of six separate genetic populations of the same species have so far been identified[15,16,23] Some of these populations inhabit small embayments and may be vulnerable to human-induced threats[14,24,25,26,27]. In waters of the southern Australian state of Victoria, for example, two genetically distinct populations[15], are currently listed as threatened under the Victorian Flora and Fauna Guarantee Act 1988

Objectives

Methods

Results

Conclusion