Atypical residency of short-beaked common dolphins (Delphinus delphis) to a shallow, urbanized embayment in south-eastern Australia.

Suzanne Mason,Kerstin Bilgmann,David Donnelly,Jeffrey Weir,Chandra Salgado Kent

doi:10.1098/rsos.160478

Suzanne Mason, Kerstin Bilgmann + Show 3 more

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https://doi.org/10.1098/rsos.160478

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Abstract

Short-beaked common dolphins (Delphinus delphis) are typically considered highly mobile, offshore delphinids. This study assessed the residency of a small community of short-beaked common dolphins in the shallow, urbanized Port Phillip Bay, south-eastern Australia. The ability to identify common dolphins by their dorsal fin markings and coloration using photo-identification was also investigated. Systematic and non-systematic boat surveys were undertaken between 2007 and 2014. Results showed that 13 adult common dolphins and their offspring inhabit Port Phillip Bay, of which 10 adults exhibit residency to the bay. The majority of these adults are reproductively active females, suggesting that female philopatry may occur in the community. Systematic surveys conducted between 2012 and 2014 revealed that the dolphins were found in a median water depth of 16 m and median distance of 2.2 km from the coast. The shallow, urbanized habitat of this resident common dolphin community is atypical for this species. As a result, these common dolphins face threats usually associated with inshore bottlenose dolphin communities. We suggest that the Port Phillip Bay common dolphin community is considered and managed separate to those outside the embayment and offshore to ensure the community's long-term viability and residency in the bay.

Highlights

Short-beaked common dolphins (Delphinus delphis) are typically considered highly mobile, offshore delphinids
We suggest that the Port Phillip Bay common dolphin community is considered and managed separate to those outside the embayment and offshore to ensure the community’s long-term viability and residency in the bay
For the widely researched bottlenose dolphin (Tursiops spp.), residency has been reported in several geographical locations both in the southern and northern hemispheres, e.g. common bottlenose dolphins (Tursiops truncatus) in Sarasota Bay, USA [22], the Shannon Estuary, Ireland [23] and the Moray Firth, Scotland [24], bottlenose dolphins (Tursiops sp.) in Shark Bay, Australia [25,26], and Indo-Pacific bottlenose dolphins (Tursiops aduncus) in Port Stephens and Jervis Bay, New South Wales, Australia [27], the Swan-Canning River, Western Australia [28] and the Richmond and Clarence Rivers, New South Wales, Australia [29]

Summary

Introduction

Short-beaked common dolphins (Delphinus delphis) are typically considered highly mobile, offshore delphinids. This study assessed the residency of a small community of short-beaked common dolphins in the shallow, urbanized Port Phillip Bay, south-eastern Australia. [12,13,14]), bioaccumulation of heavy metals such as mercury [15], and potential increased risk of disease from pollution and increased stress [16,17] These anthropogenic impacts can affect the health, survival and reproductive success of individuals and the long-term existence of resident delphinid communities in urbanized regions, in particular when communities are small. Southern Australian coastal bottlenose dolphin communities are resident to both the Gippsland Lakes [30] and Port Phillip Bay [31], Victoria and to several regions along the coast of South Australia including the Adelaide metropolitan area in Gulf St Vincent [32,33]. Even though common dolphins are a ubiquitous species, residency in urbanized marine environments is rarely reported for this species [48]

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