Abstract
Understanding species’ distribution patterns and the environmental and ecological interactions that drive them is fundamental for biodiversity conservation. Data deficiency exists in areas that are difficult to access, or where resources are limited. We use a broad-scale, non-targeted dataset to describe dolphin distribution and habitat suitability in remote north Western Australia, where there is a paucity of data to adequately inform species management. From 1,169 opportunistic dolphin sightings obtained from 10 dugong aerial surveys conducted over a four-year period, there were 661 Indo-Pacific bottlenose dolphin (Tursiops aduncus), 191 Australian humpback dolphin (Sousa sahulensis), nine Australian snubfin dolphin (Orcaella heinsohni), 16 Stenella sp., one killer whale (Orcinus orca), one false killer whale (Pseudorca crassidens), and 290 unidentified dolphin species sightings. Maximum Entropy (MaxEnt) habitat suitability models identified shallow intertidal areas around mainland coast, islands and shoals as important areas for humpback dolphins. In contrast, bottlenose dolphins are more likely to occur further offshore and at greater depths, suggesting niche partitioning between these two sympatric species. Bottlenose dolphin response to sea surface temperature is markedly different between seasons (positive in May; negative in October) and probably influenced by the Leeuwin Current, a prominent oceanographic feature. Our findings support broad marine spatial planning, impact assessment and the design of future surveys, which would benefit from the collection of high-resolution digital images for species identification verification. A substantial proportion of data were removed due to uncertainties resulting from non-targeted observations and this is likely to have reduced model performance. We highlight the importance of considering climatic and seasonal fluctuations in interpreting distribution patterns and species interactions in assuming habitat suitability.
Highlights
Understanding the factors and mechanisms that underpin species’ distribution and ecology is critical for biodiversity conservation
We investigated the influence of sea surface temperature (SST) within and between years because seasonal SST has been suggested as a driver of dolphin distribution in the offshore waters adjacent to our study area (Sleeman et al, 2007), and bottlenose dolphin distribution is influenced by El Niño-Southern Oscillation (ENSO) in southern Western Australia (WA) (Sprogis et al, 2017a)
Bottlenose dolphins were the most frequently encountered species (n = 661; 55.7%; rate of 2.90 sightings/100 km), seen across all water depths measured at lowest astronomical tide (LAT) (Geoscience Australia, 2004)
Summary
Understanding the factors and mechanisms that underpin species’ distribution and ecology is critical for biodiversity conservation. The shallow coastline of north Western Australia (WA) supports three coastal dolphin species: the Australian humpback (Sousa sahulensis) (“humpback”) dolphin; the Australian snubfin (Orcaella heinsohni) (“snubfin”) dolphin; and the Indo-Pacific bottlenose (Tursiops aduncus) (“bottlenose”) dolphin (Allen et al, 2012; Bejder et al, 2012) They are internationally listed as “Vulnerable,” “Vulnerable,” and “Near Threatened” on the International Union for the Conservation of Nature’s Red List of Threatened Species (Parra et al, 2017a,b; IUCN, 2020). Humpback and snubfin dolphins are most at risk from sub-lethal effects of habitat disturbance due to their restricted distribution within northern Australia and small, discrete populations that spatially overlap with human activities (i.e., coastal development; petroleum exploration; commercial fishing; and recreational boating) (Parra et al, 2006a; Parra and Cagnazzi, 2016; Hanf et al, 2016; Bouchet et al, 2021). The paradox is that funding is needed to obtain abundance and distribution data for these dolphins to be listed as threatened species, yet there would be a greater chance of funding being allocated for research if they were already designated as threatened
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