Dolphin Distribution and Habitat Suitability in North Western Australia: Applications and Implications of a Broad-Scale, Non-targeted Dataset

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.

Aerial abundance estimates for two sympatric dolphin species at a regional scale using distance sampling and density surface modeling

“…These findings corroborate the relatively high abundance estimates that have been reported in vessel based mark-recapture photo identification studies within the smaller and localized study areas of North West Cape and Exmouth Gulf for both bottlenose (Haughey et al, 2020) and humpback dolphins (Brown et al, 2012;Hunt et al, 2017;Sprogis and Parra, 2022) and inferred for humpback dolphins in Dampier Archipelago (Allen et al, 2012). Similar results have been reported by Hanf et al (2022) who modeled the distribution of these species based on aerial survey data from the western Pilbara. In contrast, the coastal waters between the northern end of Exmouth Gulf and Dampier Archipelago, generally had lower dolphin abundance, consistent with findings from boatbased mark recapture surveys undertaken in 2015 and 2016 in this area (Raudino et al, 2018a).…”

“…Further, preliminary evidence of populations occurring in offshore areas associated with islands (e.g., Montebello Islands) indicates that the extent of the species' distribution has yet to be fully mapped and it is not yet understood whether there is genetic connectivity between these dolphins and those using nearshore coastal waters of the Pilbara (Raudino et al, 2018b). Overall, their low density, uneven distribution (Hanf et al, 2022), and limited genetic connectivity across their range (Brown et al, 2014(Brown et al, , 2017Parra et al, 2018) make humpback dolphins particularly vulnerable to extinction (Parra et al, 2017).…”

Coastal dolphins and marine megafauna in Exmouth Gulf, Western Australia: informing conservation management actions in an area under increasing human pressure

“…The Australian snubfin dolphin was not observed, despite previous records in Exmouth Gulf, albeit limited (e.g. Allen et al 2012;Hanf et al 2022). Snubfin dolphins were also not sighted during dedicated studies in adjacent waters of the North West Cape (e.g.…”

“…The distribution of dolphins in Exmouth Gulf has been opportunistically assessed through humpback whale (Jenner and Jenner 2005;Irvine and Salgado Kent 2019) and dugong aerial surveys (Preen et al 1997;Hodgson 2007;Hanf et al 2022). However, these flights were not designed specifically as dolphin surveys, and subsequently dolphins were counted secondarily to the focus species, may have been missed/ misidentified, or not identified to species level (Preen et al 1997;Hanf et al 2022).…”

“…The distribution of dolphins in Exmouth Gulf has been opportunistically assessed through humpback whale (Jenner and Jenner 2005;Irvine and Salgado Kent 2019) and dugong aerial surveys (Preen et al 1997;Hodgson 2007;Hanf et al 2022). However, these flights were not designed specifically as dolphin surveys, and subsequently dolphins were counted secondarily to the focus species, may have been missed/ misidentified, or not identified to species level (Preen et al 1997;Hanf et al 2022). In the most recent aerial survey over Exmouth Gulf, 179 dolphin groups (species not identified) were sighted opportunistically, indicating that dolphins occur throughout most of the gulf, with the highest density in the north-western section (Irvine and Salgado Kent 2019).…”