Regional Assessment of the Conservation Status of Snubfin Dolphins (Orcaella heinsohni) in the Kimberley Region, Western Australia

Abstract

Implementing conservation measures for data-limited species is a fundamental challenge for wildlife managers and policy-makers, and proves difficult for cryptic marine animals occurring in naturally low numbers across remote seascapes. There is currently scant information on the abundance and habitat preferences of Australian snubfin dolphins (Orcaella heinsohni) throughout much of their geographical range, and especially within the Kimberley region of northern Western Australia. Such knowledge gaps curtail rigorous threat assessments on both local and regional scales. To address this and assist future conservation listings, we built the first comprehensive catalog of snubfin dolphin sightings for the Kimberley. We used these data to estimate the species’ extent of occurrence (EOO) and area of occupancy (AOO) along the region’s 7,000 km coastline, following a simple Bootstrap bivariate kernel approach to combine datasets of varying quality and quantify uncertainty. Our catalog consists of 1,597 visual detections of snubfin dolphins made over a period of 17 years (2004–2020) and collated from multiple sources, including online biodiversity repositories, peer-reviewed scientific articles, citizen science programs, as well as dedicated marine wildlife surveys with local Indigenous communities and Ranger groups. Snubfin dolphins were consistently encountered in shallow waters (<21 m depth) close to (<15 km) freshwater inputs, with high detection rates in known hotspots (e.g., Roebuck Bay, Cygnet Bay) as well as in coastal habitats suspected to be suitable (e.g., Prince Regent River and surrounds, King Sound, Doubtful Bay, Napier Broome Bay and the upper Cambridge Gulf). Bootstrap estimates of EOO and AOO were 38,300 (95% CI: 25,451–42,437) km2 and 700 (656–736) km2 respectively, suggesting that snubfin dolphins in the Kimberley are likely Vulnerable under IUCN criteria B2 at a regional scale, in keeping with their global classification. Our study offers insights into the distribution of a vulnerable coastal cetacean species and demonstrates the value of integrating multiple data sources for informing conservation assessments in the face of uncertainty.

Patterns and Trends in Cetacean Occurrence Revealed by Shorewatch, a Land-Based Citizen Science Program in Scotland (United Kingdom)

“…For example, the Joint Cetacean Protocol (Paxton et al, 2016) proposes, among other recommendations, that the data supplied on effort and sightings must be related by a common code (to ensure that each sighting can be linked to the relevant unit of effort), and both must be geographically and temporally referenced. Thus, even when protocols vary widely, there are approaches which can be used to integrate multiple data sources so as to be able to infer patterns and trends in cetacean distribution and abundance (e.g., Cheney et al, 2013;Virgili et al, 2019;Waggitt et al, 2020;Bouchet et al, 2021).…”

“…This is likely to be especially true for resident populations, like that of the bottlenose dolphin (Bailey et al, 2013). Thirdly, despite increasing use of citizen science data on cetacean distribution and abundance (Bouchet et al, 2021), there is some skepticism about the use of such data in statutory population status assessments, due to perceived quality control issues such as the use of observers with various levels of training, possible misidentifications, and unconscious bias in effort toward times and locations with high cetacean occurrence.…”

Ranging Patterns and Site Fidelity of Snubfin Dolphins in Yawuru Nagulagun/Roebuck Bay, Western Australia

“…The Australian snubfin dolphin (Orcaella heinsohni, hereafter, snubfin dolphin) was described as a separate species in 2005 and is endemic to the tropical waters of northern Australia and southern New Guinea (Beasley et al, 2005). Snubfin dolphins are typically found in shallow coastal waters (<20 m) and usually in proximity (<15 km) to freshwater inputs (Parra et al, 2002(Parra et al, , 2006bParra, 2006;Bouchet et al, 2021). Due to small population sizes and ongoing cumulative impacts across their coastal habitat, snubfin dolphins were assigned a conservation status of Vulnerable to extinction by the International Union for Conservation of Nature (IUCN) (Parra et al, 2017).…”

“…Due to small population sizes and ongoing cumulative impacts across their coastal habitat, snubfin dolphins were assigned a conservation status of Vulnerable to extinction by the International Union for Conservation of Nature (IUCN) (Parra et al, 2017). Previous research suggests they are discontinuously distributed across their range as small local populations of 50-200 individuals (Parra et al, 2006a;Palmer et al, 2014b;Brown et al, 2016;Brooks et al, 2017;Bouchet et al, 2021) that exhibit site fidelity (Parra, 2006;Brown et al, 2016), and limited gene flow between populations (Brown et al, 2014b(Brown et al, , 2017. A recent study by Bouchet et al (2021) found that snubfin dolphins occupy a relatively small area within their distribution in the Kimberley, further highlighting the limited range and vulnerability of the species.…”

“…Previous research suggests they are discontinuously distributed across their range as small local populations of 50-200 individuals (Parra et al, 2006a;Palmer et al, 2014b;Brown et al, 2016;Brooks et al, 2017;Bouchet et al, 2021) that exhibit site fidelity (Parra, 2006;Brown et al, 2016), and limited gene flow between populations (Brown et al, 2014b(Brown et al, , 2017. A recent study by Bouchet et al (2021) found that snubfin dolphins occupy a relatively small area within their distribution in the Kimberley, further highlighting the limited range and vulnerability of the species. Due to their low numbers, limited resilience, and apparent reliance upon shallow waters (Parra et al, 2006b;Bejder et al, 2012;Brown et al, 2016;Bouchet et al, 2021), combined with their geographic isolation and long-lived characteristics (e.g., late maturation and low reproductive rates), snubfin dolphins are increasingly vulnerable to anthropogenic impacts, as reflected by their IUCN status.…”