Dear MARMAM community,

 

On behalf of my co-authors, I’m pleased to share our latest publications on humpback dolphins in Western Australia.

 

Raudino, H.C., Bouchet, P.J., Douglas, C., Douglas, R., and Waples, K. (2023). Aerial abundance estimates for two sympatric dolphin species at a regional scale using distance sampling and density surface modeling. Frontiers in Ecology and Evolution 10. Open access here https://www.frontiersin.org/articles/10.3389/fevo.2022.1086686/full

 

Abstract - Monitoring wildlife populations over scales relevant to management is critical to supporting conservation decision-making in the face of data deficiency, particularly

for rare species occurring across large geographic ranges. The Pilbara region of Western Australia is home to two sympatric and morphologically similar species

of coastal dolphins—the Indo-pacific bottlenose dolphin (Tursiops aduncus) and Australian humpback dolphin (Sousa sahulensis)—both of which are believed to be

declining in numbers and facing increasing pressures from the combined impacts of environmental change and extensive industrial activities. The aim of this study was to

develop spatially explicit models of bottlenose and humpback dolphin abundance in Pilbara waters that could inform decisions about coastal development at a regional

scale. Aerial line transect surveys were flown from a fixed-wing aircraft in the austral winters of 2015, 2016, and 2017 across a total area of 33,420 km2. Spatio-temporal

patterns in dolphin density were quantified using a density surface modeling (DSM) approach, accounting for imperfect detection as well as both perception and

availability bias. We estimated the abundance of bottlenose dolphins at 3,713 (95% CI = 2,679–5,146; average density of 0.189 _ 0.046 SD individuals per km2) in 2015,

2,638 (95% CI = 1,670–4,168; 0.159 _ 0.135 individuals per km2) in 2016 and 1,635 (95% CI = 1,031–2,593; 0.101 _ 0.103 individuals per km2) in 2017. Too few humpback

dolphins were detected in 2015 to model abundance, but their estimated abundance was 1,546 (95% CI = 942–2,537; 0.097 _ 0.03 individuals per km2) and 2,690 (95%

CI = 1,792–4,038; 0.169 _ 0.064 individuals per km2) in 2016 and 2017, respectively. Dolphin densities were greatest in nearshore waters, with hotspots in Exmouth Gulf,

the Dampier Archipelago, and Great Sandy Islands. Our results provide a benchmark on which future risk assessments can be based to better understand the overlap

between pressures and important dolphin habitats in tropical northwestern Australia.

 

Raudino, H.C., Cleguer, C., Hamel, M.A., Swaine, M., and Waples, K. (2022). Species identification of morphologically similar tropical dolphins and estimating group size using aerial imagery in coastal waters. Mammalian Biology 102, 829–839. https://doi.org/10.1007/s42991-021-00214-2

 

Abstract -Detecting dolphins, accurately identifying species, and estimating group size during manned aerial surveys can be challenging. We used images obtained during a manned aerial survey over 13 non-consecutive days and covering a total of 3732 km of transects, in a high-wing aircraft flown at 185 km/h and an altitude of 152 m, equipped with three Single Lens Reflex cameras, to supplement estimates of dolphins recorded by observers. We used this opportunity to assess the adequacy of the resulting images for species identification of two morphologically similar dolphin species (i.e., with similar coloration and body size): the Indo-Pacific bottlenose dolphin (Tursiops aduncus) and the Australian humpback dolphin (Sousa sahulensis) and to accurately estimate dolphin group size. We also compared dolphin group estimates and species identification made by observers during the aerial survey, with manual review of the aerial images, where images overlapped with the observers’ field of view from the aircraft. We collected and reviewed 413000 images and found that an image resolution of 1.25 cm per pixel was adequate to distinguish between the two targeted dolphin species. Our findings suggest that aerial images can improve species identification and estimates of group size > 5. The camera setup and photography parameters that we describe here, with the survey altitude and speed that were used, has the potential to be used to identify, and accurately estimate other morphologically similar small-bodied (< 3 m) species in the marine environment. This will be an important consideration for future aerial surveys of low density, threatened species, that form small and sometimes mixed species groups, including humpback and bottlenose dolphins where their distribution overlaps.

 

If you have any trouble accessing the pdfs or have questions, please contact me holly.raudino@dbca.wa.gov.au Thanks for your interest in our work.

 

Holly Raudino, PhD

Senior Research Scientist

Marine Science Program

Biodiversity and Conservation Science