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17232
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Assessing the body condition of the world???s only non-migratory humpback whale population, the endangered Arabian Sea humpback whale
Fredrik Christiansen, Robert Baldwin, Gianna Minton, Tim Collins, Kate R Sprogis, Jessica Rudd, Suaad Al Harthi, Mattthew Leslie, Darryl MacDonald, Andrew Willson
International Whaling Commission
2020
SC/68B/CMP/23 Rev1
The Arabian Sea humpback whale (ASHW, Megaptera novaeangliae) is the only non-migratory humpback whale population in the world. This small and genetically isolated population is Endangered and extremely vulnerable to anthropogenic threats. While fisheries and shipping have been identified as direct threats to the population, non-lethal effects resulting from fishing gear entanglement, low prey availability and disease, have the potential to negatively affect survival and reproduction by reducing the body condition of whales. We assessed the body condition (residual of body volume against body length) of Oman???s ASHW population by comparing it to a healthy (growing) population of humpback whales of Western Australia (breeding stock D). Unmanned aerial vehicle (UAV or drone) photogrammetry methods were used to measure the body condition of ASHWs (n=9) in November 2019, and breeding stock D humpback whales of South-western Australia early (June, n=56) and late (October, n=111) in the 2017 breeding season. The body lengths of the sampled ASHWs ranged from 11.8 to 14.2 m, which means that all the sampled whales were adults. The body condition of ASHWs (mean=7.2%, SE=3.28, n=9) were similar to that of similarly-sized (11.2-15.3 m body length) breeding stock D adults at the beginning of the breeding season (mean=8.6%, SE=3.98, n=19), but significantly higher than stock D humpback whales at the end of the season (mean=3.4%, SE=3.57, n=48). This suggests that whales sampled in the study were not nutritionally supressed. Three of the ASHWs were identified as females, with their body condition (mean=12.5%, SE=6.10, n=3) being similar to that of early lactating females (mean=5.5%, SE=6.39, n=31) from the migratory stock D population. However, to determine the link between body condition and reproduction, additional sampling of ASHWs is needed to determine inter- and intra-seasonal variations in body condition. Continued research into the health of the ASHW population, together with continued monitoring of population demographics and assessment of fisheries interactions is therefore needed
