Using emerging hot spot analysis of stranding records to inform conservation management of a data-poor cetacean species

Abstract

Conservation monitoring of highly mobile species in relatively inaccessible habitats presents a considerable challenge to wildlife biologists. Effective conservation strategies require knowledge of cetacean ecology that is often challenging and expensive to obtain. Despite their caveats, stranding data represent an underused resource to study the long-term dynamics of cetacean populations. Using long-finned pilot whale (LFPW; Globicephala melas edwardii) strandings on the New Zealand coast as a case study, we present a novel approach to demonstrate how stranding data can inform conservation management of data-poor species. A total of 8571 LFPWs stranded on the New Zealand coast within a 40-year period between January 1978 and December 2017. Overall, where sex was recorded, mass stranded adults were significantly biased towards females, while a significant male bias was observed in juveniles. Strandings occurred in all months, though significant seasonal variation was evident, with 66% of stranding events reported during austral spring and summer months (October–February). Hot spot analysis (ArcGIS) identified the majority of LFPWs stranded at Golden Bay, Great Barrier Island, Stewart Island and the Chatham Islands, with emerging hot spot analysis (ArcGIS) used to identify spatiotemporal trends. While emerging hot spot analysis revealed no significant temporal trend in the annual frequency of stranding events or numbers of individuals stranded, it did reveal a significant spatiotemporal trend, with the numbers of stranded individuals declining in areas of the Far North, Coromandel, Canterbury, Otago and the Chatham Islands, and increasing in Golden Bay and Stewart Island. When combined with other contextual information, such trends help identify the most significant clusters of LFPW strandings on the New Zealand coast, provide baseline ecological data on a poorly understood subspecies, and can be used to guide conservation management of G. m. edwardii in New Zealand waters.