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Abundance and movement patterns of the Hawai’i Island associated spinner dolphin (Stenella longirostris) stock

Tyne, J., Pollock, K., Johnston, D. and Bejder, L. (2013) Abundance and movement patterns of the Hawai’i Island associated spinner dolphin (Stenella longirostris) stock. In: 20th Biennial Conference on the Biology of Marine Mammals, 9 - 13 December, Dunedin, New Zealand.

Abstract

The recently identified Hawai’i Island spinner dolphin (Stenella longirostris) stock forages offshore at night and enters sheltered bays to rest and socialise during the day. Within these same habitats, dolphins are frequently exposed to human interactions and disturbance. Reliable population estimates are critical to implement effective management strategies. Therefore, a systematic sampling design was developed whereby boat-based photo-identification surveys were undertaken in the four main resting bays along the Kona Coast of Hawai’i Island. From September 2010 to August 2011, and for 12 days each month with 2-4 consecutive days in each bay, surveys were undertaken over 132 days of sampling resulting in >1,150 hours of effort and > 100,000 dorsal fin images. Images were graded according to photographic quality and distinctiveness. Over 1,900 hours were spent matching dorsal fin images, with over 32,000 images included in the analyses, and 607 distinctive individuals catalogued. Open capture-recapture POPAN models were fitted based on the capture histories of all individuals that were captured at least once during each month. The abundance estimate of distinct individuals was 664 (SE 20.1, 95% CI 625-704), resulting in a total stock estimate of 820 (SE 29.5, 95% CI 764-880). Multi-state models were developed to investigate spinner dolphin movement patterns between the southern region (Kauhako, Honaunau and Kealakekua Bays combined) and the northern region (Makako Bay) of the study area. The probability of an individual moving south to north (0.43) was highest in February; for an individual moving from north to south (0.32) the highest was in March. This study represents the most concerted effort to estimate the Hawai’i Island spinner dolphin stock abundance and indicates a smaller abundance than previously known. This, coupled with the current level of human disturbance, raises further concern that the stock is more vulnerable to the negative impacts from human disturbance.

Publication Type: Conference Item
Murdoch Affiliation: Centre for Fish and Fisheries Research
School of Veterinary and Life Sciences
Notes: Oral presentation
URI: http://researchrepository.murdoch.edu.au/id/eprint/20225
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