Collaborative photo-identification data were used to calculate minimum abundance estimates and to analyze movements of individuals for three spinner dolphin (Stenella longirostris longirostris) stocks within the main Hawaiian Islands. Island-specific photographic catalogs range from 11 to 215 individuals (median=49). Mark-recapture analyses produced six closed capture estimates of minimum seasonal abundance for leeward portions of Kaua‘i – 559 (CV=0.19) in Oct-Nov 2005; O‘ahu – 149 (CV=0.12) in Jun-Jul 2002 and 330 (CV=0.05) in Jul-Sep 2007; and Hawai‘i Island – 733 (CV=0.15) in May-Jul 2003, 260 (CV=0.20) in Jan-Mar 2005, and 190 (CV=0.15) in JanMar 2006. Although negatively biased due to unmodeled survey effort variability and individual heterogeneity, the estimates suggest inter-island variation in abundance and seasonal variation in dolphin numbers along leeward coasts. Movement analyses quantified individual travel distances and rates at all islands and site fidelity (using standard distance deviations) at O‘ahu and Hawai‘i Island. Findings indicate that 1) inter-island movements occur but are infrequent, particularly between stocks; 2) observed travel distances and rates vary by island; and 3) O‘ahu individuals exhibit higher site fidelity than Hawai‘i Island individuals. This study demonstrates the value of using collaborative photo-identification data to explore the complex population characteristics of spinner dolphins in the main Hawaiian Islands.
Citation:
Hill, M.C., A.L. Bradford, K.R. Andrews, R.W. Baird, M.H. Deakos, D.W. Johnston, S.D. Mahaffy, A.J. Milette, E.M. Oleson, J. Östman-Lin, A.A. Pack, S.H. Richards, and S. Yin. 2011. Abundance and Movements of Spinner Dolphins off the Main Hawaiian Islands. PIFSC Working Paper WP-11-013, Issued 28 October 2011.
Download PDF