Journal Article

Photographic mark-recapture analysis of local dynamics within an open population of dolphins

Durban, J, Fearnbach, H, Claridge, D, Parsons, K

2012

Overview

Identifying demographic changes is important for understanding population dynamics. However, this requires long-term studies of definable populations of distinct individuals, which can be particularly challenging when studying mobile cetaceans in the marine environment. We collected photo-identification data from 19 years (1992-2010) to assess the dynamics of a population of bottlenose dolphins ( Tursiops truncatus ) restricted to the shallow (<7 m) waters of Little Bahama Bank, northern Bahamas. This population was known to range beyond our study area, so we adopted a Bayesian mixture modeling approach to mark-recapture to identify clusters of individuals that used the area to different extents, and we specifically estimated trends in survival, recruitment, and abundance of a \"resident\" population with high probabilities of identification. There was a high probability ( p = 0.97) of a long-term decrease in the size of this resident population from a maximum of 47 dolphins (95% highest posterior density intervals, HPDI = 29-61) in 1996 to a minimum of just 24 dolphins (95% HPDI = 14-37) in 2009, a decline of 49% (95% HPDI = −5% to −75%). This was driven by low per capita recruitment (average ∼0.02) that could not compensate for relatively low apparent survival rates (average ∼0.94). Notably, there was a significant increase in apparent mortality (∼5 apparent mortalities vs. ∼2 on average) in 1999 when two intense hurricanes passed over the study area, with a high probability ( p = 0.83) of a drop below the average survival probability (∼0.91 in 1999; ∼0.94, on average). As such, our mark-recapture approach enabled us to make useful inference about local dynamics within an open population of bottlenose dolphins; this should be applicable to other studies challenged by sampling highly mobile individuals with heterogeneous space use.

• Publisher: Ecological Society of America
• Subject: Bahamas / Bayesian statistics / bottlenose dolphin / capture-recapture / clusters / dolphins / hurricanes / Jolly-Seber / Little Bahama Bank, northern Bahamas / marine environment / mark-recapture studies / mixture models / population dynamics / probability / survival rate / transients / Tursiops truncatus