Application of a mark-recapture method for the abundance estimates of Tursiops truncatus (Delphinidae, Montagu, 1821) in the northern Ionian Sea, central Mediterranean Sea

Abstract

Cetacean population abundance is a criterion for assessing D1-Biodiversity of the EU Marine Strategy Framework Directive to achieve Good Environmental Status. Abundance estimates should be consistent, robust and validated across different methodologies. The present study focuses on estimating the abundance of the common bottlenose dolphin in the Northern Ionian Sea, by applying a mark-recapture approach to photo-identification data collected from 2016 to 2021. The POPAN model was applied to encounter histories of 139 individuals classified as transients, visitors, and seasonal residents. The best-fitting model accounted for both varying survival and entry probabilities by groups as well as varying capture probability by effort. Super-population estimate is 304 individuals (95% CI=254-362), among which 51 seasonal residents (95% CI=41-65), 128 transients (95% CI=107-153), and 125 visitors (95% CI=106-146). This study contributes to a deeper understanding of the population demographic parameters and highlights the importance of establishing a long-time series of photo-identification data.