Density and Abundance of Delphinus delphis in Waters South of Samos Island, Greece (Eastern Mediterranean Sea)

Guido Pietroluongo,Anastasia Miliou,Rosalia Maglietta,Roberto Carlucci,Simone Antichi,Giulia Cipriano,Heloise Carlier,Karthik Ashok,Carmelo Fanizza

doi:10.3390/jmse8030218

Abstract

The Mediterranean subpopulation of short-beaked common dolphin Delphinus delphis is ranked as endangered on the IUCN (International Union for Conservation of Nature) Red List because it has sharply declined during the last decades, resulting in sparse and decreasing populations. Monitoring the conservation status of this endangered dolphin species is particularly relevant to fulfil targets under the range of several international agreements. Moreover, estimating the abundance of D. delphis is essential to verify the effectiveness of conservation action to maintain safe population levels in the Mediterranean Sea and to suggest appropriate modifications to limit potential threats. In this regard, a monitoring program of the short-beaked common dolphin in Samos Island (Greece) was carried out from 2016 to 2019, adopting a random line transect sampling method. The overall density and abundance estimates of D. delphis, obtained by applying conventional distance sampling (CDS) on sighting data, were 0.15 individuals/km2 (CV = 13.27%; 95% CI = 0.11–0.19 individuals/km2) and 51 individuals (CV = 13.27%; 95% CI = 40-66 individuals), respectively. Although, a longer time series of sighting data should be collected and a larger area should be investigated to better understand the population trend of D. delphis and its residency pattern, the results contribute to setting up a baseline reference for future assessment of its population in the Eastern Aegean Sea.

Highlights

The short-beaked common dolphin Delphinus delphis is one of the cetacean species that regularly occurs in both the coastal and pelagic domains of the Mediterranean Sea as well as in other oceanic areas [1,2], with its spatiotemporal occurrence linked to seasonal fluctuations in sea-surface temperature and upwelling currents [3,4]
D. delphis and other cetacean species represent key taxa in the marine food web, as they are highly responsive to anthropogenic impacts, assuming a significant role in addressing a Good Environmental Status (GES) for EU marine ecosystems according to the Marine Strategy Framework Directive (MSFD) [21,22,23]
This study aims to update information on the occurrence of D. delphis in the waters of Samos Island (Greece) and to provide estimates of density and abundance by applying the conventional distance sampling (CDS) method on sighting data collected through the study period from 2016 to 2019

Summary

Introduction

The short-beaked common dolphin Delphinus delphis (hereafter, common dolphin) is one of the cetacean species that regularly occurs in both the coastal and pelagic domains of the Mediterranean Sea as well as in other oceanic areas [1,2], with its spatiotemporal occurrence linked to seasonal fluctuations in sea-surface temperature and upwelling currents [3,4]. The Mediterranean subpopulation of common dolphin was declared endangered by the IUCN [20], and recently, the local population of D. delphis in the Gulf of Corinth was proposed as critically endangered [19]. In this regard, monitoring the conservation status of this endangered dolphin species at both the local and Mediterranean regional scale is relevant to fulfil targets under the range of several international agreements such as the Habitats Directive (Annex IV), the Barcelona Convention (Annex II), the Convention on Biological Diversity, and the ACCOBAMS agreement. Providing information on the occurrence and abundance estimates of D. delphis is essential to support the implementation of effective conservation measures to maintain safe population levels and to suggest appropriate modifications to limit potential threats

Objectives

Methods

Results