A Robust Design Capture-Recapture Analysis of Abundance, Survival and Temporary Emigration of Three Odontocete Species in the Gulf of Corinth, Greece.

Olivier Gimenez,Aaron W. Reed,Giovanni Bearzi,Nina Luisa Santostasi,Lavinia Eddy,Silvia Bonizzoni

doi:10.1371/journal.pone.0166650

Olivier Gimenez, Aaron W. Reed

Open Access

https://doi.org/10.1371/journal.pone.0166650

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Abstract

While the Mediterranean Sea has been designated as a Global Biodiversity Hotspot, assessments of cetacean population abundance are lacking for large portions of the region, particularly in the southern and eastern basins. The challenges and costs of obtaining the necessary data often result in absent or poor abundance information. We applied capture-recapture models to estimate abundance, survival and temporary emigration of odontocete populations within a 2,400 km2 semi-enclosed Mediterranean bay, the Gulf of Corinth. Boat surveys were conducted in 2011–2015 to collect photo-identification data on striped dolphins Stenella coeruleoalba, short-beaked common dolphins Delphinus delphis (always found together with striped dolphins in mixed groups) and common bottlenose dolphins Tursiops truncatus, totaling 1,873 h of tracking. After grading images for quality and marking distinctiveness, 23,995 high-quality photos were included in a striped and common dolphin catalog, and 2,472 in a bottlenose dolphin catalog. The proportions of striped and common dolphins were calculated from the photographic sample and used to scale capture-recapture estimates. Best-fitting robust design capture-recapture models denoted no temporary emigration between years for striped and common dolphins, and random temporary emigration for bottlenose dolphins, suggesting different residency patterns in agreement with previous studies. Average estimated abundance over the five years was 1,331 (95% CI 1,122–1,578) striped dolphins, 22 (16–32) common dolphins, 55 (36–84) “intermediate” animals (potential striped x common dolphin hybrids) and 38 (32–46) bottlenose dolphins. Apparent survival was constant for striped, common and intermediate dolphins (0.94, 95% CI 0.92–0.96) and year-dependent for bottlenose dolphins (an average of 0.85, 95% CI 0.76–0.95). Our work underlines the importance of long-term monitoring to contribute reliable baseline information that can help assess the conservation status of wildlife populations.

Highlights

The need for preserving cetaceans in the Mediterranean Sea is recognized in several international agreements (e.g. ACCOBAMS, the Agreement on the Conservation of Cetaceans of the Black Sea, Mediterranean Sea and Contiguous Atlantic Area) and robust assessments of population abundance, trends and distribution are necessary to inform conservation actions [1]
The evaluation of the conservation status of Mediterranean cetaceans has been hampered by poor information for all cetacean species, especially in the southern and eastern portions of the region [3]. We partially fill this gap by providing detailed quantitative information on the abundance of three cetacean species inhabiting the Gulf of Corinth in Greece: the striped dolphin (Stenella coeruleoalba), the short-beaked common dolphin (Delphinus delphis; hereafter “common dolphin”) and the common bottlenose dolphin (Tursiops truncatus; hereafter “bottlenose dolphin”)
From 2011 to 2015 navigation was performed on 211 days and covered 21,435 km, yielding a total of 468 sightings of striped dolphins or mixed-species groups including striped dolphins, common dolphins, or animals of intermediate pigmentation, and 53 sightings of bottlenose dolphins

Summary

Introduction

The need for preserving cetaceans in the Mediterranean Sea is recognized in several international agreements (e.g. ACCOBAMS, the Agreement on the Conservation of Cetaceans of the Black Sea, Mediterranean Sea and Contiguous Atlantic Area) and robust assessments of population abundance, trends and distribution are necessary to inform conservation actions [1]. Because of its relevance for cetaceans, the Scientific Committee of ACCOBAMS listed the Gulf of Corinth as an area of special conservation importance and called for the creation of a marine protected area (Resolution 3.22; [5]). In this area, striped dolphins are the most abundant cetacean species [4, 6]. Bottlenose dolphins occur in the Gulf in single-species groups

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