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

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.

Modelling dolphin distribution within an Important Marine Mammal Area in Greece to support spatial management planning

“…Parts of the Gulf of Corinth were included in a proposed network of marine protected areas (Giakoumi et al, ; Issaris et al, ; Stelzenmüller et al, ; Vassilopoulou et al, ). In recent years, much more detailed information has become available on the abundance, distribution, movements, and genetics of dolphin populations within the Gulf (Antoniou et al, ; Bearzi et al, ; Bearzi, Bonizzoni, Agazzi, et al, ; Bearzi, Bonizzoni, & Gonzalvo, ; Santostasi, Bonizzoni, Bearzi, Eddy, & Gimenez, ), on the critical conservation status of common dolphins (Santostasi et al, ), and on the specific anthropogenic impacts threatening marine mammals in this area (Bearzi et al, ). So far, however, all this information has not produced management action that can ensure a favourable conservation status for dolphin populations in the Gulf, let alone prevent the eradication of common dolphins (Santostasi et al, ).…”

Abundance, activity and critical habitat of the striped dolphinStenella coeruleoalbain the Gulf of Taranto (northern Ionian Sea, central Mediterranean Sea)

“…The ordinary Kriging maps predicted for each activity were transformed into binary maps using the corresponding cut-off values (Table 5). Therefore, the binary maps generated within each activity The overall density value estimated for S. coeruleoalba in the present study (0.97 specimens/km 2 ) is the highest among those reported for both the eastern (Bearzi, Bonizzoni, Agazzi, & Gonzalvo, 2011;Panigada et al, 2017;Santostasi, Bonizzoni, Bearzi, Lavinia, & Olivier, 2016) and western Mediterranean regions (Cotté et al, 2010;Forcada et al, 1994;Forcada & Hammond, 1998;Forcada, Notarbartolo di Sciara, & Fabbri, 1995;Gannier, 1998;Gómez de Segura, Crespo, Pedraza, Hammond, & Raga, 2006;Gómez de Segura, Hammond, Cañadas, & Raga, 2007;Lauriano, Panigada, Cannieri, Zeichen, & Notarbartolo di Sciara, 2010;Panigada et al, 2017;Panigada, Burt, Lauriano, Pierantonio, & Donovan, 2009;Panigada, Lauriano, Burt, Pierantonio, & Donovan, 2011). However, in these latter studies, much larger areas were considered and different observation platforms and estimation methods were used, thus caution is required in any further comparative considerations.…”

Effects of Social Organization, Trap Arrangement and Density, Sampling Scale, and Population Density on Bias in Population Size Estimation Using Some Common Mark-Recapture Estimators

“…Uniformly spaced sampling, which provided biased estimates in our study, has been used in the estimation of abundance of several whale species and the bottlenose dolphin [54][55][56]. Robust Design analysis has been used to estimate the abundance of dolphin species [57], although capture probabilities in that study were larger than 0.1 (which was the capture probability in our study). Mark-resight models that accommodate detection heterogeneity have been used to estimate population size of ungulates [58,59], although these models assume population closure and may not be applicable to more wide-ranging species.…”