Association patterns and population dynamics of bottlenose dolphins in the Strait of Sicily (Central Mediterranean Sea): implication for management

Abstract

An understanding of the population dynamics and social organization of cetaceans is essential to manage the influence of anthropogenic activities. In this study, the population size, site fidelity and social interactions of bottlenose dolphins in the Strait of Sicily (Italy) were investigated to provide recommendations for their conservation. Mark‐recapture analysis was based on the encounter histories of 103 marked dolphins from 2004 to 2015. The POPAN formulation of the Jolly–Seber model in MARK software was used to estimate the size of the super‐population. Site fidelity and social organization were estimated for individuals re‐sighted ≥3 times. The estimated population size was 140 (SE = 15.75; 95% CI = 106–164). Dolphins had low site fidelity, and both adults and sub‐adults move outside the study area. Females with calves used the area longer than other individuals. Based on our results, dolphins’ home range likely extended beyond the study area. The mean value of the Half‐Weight Association Index was low and the preferred association was by casual acquaintance. However, we found a distinct aggregation of post‐parturition females during the final 2 years of the study. Therefore, the pattern of association was apparently a response to an ecological requirement, which was the possibility to breed in high productivity waters. Whether these individuals are part of a larger pelagic population is unknown; however, we can conclude that the management of only coastal waters is insufficient for the conservation of dolphins in the Strait of Sicily.

Bottlenose dolphins (Tursiops truncatus) in North Dalmatia, Croatia: Occurrence and demographic parameters

“…Although definitions of regular vs. rare individuals, or residents vs. transients when actual residency can be established, vary among studies, the link between site fidelity and habitat characteristics was found in other studies. For instance, populations in open habitats off Sicily (Papale et al, 2017) and in the Madeira Archipelago (Dinis et al, 2016) comprised a low proportion of residents, while studies in the enclosed Amvrakikos Gulf, Greece (Bearzi, Agazzi, Bonizzoni, Costa, & Azzellino, 2008a; Gonzalov et al, 2016) and Sado Estuary, Portugal (Augusto, Rachinas‐Lopes, & dos Santos, 2012) found a high degree of site fidelity for the local communities. In the eastern Adriatic Sea, and using the same arbitrary criteria as in this study (observed in 1 year only), 56% of all identified individuals in the island of Vis area were rare (Holcer, 2012), whereas in Slovenian and adjacent waters 48% of individuals were rare (Genov, Kotnjek, Lesjak, Hace, & Fortuna, 2008).…”

“…Bottlenose dolphins show a high diversity in site fidelity across their distribution, ranging from year-round presence in a defined area, as in Gulf of Ambracia, Greece (Gonzalvo et al, 2016), Moray Firth, Scotland (Wilson et al, 1997), and Sarasota Bay, Florida (Wells & Scott, 1990) to seasonal (Lodi, Cantor, Daura-Jorge, & Monteiro-Neto, 2014) or occasional presence (Papale et al, 2017). The site fidelity can depend on habitat type, prey availability, social structure, and natal philopatry, and is therefore indicative of the ecology of a local population (Dinis et al, 2016;Rako-Gospi c et al, 2017).…”

Bottlenose dolphin (Tursiops truncatus) social structure in the Shannon Estuary, Ireland, is distinguished by age‐ and area‐related associations

“…), St Johns River, Florida (0.05 ± 0.02; Ermak ), Sicily, Italy (0.06 ± 0.02; Papale et al . ), and the Sado Estuary, Portugal (0.45 ± 0.15; Augusto et al . ).…”

The influence of fish farm activity on the social structure of the common bottlenose dolphin in Sardinia (Italy)

“…This pattern was also detected in other Mediterranean sites. For example, in the Aeolian Archipelago (Italy) females in similar reproductive status formed strong association (Blasi & Boitani, 2014), while in the Straits of Sicily social relationships among post-parturition females were identified (Papale et al, 2016).…”