Capitoline Dolphins: Residency Patterns and Abundance Estimate of Tursiops truncatus at the Tiber River Estuary (Mediterranean Sea)

Abstract

Periodic assessments of population status and trends to detect natural influences and human effects on coastal dolphin are often limited by lack of baseline information. Here, we investigated for the first time the site-fidelity patterns and estimated the population size of bottlenose dolphins (Tursiops truncatus) at the Tiber River estuary (central Mediterranean, Tyrrhenian Sea, Rome, Italy) between 2017 and 2020. We used photo-identification data and site-fidelity metrics to study the tendency of dolphins to remain in, or return to, the study area, and capture–recapture models to estimate the population abundance. In all, 347 unique individuals were identified. The hierarchical cluster analysis highlighted 3 clusters, labeled resident (individuals encountered at least five times, in three different months, over three distinct years; n = 42), part-time (individuals encountered at least on two occasions in a month, in at least two different years; n = 73), and transient (individuals encountered on more than one occasion, in more than 1 month, none of them in more than 1 year; n = 232), each characterized by site-fidelity metrics. Open POPAN modeling estimated a population size of 529 individuals (95% CI: 456–614), showing that the Capitoline (Roman) coastal area and nearby regions surrounding the Tiber River estuary represent an important, suitable habitat for bottlenose dolphins, despite their proximity to one of the major urban centers in the world (the city of Rome). Given the high number of individuals in the area and the presence of resident individuals with strong site fidelity, we suggest that conservation plans should not be focused only close to the Tiber River mouths but extended to cover a broader scale of area.

First Report of Epimeletic and Acoustic Behavior in Mediterranean Common Bottlenose Dolphins (Tursiops truncatus) Carrying Dead Calves

“…The area is rich in habitats and environmental conditions, and is characterized by a flourishing marine community that developed partly because of the large amount of organic material transported by the river [ 21 ]. However, crossing the city of Rome, the Tiber also contributes to enhancing pollution levels, bringing to the sea big quantities of pollutants, heavy metal and waste [ 21 ].…”

“…The area is rich in habitats and environmental conditions, and is characterized by a flourishing marine community that developed partly because of the large amount of organic material transported by the river [ 21 ]. However, crossing the city of Rome, the Tiber also contributes to enhancing pollution levels, bringing to the sea big quantities of pollutants, heavy metal and waste [ 21 ]. The study site also includes the “Secche di Tor Paterno” marine protected area and two single point moorings (SPMs, called R1 and R2) for the reception of crude oil and the supply of petroleum products (structures known to attract bottlenose dolphins [ 22 ]).…”

“…The area is well recognized for the presence of bottlenose dolphins [ 23 ], with the regular observation of mother-calf pairs and foraging behavior, thus appearing a suitable calving and feeding ground for the species [ 20 , 21 ]. To date, 347 unique individuals have been photo identified in the area, showing different patterns of site fidelity [ 21 ]. A resident group of 42 individuals with low dispersion level has been identified, half of which are classified as females [ 21 ].…”

Integration of presence‐only data from several sources: a case study on dolphins' spatial distribution

“…bathymetries), structures (e.g. seamounts) and types of habitats (Pace et al 2019(Pace et al , 2021a. Several rivers flow in this region, including the Tiber, and the simultaneous presence of both fresh and salt waters, as well as the geomorphological action of sedimentation and erosion, generate different ecological gradients, making the coastal area highly productive and rich in biodiversity (Ventura et al 2015, Ardizzone et al 2018, Casoli et al 2019.…”

Site Fidelity and Residency of Tursiops truncatus off the Aragua Coast, Venezuela-First Records of Long Residency

“…T. truncatus can show a wide range of variability in residency and site fidelity [22,40,43,46,56,58,62,65,66] . Prolonged residency and high site fidelity in the species has previously been reported; Sarasota Bay (USA) where five generations have been studied to date [67] and residency periods of 15 to 37 years recorded; Pequeña Bahama (USA) where residency of 17 years has been documented [42] ; and within Latin America the Tramandaí estuary (Brazil) with residency of 18 years confirmed [62] .…”