Photographic Capture-Recapture Analysis Reveals a Large Population of Indo-Pacific Bottlenose Dolphins (Tursiops aduncus) With Low Site Fidelity off the North West Cape, Western Australia

Abstract

Little is known about the ecology of Indo-Pacific bottlenose dolphins (Tursiops aduncus) inhabiting the coastal waters of tropical north-western Australia. We used photoidentification data collected between 2013 and 2015, site fidelity indexes and capturerecapture models to estimate the abundance and site fidelity patterns of Indo-Pacific bottlenose dolphins (T. aduncus) inhabiting the coastal waters off the North West Cape (NWC), Western Australia. A standardized site fidelity index (SSFI) indicated low site fidelity (SSFI = 0.019) at the population level to the 130 km 2 study area. Agglomerative hierarchical clustering (AHC) of individual re-sight rates classified 58% of individuals as "non-residents." Open POPAN modeling estimated a super-population size of 311 (95% CI: 249-373) individuals over the study period. A maximum likelihood transient model which considers both resident and non-resident individuals in a population, estimated a resident population of 141 (95% CI: 121-161) individuals and a super-population of 370 (95% CI: 333-407) individuals. These models indicate that a large population of Indo-Pacific bottlenose dolphins of relatively high density (an average of 2.4-2.8 bottlenose dolphins per km 2 ) inhabits the waters off the NWC. The large number of both resident and non-resident bottlenose dolphins found throughout the coastal waters off the NWC suggest this area, as well as neighboring waters outside our study area, are of high importance to this species.

Using Cost-Effective Surveys From Platforms of Opportunity to Assess Cetacean Occurrence Patterns for Marine Park Management in the Heart of the Coral Triangle

“…Consequently, both species were recorded as bottlenose dolphin (Tursiops spp.). Bottlenose dolphins are known to form stable social groups, sometimes with small resident populations that have a high affiliation to a relatively small area, likely linked to high prey availability and low predation risk (Shirakihara et al, 2002;Dulau et al, 2017;Passadore et al, 2018a;Haughey et al, 2020). In Wakatobi bottlenose dolphins occur wide-spread in the area on a regular basis, thus residency for at least some of these animals is likely.…”

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

“…For the majority of delphinids, abundance estimates are particularly challenging. They are a highly mobile and often wide-ranging top-predator species, with often open-population structures, thus requiring robust analytical methods to prevent the potential of incorrect estimates associated with irregular sampling effort, variable probability of animal detection, and non-random movement patterns [ 10 , 11 ]. Individuals may persistently or unevenly occur in a given area, being regularly or only present for short periods of time, showing different degrees of site fidelity (i.e., tendency to return to a previously occupied place; [ 12 ]).…”

“…The species is included in Annex IV of the priority species of the EU Habitats Directive (92/43/EEC), and in 2012, the International Union for Conservation of Nature (IUCN) classified the Mediterranean bottlenose dolphins as “Vulnerable” in the Red List, according to the criteria A2cde and based on a suspected population decline of at least 30% over the last 60 years [ 25 ]. As a mainly coastal species, the bottlenose dolphin is extremely exposed to anthropogenic pressures due to increasing human interaction within its habitats [ 10 ], and the decline in the Mediterranean is presumably related to the cumulative impact of several threats, including reduced availability of key prey due to overfishing and incidental mortality in fishing gear, human disturbances (recreational activities and shipping), pollution (noise and environmental contaminants), and marine debris [ 25 ].…”

Occurrence of Indo‐Pacific bottlenose dolphins (Tursiops aduncus) off the Wild Coast of South Africa using photographic identification

“…In open or exposed coastlines like the Wild Coast, mobile species are expected to range more widely and have lower site fidelity than in protected shallow bays (Cobarrubia‐Russo, Barreto, Quintero‐Torres, Molero‐Lizarraga, & Wang, 2019; Defran & Weller, 1999; Haughey, Hunt, Hanf, Rankin, & Parra, 2020; Hwang et al, 2014). In total 253 individuals (46.7%) were seen more than once off the Wild Coast, and most of them were resightings within the same study area months or years later.…”