Site fidelity, residency, and abundance of bottlenose dolphins (Tursiopssp.) in Adelaide's coastal waters, South Australia

Abstract

Little is known about the ecology and behavior of southern Australian bottlenose dolphins (Tursiops sp.). This hinders assessment of their conservation status and informed decision‐making concerning their management. We used boat‐based surveys and photo‐identification data to investigate site fidelity, residency patterns, and the abundance of southern Australian bottlenose dolphins in Adelaide's coastal waters. Sighting rates and site fidelity varied amongst individuals, and agglomerative hierarchical cluster analysis led to the categorization of individuals into one of three groups: occasional visitors, seasonal residents, or year‐round residents. Lagged identification rates indicated that these dolphins used the study area regularly from year to year following a model of emigration and reimmigration. Abundance estimates obtained from multisample closed capture‐recapture models ranged from 95 individuals (SE ± 45.20) in winter 2013 to 239 (SE ± 54.91) in summer 2014. The varying levels of site fidelity and residency, and the relatively high number of dolphins found throughout the study area highlights the Adelaide metropolitan coast as an important habitat for bottlenose dolphins. As these dolphins also appear to spend considerable time outside the study area, future research, conservation, and management efforts on this population must take into account anthropogenic activities within Adelaide's coastal waters and their adjacencies.

Demography of southern Australian bottlenose dolphins living in a protected inverse estuary

“…These densities, particularly in the inner area, are higher than the dolphin densities observed for coastal Adelaide (i.e. 0.48–1.22 individuals km −2 , derived from Zanardo et al, ). Thus, Coffin Bay, and particularly the inner area, appears to be an important habitat for southern Australian bottlenose dolphins in South Australia.…”

Decline in abundance and apparent survival rates of fin whales (Balaenoptera physalus) in the northern Gulf of St. Lawrence

“…AHC analysis was chosen over alternative clustering and ordination methods because it follows a bottom‐up approach that does not require prior specification of the expected number of clusters. The method has been applied to study residency patterns in other marine vertebrates (Daly, Smale, Cowley, & Froneman, ; Zanardo, Parra, & Möller, ). The site fidelity indices were standardized relative to the median and the median absolute deviation using the scale function in R, in order to enable comparisons of the two indices.…”

High site fidelity and restricted ranging patterns in southern Australian bottlenose dolphins

“…To identify clusters of individuals with similar degrees of site fidelity, the individuals’ values of site‐fidelity index, survey‐route sighting rate, and fieldwork‐season sighting rate were used in an agglomerative hierarchical clustering (AHC) analysis (Hunt et al., ; Zanardo et al., ). The AHC builds a dendrogram based on a bottom‐up clustering method, which starts with each observation as an individual cluster and successively combines the clusters according to their similarity until resulting into a single final cluster (Legendre & Legendre, ).…”

“…Delphinids show a wide variety of site fidelity and ranging patterns. Some individuals may occupy large ranges while others are restricted to smaller areas; some display year-round residency patterns while others are seasonal or transient visitors (e.g., Connor, Wells, Mann, & Read, 2000;Hunt et al, 2017;McGuire & Henningsen, 2007;Parra, Corkeron, & Marsh, 2006;Silva et al, 2008;Zanardo, Parra, & Möller, 2016). This variety of site fidelity and ranging patterns is thought to be mainly linked to the spatial and temporal predictability of available food resources (Gowans, Würsig, & Karczmarski, 2008).…”