Delphine Chabanne

This study assessed the status of Indo-Pacific bottlenose dolphins (Tursiops aduncus) within the Swan Canning Riverpark (SCR), Perth, Western Australia following the death of six dolphins in 2009. Between June 2011 and February 2013, 29 dolphins (excluding calves) were photo-identified during boat-based surveys (n = 76 days). Analyses of sighting rates, Lagged Identification Rates (LIR), and association patterns (Simple Ratio Index, preferred dyadic association analyses, and Lagged Association Rates (LAR)) yielded an estimated ‘community size’ of 16-18 individuals (excluding calves), similar to the estimated 17-18 residents present in 2001-3. Only 9 dolphins identified in 2001-3 were still present. LARs for adult males and adult females were best explained by a constant companion association model and a long-lasting association model, respectively. Six females (including 3 with dependent calf) were mainly observed in coastal waters adjacent to the SCR. The model best-fitting the LIRs indicated a pattern of emigration and reimmigration in which individuals were not sighted in the SCR for a period of 12-17 days. Thus, dolphins considered resident within the SCR also range within adjacent coastal waters and interact with other dolphins there. Several females with calf were consistently observed in the SCR in late summer, suggesting the estuary provides particular benefits to nursing females at that time. Future studies should investigate the genetic and demographic connectivity of the community to other dolphin populations and the appropriateness of the resident community as a management unit for the SCR.

Indo-Pacific bottlenose dolphins (Tursiops aduncus) inhabit the coastal and estuarine waters of Perth, Western Australia, a rapidly-expanding city of 1.8 million. To assess dolphin distribution and abundance, we conducted boat-based photo-identification surveys between June 2011 and February 2013 using systematic transect routes in estuarine (Swan Canning Riverpark, SCR) and adjacent coastal areas and balanced sampling effort across seasons defined according to the Australasian calendar. Seasonal abundances were estimated using mark-recapture methods following the Robust Design. The highest overall abundance was in winter 2011 (n = 252 ± 43.6, 95% CI 180-353) and the lowest abundance in summer 2012-3 (n = 109 ± 12.7, 95% CI 86-136). Estimates of dolphin abundance within the SCR were constant (n =18 ± 1.04 individuals) over the study period. The number of groups encountered in coastal areas was the lowest during summer (n =11 ± 2.7 in 2011-2 and n = 12 ± 2.5 in 2012-3), with smaller group size in summer 2012-3 (n = 3 ± 0.6 individuals per group) than summer 2011-2 (n = 6 ± 0.9 individuals per group). Most of the individuals sighted (n = 11 of 20, 55%) in each season were observed in the SCR. Many individuals (n = 89 of 198, 45%) were only observed in two seasons, with most of these sighted in winter and spring 2011. The apparent peak in abundance in 2011 may reflect the La Niña conditions present that year, perhaps through greater prey availability (e.g. baitfish assemblages). While SCR appears to maintain a small resident community, populations in coastal areas appear less defined. Continued study will further examine seasonal and spatial trends and assess possible explanatory factors, including oceanographic conditions, dolphin ranging patterns, and limitations of the sampling design.

From October 2001 to June 2003 we photo-identified 55 (including 12 calves) Indo-Pacific bottlenose dolphins (Tursiops aduncus) within the Swan-Canning Estuary in Perth, Western Australia (n = 223 survey days). Analyses of occupancy, ranging and association patterns among adults and sub-adults (n = 43, 78%) identified two main groupings: (a) transient - dolphins sighted only once and generally near the estuary mouth (n = 13, 30.2%) and (b) resident - dolphins consistently observed (n > 23 sightings) throughout the estuary (n = 18, 41.9%). Analysis of the association patterns of resident dolphins showed four groupings: two dyads of adult males; one group of adult females; and one group of sub-adults (STRESS < 0.2 and Lagged association rate (LAR) > Null LAR). The small size of the resident community and the deaths of six dolphins within the estuary in 2009 emphasise the need for new research. As part of a broader study of dolphins in the Perth metropolitan waters, from June 2011 we have been conducting systematic boat-based surveys within the estuary and adjacent waters using belt transect sampling. The aims of this research are to: (1) estimate dolphin abundance across the study area using photo-identification and mark-recapture methods; (2) determine individual residency and ranging patterns in order to better understand site fidelity and population structure; (3) determine habitat use patterns through habitat modelling; and (4) collect behavioural, environmental, and epidemiological data related to interactions with human activities and dolphin health (e.g. entanglements, epidermal diseases).

Bottlenose dolphins are valued feature of the Swan Canning river system. Sighting data indicate that dolphins use the rivers year-round and range throughout their extent. The 2009 mortality event emphasised the need to improve our understanding of the connections between dolphins and the estuary ecosystem. We address three elements of an ecosystem-based approach to dolphin conservation: (1) environmental influences on dolphins; (2) interactions between dolphins and other biological components; and (3) dolphins as a means to increase community understanding about river health. To investigate environmental influences, we are investigating: (a) the prevalence and severity of tattoo skin disease lesions on known dolphins from the river system and adjacent waters (e.g. Cockburn Sound); (b) spatial and temporal patterns in lesion occurrence; and (c) associations with salinity and other environmental factors. A preliminary investigation into dolphin foraging ecology in 2009 indicated differences between the stable isotope ratios of dolphins associated with the river system and dolphins associated with two coastal sites, and also supported behavioural observations indicating that dolphins associated with the river system are likely to feed on both marine and estuarine-based prey. Climate change and population growth will continue to alter the Swan Canning river system, suggesting that the long-term retention of dolphins as functioning ecological components of this ecosystem will on-going adaptation and change, both by dolphins and by human managing the environment around them.

Prey availability is a driving force in the distribution, behavior, and movement patterns of predators. Relative abundance, concentration, and energy content of prey all influence predator choice in space use. Bottlenose dolphin (Tursiops aduncus) abundance in the nearshore waters of Bunbury, Western Australia is found to be higher during the summer months (Smith et al, in prep). It was therefore hypothesized that the seasonal movement patterns of dolphins is influenced by higher quantity or quality of available prey during the same temporal period. To ascertain the potential influence of prey availability (quantity and diversity) and quality (calorific content) on the seasonal movement patterns of dolphins, the relative abundance and diversity of fish were sampled in three near shore habitats (coastal ocean, bay and estuary) using three fishing techniques: z-traps, beach seines, and gillnets, which targeted different prey species. Sampling was conducted in three summer and two winter seasons between 2008-2010. Three replicate samples were taken at each of the three sampling sites per season. Seasonal, annual, and regional comparisons in fish assemblage, abundance and calorific content were made. Seasonal trends in fish abundance (numbers and biomass of fish caught) and available calories vary depending on the species in question. Overall, there appears to be higher biomass and higher density values of calories available to the dolphins in the winter months. It appears that dolphin abundance is influenced more by social or physiological factors such as predator avoidance or breeding opportunities in summer (when the majority of breeding occurs (Smith et al. in prep)) and prey availability in winter. Understanding relationships between the dolphins and local fish populations is critical in managing the substantial fisheries of the region, as well as managing other factors, such as coastal development, that could affect dolphin and fish behavior.

From October 2001 to June 2003 we photo-identified 35 Indo-Pacific bottlenose dolphins (Tursiops aduncus) within the Swan-Canning Estuary in Perth, Western Australia (n = 223 survey days). Analyses of occupancy, ranging, and association patterns identified two main groupings: (a) transient - dolphins sighted less than six times generally near the estuary mouth (n = 13, 37.1%) and (b) resident - dolphins consistently observed (n > 23 sightings) throughout the estuary and in association with each other (n = 18, 51.4%). The current status of dolphins in the estuary is not known. Low-level monitoring (n = 17 survey days) in 2008-9 re-sighted nine (50%) of the 2001-3 residents, while the carcasses of two (11.1%) were recovered in 2006 and 2009, one (5.6%) was presumed dead in 2002, and the status of the other six (33.3%) is not known. The deaths of six dolphins within the estuary in 2009 raised concerns about the long-term conservation of dolphins in the estuary and emphasised the need for new research. As part of a broader study of dolphins in the metropolitan waters of Perth, from June 2011 we will be conducting systematic boat-based surveys using belt transects coupled with individual focal follows within the estuary and adjacent coastal waters. This research has several objectives: (1) estimate dolphin abundance across the study area using photo-identification and mark-recapture methods; (2) determine residency and ranging patterns for individuals in order to better understand site fidelity and population structure; (3) determine habitat use patterns through habitat modelling; and (4) collect behavioural, environmental, and epidemiological data related to interactions with human activities and dolphin health (e.g. entanglements, epidermal diseases).