Social, spatial and isotopic niche partitioning identify an estuarine community of bottlenose dolphins as a discrete management unit

Abstract

1. Investigations of population structure across multiple niche dimensions can identify discrete management units within populations. This study examined social, spatial and isotopic niche partitioning in Indo-Pacific bottlenose dolphins (Tursiops aduncus) across ca. 600 km 2 of coastal and estuarine waters in south-western Australia, to evaluate whether estuarine dolphins should be treated as a discrete management unit.2. Photo-identification data and tissue samples were collected in 2016 and 2017 in a study area covering the Peel-Harvey Estuary (PHE) and adjacent coastal waters.A total of 1,038 dolphin groups were encountered, and 481 individuals were identified. Tissue samples for stable isotope (δ 13 C and δ 15 N) analyses were collected from 96 individuals. Social structure and complexity analyses were conducted, full and core activity spaces were identified, and their size estimated for identified social communities. Differences in stable isotope composition among individuals and communities were examined.3. A socially, spatially and isotopically distinct dolphin community occurred in the PHE. The coastal waters contained four socially and spatially, but not isotopically, distinct communities as well as a substantial number of dolphins (n = 185) that were sighted infrequently and therefore were not assigned to any community. Individuals formed three levels of relationships; the majority (78%) were weak association relationships (mean half-weight index 0.006). The estuarine community had significantly higher mean δ 13 C and significantly lower mean δ 15 N values than any of the coastal communities. 4. There is a strong scientific basis for treating the PHE dolphin community as a discrete management unit. The estuarine and coastal communities occupied different social environments, with coastal individuals sharing space with more transient individuals. This study shows the value of integrating information from multiple niche dimensions when identifying management units, and the need to consider all encountered individuals in management planning.

Isotopic Niche Analysis of Long-Finned Pilot Whales (Globicephala melas edwardii) in Aotearoa New Zealand Waters

“…Resource partitioning of socially and spatially distinct groups has been noted in other cetacea [ 115 , 143 ]. Although stranding records and sightings data show that G. m. edwardii strand all around New Zealand, only two stranding hotspot locations [ 50 ] were explored here.…”

Habitat decline of the largest known Indo-Pacific humpback dolphin (Sousa chinensis) population in poorly protected areas associated with the hypoxic zone

“…However, our findings showed that the distribution of humpback dolphins in the PRE was narrower, and their suitable habitat range could be smaller than previously expected in the PRE. The distribution of cetaceans is likely related to the internal structure of the population (Nicholson et al, 2021), and many studies have shown that the humpback dolphins population in the PRE has spatial heterogeneity in their survival rate, age compositions, nutrient status and pollutant accumulation (Gui et al, 2017;Chan, 2019;Zhang et al, 2019;Guo et al, 2020). The multiple dispersed core habitat areas of the dolphin populations recorded based on the identification of the dolphin distribution density in this study, indicates that number and distribution of the dolphin community structures (Chan, 2019) requires further exploration.…”

Demographics and viability of an estuarine community of Indo‐Pacific bottlenose dolphins

“…Only individuals identified from excellent quality photographs (as per Nicholson et al, 2012) were added to the catalog. Supplemental information on births and deaths in the identified estuarine dolphin community (Nicholson et al, 2021b), as well as photographic confirmation of resident individuals being alive and present in the estuary, came from regular monitoring effort by the Mandurah Dolphin Volunteer Rescue Group and a tour operator, Mandurah Cruises. The resulting census-level data enabled demographic rates to be calculated directly for each age class and sex.…”

“…Channel and comprised solely of individuals identified as part of social communities residing in coastal waters (Nicholson et al, 2021b). Thirteen transects were conducted in the estuary in 2018 ($109 hr) with additional effort conducted on six days ($40 hr).…”

“…The demographic parameters calculated and used as PVA inputs for the base model were considered largely unbiased. All individuals identified as part of the estuarine community (as per Nicholson et al, 2021b) were regularly sighted to confirm they were alive and resided in the estuary. Carcasses were retrieved/identified for a relatively high number (45%) of individuals (adults and juveniles) that went missing from the community.…”