Monitoring Dolphins in an Urban Marine System: Total and Effective Population Size Estimates of Indo-Pacific Bottlenose Dolphins in Moreton Bay, Australia

Abstract

Moreton Bay, Queensland, Australia is an area of high biodiversity and conservation value and home to two sympatric sub-populations of Indo-Pacific bottlenose dolphins (Tursiops aduncus). These dolphins live in close proximity to major urban developments. Successful management requires information regarding their abundance. Here, we estimate total and effective population sizes of bottlenose dolphins in Moreton Bay using photo-identification and genetic data collected during boat-based surveys in 2008–2010. Abundance (N) was estimated using open population mark-recapture models based on sighting histories of distinctive individuals. Effective population size (Ne) was estimated using the linkage disequilibrium method based on nuclear genetic data at 20 microsatellite markers in skin samples, and corrected for bias caused by overlapping generations (Nec). A total of 174 sightings of dolphin groups were recorded and 365 different individuals identified. Over the whole of Moreton Bay, a population size N of 554±22.2 (SE) (95% CI: 510–598) was estimated. The southern bay sub-population was small at an estimated N = 193±6.4 (SE) (95% CI: 181–207), while the North sub-population was more numerous, with 446±56 (SE) (95% CI: 336–556) individuals. The small estimated effective population size of the southern sub-population (Nec = 56, 95% CI: 33–128) raises conservation concerns. A power analysis suggested that to reliably detect small (5%) declines in size of this population would require substantial survey effort (>4 years of annual mark-recapture surveys) at the precision levels achieved here. To ensure that ecological as well as genetic diversity within this population of bottlenose dolphins is preserved, we consider that North and South sub-populations should be treated as separate management units. Systematic surveys over smaller areas holding locally-adapted sub-populations are suggested as an alternative method for increasing ability to detect abundance trends.

Bycatch and strandings programs as ecological indicators for data-limited cetaceans

“…There has been no reliable long-term monitoring for either the Indo-Pacific (Tursiops aduncus) or common bottlenose (Tursiops truncatus) dolphins in Queensland waters, and comparisons between surveys undertaken in different time periods are confounded by differences in methodology (Ansmann et al, 2013).…”

Sex-Specific Patterns in Abundance, Temporary Emigration and Survival of Indo-Pacific Bottlenose Dolphins (Tursiops aduncus) in Coastal and Estuarine Waters

“…We classified individuals into three age categories: adult, juvenile and calf. Following published work on bottlenose dolphins (e.g., Mann et al, 2000;Ansmann et al, 2013), adults were >2 m (Hale et al, 2000). It is noted that T. aduncus in Australia are smaller than other Tursiops spp.…”

Short Note: Performance of Computer-Assisted Photographic Matching of Guiana Dolphins (Sotalia guianensis)

“…Photo-identification is a well-established method in aquatic mammal research (e.g., Hammond et al, 1990;Hastings et al, 2008;Ansmann et al, 2013). Recognition of individuals through natural markings is the standard approach for addressing questions on population dynamics (e.g., Ansmann et al, 2013), social structure (e.g., Lusseau, 2003), movements and site fidelity (e.g., Rossi-Santos et al, 2007), general behavior (e.g., Ottesmayer & Whitehead, 2003), human threats, and general health condition (Van Bressem et al, 2007).…”

“…Recognition of individuals through natural markings is the standard approach for addressing questions on population dynamics (e.g., Ansmann et al, 2013), social structure (e.g., Lusseau, 2003), movements and site fidelity (e.g., Rossi-Santos et al, 2007), general behavior (e.g., Ottesmayer & Whitehead, 2003), human threats, and general health condition (Van Bressem et al, 2007). Individual identifications are possible by long lasting and temporary marks in flukes and dorsal fins, acquired during interactions with conspecifics or other species (e.g., Würsig & Jefferson, 1990).…”