Marine Mammal Research Jervis Bay (MMR) presented at the Society for Marine Mammalogy
(SMM) 25th Biennial Conference on the Biology of Marine Mammals in Perth, Western Australia, 2024.
Foraging strategies on a diverse prey of resident bottlenose
dolphins (Tursiops aduncus) in Jervis Bay, NSW
Scott Sheehan1,2
1 Marine Mammal Research JB, PO Box 117, Huskisson, Jervis Bay, NSW 2540, Australia
2 Australian Marine Explorer, PO Box 117, Huskisson, Jervis Bay, NSW 2540, Australia
scott@marinemammalresearch.com
Introduction
This poster details observations of foraging strategies on a diverse prey of Indo-Pacific bottlenose dolphins (Tursiops aduncus)1 resident to Jervis Bay, New South Wales. The area is a 115 km2 embayment that is around 8km across. Jervis Bay is a multiple use marine park with high vessel traffic associated with commercial fishing, ecotourism operators and recreational boat users that is jointly managed by the Jervis Bay Marine Park, Booderee National Park, and The Australian Defence Force which also accommodates active training by the Royal Australian Navy. Based on photo-identification research2 a total of 118 individuals have been identified, 57 of these classified as ‘residents’ of the bay. The remainder of the individuals were classed as ‘occasional visitors’ or ‘transients’ from outside of Jervis Bay.
Methods
Sighting data were collected under research projects and opportunistically by volunteers such as citizen science contributions from multiple platforms including small recreational craft, commercial dolphin watch operators, and land-based observations. Date, time, location, GPS coordinates (where possible), estimated number of individuals and group composition and environmental data were recorded. Digital photographic images were used for confirming and aiding in group composition and abundance, recording foraging events and aiding in prey identification. Dorsal fin and body
markings were photographed for tracking individuals during foraging events and to add in long-term mark-recapture3 studies for the animals utilising the bay. Behaviour recorded included foraging and travelling4, where foraging involved dolphins displaying long dives or erratic movements at the water surface engaged in the pursuit of prey and/or capture and consumption of prey.
Results and Discussion
Rocky reefs and seagrass meadows are highly preferred foraging grounds. Two specialised feeding strategies have been recognised, with only a small group of individual resident dolphins observed engaging in theses specialties 1. Octopus handing5. This skill displays a high degree of difficulty wrangling prey. 2. Tidal movement6 as a feeding strategy. Swimming against the current makes them seem stationary momentarily as the prey (baitfish and/or garfish) is flushed towards awaiting dolphins.
Observations highlight the importance of estuaries as preferred habitats for foraging activities. These shallow protected habitats include7 coastal fringes, embayments, sandy bottom, seagrass, saltmarsh, mangrove, subtidal reef, intertidal reef, deep reef, rocky reef, rocks, tidal estuaries and creek systems around Jervis Bay, which provide a constant food supply for the dolphins.8
Foraging strategies ranged from shallow to deep diving, speed burst (feeding rush), tail slapping (stunning), head slapping, snaking (belly up reflection), herding (small to large area), barrier (against vessel or breakwall), and tidal movement (creeks or estuaries). Strand feeding was not recorded during our observations, however historical anecdotal reports suggest it has occurred in the study area.
A diverse range of prey was documented including octopus (Octopus tetricus), Eastern Australian salmon (Arripis trutta), Eastern sea garfish (Hyporhamphus australis), Eastern striped grunter, (Pelates sexlineatus), white trevally (Pseudocaranx dentex), snapper (Chrysophrys auratus) juvenile, blue swimmer crab (Portunus armatus) zoea, cuttlefish (Sepia esculenta), hammerhead shark (Sphyrna sp.) juvenile, yellowfin bream (Acanthopagrus australis), dusky flathead (Platycephalus
fuscus), pilchards (Sardinops sagax), and bonito (Sarda australis).
Conclusions
These data display a small sample of the diversity of prey sighted and the range of foraging strategies used by the resident population of bottlenose dolphins within a core home range9 of Jervis Bay. Foraging extends outside of Jervis Bay to Crookhaven Heads in the north and St Georges Basin and Sussex Inlet to the south. Future research is needed to investigate these areas of critical habitat use, distribution and abundance of Tursiops aduncus with photo-ID to help determine updated population estimates. Continued monitoring of foraging strategies and habitat use is recommended to
mitigate against existing threats such as disturbance from boating activities, vessel strike, human provisioning and swimming interactions, anthropogenic noise10 and pollution, and to better inform on management issues with the emerging threats to predator and prey from habitat alteration and destruction, fisheries and climate change.
Acknowledgments
The author would like to thank, Dr Michelle Lemon Blewitt, Marine Mammal Research Jervis Bay’s team of volunteers and citizen science contributors, Paul Sheehan, Gavin Swan, Greg Molony, Richard Tadday, Maree Clout, John Mortimer, Glenn Maybury, Libby Eyre, Pete Garbett, Cetal Fauna, Dolphin Watch Cruises Jervis Bay, Jervis Bay Wild, Jervis Bay Marine Park, and Booderee National Park for their ongoing support of research within Jervis Bay.
We acknowledge the Traditional Owners of Country throughout Australia and recognise their continuing connection to land, waters and culture. We pay our respects to their Elders past, present and emerging.
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References
1 Möller, L., & Beheregaray, L. (2001). Coastal bottlenose dolphins from southeastern Australia are Tursiops aduncus according to sequences of the mitochondrial DNA control region. Marine Mammal Science, 17(2), 249-263.
2 Möller LM, Allen SJ and Harcourt RG, 2002. Group characteristics, site fidelity and seasonal abundance of bottlenose dolphins Tursiops aduncus in Jervis Bay and Port Stephens, southeastern Australia. Australian Mammalogy 24: 11-21.
3 Hawkins, ER and Gartside DF. 2008. Social and Behavioural Characteristics of Indo-Pacific Bottlenose Dolphins (Tursiops aduncus) in northern New South Wales, Australia. Australian Mammalogy 30: 71–82.
4 Shane, S.H. (1990a). Behavior and Ecology of the Bottlenose Dolphin at Sanibel Island, Florida. In Leatherwood, S. & Reeves, R.R. (eds). The Bottlenose Dolphin. Academic Press Inc., San Diego.
5 Sprogis, Kate R., et al. “Complex prey handling of octopus by bottlenose dolphins (Tursiops aduncus).” Marine Mammal Science 33.3 (2017).
6 Albrittain, Lauren, “Influence of Tidal Cycles on Movements of Atlantic Bottlenose Dolphins (Tursiops truncatus) in South Carolina Coastal Environments” (2012). Honors Theses. 47.
7 Marine and estuarine habitats of Jervis Bay Maps, CSIRO Australia, Division of Fisheries. 1992
8 Mandelc, F., 1997. Ecology and Conservation of the Bottlenose Dolphin (Tursiops truncatus) in Jervis Bay, NSW. PhD thesis. Graduate School of the Environment, Macquarie University, Sydney, Australia.
9 Mandelc, F.G., Fairweather, P.G., 1995. Jervis Bay’s dolphins: conservation and management. In: Cho, G., Georges, A., Stoutjesdijk, R. (Eds.), Jervis Bay: A Place of Cultural, Scientific and Educational Value. Australian Nature Conservation Agency, Canberra,
10 Lemon, M., Lynch, T.P., Cato, D.H. and Harcourt, R. 2006. Response of bottlenose dolphins (Tursiops aduncus) to powerboat approaches in Jervis Bay, New South Wales, Australia. Biological Conservation 127 363-372.
Video - Marine Mammals of Jervis Bay: Foraging and prey of resident bottlenose dolphins (Tursiops aduncus)
This data presented at (SMM) 25th Biennial Conference in Perth, Western Australia, 2024.
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