Apr 2019 – Dolphins in hot water, new paper out in Current Biology

Feature image: This tiny calf of “Sunny”, a sponging mother dolphin in Shark Bay, did not make it to one year of age in the hard times following a marine heatwave.

 


Blurb: 
The remote and beautiful Shark Bay World Heritage Area (and marine park) got itself into some hot water in the summer of 2011. Various negative impacts across trophic levels followed this unprecedented marine heat wave, exacerbated by some anomalous flooding events, including the loss of habitat-forming seagrass meadows, crashes in invertebrate and fish populations, as well declines in marine turtle health.

For a little not-so-light reading, check out these prior papers by our friends and colleagues: Thomson et al. (2015). Extreme temperatures, foundation species, and abrupt ecosystem change: an example from an iconic seagrass ecosystem. Global Change Biology 21:1463–1474. And: Arias-Ortiz et al. (2018). A marine heatwave drives massive losses from the world’s largest seagrass carbon stocks. Nature Climate Change 8: 338–344.

Piccolo, daughter of Puck, is a famous Shark Bay dolphin. Here, she works hard to round up a bream in the shallows of Monkey Mia beach.

 

Highlights:This should probably read “lowlights” but, in this paper, we used our long-term demographic data to report on the subsequent (arguably cascading) effects of habitat degradation on the survival and reproduction of the iconic bottlenose dolphin population that inhabits this globally unique ecosystem.

Title: Long-term decline in survival and reproduction of dolphins following a marine heatwave. 

Authors: Sonja Wild, Michael Krützen, Robert W Rankin, Will JE Hoppitt, Livia Gerber, Simon J Allen.

Abstract: It’s a two-page correspondence piece, so there isn’t really an abstract per se, but here is the first paragraph, a pseudo-abstract of sorts: One of many challenges in the conservation of biodiversity is the recent trend in the frequency and intensity of extreme climatic events. The Shark Bay World Heritage Area, Western Australia, endured an unprecedented marine heatwave in 2011. Catastrophic losses of habitat-forming seagrass meadows followed, along with mass mortalities of invertebrate and fish communities. Our long-term demographic data on Shark Bay’s resident Indo-Pacific bottlenose dolphin (Tursiops aduncus) population revealed a significant decline in female reproductive rates following the heatwave. Moreover, capture–recapture analyses indicated 5.9% and 12.2% post heatwave declines in the survival of dolphins that use tools to forage and those that do not, respectively. This implies that the tool-using dolphins may have been somewhat buffered against the cascading effects of habitat loss following the heatwave by having access to a less severely affected foraging niche. Overall, however, lower survival has persisted post-heatwave, suggesting that habitat loss following extreme weather events may have prolonged, negative impacts on even behaviourally flexible, higher-trophic level predators.

 

Oakley and calf cruise over the seagrass and sand in western Shark Bay.

 

Full citation: Wild S, Krützen M, Rankin RW, Hoppitt WJE, Gerber L and Allen SJ. 2019. Long-term decline in survival and reproduction of dolphins following a marine heatwave. Current Biology 29: R1-R2. DOI: 10.1016/j.cub.2019.02.047

Funding and acknowledgements: This research was funded by grants from the Swiss Science Foundation, National Geographic Society, Sea World Research and Rescue Foundation, WV Scott Foundation and the AH Schultz Stiftung. We thank Mitsui, Shark Bay Resources, and the Useless Loop community for in-kind support, and field assistants for contributions to data collection. This research was conducted with scientific investigation permits from the Department of Biodiversity, Conservation and Attractions, as well as animal ethics approvals from the University of Zurich, University of Western Australia, Murdoch University and the University of New South Wales.

 

An alliance of males follows the foraging female in western Shark Bay. We hope we are not consigned to documenting the demise of the remarkable wildlife population.

 

Watch this space for more research findings in the coming months…

Mar 2019 – New paper (moonlighting north again) in Behavioral Ecology

The remote and beautiful North West Cape to the north of Shark Bay appears to be important habitat for both Indo-Pacific bottlenose and Australian humpback dolphins. Don’t believe us? See the place for yourself, the images below, or the papers Allen et al. 2012, 2017, Brown et al. 2012, 2016 and Hunt et al. 2017 on the www.sharkbaydolphins.org publications page. 🙂

Dolphin research up North West Cape way is ongoing under the direction of our friend and collaborator Guido Parra of Flinders University, and here we are happy to promote the second of his former student Tim Hunt’s PhD data chapters – this one on Sousa social structure.

Title: Assortative interactions revealed in a fission-fusion society of Australian humpback dolphins.

Authors: Tim N Hunt, Simon J Allen, Lars Bejder, Guido J Parra.

Abstract: Understanding individual interactions within a community or population provides valuable insight into its social system, ecology, and, ultimately, resilience against external stimuli. Here, we used photo-identification data, generalized affiliation indices, and social network analyses to investigate dyadic relationships, assortative interactions, and social clustering in the Australian humpback dolphin (Sousa sahulensis). Boat-based surveys were conducted between May 2013 and October 2015 around the North West Cape, Western Australia. Our results indicated a fission–fusion society, characterized by nonrandom dyadic relationships. Assortative interactions were identified both within and between sexes and were higher among members of the same sex, indicating same-sex preferred affiliations and sexual segregation. Assortative interactions by geographic locations were also identified, but with no evidence of distinct social communities or clusters or affiliations based on residency patterns. We noted high residency among females. Models of temporal patterns of association demonstrated variable levels of stability, including stable (preferred companionships) and fluid (casual acquaintances) associations. We also demonstrated some social avoidance. Our results point to greater social complexity than previously recognized for humpback dolphins and, along with knowledge of population size and habitat use, provide the necessary baseline upon which to assess the influence of increasing human activities on this endemic, Vulnerable species.

Full citation: Hunt TN, Allen SJ, Bejder L, Parra GJ. 2019. Assortative interactions revealed in a fission-fusion society of Australian humpback dolphins. Behavioral Ecology 29: 1-14 (doi: 10.1093/beheco/arz029).

Funding and acknowledgements:This work was supported by funding from the Australian Marine Mammal Centre (Project 12/11) and the Winifred Violet Scott Charitable Trust. We sincerely thank all “Team Sousa” volunteers who assisted with data collection in the field over the 3 years of surveys. Data collection was permitted by the Western Australia Government Parks and Wildlife Service (PWS; SF009240, SF009768, SF010289), WA Government Agriculture and Food Division (U38/2013–2015), and the Australian Government Department of Defence (Harold Holt Naval Base Exmouth), with approval from Flinders University Animal Welfare Committee (E383). We also thank the community and businesses of Exmouth, the staff at PWS Exmouth, the Cape Conservation Group, and MIRG Australia for supporting the North West Cape Dolphin Research Project. We thank Fernando Diaz-Aguirre for assistance with GAI analyses, Alex Brown for his assistance with the dorsal fin analysis for sex determination, and Hal Whitehead and Mauricio Cantor for their advice on GAI and modularity interpretations.

…and watch this bloggy-space for more research outputs soon!

 

All images by Simon Allen and available (higher res) on request.

Jun 2018 – New publication on signature whistles in male alliances

The Dolphin Alliance Project and colleagues are pleased to announce the publication of our recent work on communication in Shark Bay’s “teams of rivals”, the male alliances…

Citation: King SL, Friedman W, Allen SJ, Gerber L, Jensen F, Wittwer S, Connor RC, Krützen M 2018. Bottlenose dolphins retain individual vocal labels in multi-level alliances. Current Biology https://doi.org/10.1016/j.cub.2018.05.013.

Field methods at a glance: A trio of dolphins forages in the shallows near Peron Peninsula. The research team confirms their identities with photo-identification, records their vocalisations with a four-hydrophone array and obtains aerial video with either a helikite- or a drone-mounted HD video camera (photo: Simon J Allen).

Summary: Cooperation between allied individuals and groups is ubiquitous in human societies, and vocal communication is known to play a key role in facilitating such complex human behaviours. In fact, complex communication may be a feature of the kind of social cognition required for the formation of social alliances, facilitating both partner choice and the execution of coordinated behaviours. As such, a compelling avenue for investigation is what role flexible communication systems play in the formation and maintenance of cooperative partnerships in other alliance-forming animals. Male bottlenose dolphins in some populations form complex multi-level alliances, where individuals cooperate in the pursuit and defense of an important resource: access to females. These strong relationships can last for decades and are critical to each male’s reproductive success. Convergent vocal accommodation is used to signal social proximity to a partner or social group in many taxa, and it has long been thought that allied male dolphins also converge onto a shared signal to broadcast alliance identity. Here, we combine a decade of data on social interactions with dyadic relatedness estimates to show that male dolphins that form multi-level alliances in an open social network retain individual vocal labels that are distinct from those of their allies. Our results differ from earlier reports of signature whistle convergence among males that form stable alliance pairs. Instead, they suggest that individual vocal labels play a central role in the maintenance of differentiated relationships within complex nested alliances. 

Figure 1 from the paper deftly illustrates the strength of social bonds between first- and second-order alliance partners, while the spectrograms display the whistle contours of each individual male dolphin (King et al. 2018). Note the differences between contours relative to the strength of particular social bonds.

Media: There was some very nice coverage from funders National Geographic (which you can view at: https://news.nationalgeographic.com/2018/06/dolphins-animals-courtship-friends/#), a great summary appeared in The Conversation (http://theconversation.com/male-dolphins-use-their-individual-names-to-build-a-complex-social-network-97780) and, 48 hours later, it’s pretty much everywhere!

BUBBLES! Are you talkin’ to me!? (photo: Simon J Allen)
Acknowledgements: Stephanie is a Branco Weiss Fellowship—Society in Science Fellow. Stephanie, Richard and Whitney received grants from the National Geographic Society. The study was also supported by a Swiss National Science Foundation grant to Michael. Whitney was supported by a Graduate Fellowship in Anthropogeny from the University of California, San Diego. Frants was supported by the US Office of Naval Research and a fellowship from the Aarhus Institute of Advanced Studies, Aarhus University. Permits for the scientific use of animals were obtained from the Department of Biodiversity, Conservation and Attractions (DBCA), Western Australia. The University of Zurich and University of Western Australia granted animal ethics approvals. The authors thank RAC Monkey Mia Dolphin Resort, Monkey Mia Wildsights, and the DBCA’s Shark Bay Rangers, all field assistants and our human judges for their help during this study. Lastly, we grateful to three anonymous reviewers for their valuable comments on the manuscript.
Stay tuned for some more exciting findings in the next few months.

Jan 2018 – The papers and presentations of 2017

Happy 2018! Time for a quick update: The last year has been a productive one for the Shark Bay Dolphin Research Alliance (SBDRA), with successful field seasons in both eastern (#36!) and western (#11) gulfs, a solid showing at the 22nd Biennial Conference in Halifax, Nova Scotia, and a number of papers published.

With field seasons wrapped up, we went on our way to Canada for the conference. Quite a few of us shared flights with other members of the group, plus colleagues from other labs. In various airports, we’d find the time to catch up and talk marine mammal science… oh wait. No, we wouldn’t. We’d just stare at our mobile devices…

 

 

Members of the SBDRA gave eight oral presentations and one poster presentation…

 

We also had a lovely ‘Friends of Shark Bay’ dinner for a gaggle of researchers past, present and future…

 

Amongst a few others, we published a paper on male alliance behaviour and mating access in the open social network of Shark Bay’s bottlenose dolphins (http://www.nature.com/articles/srep46354) in Nature’s Scientific Reports.

 

Also in Scientific Reports, another on sexual displays involving posturing and sponge presentation by male Australian humpback dolphins across north-western Australia (http://rdcu.be/w3tL).

 

There are so many intriguing parallels in behaviour and social complexity that exist between some of the cetacea and the great apes, but who would have thought that one charismatic, tool-using species might remain undiscovered until late 2017!? Congrats to Michael and colleagues on this wonderful result: http://www.cell.com/current-biology/fulltext/S0960-9822(17)31245-9.

 

2018 is shaping up to be a bumper year for papers and fieldwork. We look forward to sharing it with you, so stay tuned…

Oct 2017 – New publication on sponge presentation in humpback dolphins

We’re very pleased to announce the publication of some of our work on Australian humpback dolphins across north-western Australia. Like Shark Bay’s bottlenose dolphins, this intriguing coastal dolphin species also engages in the manipulation of marine sponges, only this time, it’s got little to do with foraging. Furthermore, we present preliminary evidence of possible alliance formation by pairs of adult male humpback dolphins.

Citation: Allen SJ, King SL, Krützen M & Brown AM 2017. Multi-modal sexual displays in Australian humpback dolphins. Scientific Reports 7: 13644.DOI:10.1038/s41598-017-13898-9.

Link: http://rdcu.be/w3tL

An adult male Australian humpback dolphin with a large marine sponge approaches an adult female with a calf of weaning age in the Dampier Archipelago, Western Australia (photo: Simon Allen).

Abstract: Sexual displays enriched by object carrying serve to increase individual male fitness, yet are uncommon phenomena in the animal kingdom. While they have been documented in a variety of taxa, primarily birds, they are rare outside non-human mammals. Here, we document marine sponge presenting associated with visual and acoustic posturing found in several, geographically widespread populations of Australian humpback dolphins (Sousa sahulensis) over ten years of observation. Only adult males presented marine sponges, typically doing so in the presence of sexually mature females, although social groups predominantly consisted of mixed age and sex classes. Male humpback dolphins appear to be using sponges for signalling purposes in multi-modal sexual displays. Further, based on limited behavioural and genetic data, we hypothesise that pairs of adult male Sousa form at least temporary coalitions or alliances. The use of objects in sexual displays by non-human mammals is rare and, moreover, cooperation between males in the pursuit of an indivisible resource is an evolutionary hurdle relatively few species have overcome. These findings suggest a hitherto unrecognised level of social complexity in humpback dolphins.

Media: There was some nice coverage in Nat Geo at: https://news.nationalgeographic.com/2017/10/dolphins-sex-mating-sponges-courtship/

Two adult male humpback dolphins, one holding a sponge, approach some mother-calf pairs in Cone Bay, Western Australia (photo: Simon Allen).

 

Funding and acknowledgements: The Australian Marine Mammal Centre, the Western Australian Marine Science Institution, the Department of Parks and Wildlife and the Sea World Research and Rescue Foundation funded the research programs during which these data were accumulated. The Coral Bay and Kimberley Marine Research Stations, Pilbara Ports Authority, Hampton Harbour Boat and Sailing Club and Marine Produce Australia provided logistical support to our research teams. SLK was supported by Society in Science, The Branco Weiss Fellowship, administered by the ETH Zurich. This type of research would not be possible without the generous support of numerous volunteers, research assistants and collaborators contributing to funding and/or data acquisition over numerous projects and field trips. In particular, we thank A. Hodgson, A. Quinn, D. Cagnazzi, D. Chabanne, F. Smith, G. Parra, H. Raudino, J. Fromont, J. Smith, J. Tyne, K. Pollock, L. Bejder, N. Loneragan and T. McMurray. This manuscript represents contribution no. 12 of the Dolphin Innovation Project. Finally, we acknowledge the constructive comments provided by two anonymous reviewers and the handling editor, which improved the clarity of this manuscript. This research was conducted under permits for the scientific use of animals from the Western Australian (WA) Department of Parks and Wildlife, and a firearms licence from the WA Police. The Murdoch University Animal Ethics Committee approved all experimental protocols and the research was carried out following consultation with Murujuga, Bardi Jawi and Dambimangari traditional owners.

 

Sep 2017 – PhD research with the Dolphin Alliance Project

The Dolphin Alliance Project is seeking high calibre students for two PhD projects to start in 2018. The first project will use acoustic, behavioural and genetic data to investigate the ontogeny of alliance formation in the Shark Bay dolphin population, focussing on juvenile and adult dolphins. The second project will explore how ecology, particularly the acoustic properties of the environment, contributes to variation in alliance behaviour and mating success in this remarkable population.

The students will be based at the University of Western Australia (UWA) under the supervision of Dr Stephanie King (UWA), and will be co-supervised by Professor Michael Krützen (University of Zürich), Professor Richard Connor (UMass Dartmouth) and Dr Simon Allen (UWA). Students will work in a dynamic research environment with access to a behavioural and demographic database spanning 30+ years, biopsy samples from 700+ individuals, and acoustic data from 15 well-documented alliances.

Applications are open to both domestic and international students, who should be eligible for an RTP scholarship: http://www.science.uwa.edu.au/future-students/scholarships.

Exceptional students are encouraged to apply for the Dean’s Excellence in Science PhD Scholarships: http://www.science.uwa.edu.au/future-students/scholarships/deans-excellence, as well as the Keiran McNamara World Heritage PhD Top-Up Scholarship: http://www.scholarships.uwa.edu.au/search?sc_view=1&id=5521&all=1&page=27.

General requirements include a background in evolutionary and behavioural biology, a BSc (Hons) or MSc degree (first class) in a relevant discipline, and fieldwork experience (preferably with marine mammals and/or primates). Knowledge or experience in bio-acoustics and/or small boat handling skills would be advantageous.

Ideal candidates will have strong oral and written communication skills and the ability to work and share ideas in a highly collaborative setting. International students, in particular, should have at least one peer-reviewed publication.

Applicants should send an expression of interest and CV, including the contact details of two academic referees, to Dr Stephanie King (stephanie.king@uwa.edu.au) by 7th October 2017.

Successful candidates will be informed prior to the 21st October to ensure scholarship applications are submitted prior to the 31st October deadline.

July 2017 – (Another) New paper in Scientific Reports

A short sail to the north-east (~700 nautical miles) of Shark Bay lies the shallow tropical seas of the Pilbara region. Other than oil and gas fields, there you’ll find a demersal trawl fishery and a faithful population of common bottlenose dolphins. Intrigued!? Learn more by clicking on (or copy-pasting into your browser) one of the links below:

Title: Preliminary estimates of the abundance and fidelity of dolphins associating with a demersal trawl fishery

Authors: Simon J. Allen, Kenneth H. Pollock, Phil J. Bouchet, Halina T. Kobryn, Deirdre B. McElligott, Krista E. Nicholson, Joshua N. Smith & Neil R. Loneragan 

Link: Get your own piece of this action at http://rdcu.be/t5Y2 or www.nature.com/articles/s41598-017-05189-0

Highlights: *1. An aerial survey to estimate dolphin abundance in the PTF suggests population size is smaller than expected at somewhere between 2,000 and 5,000 individuals.   *2. As expected, boat-based photo-ID and genetic sampling suggest a community of dolphins show fidelity to trawler-associated foraging over days, weeks and years.   *3. Fisheries-related mortality events are likely to have an impact on the viability of a small dolphin population, but this cannot be demonstrated without more precise estimates of mortality rates (through an observer program) and/or further estimates of abundance (to detect trends).   *4. The tendency for the dolphins to exploit the fishery as a high-risk but efficient means of procuring resources is problematic for bycatch mitigation, as foraging “traditions” tend to be handed down from one generation to the next.   *5. The data presented here do, however, provide the basis for some further assessment of the level of impact that dolphin bycatch has on the population, through either the application of Potential Biological Removal estimation (as per the US system) or completing a Population Viability Analysis.

Abstract: The incidental capture of wildlife in fishing gear presents a global conservation challenge. As a baseline to inform assessments of the impact of bycatch on bottlenose dolphins (Tursiops truncatus) interacting with an Australian trawl fishery, we conducted an aerial survey to estimate dolphin abundance across the fishery. Concurrently, we carried out boat-based dolphin photo-identification to assess short-term fidelity to foraging around trawlers, and used photographic and genetic data to infer longer-term fidelity to the fishery. We estimated abundance at ≈ 2,300 dolphins (95% CI = 1,247–4,214) over the ≈ 25,880-km2 fishery. Mark-recapture estimates yielded 226 (SE = 38.5) dolphins associating with one trawler and some individuals photographed up to seven times over 12 capture periods. Moreover, photographic and genetic re-sampling over three years confirmed that some individuals show long-term fidelity to trawler-associated foraging. Our study presents the first abundance estimate for any Australian pelagic dolphin community and documents individuals associating with trawlers over days, months and years. Without trend data or correction factors for dolphin availability, the impact of bycatch on this dolphin population’s conservation status remains unknown. These results should be taken into account by management agencies assessing the impact of fisheries-related mortality on this protected species.

 

1: Aerial survey tracks across the Pilbara Trawl Fishery management areas, north-western Australia, and dolphin group sightings.

 

2: Boat-based photo-identification reveals a community of dolphins, like this mother and calf, that regularly follow trawlers over days and weeks, feeding on injured or discarded fish. Sharks also follow the trawlers scavenging on discards, like the sizeable whaler pictured her below the dolphins.

 

3: Locations and times between sampling events of dolphins around trawlers. Genetic re-sampling and opportunistic photo-ID confirmed that some dolphins also follow the trawlers in the Pilbara over months and years.

 

4: Aggregations of dolphins follow the trawlers day-in day-out, leading to the impression that the population as a whole is large, but these preliminary results indicate that the population is smaller than expected.

 

5: This newborn is likely to learn about foraging around trawlers from its mother. Unfortunately the level of risk associated with foraging in and around fishing nets is not so easily taught.

All figures are from the paper in Scientific Reports and all images are ©Simon Allen.  🙂

Funding and acknowledgements: The Australian Marine Mammal Centre was the primary funder of this research, with additional contributions from the Fisheries Research and Development Corporation, the Western Australian Department of Fisheries, and the Nickol Bay Professional Fishers Association. We thank the commercial trawl operators for in-kind support and acknowledge the logistical assistance provided by the skippers and crews of the Pilbara Fish Trawl Interim Managed Fishery. Amanda Hodgson and Maria Jedensjö were instrumental in helping design and conduct the aerial survey, respectively. The research was carried out under cetacean research permits from both the Western Australian State Government and the Australian Commonwealth Government. Dolphin tissue samples were transferred to the University of Zurich under CITES using institutional permits for scientific exchange, and the research was conducted with animal ethics committee approval from Murdoch University.

 

July 2017 – Field seasons start (and the Dolphin Alliance Project turns 35!)

The Shark Bay Dolphin Research Alliance field teams have now been back on the water for a month or so in Western Oz. This surely makes it time for a pictorial update of the first successes in pursuit of data on dolphins.

 

First things first, having kicked off in 1982, the Dolphin Alliance Project turns a healthy and productive 35 years old this season. Happy 36th field season DAP!

 

When packing for the field, there were a couple of team mascots a little concerned about whether or not they were joining us…

 

Indeed this day of departure image was no set-up – the door was left open and we came out to the project ute to find these rascals staking their claim…

 

One team went East (to Monkey Mia) with the hounds, while the other went West (to Useless Loop) with new team members and a recently serviced ‘Squidward’…

 

The Dolphin Alliance Project got amongst the action early, with popping males and foraging females on a glassy morning out…

 

The Dolphin Innovation Project got sampling on some glassy evenings in Useless Inlet…

 

And while Sonja did all the work driving and retrieving boats, Nahiid got busy with some serious shell photography (what a trooper!)…

 

Ol’ Bytfluke, the sponging grandmother, chasing brunch in a channel off Monkey Mia…

 

A trio of adult males from the 2nd-order alliance, the ‘Kroker Spaniels’, snagging near the pearl farm in Red Cliff Bay…

 

More of Stephanie’s acoustic targets, some of the ‘Hooligans’ alliance snagging in Whale Bight…

 

A beautiful young lady, Dokley, bow-riding in the shallows off Useless Loop…

 

Here is the delightful sponger Daiquiri in the Denham Channel, 2007…

 

And here she is, same fin, same old shark bite, same behaviour, same place, 2017…

 

Everyone’s favourite, the little boat-friendly Kimo in Useless Inlet…

 

And Kimo making photo-ID easy…

 

For those champing at the bit for an update on Osmo, the King of the Inlet, who lost his dorsal fin in a big fight over a female in 2016…

 

Here he is in 2017, looking cool, calm and healed…

 

And speaking of legends, here is the ‘Silver Bullet’ towing ‘Spongebob’ in the inaugural Dolphin Innovation Project season, 2007…

 

The end of an era, the last time the Bullet is used to launch the Bob before being handed over to a new owner (no, Silver Bullet has NOT crossed the rainbow bridge just yet)…

 

Of course, being in Shark Bay means some pretty sunsets. Sometimes it is important to ignore the rule of thirds…

 

Sunsets AND dolphins…

 

AGAIN!

 

In case people are getting bored with dolphins and sunsets, here are some BUDGIES!

 

For the picky/pedantic/thorough folk out there: photo credits go to the likes of Stephanie King, Nahiid Stephens, Sonja Wild and I of the Shark Bay Dolphin Research Alliance (Dolphin Alliance Project and Dolphin Innovation Project); image collection and other sampling/research was carried out under permit from WA Dept of Parks and Wildlife; and no doggies, dolphins or budgies were harmed in the making of this blog.

Apr 2017 – New paper on alliances published in Nature’s Scientific Reports

 

Title: Male alliance behaviour and mating access varies with habitat in a dolphin social network

Authors: Richard C. Connor, William R. Cioffi, Srđan Randić , Simon J. Allen, Jana Watson-Capps & Michael Krützen

Highlights: We discovered that male dolphin alliance behaviour varies systematically along the Peron Peninsula in the World Heritage Listed Shark Bay, Western Australia. It is rare to find such variation in a single population of mammals, and indeed even more so in a single social network. This exciting discovery was made by pure serendipity, as often happens in science. We set out to work on a completely different issue, and discovered this!

Abstract: Within-species variation in social structure has attracted interest recently because of the potential to explore phenotypic plasticity and, specifically, how demographic and ecological variation influence social structure. Populations of bottlenose dolphins (Tursiops spp.) vary in male alliance formation, from no alliances to simple pairs to, in Shark Bay, Western Australia, the most complex nested alliances known outside of humans. Examination of ecological contributions to this variation is complicated by differences among populations in other potentially explanatory traits, such as phylogenetic distance, as well as female reproductive schedules, sexual size dimorphism, and body size. Here, we report our discovery of systematic spatial variation in alliance structure, seasonal movements and access to mates within a single continuous social network in the Shark Bay population. Participation in male trios (versus pairs), the sizes of seasonal range shifts and consortship rates all decrease from north to south along the 50 km length of the study area. The southern habitat, characterised by shallow banks and channels, may be marginal relative to the open northern habitat. The discovery of variation in alliance behaviour along a spatial axis within a single population is unprecedented and demonstrates that alliance complexity has an ecological component.

 

2 Figure 1

Figure 1: The study site in waters off the east side of Peron Peninsula, which bisects Shark Bay, Western Australia. Centroids for seven northern 2nd-order alliances, which occupy relatively open habitat, are shown divided from the five southern 2nd-order alliances, which occupy habitat subdivided by shallow banks and channels.

 

3 Figure 2

Figure 2: The proportion of trios (triangles), consortship rate (circles), and adjusted consortship rate (squares) in 2nd-order alliances decreases in a SE direction across the study area/two habitats. Fitted logistic curves are shown from generalized linear models. prop. trios = proportion trios, CR = consortship rate.

Citation: Connor, R.C. et al. 2017 Male alliance behaviour and mating access varies with habitat in a dolphin social network. Sci. Rep. 7, 46354; doi: 10.1038/srep46354.

Link: http://www.nature.com/articles/srep46354

Acknowledgements: This study was supported by grants from the Australian Research Council (A19701144 and DP0346313), The Eppley Foundation for Research, The Seaworld Research and Rescue Foundation, The W. V. Scott Foundation, The National Geographical Society’s Committee for Research and Exploration and NSF (1316800). Accommodation was very generously provided by the Monkey Mia Dolphin Resort. Permits for the scientific use of animals were obtained from the West Australian Department of Parks and Wildlife. The University of Massachusetts at Dartmouth approved this study. Many generous people helped make this project possible. Landsat 7 ETM+ imagery of Shark Bay courtesy of the U.S. Geological Survey.

Feb 2017 – New paper (moonlighting to the north) in Endangered Species Research

About 400 km to the north of our wondrous focal study site of Shark Bay lies the spectacular Ningaloo Reef and North West Cape. Some of our initial field efforts to study bottlenose and humpback dolphins up that way have involved collecting data that has already contributed to several papers (see Allen et al. 2012 and 2016, and Brown et al. 2012 and 2014 on the publications page, for example). We then obtained some funding from the Australian Marine Mammal Centre (to PI Guido Parra of Flinders Uni, and Co-Is Lars Bejder and Simon Allen) to look specifically at Australian humpback dolphin (Sousa sahulensis) ecology, and a PhD was taken on by Tim Hunt. That research is now coming to fruition, with Tim’s PhD nearing completion and his first thesis data paper hot off the (online) press.

Title: Demographic characteristics of Australian humpback dolphins reveal important habitat toward the south-western limit of their range

Authors: Tim N Hunt, Lars Bejder, Simon J Allen, Rob W Rankin, Daniella Hanf, Guido J Parra.

1 simo

An adult Australian humpback dolphin off the North West Cape, Western Australia.

 

Highlights: 

  • Our very own Australian humpback dolphins were only classified as a separate species from their south-east Asian cousins as recently as 2014. Given their somewhat cryptic nature and their distribution across Australia’s remote northern coastline, they remain elusive to the extent that we do not have enough information to assign them a conservation status (other than ‘data deficient’).
  • In this study, we sought to estimate the abundance, site fidelity and residence patterns of Australian humpback dolphins around the North West Cape, Western Australia.
  • We estimated a population of 129 individuals in the 130 km² study area and documented the highest density recorded for this species to date. Incidentally, we also documented almost double that number of Indo-Pacific bottlenose dolphins in the study area, but that remains for a future study/publication.
  • The density, site fidelity and residence patterns of Aussie humpback dolphins around the North West Cape suggest it is an important habitat for the species.
  • We provide a methodological framework for future Impact Assessments and a baseline for longer-term studies on this enigmatic species.

 

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Cumulative discovery curve of identified Australian humpback dolphins (n = 98) within the North West Cape study area over the 2013, 2014 and 2015 survey periods (total 195 d).

 

Abstract: The paucity of information on the recently described Australian humpback dolphin (Sousa sahulensis) has hindered assessment of its conservation status. Here, we applied capture-recapture models to photo-identification data collected during boat-based surveys between 2013 and 2015 to estimate the abundance, site fidelity and residence patterns of Australian humpback dolphins around the North West Cape (NWC), Western Australia (WA). Using Pollock’s Closed Robust Design, abundance estimates varied from 65 to 102 individuals, and POPAN open modelling yielded a super-population size of 129 individuals in the 130 km² study area. At approximately one humpback dolphin per km², this density is the highest recorded for this species. Temporary emigration was Markovian, suggesting seasonal movement in and out of the study area. Hierarchical clustering showed that 63% of individuals identified exhibited high levels of site fidelity. Analysis of lagged identification rates indicated dolphins use the study area regularly over time, following a movement model characterized by emigration and re-immigration. These density, site fidelity and residence patterns indicate that the NWC is an important habitat toward the south-western limit of this species’ range. Much of the NWC study area lies within a Marine Protected Area, offering a regulatory framework on which to base the management of human activities with the potential to impact this threatened species. Our methods provide a methodological framework to be used in future environmental impact assessments, and our findings represent a baseline from which to develop long-term studies to gain a more complete understanding of Australian humpback dolphin population dynamics.

Full citation: Hunt TN, Bejder L, Allen SJ, Rankin RW, Hanf D, Parra GJ. 2017. Demographic characteristics of Australian humpback dolphins reveal important habitat toward the south-western limit of their range. Endangered Species Research 32: 71-88.

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Socialising humpback dolphins. Note the scarred dorsal fin of an adult male and the long beak of the other individual – classic Australian humpback dolphin characteristics.

 

Funding and acknowledgements: The Australian Marine Mammal Centre (Project 12/11) and the Winifred Violet Scott Charitable Trust funded this research. We sincerely thank all ‘Team Sousa’ volunteers that assisted with data collection in the field over the 3 years of surveys. Data collection was permitted by the WA Department of Parks and Wildlife (DPaW; SF009240, SF009768, SF010289), WA Department of Agriculture and Food (U38/2013-2015) and the Australian Government Department of Defence (Harold Holt Naval Base Exmouth), with approval from Flinders University Animal Welfare Committee (E383). We would also like to thank the community and businesses of Exmouth, the staff at DPaW Exmouth, the Cape Conservation Group, and MIRG Australia for supporting the North West Cape Dolphin Research Project. We thank Ken Pollock for providing initial statistical advice on earlier versions of this manuscript.