Update from Bunbury: male dolphins, lots of calves and hammerhead sharks

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A year of reflection
It has been over a year since I began my PhD project as part of the South West Marine Research Program. My project is investigating the habitat use and population dynamics of Indo-Pacific bottlenose dolphins in Bunbury, some 150 km south of Perth. It has been an exciting year of research! Some of my more interesting findings to date are:

Adult male movements:
One of the aims of my PhD is to explore the movements and home ranges of dolphins, particularly adult males. It is thought that here in Bunbury adult male home ranges are larger than adult females and it was hypothesised that adult males venture further offshore. So to test this theory I extended the study area from 120km2 to 520km2. I added on three extra transects to the original three; two offshore and one further south (Busselton). Throughout the year we have been exploring these areas for dolphins. Interestingly, in the twenty times we have been offshore, we have only sighted adult males on three occasions. This is puzzling because we have encountered mum and calf groups eight times, which was the opposite of what we expected. Assuming that the adult males are not commonly encountered offshore then perhaps they travel down south to Busselton? To date though, we have only spotted one “Bunbury” male alliance in Busselton (Nosey, Double Dip and Plateau). We are now looking forward to our winter 2012 season, hoping that we will find some more adult males to help explain the expanse of their home ranges.

Arataki and Apis leaping

Busselton dolphins:
The Busselton transect is one of our favourites. It takes us 45 minutes to drive to the boat ramp each time but when the weather is just right everything is worth while. The water quality is crystal clear, the water surface is mirror like and each time we run the transect we encounter new dolphins. As of May 2012, we have identified around 33 dolphins in this area and 10 of these were observed on a genetic sampling trip in 2007. From this, we can now tell that we have encountered two known adult males, Tornado and Shock, amongst mum and calf groups. It will be interesting now that winter is here to find out how many and which dolphins we will encounter during the season.

Individual movements:
An exciting find is the story about “Icecream” the dolphin. Icecream was a dolphin that was commonly sighted in Bunbury in 2008 and 2009. However, over 2010 and 2011, Icecream was not sighted at all. We were thinking that Icecream’s dorsal fin had changed so dramatically that we could not identify it anymore or that it had passed away. Excitingly though, in October 2011 and May 2012 we spotted Icecream again! It was 50km south of its initial “home” in the Busselton marina. This is an example of how far individual dolphins can range and why it is important to look after their habitat.

Neonate with feotal folds, Osiris, calf of Isis

Birthing season:
The main birthing season in Bunbury is in Summer and Autumn. In 2010/11 there were around 19 dolphin births. Similarly in 2011/12, we have recorded 20 dolphin births in Bunbury and 3 in Busselton. However, newborn calves are vulnerable and 44% of calves do not survive to weaning or independence (Mann et al. 2000). Long term research like ours helps to keep track of adult females and the success of their calves.

Hammerhead sightings:
To make our transects even more exciting, we come across sea lions, penguins, flying fish, sea birds, whales, jelly fish and on the rare occasion sharks. During the year we have seen eight endangered scalloped hammerheads (Sphyrna lewini) on our coastal transects. On very calm days we see them swimming slowly on the surface. These small specimens, generally around 1m in size, are typically wary of the boat. But we have been able to capture some images (see picture).

Scalloped hammerhead shark offshore.

Mapping the benthic habitat:
To explore the habitat use of the dolphins we need to know what the benthic (seabed) habitat is like. This can be done by accessing data from satellite images and then validating these images through benthic habitat mapping. We drop a 1m x 1m metal quadrate frame into the water with a camera on top and capture an image of the seafloor. We are aiming to obtain up to 150 images in total and during February and March of this year we recorded 80 images. However, as April approached the water clarity deteriorated and we could no longer take anymore images. So stay tuned until next year…

We have recently finished our autumn season for the second year of my PhD research. We were on the water for 22 days (133hours) and encountered 76 dolphin groups. I want to thank my assistants who have been so helpful on the boat and in the office for this season; Welmoed and Anne from Holland, Riona from Ireland, Rebecca from America and Philippine from France.

The research for the South West Marine Research Program is made possible through the funding partners, including, the Bunbury Dolphin Discovery Centre, Bemax Cable Sands, BHP Billiton Worsley Alumina, Bunbury Dolphin Discovery Centre, Bunbury Port Authority, City of Bunbury, Cristal Global, Department of Environment and Conservation, Iluka, Millard Marine, Naturaliste Charters, Newmont Boddington Gold, South West Development Commission and WAPRES.

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