SHARK RESEARCH UPDATE
December 10, 2015 by dyertrust
Alison Towner DICT’s senior biologist and a PhD student at the University of Rhodes, has been looking at Great White Shark, Carcharodon carcharias populations for the past nine (9) years in Gansbaai, South Africa. As another year comes to a close we are reflecting back on our achievements with white shark research at the DICT and we are feeling quite proud!
Alison and the team completed the Initial deployment phase of 10 VR2W listening stations, which took place in July; these stations are due to be changed out soon. They have been capturing data behind Dyer Island with acoustic receivers as part of a collaborative African Tracking Platform ATAP since 2013. This network incorporates data from all tagged species along our coastline, not just white sharks; we are always very interested to see who has ‘pinged in’ at our stations around the bay!
Acoustic tagging of white sharks has continued. The team initially struggled with low shark activity, rough seas and alterations to the design of the tag tethers. However they were able to successfully deploy seven R-code transmitters on white sharks. These tags speak directly to moored listening stations and have allowed us to capture data from the end of the Dyer Island season and beginning of the inshore summer season.
Over the next few months the DICT team is using every weather gap to deploy more external acoustic tags on GWS, including continuous tags which allow for active tracking of individual sharks from the DICT’s research vessels. A 3.5 meter male shark was recently actively tracked in December and the team managed to obtain over 850 data points yielding some incredibly high resolution information on his movements inshore and around cage diving boats. This research recorded the shallowest depths white sharks have been tracked in Gansbaai to date. The work is crucial to understand the fine scale behaviour and habitat use of white sharks in our area . The DICT team’s previous publications on this work explored the interesting relationships white sharks have with specific habitats such as Dyer Island as well as how they interact with their prey species.
Our daily monitoring continues on our cage diving vessel Slashfin, where Marine Dynamics guiding biologists Kelly Baker and Mike Baron continue to collect crucial daily data and observations of GWS. These extensive datasets have been used for important monitoring studies such as population studies and environmental influences. Alison recently co-authored a paper with Manuel Dureuil from university of Dalhouise Canada which was published in African Journal of Marine Science titled: ‘A computer-aided framework for subsurface identification of white shark pigment patterns’. All data was collected with Marine Dynamics.
Interestingly as of late there have been some rare interactions between our white sharks and other marine species such as Short tailed stingrays, Bronze whaler sharks and even two Orcas! The team intend to tag and track more white sharks and continue to involve volunteers with shark and cetacean dissections when deceased specimens wash up locally. They have ongoing work every month: educational presentations to local guest house owners, volunteers, and eco-tourism clients through marine evenings.