Posted on Friday, 29 May 2015
No day is the same when at sea. Not everything that happens in nature has an answer. The past month has reminded us that this is a phenomenon that takes place frequently when working with nature.
It's as though someone sent out an evacuation siren to all the shark species a long the False Bay coastline. Our Great White sharks disappeared on the 15th April. It has been a long and trying time for our guests who have booked their trip of a lifetime months in advance, only having to have their trip rescheduled to another location or cancelled. 31 days later the sharks made a brief appearance which was witnessed by another shark operator whilst out at Seal Island. Thus far, I can confirm that their arrival has been curtailed.
My blog is not to focus on the sharks not being at Seal Island, but rather I would like to share another fascinating and equally puzzling mystery. At the precise time the Great Whites departed, so did the Broadnose Sevengill shark (Notorynchus cepedianus), commonly known as Cow sharks. Was the disappearance of both species somehow related?
The Cow shark is a beautiful, prehistoric animal and is equally formidable to that of a Great White shark, yet very little is known about this species. This apex coastal predator ranges in a mature male 1.3 - 1.7 metres, while a mature female can be 2 – 3 metres.
Usually they can be seen at Miller's Point, about a 10 minute drive from Simon’s Town. Nature can never be guaranteed; nevertheless divers experience a fairly consistent number of encounters with these magical animals
Research on Cow Sharks
“We suspect that pregnant females reside in False Bay,” says Dr Alison Kock, Research Manager for Shark Spotters, who is leading a research project on Cow sharks. “There is little known information on pregnant females elsewhere in the world, so this presents a great opportunity to collect more data, which will be done by using non-destructive methods, e.g. analysing hormones in the blood samples that are collected.”
Cow sharks have a low conservation priority which may be attributed to the lack of available data (classified as data deficient on the IUCN Red List). One of the aims of this project will be to collect enough data to inform management as to whether any threats exist.
Cow sharks are currently being tagged with acoustic and pop-off archival satellite transmitters, also known as “PAT tags”, which are programmed to collect and archive data such as depth and temperature, before the tag releases from the animal at a pre-programmed time. The tag then pops up to the surface and the GPS position of the release location and archived data are sent to satellites passing overhead. The acoustic tags transmit a signal that can be picked up by one of 24 acoustic receivers that have been deployed in Cape Town waters.
The sharks will be measured, sexed, and biological samples will be collected. Blood and muscle samples allow for the analysis of genetics, for stable isotopes to determine diet without the need for lethal sampling, and for reproductive hormone analysis, which allows the team and researchers to the assess maturity status and reproductive status that a specific shark may be in.
The team takes the utmost care of the sharks to ensure their welfare, and all methods have been approved by the University of Cape Town’s ethics committee. All surgical procedures are overseen by the Aquarium’s resident veterinarian, Dr Georgina Cole.
The research is being co-ordinated by Dr Kock, and Dr Adam Barnett from James Cook University (Australia), with assistance from colleagues and students from the University of Cape Town, the Department of Agriculture, Forestry and Fisheries, the South African Shark Conservancy, Bayworld Centre for Research, SAIAB’s Acoustic Tracking Array Platform, the Ocean Tracking Network, and the Oceanographic Research Institute.
Sevengill release. Photo courtesy of Alison Kock.
Funding is primarily from the Two Oceans Aquarium, with additional financial or equipment support from the University of Cape Town, University of Tasmania, Save Our Seas Foundation and Ocearch.
It is amazing at how our ocean is so complex and the importance of preserving our marine eco system and surrounding environment. They form such a vital component to all life on Earth. Even though we do not have an answer for the disappearance of both these species, we may conclude that they might be connected in some way. For me I find this simply fascinating.