Ocean News

Alison Dives with Cow Sharks

3rd April 2008

The wind here in Cape Town just refuses to stop blowing and has prevented Alison from going out to sea to study the White Sharks of False Bay. It does, however mean that she does get to spend a lot more time writing up her PhD thesis! Alison is currently sorting through hundreds of thousands of records, which is definitely not half as much fun as playing tag with sharks, but she is starting to get a good idea of what these large apex predators are doing along our coasts. Over the next few weeks, when Alison can’t get out onto the water for field study, she will be updating us on some of her findings and some of her past experiences with these magnificent sharks, as well as various other shark species found off South Africa’s coastline.

Photo Courtesy of Phil Parr

Today, Alison thought that she would show you another shark species which she plans on studying, the Broadnose Seven Gill Shark (also well known as the Cow Shark). The sharks are common along South africa’s west and south-western coasts, in shallow bays and close to the shore. They can attain a size of 3 metres and like white sharks, they are formidable predators of Cape Fur Seals, smaller shark species and fish. Occasionally though, they may find themselves on the white shark’s menu.

Photo Courtesy of Phil Parr

Cow Sharks may seem very lethargic and slow whilst one is diving with them, but Alison has expert opinion on the subject from Dr. Dave Ebert, that this is in fact deceiving, as he has seen them hunt their prey and they are extremely agile and fast. Alison definitely agrees with this, especially if they are capable of hunting and catching agile seals, which constitute up to 1/3 of their diet in False Bay and up to 2/3 of their diet along our west coast.

Interestingly, fishermen have reported seeing cow sharks hunt their prey in packs, much like wolves. They have described scenarios where a few sharks have circled a lone seal and then one would move in for the kill, which triggers the others to react as well. This co-operative hunting technique is not commonly described in sharks, but does suggest a level of intelligence that people do not usually atribute to sharks. It has also been suggested that white sharks may pack-hunt on large species like whales, or on groups of fish such as large tuna, but to date no reliable evidence on this behaviour has been presented.

Cow shark populations are listed as Near Threatened globally on the IUCN Red List as they are targeted by commercial fisheries, in addition to being caught as bycatch. They are also targets for recreational fishermen, for sport due to their large size and weight.

Photo Courtesy of Phil Parr

Alison recently went diving with these rather strange sharks, which are easily identified by their broad head, seven gills (instead of the usual five gills) and the presence of a single dorsal fin situated far back along the body near the caudal fin.