If only we would get a Rand for every time student divers or just people on the beach ask us; “Have you seen a shark?”. This might seem an easy enough question, however it actually leaves us with a rather complicated answer. The answer is yes, on every single dive in Cape Town we see one or more sharks. Are these the sharks most people are referring to? most likely not. The shark they want to hear about is the majestic Great White shark. Though this is a shark common to this part of the South African coast; they are in all honestly rarely ever seen while scuba diving. What we do see a lot are Shysharks and Catsharks.
These significantly smaller sharks are often overlooked, or should I rather say underappreciated. Worldwide there are 204 different Chondrichthyan species (cartilaginous fish) of which 56 occur in South Africa. Of those 36 of them are endemic to Southern Africa and therefore cannot be seen anywhere else in the world. Despite the fact these species are so special and unique to South Africa, there is actually very little known about these fish. That is why we decided to become citizen scientists and join the search with ELMO.
ELMO stands for South African Elasmobranch Monitoring, a project set up by marine ecologist Lisa Schroeter to study Elasmobranches; or in other words sharks, rays and skates. All of these belong to the class of cartilaginous fish, which means that their skeletons are not made of bones like humans, but are made of cartilage, and additional to that they also do not have a swim bladder. This skeleton structure is crucial in understanding the survival chances of the species after for example being caught by fishermen, something that regularly happens as these Shysharks are mostly found in shallow water. Because these fish do not have a bone structure in place, it means as soon as they are taken out of the water their intestines collapse as nothing keeps these is place. So even when one of these sharks is caught and released, the chance of survival because of internal organ damage is very slim. This in combination with threats such as marine pollution, bycatch and habitat loss contribute to a possible decline in their populations, something we know very little about as there is a lack of long term information. This makes it difficult to monitor their conservation status, therefore increasing the possibility that the species might go extinct before being able to protect it.
So when ELMO needed divers to help monitoring Elasmobranches in False Bay, we were quickly on board and so our hunt for mermaid’s purses (egg cases) began. All skates and some sharks are oviparous; this means they lay eggs instead of giving live birth. They attach these egg capsules to rocks, sea fans or seaweeds and it contains an embryo that feeds on the yolk until it is big enough to hatch. The most common oviparous species in False Bay are Shyharks and Catsharks; those smaller sharks we see very often but know so little about. So from now on the Puffadder and Brown Shysharks and Pyjama Sharks and their eggs will have our special attention. The eggs encountered will be labelled and we will monitor “our” eggs to see how they grow and for example survive a storm like we had a few weeks ago.
We are extremely excited to be part of this project and to learn and contribute to the knowledge about these sharks life cycles and habitats that from this point on will only grow further. And next time when we encounter one of those “normal” Shysharks or Catsharks in False Bay, we will remember how exceptional they actually are.
To Be Continued.