So things have been a bit quiet for me lately since I’ve been a bit sick but that doesn’t mean nothing cools been happening.
Recently, we took the interns out to take part in a citizen science project studying the breeding patterns of small sharks and skates found along the coastal waters here. Specifically we were down on the beach collecting their egg casings. The project is being run by Whale Coast Conservation. It covers around thirty different beaches on the Western Cape of South Africa. Anyone can take part in collections and the idea is that after two years, the pooled data will hopefully help us understand if certain species of egg laying shark breed at certain times of the year, and if they favor particular areas(Head to http://www.whalecoastconservation.org.za to find out more). This has obvious benefits for targeting conservation efforts. It also happens to make for a great afternoon out
But Back to the Sharks
Roughly 25% of know shark species lay eggs. But they dont look anything like what you’d imagine an egg to be, Here is an example.
This is just one example of the weird and wonderful shapes out there. The Port Jackson Shark, found in South Australia has corkscrew shaped eggs. There are others that look like leafy fronds, some that look like they have a tangled mess of string protruding from one or both ends and a wide array of other strange shapes. They don’t even feel like your typical chicken egg. They aren’t hard and easily smashed but instead have more of a tough leathery shell. But this all begs the question…
Why?
Well to answer that you need to think about the environment they’ve evolved in. When a chicken for example lays an egg, that egg will more or less stay in the same spot unless moved by someone else. Its not like a strong gust of wind will blow it away. The problem a chicken egg faces is air. Its pretty dry biologically speaking and an embryo needs to stay wet, so a thick, hard shell make sense from a protection point of view. But lets apply the same thinking to sharks. They live in a wet environment so they don’t need to invest in the extra protection of a rigid egg case. But more importantly, that gust of wind analogy suddenly has serious consequences in water. A strong water current could easily pick up a light shark egg and carry it far away. If that happened, the new born shark might find itself far from home and unable to survive. Thats where those weird shapes come in, they create ways for shark eggs to get caught on rocks, seaweed or anything else that might keep it in place.
So thats all for this post. As always, feel free to comment or ask questions, and most importantly share it around. Next week I should hopefully have some ROV dives to share!
Tomasz Pedlow
Ocean Minded 