Naked Science Forum

Life Sciences => Plant Sciences, Zoology & Evolution => Topic started by: turnipsock on 19/08/2009 22:37:45

Title: Why aren't there more sharks?
Post by: turnipsock on 19/08/2009 22:37:45: Why aren't there more sharks?

It seems to me that they have an ample food source and no natural preditors. They are at the top of the food chain and are so well developed the seas should be overrun with them yet they seem very rare.

Dolphins seem to be in the same boat and they are all over the place.

So why are there so few sharks?

(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fpaxarcana.files.wordpress.com%2F2008%2F02%2Fshark_kayak.jpg&hash=5cad973887a3e5315da9fc2793a95500)

A Shark.
Title: Why aren't there more sharks?
Post by: RD on 20/08/2009 02:24:31: Q. Why aren't there more sharks?

A. Shark fin soup (http://en.wikipedia.org/wiki/Shark_finning)

Quote
The United Nations has estimated that only about ten million sharks are harvested each year.
Some conservationists, however, put the number at closer to a hundred million.
http://news.nationalgeographic.com/news/2006/10/061012-shark-fin.html
Title: Why aren't there more sharks?
Post by: Chemistry4me on 20/08/2009 06:26:47: Maybe also shark cannibalism?
Title: Why aren't there more sharks?
Post by: Don_1 on 20/08/2009 09:09:28: Sharks do have enemies. Dolphins are known to attack sharks as a means of attack being the best form of defence. At full speed and with a good aim, a Dolphin can do a great deal of harm to a shark and can kill.

There is also the Orca (Killer Whale) which will predate sharks, and other fish will take young (pup) sharks. Perhaps this is also a means of attack being the best form of defence; get them before they are big enough to get you.

Sharks are not 'mass producers', they will have between 1 & 100+ young, not lay the thousands of eggs which most fish do. Some species will give birth to just two pups. I say 'give birth', because some sharks bear fully developed live young.

As C4M suggested, sharks will prey on other sharks.

But the shark's biggest predator is man, not just for shark fin soup or shark steaks, but also out of fear of these ultimate predators. See RD's post above.
Title: Why aren't there more sharks?
Post by: Nizzle on 20/08/2009 12:08:47: Quote from: Don_1 on 20/08/2009 09:09:28
... these ultimate predators...

Sharks aren't ultimate predators if they can't even beat a lame dolphin [;)]
Orca's however have nothing to fear in the ocean except mankind.
Title: Why aren't there more sharks?
Post by: Chemistry4me on 21/08/2009 05:25:54: Quote from: Nizzle on 20/08/2009 12:08:47
Orca's however have nothing to fear in the ocean except mankind.

Try telling that to this guy eh!?

(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fpaxarcana.files.wordpress.com%2F2008%2F02%2Fshark_kayak.jpg&hash=5cad973887a3e5315da9fc2793a95500)
Title: Why aren't there more sharks?
Post by: JimBob on 25/08/2009 03:11:02: Human predation (over fishing) is a VERY serious problem - I have read (don't ask me where one of the synoptic science news fees, probably) that some marine ecosystems are near collapse due to overfishing. The band on whaling is an example. The use of dolphin-safe tuna nets is also an example. An if you think are safe from extinction, think again. Both blue fin tuna and swordfish are among the fish that are close to being in Jjpordy. Even such once-common fish as the Atlantic cod and Monkfish are seriously over fished and compromised.

Sharks are among these.
Title: Why aren't there more sharks?
Post by: Don_1 on 25/08/2009 08:04:37: Films, such as 'Jaws', give us a great fear of sharks, which doesn't help their situation.

There are over 400 species of shark, from the huge Whale Shark to Etmopterus hillianus the Caribbean Lanternshark. Over 200 are listed by CITES as endangered, with almost 100 thought to be in grave peril, some already beyond the point of no return.