smicko said...
Now just to be clear Suba, I'm not taking the piss, serious question.
If we know so little about Whites how do we know that their usual habitat is over the shelf?
That's a very good question. Still one to properly be answered I suppose. The theory that they spend (normally) much of their time out in deeper waters was supported by tagging data from whites tagged in South Australia.
The majority of a white's diet is NOT mammals like most people assume. They tend to feast heavily (especially when they are juvenile and sub adult) on finfish like snapper and tuna, squid (only really when the shark is young and the squid large) as well as other elasmobranchs which tend to also hang out in deeper waters. From what I've read of a report done in the early 1990s, there were many cases of archival tagged white sharks that almost entirely bottom dwelled in deeper waters, feasting most likely on elasmobranchs and forgoing much of the other food sources.
But yeah, this is the thing. We just don't know enough about them. The last decade or so of tag data in Australian waters suggest they spend much of their time out at sea in pelagic and deeper waters. There is an idea that there is some kind of ecological switch (possibly the seasonal movements of schooling fish like the tailor) that draws sharks into our coastal waters. As has been proven, especially in America, when a shark moves into the coast and finds the feeding is good they tend to stick around. With a dramatic increase in whale numbers in WA (according to what I've been told by the DEC) there would most certainly be more natural whale fatalities and the carcasses tend to stay in near the coast. A white shark cannot resist that! This is probably just one of many reasons they appear to be hanging around. That and my theory that there is less substantial food out in the deeper waters than they are use to. But, at the moment it's just all theory and hopefully this $14m might help us figure it out a little better!
barn said...
Has anybody done any experiments on the drag that these tags induce?
There's been plenty of research done. Quite in depth mathematical modelling and trail and error has been used to try and create the best tag design possible. Not just for the sharks benefit but also because there is no point going to all the effort to tag something if the drag will pull the tag out
Basically if the tag weight to body weight ratio is within a suitable range and the design is streamline then there shouldn't be a problem. White sharks travel on average at around 3km/h. It's not quick enough to really create drag.
As for my project. Nothing exciting. Basically want to go out and lure in and catch white sharks, aswell as have a 'rapid response' capability to go out and tag sharks when they come into our beaches (such as cott and rotto). Also hoping to do some serious tagging of bullsharks in our river...seeing as we know just as little about them.
