Saturday, June 01, 2019

White Shark Nutrition and Cage Diving - Paper!

Well well.

Remember Kátya's stellar paper?
As a reminder, it showed that despite of being fed one ton of  highly nutritious Tuna heads every week, our Sharks showed only negligible nutritional impacts, i.e. a) no evidence of bait incorporation by our non-resident Bull Sharks, whereas b) for some of our much more resident Whitetip Reefies, the Tuna incorporation was a mere 8–22%.
Consequently, we surmised that both species are not being harmed but instead continue to fulfill their ecological role practically unchanged.

I'm obviously totally not surprised.
All global cage diving regulations stipulate that the Sharks can only be teased but not fed, which far from being "good" let alone "eco", actually appears to harm them as they incur a metabolic loss as a consequence - and if our highly fed Bulls show no bait incorporation, there was never any way that the tiny amount of Tuna pilfered by those GWS would have any effect at all!

And then there is this, and I cite,
The provisioning attracts a number of animals, including birds, teleosts and other chondrichthyans, some of which are potential white shark prey items (e.g. yellowtail kingfish Seriola lalandi, bronze whalers Carcharhinus brachyurus, and rays). However, the shark's unaltered diet negates concerns that large groups of teleosts, encouraged by the presence of bait and chum, create additional feeding opportunities around the cage-diving operators....

Additionally, dive operators and scientists have yet to witness attempted predation on any of the species attracted by the bait and chum, despite close proximity and apparent ease of capture (pers. com. A. Fox and A. Wright). This combination of observation and dietary biomarkers negates the hypotheses that provisioning creates additional or unnatural foraging opportunities for white sharks around cage-diving operations.
Bingo - this is totally our observation, too! 
Those prey items obviously know that the Sharks are there and remain highly vigilant - and having lost the element of surprise, those Sharks don't even bother trying.

And there you have it.
Well done Lauren and Charlie for having added another piece to the puzzle - and I may add, for once again exposing all those irritating unsubstantiated reservations by our detractors as being just that, and pretty much rubbish to boot! 

Let's go Shark diving - sustainably!

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