Sunday, June 10, 2018

The Impact of GWS Cage Diving - Paper!


Bingo, and I cite,
"Best practice" among cage diving operations apparently consists in just teasing, but never actually handing any bait to the Sharks.
Were I a Shark hugger, I would immediately object that letting the Sharks waste precious energy on fruitless "hunts" is to be rejected as it is likely harmful to the animals.
Yup that would be yours truly a whopping ten years ago!
And now Charlie has concluded his investigation and comes to the following conclusion (emphasis is mine)
Although sharks are enticed to the cage-diving vessels with baits, industry regulations do not allow operators to feed white sharks and strict limits on the amount of bait and berley are now in place in South Australia and at other white shark cage-diving locations (Bruce, 2015).
Energy burden from the increased activity is, therefore, not rewarded by regular bait provisioning.

Some baits can, however, be consumed when sharks approach the baits using high speed or stealth (Huveneers et al., 2015).
The baits used in SA are composed of gills and stomach lining of southern bluefin tuna and are not as energy-rich as white shark’s natural prey while at these sites (e.g. pinnipeds). Whether the infrequent consumption of these baits provide sufficient energy to compensate for the increased energy expenditure associated with sharks interacting with the operators would depend on the calorific value of these baits and the frequency of white sharks successfully feeding on the baits, both of which are currently unknown (Brunnschweiler et al., 2017).
Spending time interacting with cage-diving operators might also distract sharks from normal behaviours such as foraging on natural, energy-rich prey like pinnipeds.
Combined, these suggest that the increased energy expenditure associated with cage-diving interactions might not be compensated for by either bait or natural prey consumption.

One could, therefore, argue that white sharks should be able to feed on some bait to compensate for the energetic losses resulting from interacting with cage-diving operators.
Bioenergetic models (e.g. Barnett et al., 2016) would, however, be necessary to accurately assess the likely effect of cage-diving on white shark energy balance and whether such compensation is necessary or beneficial. Beyond the potential for short-term energy intake, other aspects of food provisioning (e.g. quality of food, potential for changes in foraging behaviour) would also need to be considered.
Good one - and obviously, totally not surprised!
This is now the second paper (re-read this!) stating that NOT feeding is probably not a good idea - and whereas I concur that further investigation into the precise energy balance, etc may be beneficial, we should really not caught up in minutiae and finally do the right thing.

So what's it gonna be?  
Now that the evidence is in, will the regulators in Australia and elsewhere do the right thing and allow for proper feeding of those Sharks - or are they going to continue cow-towing to those in the populace who will contend that it would lead to more Shark attacks, and the like?
Remember that when it comes to feeding and conditioning Sharks, 99.999% is being perpetrated by the fishermen and not us - so assuming that it really is a big problem (spoiler = it aint: these are the real problems, with overfishing being the principal threat to Shark populations) let's maybe first look there! !
Anybody taking bets?

Anyway, enjoy Charlie's paper!
To be continued no doubt!

1 comment:

Daniel Norwood said...

I remember we discussed this on a number of occasions, and it makes sense that cage diving operators are creating a calorific deficit by attracting sharks to the boat without actually feeding them. I know that many of the regular sharks that appear year after year at the Neptune Islands lose interest in the cat and mouse game played with the baits at the surface, and can only be seen on submersible cage dives, so this also suggests the effort involved is not worth their while. Feeding the animals occasionally may also help prevent further incidents involving high speed, surprise attacks where the sharks end up smashing into the cages etc...
I am not sure what the operators think about it, but I agree it seems to be the right thing to do!