Sunday, April 14, 2013

Scavenging on Whales - new GWS Paper!

I've been so busy with the Fischer fiasco and according complete vindication of Domeier that I've been remiss in not posting about this paper.

Check this out.

So there you have it.
Of course, ever since the Blue Water White Death team bought a Whale carcass off Durban in their search for GWS, we knew that they scavenge on Whales - but it's nice to see such an in-depth analysis of the phenomenon. Great also to see Neil concede the first authorship to Fallows - tho why such a staunch crusader against Fischer's SPOT tagging would align himself with a prolific SPOT tagger like Neil leaves me somewhat perplexed.

Obviously, with N=4, much remains conjecture.
Although the insight about selective feeding is not completely new (but now further confirmed), the other hypotheses are certainly plausible and warrant further investigation.. Personally, I was intrigued by two observations in particular
  • The initial predilection of the calorically poor fluke and caudal peduncle.
    This reminds me of Gary's account (and video!) of how he got jumped by a GWS when outside of the cage many years ago in SA. The Shark went for his fins, prompting the speculation that they may be first targeting the locomotion, much like Makos are reported to do when attacking Billfishes.
    Maybe this is yet another clue verifying that hypothesis.
  • The lack of intra-specific aggression, and the pecking order.
    I've always described our baited dives as an artificially induced communal scavenging event, and I can confirm that our observations fully match that pattern. Somewhere, I've read that Sharks are not known to bite conspecidfics when competing for food whereas they will certainly exclude and when necessary, even attack other species. I see that daily on our dive but have also heard the same from other foraging events on Whale carcasses, namely from a well documented event in New Caledonia where dozens of Tiger Sharks retreated from a Whale carcass upon the advent of two GWS.
    If my intuition is correct, those chummed and baited GWS dives may thus offer a great opportunity to further record such inter- and intra-specific interactions.
    From what we can discern here, when it comes to rank, size certainly plays a very high role - but in addition to it, there are definite individual character traits, foremost of which assertiveness/boldness that break the general pattern whereby particularly assertive Sharks (usually males) will barge in ahead of the rather placid large females. And one other factor may even be desperation, whereby some possibly particularly hungry and thus desperate subadults will try and dash in and steal a Tuna head, only to then abscond precipitously followed by a whole gaggle of competitors!
Anyway, just a hint.
All-in-all, a very charming little paper that will hopefully once lead to more and stronger insights.about GWS life history and their functions within their ecological niche.

Oh - and I've learned a new word!
Post-prandial torpor = food coma! Didn't know Sharks had that, too!

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