30 March, 2013

The effect of shark cage diving on my patience

First off, thanks to DaShark and Patric for the warm welcomes to the shark blogosphere!  Especially Patric’s observation that …it's about bloody time someone grew a pair of steaming hot bolas and got on to the Internet to blog about South African shark diving. Perhaps my greatest strength lies in my lack of bolas in the first place. J

When starting this blog, I promised myself to limit posts to South African related issues, to not criticize shark research and not to have loads of posts about the cage diving industry.  I now break all of those promises in my second blog… damn!

And it’s all due to Bruce & Bradford’s paper “The effects of shark cage-diving operations on the behaviour and movements of white sharks, Carcharodon carcharias, at the Nepture Islands, South Australia”.  I actually don’t know how these papers keep getting published.

The work demonstrates how chumming and baiting sharks can affect the fine-scale spatiotemporal patterns of white sharks within their aggregation areas within the small window operators are present.  No shit.  If chumming and baiting sharks didn’t attract them, you wouldn’t have an industry which is measured in hundred of millions of USD/year would you? 

What is lacking in all of these studies is whether or not these extremely localized fine-scale spatiotemporal shifts are a bad thing for sharks.  Bruce & Bradford do point out how woodland caribou (a socially complex, terrestrial, mammal) can suffer from petroleum exploration activities… which is naturally the best comparison in the literature to white shark cage diving?  Eish…

There are several generally irritating parts of this paper which DaShark has already highlighted.  However, there are three questions I have about the research specifically, including what appears to be one epic fail in the methodology.

1) What are the seals doing?  Bruce & Bradford highlight how the sharks are aggregating on the east side of the islands which corresponds to the corridors seals use to commute to and from the colony. There is no specific mention of the temporal patterns of seals, however...

By 2010 the peak arrival time of sharks at the island appears to be just after dawn, a few hours before the operators get there.  I don’t think Bruce means to insinuate that sharks are predicting the arrival of the operators (every WSCG operator wishes this were true!).  EDIT: OMFG he does! "Arrival of sharks at 'provisioning' sites in anticipation of vessel arrival has been observed or suggested in a number of studies... but has not previously been demonstrated in white sharks."  Rather, this graph is a clear indication that white sharks at the Neptunes are executing the same hunting strategy documented practically everywhere else on Earth (i.e. Kock et al. 2013Fallows et al. 2012 and De Vos & O’Riain 2010, Klimley Klimley Klimey... the list goes on!!!) and certainly does not provide any clarity on Bruce & Bradford’s subject of cage diving effects.  

2) Shark presence at a VR2 does NOT equate shark presence at a WSCG operator’s vessel.  We’ve had many sharks pass right under vessels and cut through multiple chum lines without ever being spotted at the surface by operators.  This conundrum could easily be solved by looking at operator logbook data to see how many sharks they observed were tagged.  Why Bruce & Bradford utilize logbook data from operators but do not publish this key aspect is beyond me! 

3) The 2010 animals have better tags with higher battery life and they are using better receivers.  When I got to this section;

Transmitters used in the 2001-2003 study were rated for a battery life of approximately 2.0 years and those used in the 2010-2011 study were rated for approximately 6.5 years.” – Bruce & Bradford 2013  

I had an epic face-palm.  Those are not the approximate tag battery life expectancies, those are the maximum battery-life expectancies.  The cold temperate waters white sharks occur in zap tag battery life, so you are lucky to get more than 6 months of transmissions from those old (circa 2000) acoustic tags whereas you may get a few years out of the 2009 models.  Also they got a nice upgrade in receivers for the 2010 study, because two of the 2001 receivers were flooded/highly fouled, one of the receivers was lost in a storm and subsequently that data was lost…

“Due to a combination of battery failures and lost stations, there were periods of no coverage from any of the stations at the North Neptune Islands from 12 February 2002 to 19 March 2002 (36 days), at the South Neptune’s from 9 February 2002 to 20 March 2002 (37 days) and at Dangerous Reef from 12 November 2001 to 21 March 2002 (126 days)…” – Bruce et al. 2005.

If that’s how the receivers fared, how likely is it that all those circa 2000 tags worked perfectly for their maximum life expectancy of 2 years?  It is possible that the short residency times and lack of diurnal patterns observed with the 2001 animals can be explained by a combination of high tag battery failure and the multiple lost/battery failed/fouled listening stations.  I am concerned that Bruce & Bradford fail to mention this, and also side-step it by not including an n=individual sharks value for any of their graphs and only n=detections…

So as much as Bruce (apparently) dislikes the industry, he certainly owes this Marine Biology publication to the controversial title and the white shark’s “iconic nature”.  Moving forward, will someone please take a look at this question: do the potential localized spatiotemporal shifts in white shark patterns associated with cage diving vessels have long-term negative effects on white shark fitness?  Consider this white shark which stranded at Dyer Island that had six Cape fur seals stacked in its stomach.  Dyer Island is the epicenter of the Gansbaai cage diving area where eight operators are chumming or berleying, and baiting on a daily multiple trips/day basis!  Yet, this omnipresent WSCG effort did not seem to affect this sharks’ appetite for seal.  One example, I know that's weak, but this is a blog.

As for my opinion, I do not think cage diving operators have long term negative effects on the overall fitness of white sharks within an aggregation area, when done ethically!  There are definitely short-term negatives like the energy sharks lose breaching on rubber seal decoys, and when sharks get totally fucked up by cages but since we know how well sharks can heal themselves – even from a propeller to the spine – I doubt many cases of cage related injuries have long-term effects.  However, we are still waiting to resight the shark that split its gills open inside a cage last week…


  1. Um, genius. Um, love it. Keep up the great blogging; what a great start!

    As for "will someone please take a look at this question: do the potential localized spatiotemporal shifts in white shark patterns associated with cage diving vessels have long-term negative effects on white shark fitness"...not to criticize but shouldn't all such research start with questions about the LONG TERM IMPACTS to OVERALL FITNESS? Isn't all this initial, spatial minutia really just about putting publication before conservation, yet again? Exhausting, really.

    1. Thanks TS!

      Absolutely agree! Bruce is associated with the government that side, and I'm sure they (the gov't) were desperate to produce something on cage diving. So this is the result of rushed research in comparison to a shotty baseline study written with... dare I say an agenda? Really disappointed in Marine Biology for this one...

  2. The "steaming hot bolas" was meant figuratively of course;)

    Welcome to the blog world, I have no doubt you will do well here. One of the primary issues with any research paper be it ocean based or terrestrial is, "interpretation and cherry picking."

    In the hands of rabid anti-shark diving elements you can pick out and use any part of a paper, wielding it like a crudely designed Facebook Hakapik to move your agenda forward. The same goes for the rabid conservation elements and we see this time and again.

    Don't even get me started on politico's and research papers - there's a blog rant in there somewhere.

    Papers seem to me to be almost quaint, they are released like fragile ships into the hyper connected and frenzied media tide that is the face of today's communication and summarily ripped apart piece meal to serve whatever interest they might.

    The true meaning and import of them often gets lost.

    Solutions? Damned if I know, that's a tin cup world that I do not swim in.

    Researchers, funding, papers and politics are a crazy mix that few can effectively negotiate and even fewer make a living from.

    1. Lead researchers (or, shark experts!), funding, papers and politics are not at all dissimilar to the "industry leaders", profits, sham-marketing and political issues seen with some operators. There are definitely a few blogs one could write on this!

      The solution to both unfortunately relies on the general public to do their homework before making decisions (i.e. following real research or booking with a legit operator). Most won't do their homework, so we must blog. :)