Sunday, March 17, 2013

Feeding Bull Sharks in Fiji - the Paper!

This pic by Doug is so good that I catch myself using it time after time again - click for detail!

Stating that I'm mighty proud would clearly be the understatement of the year!

Opportunistic Visitors: Long-Term Behavioural Response of Bull Sharks to Food Provisioning in Fiji
Juerg M. Brunnschweiler, Adam Barnett


Shark-based tourism that uses bait to reliably attract certain species to specific sites so that divers can view them is a growing industry globally, but remains a controversial issue. 
We evaluate multi-year (2004–2011) underwater visual (n = 48 individuals) and acoustic tracking data (n = 82 transmitters; array of up to 16 receivers) of bull sharks Carcharhinus leucas from a long-term shark feeding site at the Shark Reef Marine Reserve and reefs along the Beqa Channel on the southern coast of Viti Levu, Fiji. 

Individual C. leucas showed varying degrees of site fidelity.
Determined from acoustic tagging, the majority of C. leucas had site fidelity indexes greater than 0.5 for the marine reserve (including the feeding site) and neighbouring reefs. However, during the time of the day (09:00–12:00) when feeding takes place, sharks mainly had site fidelity indexes smaller than 0.5 for the feeding site, regardless of feeding or non-feeding days

Site fidelity indexes determined by direct diver observation of sharks at the feeding site were lower compared to such values determined by acoustic tagging. 

The overall pattern for C. leucas is that, if present in the area, they are attracted to the feeding site regardless of whether feeding or non-feeding days, but they remain for longer periods of time (consecutive hours) on feeding days. The overall diel patterns in movement are for C. leucas to use the area around the feeding site in the morning before spreading out over Shark Reef throughout the day and dispersing over the entire array at night. Both focal observation and acoustic monitoring show that C. leucas intermittently leave the area for a few consecutive days throughout the year, and for longer time periods (weeks to months) at the end of the calendar year before returning to the feeding site.

So this is it.
Like we never tire to say, BAD has essentially been established in order to manage a Shark research and conservation project and consequently, everything we do is geared towards those aims whilst generating just enough income to compensate the various stakeholders and ensure our long term survival.
So far so good - touch wood!

But of course the beginning was everything but easy.
I had reached out to Gary Adkison when formulating the Fiji Shark Project, and when Juerg lost his Bull Shark research site in the Bahamas, Gary suggested that he go check out the crazy dude who was trying to set up a Shark MPA in Fiji. I desperately needed to find a conservation-oriented researcher, something that in those times was far from common; and Juerg desperately needed to find a new and and above all, reliable Bull Shark research site for his Bull Shark Tagging Programme. We met, took each other's measure, liked what we saw and decided to give it a try.
Gesagt getan and the rest, as they say, is history.

That was in 2003.
Ten years and countless adventures, discussions and heated debates (!) later, I must really say that it was a match made in heaven. I really, really like and respect Juerg and the feeling is likely reciprocal, the more as we really completely see eye to eye on conservation matters (sometimes less so on research techniques), are completely result-driven and despise  bullshit - and we even share the same degree of incisive humor!

But I'm digressing as always.
Back then, Shark conservation was very much in its infancy and the exclusive domain of a handful of idealistic and rather clueless loons (and probably still is!), we were both essentially rookies, and progress only happened in baby steps and with plenty of setbacks. This also on the research side where the first generation of PAT tags was rather temperamental and where for ethical reasons, we had burdened ourselves with the challenge of trying to tag the animals underwater, first intra-gastrically and then externally.
But Juerg and Gary did persevere and eventually got it done - and this very much despite the vocal objections of your truly who developed an increasing distaste for the invasive techniques.
Love you guys! :)

At the same time, we started our long term monitoring.
This is a first (and by no means last!) look at our enormous data base where we have so far meticulously recorded close to 10 years, or approx. 4,000 individual baited Shark dives in the Shark Reef Marine Reserve. Over those years, we have named and monitored more and more individual Sharks and have been keeping particularly detailed records of presently approx 150 individual Bulls.
The paper is the comprehensive analysis of only one subset of those observations, i.e. simple presence/absence data, this in comparison to several years' worth of acoustic tagging data of the same 48 individual Sharks.
Thankfully it is open access - read it!

The take-away message as I see it is this.
This particular Shark dive has been operating continuously since 1998 and it is fair to state that if there has ever been a population of conditioned Sharks, it would be the Bull Sharks of Shark Reef.
And yet,
  • Our Bulls remain wild animals.
    Once they have discovered Shark Reef, they do come back; but at the same time, it is quite obvious that they continue to roam the area and undoubtedly fulfill their ecological function like any other non-provisioned Bull Shark, much in line with what we postulated years ago - and now we have the peer-reviewed science to back it up!
  • Effects at large spatial and temporal scales appear minimal.
    This is consistent with all research into provisioned Sharks, i.e. that there may well be conditioning on site but that typically, the long term migrations and life history in general remain largely unaffected.
  • Feeding does not appear to significantly effect the Sharks' diel patterns, this with the only exception that they will spend more time at the feeding site on feeding days - however only to depart and continue their usual daily roaming patterns. Note the observation about night-time foraging at and possibly even within the Navua River - very interesting and eminently testable!
  • Same-same for their propensity, or lack of, to approach humans.
    There are obviously pronounced differences at the individual level, something I experience on a daily basis - but despite of the fact that there are Sharks that are decidedly more friendly (or bold), it is equally true that none of them comes begging for food when there is no bait in the water. In fact, the observation that during the time of the day (09:00–12:00) when feeding takes place, sharks mainly had site fidelity indexes smaller than 0.5 for the feeding site, regardless of feeding or non-feeding days may be an indication for the fact that the presence of bait barely compensates for the notorious shyness of this species!
  • Long-term exposure to feeding does not appear to cause any conditioning in terms of dependence on that food source.
    One could stipulate such conditioning if the data showed increased presence over the years - but the fact is that the data appear to absolutely negate that hypothesis, as e.g. illustrated by the site fidelity indexes for 2004-2011 of Crook, a friendly old-timer and voracious hand feeder., to wit 0.48, 0.20, 0.16, 0.24, 0.23, 0.22, 0.14 and 0.47  (Table S1), an observation that is consistent for all monitored Sharks.
  • The Shark Corridor appears to confer a solid degree of protection.
    Yes the animals do regularly leave that area - but site fidelity indexes that are larger than 0.50 indicate that the protected area is apparently large enough to have a positive effect.
Long story short?
Granted, strictly speaking, this only applies to Fiji Bull Sharks that are being fed in Fiji and not to "Sharks" in general - but after Aleks' paper on Caribbean Reefs and Neil's Tiger Shark paper, we now have one more indication that one cannot simply draw conclusions from other research showing conditioning, and possibly negative consequences for other species: not from those Lemons in Moorea, not from the Southern Stingrays in Cayman - and certainly not from teleost Fishes that appear to have a higher propensity for being conditioned, let alone the proverbial bloody Bears!

On the contrary and with the caveat that this may well be species- but possibly also situation-specific (see the Moorea Lemons where there may be procedural issues), it appears that those larger Sharks may just be a tad too smart for the simplistic cause-effect bullshit spouted by our detractors.

In fact when it comes to the risk they pose to humans, I'm of the strong opinion that provided that those baited dives are conducted responsibly, those "tame" Sharks pose less and not more of a threat! Yes I'm obviously speculating - but after thousands of Shark dives, I've earned myself the right to do so!

And their long term life history?
If there there is one constant observation among all papers analyzing Shark provisioning, it is that over the longer term, the animals keep their normal migration and mating/birthing patterns - e.g. think of the GWS in Lupe, the Playa Bulls and the Bimini GHH that are all seasonal irrespective of the fact that they are being fed! This is once again a strong indication that feeding causes no harm, at least not to the Sharks that are being fed.

Anyway - is this cool, or what!

Keep watching this space.
As I said, this is only the beginning, meaning that our data base contains the answers to many more questions. And, we're already conducting and are about to roll out several more new large multi-year projects that will hopefully lead to new important insights - especially about reproductive and possibly even natal philopatry that would greatly assist us in refining local Shark conservation measures.

In the meantime, enjoy Juerg and Adam's paper!

PS thanks Patric!
PS2: thanks Georgina!


Tropical Selkie said...

Fan-freakin-tastic! Congratulations on some solid research and impressive results. Didn't I JUST ask for more published research with direct conservation application? THANKS! :-)

OfficetoOcean said...

Once again, some more great, super solid and fascinating stuff coming out of Fiji and once again, from Juerg and the crew at BAD.

Not only is this great info to have in the public realm, this is also going to prove an invaluable reference resource for Of Shark and Man! Congrats to all!

Martin Graf said...

Congratulations, great job!

I'm not sure about the other aspects of your observations, since I have just a few weeks of observing the Bull sharks in Bimini, but the sharks here are definitely reluctant to approach divers as well and they individually show distinctly different behaviors.

Again, you da Man!