Saturday, March 10, 2012

Fantastic new paper by Neil!

Neil & Tiger, by Jim.

What can I say, I am deeply impressed!
This is what we in the industry have been waiting for, irrefutable proof that at least when it comes to one species in one location, i.e. the Tiger Sharks that frequent Tiger Beach, the feeding has zero incidence on their overall long term mobility and very likely, none on their life history in general!
Bravo Neil, and thank you!

  • 1. There has been considerable debate over the past decade with respect to wildlife provisioning, especially resultant behavioural changes that may impact the ecological function of an apex predator. The controversy is exemplified by the shark diving industry, where major criticisms based on inference, anecdote and opinion stem from concerns of potential behaviourally mediated ecosystem effects because of ecotourism provisioning (aka‘chumming’ or feeding).
  • 2. There is a general lack of empirical evidence to refute or support associated claims. The few studies that have investigated the behavioural impacts of shark provisioning ecotourism have generated conflicting conclusions, where the confidence in such results may suffer from a narrow spatial and temporal focus given the highly mobile nature of these predators. There is need for studies that examine the potential behavioural consequences of provisioning over ecologically relevant spatial and temporal scales.
  • 3. To advance this debate, we conducted the first satellite telemetry study and movement analysis to explicitly examine the long-range migrations and habitat utilization of tiger sharks (Galeocerdo cuvier) originating in the Bahamas and Florida, two areas that differ significantly with regards to the presence/absence of provisioning ecotourism.
  • 4. Satellite telemetry data rejected the behaviourally mediated effects of provisioning ecotourism at large spatial and temporal scales. In contrast, to the restricted activity space and movement that were hypothesized, geolocation data evidenced previously unknown long-distance migrations and habitat use for both tiger shark populations closely associated with areas of high biological productivity in the Gulf Stream and subtropical western Atlantic Ocean. We speculate that these areas are likely critically important for G. cuvier feeding forays and parturition.
  • 5. We concluded that, in the light of potential conservation and public awareness benefits of ecotourism provisioning, this practice should not be dismissed out of hand by managers. Given the pressing need for improved understanding of the functional ecology of apex predators relative to human disturbance, empirical studies of different species sensitivities to disturbance should be used to guide best-practice ecotourism policies that maximize conservation goals.
Here is a great synopsis and in line with his usual stellar outreach, Neil has even posted this brilliant video recap.

Kudos once again!

Any parallels to what we see here in Fiji?
Enter Mike's totally speculative hypothesis that goes thusly.
Contrary to the open ocean where food comes in large packages, e.g. schools of Tuna, Billfishes etc, the potential prey for Sharks on a coral reef consists of squillions of small Fishes interspersed with the occasional large prey like Stingrays, Turtles, Dugongs, even other Sharks.
The big Sharks like Tigers and Bulls require quite a lot of food (Neil's paper mentions a daily requirement of approx 4%, this of 400+ lbs in large animals) and it would make no sense for them to engage in catching small prey as they would be likely spending more energy on the hunt than would be coming back through those small meals.
Thus, postulates Mike's hypothesis, evolution would select for those Sharks not to be fussy but to be highly opportunistic when it comes to prey choice, and to be continuously roaming a large home range in search of those elusive more substantial meals - and this individually and not as a group as under that scenario, co-operative hunting and sharing would really make no sense.

Remember the paper by Meyer about the Hawaiian Tigers?
Apart from what I quote in that post, I also remember reading that individual animals would chance upon particularly attractive feeding opportunities (like the fledgling Albatrosses in Midway, or Turtle nesting and mating beaches), remember that experience and return there at the same time in the following years - whereas other Tigers that have not discovered those sites would not, meaning that this behavior is the result of individual learning and not somehow genetically encoded.

Nine years of collecting data about our Bulls shows this.
  • Individual animals (we now have identified approx. 130, with at least the same number that have no distinguishing features and can thus not be named) will come and partake in the feed for 4-5 days, after which they leave again, sometimes for weeks or even months.

  • There are individuals that turn up more regularly whereas other individuals are more sporadic - but we don't have a single resident Bull Shark and we also cannot observe that the frequency of visits by individual Sharks that have been coming for many years has increased, something that one would expect if there were any dependency on our hand-outs.

  • With the exception of a few sub-adults, all the Bulls leave (i.e. don't turn up for feeding) from approx. mid-October to mid-December when the pregnant females leave to give birth in the nurseries and the other Bulls engage in mating, likely in the deeper reaches of Beqa Channel as when they come back, the mating scars are totally fresh and heal within days.

  • Over the years, the number of Bulls has kept increasing, to a temporary maximum of approx 100 individuals on one dive last year - and I say, this year we will count more!
The analogy I use is that of a popular restaurant.
  • people discover it and come back regularly because they like the food
  • because a lot of people like it, the restaurant is increasingly fully booked - but the composition of the patrons changes all the time
  • none of the patrons takes up regular residency there but instead, they continue to come and go as they please, turn up at meal times and obviously eat in other places as well
  • and they certainly don't attack the waiters - well, at least most of them don't! :)
In brief, I strongly believe that we're witnessing the same exact phenomenon here.
But at least for the time being, that's all we can say and barring any telemetric data, much of it will always remain somewhat speculative, the more as we share the Bulls with the guys down the road. From what we hear, Bull Shark numbers on Lake Reef are way lower - but still, we cannot fully exclude that some of the Sharks that leave Shark Reef do not simply go and dine there and then come back to the SRMR.

And what about bolting on a couple of SPOT tags and finding out?
Much to the chagrin of some of my very best friends, I won't have any of that. I absolutely love those tracks but I hate the invasive technology and just cannot bring myself to accept that those tags be deployed on our animals. Hopefully one day, somebody will finally develop a sat tag that is less invasive and can be reliably attached on the fly underwater - but until then, there will be no tagging and we will thus have to continue relaying on visual observations.
So fingers crossed for a technological break-through!

Anyway, I'm digressing as usual.
What I really wanted to do is congratulate Neil for yet another excellent paper and commend him for getting the science out to the public in his usual brilliant way.

As I said, I am impressed - bravo and thank you again! :)

PS compare to Aleks' paper here: there definitely appears to be a pattern!

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