Sunday, September 16, 2012

Learning in Sharks - new Paper!

 Beautiful pic of juvenile Lemon Shark. Source: Battling for Bimini. Click for detail!

Cool stuff!
From the paper.

Social learning is taxonomically widespread and can provide distinct behavioural advantages, such as in finding food or avoiding predators more efficiently.
Although extensively studied in bony fishes, no such empirical evidence exists for cartilaginous fishes.
Our aim in this study was to experimentally investigate the social learning capabilities of juvenile lemon sharks, Negaprion brevirostris. We designed a novel food task, where sharks were required to enter a start zone and subsequently make physical contact with a target in order to receive a food reward.

Fig. 1 Set-up of social learning experiment: a positions and measurements of zones, target and reward; b schematic of the target mechanism showing covered and exposed position as well as side and front views; and c steps of the food task or trial - click for detail!
Naive sharks were then able to interact with and observe (a) pre-trained sharks, that is, 'demonstrators', or (b) sharks with no previous experience, that is, 'sham demonstrators'.

On completion, observer sharks were then isolated and tested individually in a similar task.
During the exposure phase observers paired with 'demonstrator' sharks performed a greater number of task-related behaviours and made significantly more transitions from the start zone to the target, than observers paired with 'sham demonstrators'. When tested in isolation, observers previously paired with 'demonstrator' sharks completed a greater number of trials and made contact with the target significantly more often than observers previously paired with 'sham demonstrators'.
Such experience also tended to result in faster overall task performance.

Fig. 5 Testing phase: median (±interquartile range) number of physical contacts made with the target and the target cover by individual observer sharks previously paired with demonstrators (D) or sham demonstrators (SD). P\0.05 in both cases, Wilcoxon signed-ranks test, n = 5 - click for detail!
These results indicate that juvenile lemon sharks, like numerous other animals, are capable of using socially derived information to learn about novel features in their environment.
The results likely have important implications for behavioural processes, ecotourism and fisheries.

From the Discussion

It has previously been hypothesised that sharks can form groups for increased foraging opportunities (Jacoby et al. 2011) and that sharks exhibiting feeding behaviour attract nearby conspecifics or heterospecifics (Myrberg et al. 1969; Bres 1993; Klimley et al. 2001). Although we did not determine specific social learning processes, our findings empirically demonstrate the sensitivity to, and likely importance of, social cues in sharks.

These and other recent findings that stress the importance of social behaviour to the efficacy of shark deterrents (O’Connell et al. 2011; Robbins et al. 2011) emphasise the need for further experimentation on how changes in sharks social environment (presence of competing or informed conspecifics) might affect their foraging strategies or performance and exploitation of a novel food source.
As I said, great job - which is of course no wonder!
After all, Tristan is one of Doc's disciples and the whole thing did happen in Bimini as part of a wider endeavor and very much under the supervision and leadership, but undoubtedly also scathing criticism by the great man himself! This is your classical behavioral experiment aimed as testing a previously formulated hypothesis, and this thankfully (and very much unsurprisingly!) involving a control group - as it should be!

Of course we in the Industry knew that already.
There are plenty of examples of Sharks appearing to learn from their conspecifics (and who knows, maybe other species as well?) during baited dives, this from species as vastly different as the Whale Sharks in Oslob or Cendrawasih Bay to, it appears, the Sicklefin Lemons in Moorea.

Here are some examples by Doc himself.
We know from simple observations that throwing a piece of bait to a naïve lemon shark will take about three pieces for that shark to get the idea that the sound of a splash means that food has landed in the water near it. Then you see other lemon sharks watch the smart one and pick it up right away...splash=food.

This is especially so with the larger reef sharks.
It is easy to tell a new, inexperienced (new comer) reef shark from the experienced group. tThe newcomer has no clue when a piece of food is thrown a foot in front of its nose. It just swims on by. A trained shark however will have already associated food=splash and will immediately turn, orient to the sound and gobble up the piece. When the new comer watches the trained group orienting to the sound of bait hitting the water it picks it up immediately and gets it from there on. Additionally the other trained reef shark appear to the sound of the boat when we anchor up at the feeding site with no bait.
They are smart animals but you already know that.
Indeed we do!
We have observed learning in our social Reef Blacktips but above all, in our Bulls where we are convinced that the fact that the newbies follow the correct feeding protocols from the get-go is due to the fact that they have learned to behave correctly by observing the experienced old-timers!

So, what do the findings of the paper mean?
Do they prove that Sharks are intelligent?

No they do not!
They show that juvenile (= an adjective) Lemon Sharks (= a species) are able to learn a task by observing other juvenile Lemons and, as Doc tells me, that they could learn faster than rabbits or cats (= other species) on a conditioned response and could recall the response up to a year.

And what about the other Sharks? No idea!
Hell we don't even know whether those findings extend to adult Lemon Sharks, see the various hypotheses about slower and/or different learning that are being put forth for humans! Maybe Sharks, too, get more set in their ways and are less prone to experimenting as they grow up? I'm asking this as some of our old ladies do things in always the exact same way, likely because they have learned that it works!

My hunch is that if tested, different species will show different results.
And I'm also quite confident that there will be differences at an individual level - and possibly even at the level of gender or life stages, who knows!
I'm also expecting that the results will correlate with the extent to which those species are social (remember this is about social learning - which of course begs the question whether our Bulls are social!), but possibly, also with the extent to which learning is a useful strategy considering the specific Shark's life history - and yes I'm still of the opinion that Whale Sharks come across as being particularly thick!

But one thing is clear, at least to me.
Despite of all those caveats, I too am convinced that far from being the ever lurking instinctive killing machines some quarters would have them be, Sharks are way smarter, and their life history and behavior, way more nuanced and sophisticated - and this paper is yet another step in revealing that fascinating and beautiful tapestry.

Thank you Tristan and thank you Doc!

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