02 July, 2014

11 June, 2014

First white shark recorded in Indonesia

Beautiful shot - anyone know who took it?? Source needed!

And it was a 6m adult male - wow!

Journal article here.

21 April, 2014

We have now lost contact with planet Earth...

Now I have read everything, well I certainly hope I have... Full article here.
Here was the reaction from another "mermaid"...

12 April, 2014

Making sense of shark senses

If you have ever been asked, which sense is the most important sense to sharks?   Keep reading…

The good people at Mote Marine Lab have done it again.  They seem to always crank out the good stuff, but this study is simply exemplary.  Here’s an overly simplified version of the bits I liked the most – for all the bits, go read it yourself!

They collected several individuals of three species of shark - blacktips C.limbatus, bonnetheads S.tiburo, and nurses G.Cirratum.  They also collected live prey items from the diets of each (blacktip+nurse = pinfish L.rhomboides and bonnethead = pink shrimp F.duorarum).  Each species’ general 'norm' of how they go about detecting, tracking, orientating, striking and capturing their prey was established.  Researchers then blocked some of four senses (smell, vision, electroreception, lateral line) one at a time or in combination and observed how the individuals adapted to these changes and shifted their behaviours from the established ‘norm’ of all senses firing.     

When it comes to the initial detection of prey, the sense of smell reined king for all three species.  While blacktips and bonnetheads would still capture the prey when they eventually came into visual contact with it, they did not detect and track the prey from a distance as they would normally.  For nurse sharks, sense of smell was an absolute necessity.  With their nares blocked, nurse sharks sat at the bottom of the tank and failed to feed entirely.  When smell and vision were blocked, blacktips and bonnethead also failed to feed.  This, of course, makes sense.  Nurse sharks primarily hunt at night or hunt prey animals hidden from view in reefs, whereas blacktips and bonnetheads have light available to them.  So guess who performed the best when vision and lateral line were blocked?  Yep, the nurse shark.  Who did the worst?  Bonnetheads.

The sense of electroreception was linked with successfully capturing prey.  When blocked, the sharks could still detect, track, orientate and strike at the prey, but would simply forget to open their jaws in time to capture it, even if the prey actually touched the shark! 

SourceA. A bonnethead, Sphyrna tiburo, with all senses intact opens the mouth to capture shrimp using ram-biting. B. The same bonnethead fails to open the mouth when electroreception is blocked and misses the shrimp, despite making tactile contact with the prey. doi:10.1371/journal.pone.0093036.g006

Vision and lateral line seemed to go hand in hand:  “…animals with simultaneous vision and lateral line blocks did not orient or strike, even when they were within electrosensory prey detection range.”  Thus, “these results suggest that sharks do not recognize electrical cues alone and prey, but require an additional visual or olfactory cue.”

In conclusion:
Our results demonstrate that sharks are capable of attending to multiple sensory cues simultaneously, switching sensory modalities in a hierarchical fashion as they approach their prey, and substituting alternate sensory cues, when necessary, to accomplish behavioural tasks.  This flexibility in behaviour suggests that sharks are well adapted to success, even in the face of a changing environment and evolutionary advancements in prey defenses including chemical, visual, and mechanical camouflage. Gardiner et al. 2014

The bottom line?  Sharks are not the super simple one-sensory fish that some may want you to believe that they are.  Elegant behavioural research, bravo! 

It would be very interesting, but impossible, to do a similar study on large migratory sharks to see what senses they may use to navigate over long (say, Dyer Island to Mozambique) distances, but alas...

Well done Mote lab!

08 April, 2014

What else is in that wave?


Could be shark, tuna, ray, or anything that is counter-shaded that hangs out along the surf zone.  Looks too chill to be a dolphin, and if that is a pectoral fin it is long and has a black tip.  Or it could just be another damn surfer (thanks David!).

One thing's for sure, Kelly 'I would be honored to be eaten by a shark' Slater has zero f*cks to give.

03 April, 2014

Why these wetsuits will never protect you from sharks

Shark repellents seem to creep up in the news once every three months or so.  Some make me laugh, some show promise, and others straight up vex me.  The above wetsuits fall into the latter because they can never work, definitely not for the reasons the sellers are trying to convince you, at least.  So let’s examine the pseuodoscience behind this, delve into the true science, and see how these suits measure up. 

The concept behind the wetsuit is that the coloration on them mimics the colouration of sea snakes, and that sharks will avoid sea snakes (or anything black and white striped) because they are poisonous. Therefore any shark would recognize the coloration of the sea snake on your wetsuit as poisonous and avoid you – thus preventing shark attacks. 

This idea is based on Batesian mimicry, which is when non-harmful species mimic the 'warning'coloration of a harmful species in order to reduce their predation risk from a common predator.  The classic example of this is the monarch butterfly and the viceroy:

The monarch (on the right) is poisonous.  If a predator – like a Blue Jay – consumes the monarch, it will be instantly sick.  This instantaneous negative reaction is key, because the Blue Jay immediately associates being ill with the consumption of that orange and black coloured prey.  If the negative reaction is delayed, say a few minutes later after the Blue Jay has eaten another beetle, the Blue Jay will not learn that it was the monarch that caused the reaction.  So, the monarch has taught the Blue Jay to avoid orange and black coloured butterflies.

The non-harmful viceroy, through the random luck of mutations and natural selection, mimics the coloration of the monarch butterfly.  This is because these warning colours are highly advantageous, thus increasing the viceroy’s fitness.    

The same applies to the Eastern coral snake and the scarlet king snake, several species of dart frogs, and my personal favourite – the Hawkmoth larva and green parrot snake.    

Do you see the failings of taking this concept and applying it to snakes and wetsuits?

For one, aversion of particular colourations is a learned behaviour.  Predators, like the Blue Jay, are not born knowing to avoid orange and black.  They have to experience it first. 
a.       This means that a shark must have already eaten a sea snake and then something negative happened to it immediately.  This wetsuit would only work on that individual shark, not all sharks.
b.      Tiger sharks eat sea snakes – some poisonous - as part of their diets.  So you’re dressing up as a tiger shark prey item, smart.
c.       As for the sharks that don’t eat poisonous sea snakes, they would have not learned aversion to the colouration now would they?    

Secondly, the effectiveness of warning colouration is measured on the species level (less monarchs are eaten overall – the species survives) not the individual level.  So even if sharks did avoid anything with black and white stripes, that doesn't necessarily mean you would be 100% safe.  This is because learned behaviours often have to be relearned.  The Blue Jay in the above example won’t eat another monarch for quite some time, but next season he may very well have forgotten and experience another negative reaction to orange and black butterflies to remind him that they should be avoided (unless he eats a viceroy first and has no negative reaction... see how this goes?).   

So, applying what we now know from above, what are the odds that a non-Tiger shark will approach you in the water combined with 2) the individual shark approaching you has recently eaten a poisonous snake of black and white colouration and 3) it was ill immediately after eating that snake, therefore has learned an aversion??  ZERO. 

The second hypothesis, and style of wetsuit, concerns cryptic colouration.  They say,


Yes, because sharks only attempt to eat what they can see.  This is why sharks only eat prey in clear water and high light levels... wait, what?  Bottom line is, if you are in the water near a shark, it has already noticed you.  Several variables afterwards will determine whether or not it comes in for a closer inspection, and none of those variables concern what color your wetsuit is.  

And remember, you are still more likely to be killed by a hot dog.  

24 March, 2014

Fatal shark encounter no.8

