Stegostoma tigrinum?

The sandy morph of S. tigrinum: transitional (A–D) and adult (E–H). Close up of the skin pattern on the right lateral flank of a transitional specimen (B–C) and of remnants of the transitional pattern on flank and caudal-fin tip of adults (F–G). Click for detail.

Oh well

After the demotion of the Manta Rays, now this.

Looks like they've changed the species name of the mimic Zebra Shark. I first thought it was just a bad joke - but having asked my Zebra Shark guru, she replies,

Yes. I reviewed it as did Will White. 
They did a pretty thorough job with the taxonomy, though whether it’s worth changing the species name is open to debate me thinks.

Methinks, too.

But then again, they really did do a thorough job so this may indeed be it.

But see for yourselves.

Le fasciatum est mort - vive le tigrinum!

 

Mimic Shark?

How bloody cool is this!

First record of potential Batesian mimicry in an elasmobranch: do juvenile zebra sharks mimic banded sea snakes?

Christine L. Dudgeon and William T. White

Abstract

Various forms of mimicry have been recorded in a large number of marine fishes; however, there have been no records of mimicry for any elasmobranch species.

We propose that the distinctly banded neonates of the zebra shark (Stegostoma fasciatum) are Batesian mimics of banded sea snakes (Elapidae).
Observations of banded juveniles of S. fasciatum swimming close to the surface strongly resemble banded sea snakes in colour and body form as well as the undulatory swimming movements. Sea snakes are venomous and are known to defend themselves against predators. Although several shark species prey on them, most species appear to avoid sea snakes as prey items. Juvenile S. fasciatum possess a very long, single-lobed caudal fin that remarkably resembles the broad, paddle-like tail of sea snakes. This may be an adaptation enabling this species to mimic sea snakes, at least in the earliest life stages.
There is a need for empirical testing of the hypothesis that juvenile S. fasciatum is a true example of Batesian mimicry, but here we provide evidence that suggests this may be the first example of mimicry in an elasmobranch species.

Yes so far this is only a hypothesis!
But is it plausible?

The paper offers a variety of good reasons, and here's the picture from the paper that I find totally compelling.

Fig. 1. Colour pattern changes in Stegostoma fasciatum: (a) 40.5 cm total length (TL) newborn from Bahrain (photo: J. Randall); (b) 58 cm TL from Bahrain (photo: J. Randall); (c) ,220 cm TL adult from northern Australia (photo: CSIRO). (d) Newborn Stegostoma fasciatum swimming at the surface in shallow inshore, turbid waters off the Kimberley coastline of north-western Australia (photo: M. Pember); (e) a sea snake on the swimming on the surface in Shark Bay, north-western Australia (photo: W. White).

Wouldn't testing that hypothesis be the coolest Masters thesis, ever?
Here's a possible recipe, right from the paper.

Initially, it is necessary to isolate which of the banded sea snakes is/are the model species as well as which of the potential predators the deception is aimed towards.
It will then be possible to design experiments that test the behavioural and physiological responses of the predators to the model and mimic species as well as to target ecological and evolutionary data collection.
Whether juvenile zebra sharks are truly Batesian mimics of sea snakes and present the first example of mimicry in an elasmobranch remains to be proven; however, we believe that there is good evidence, as presented here, to support such a conclusion.

Any takers?
Fiji: we got the Shark and at least one Banded Sea Krait right here - and by the way, check out its tail: does it mimic the head?

Questions questions! :)

Gay Sharks?

Andrew hates this picture.

Rather quiet and modest by nature, he was suddenly catapulted into Fiji-wide notoriety (and consequently, had to endure plenty of heckling by the Staff) when Fiji Times decided to ask for his "expert opinion" about this poor lil fella (check out the size of the hand holding it) that had the misfortune of having been caught, and then severely mishandled by a burly fisherman down the coast. Having been offered, we ended up not buying it for fear of starting a new commerce and our hope is that it was finally returned to the Ocean where it belongs.

This is obviously a sub-adult Zebra (often called "Leopard") Shark, an uncommon but locally abundant and totally harmless Indo-Pacific carpet shark. Why do I know it's a sub-adult? Because despite being tiny, it doesn't anymore display the characteristic juvenile zebra pattern that has led to naming the species. Proper Leopard Sharks, by the way, are equally harmless coastal Sharks of the Eastern Pacific. To confuse matters, they display much more of a zebra pattern than Zebra Sharks!

I've seen Zebras all over the place, starting with my first-ever tropical dives in Israel all the way to here in Tonga where it is regularly seen in one specific current-swept channel. But the honey hole must be the Andaman Sea and specifically, the rock of Kho Bon on the way from the Similans to Richelieu Rock. Once you get down below the thermocline, they're absolutely everywhere, beautiful, placid and absolutely unafraid of divers.

And it is precisely from this region that Juerg got hold of a sequence of pictures of two canoodling male Zebra Sharks. Remember my post in July?

Two males?
This being Thailand, could it be that somebody has stumbled across a pair of Zebra Shark ladyboys?

Well, as usual, ah ain't telling!
Go see for yerself on Juerg's research page!
It's the third paper from the top, freshly published.

Enjoy - ain't Science a wonderful thing!!