Fiji Bull Sharks - Paper!

Yes those would be our samples - click for detail!

Remember?

 

That was then and alas, nothing much has come of it.

For some reason that eludes me, Christine never got around to actually publishing the relevant paper, and a later attempt at resuscitating the effort failed due to a general lack of interest and/or funding and/or time, or whatever. Plus I've been told that nowadays, the newest and shiniest tool for population studies is SNP markers and not anymore microsatellite DNA - and I'll most certainly leave it that, the more as that's about as much as I understand.

Or not - so correct me if I'm wrong.

Enter our indefatigable friend Kerstin!

She is now a newly minted, and highly deserving PhD - and the latest paper from her thesis once again confirms that the insular Bull Shark population from Fiji is genetically different, and likely closed = isolated from its continental counterparts. 

In essence, this means that our Bulls are truly unique and that they spend their whole life right here in the archipelago without ever engaging in large transoceanic migrations across deep water trenches and vast distances. And no, they also most definitely do not travel to Vanuatu and Australia for mating as was recently publicly proclaimed from the peak of Mount Stupid!

Obviously, this makes them specially precious but also, especially vulnerable - and Tashi's My Fiji Shark initiative, especially pertinent!

 

And the taxonomic consequences?

Years ago my ichthyological guru told me that a species is what a geneticist tells you it is - and very sadly and despite of my best efforts all the way to outright begging, the relevant Shark taxonomists remain firmly of the opinion that the present genetic distinction doesn't warrant declaring a new species. 

And when it comes to our Bulls at least being a possible (and I would add: obvious!) subspecies or race, I'm being told that apparently, in Shark taxonomy one just doesnt do that . 

Oh well - but we will keep on trying!

Anyway, great job!

Enjoy Kerstin's paper!

 

Oh and - please, Adopt Your Shark Now! 

Thank you.

 

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!

 

What Shark is this??

Notice the caudal peduncle - click for detail!

Behold!

This is from the second 15m dive at Shark Reef a few days ago. 

For once I was not diving, and the footage is courtesy of Martin who is here for his yearly Bull Shark fix. I'm being told that the Shark was curious and circled above - but with a gaggle of Bulls dominating the feed, she remained wary and never tried to join the mêlée. 

At a reported 3 meters in length, this is a big Shark.

When they first told me, they stated that she was an emaciated, sickly Bull Shark - but from the video I can instead discern that despite of the tumor and the buckled first dorsal, she is in rather good shape. I also notice the elegant sinuous way she moves, and the keel-like bulge on her caudal peduncle, both of which are not at all diagnostic of Bull Sharks, sickly or otherwise.

So what is this?

Years ago there was another mystery Shark with a similar shape of the caudal peduncle. Back then, somebody stated that it was a Dusky - but that's a Shark living off continental shelves and we are obviously on an island, so today I'm rather skeptical.

I got my thoughts but would love to hear yours.

Opinions welcome - here on the blog and not on Facebook please!

Thank you!

PS! - May, 2022: having now sadly witnessed several moribund bull sharks, I can state with absolute certainty that this is one of those - likely Lumpy who had a large tumor and was getting ever more emaciated last time I saw her. Those Bulls are real badasses and will fight, and even compete for food til the very end.

No more Galapusky - Paper!

Or is it, Duskapagos?

Anyway, check this out.

I was sent to me by the Saffron Pimpernel under the heading of mumbo jumbo - and for a genetic ignoramus like me, it sure very much is! 

But having double checked with my trusted geneticist, she confirms that Gavin and Will's putative lumping of the Dusky and the Galapagos is no more, meaning that the two species continue to be valid.

And this mystery Shark?

Likely not a Dusky (see the map at the top) but a Silky like first assumed!

Ain't taxonomy fun - and it's so easy, too!:)

 

El Diego - it's a Boy!

Bravo!

El Diego has just published his master's paper.

I must say that in its details, it far surpasses the knowledge accumulated in my truncated biology studies many decades ago - but what I (maybe) understand, is that it provides evidence for two distinct populations of Pelagic Threshers in the Pacific. Considering that this is an extremely wide-ranging epipelagic Shark, this is rather spectacular - as is the fact that individuals from the two groups are living sympatrically in Hawaii without interbreeding, a fact that could indicate that they may well be distinct subspecies or species.

Or maybe I understand nothing and it's all different.

You be the judge of that - open-access paper here!

Enjoy!

wheeleri!

Source.

Remember that redescription of Sharks and Rays?

Watch.
Try not to be deterred by the pathos - just keep an eye on those Grey Reefies that are recognizable by the black trailing edge of their tails.

Notice those big white tips on the first dorsals?

Those would be those infamous Carcharhinus wheeleri, the (Short Nosed) Blacktail Reef Shark, one of JSD's favorite photographic subjects - compare to the Reef Whitetip and the Silvertip that are equally featured, and then compare to these "normal" Grey Reefies.

Convinced? Me, not so much!

And those Sharksuckers at 0:46?

Go wonder - must be some Maldivian thing as Lill saw the exact same mobbing on a trip to the Maldives in November of last year!

Opinions?

Anyway.

Good to see so many Sharks in the Maldives!

Enjoy!

A Fiji Bull Shark?

Carcharhinus dakuwaqa? Quite possibly!
Click for detail - and I mean it!

I knew it!
Not only are our bulls huge and the most incredible collection of charismatic, intelligent sharks on the planet, they may well be a totally unique population - if not more than that!
This was revealed last week at the AES meeting.

From the poster.

Global Population Genetic Structure and Parentage Analysis of the
Bull Shark (Carcharhinus leucas)

C. Testerman1, J. Brunnschweiler2, M. Heithaus3, S. Gulak4, J. Werry5, R. Jabado6, C. Jones7, and M. Shivji1

1Save Our Seas Shark Center USA and Guy Harvey Research Institute, Nova Southeastern University, Dania Beach, FL, USA, 2ETH Zurich, Zurich, Switzerland, 3Florida International University, North Miami, FL, USA, 4National Marine Fisheries Service, Panama City, FL, 5Ocean and Coast Research, QLD, Australia, 6United Arab Emirates University, Al Ain, UAE, 7University of Aberdeen, UK

Project Synopsis

The bull shark (Carcharhinus leucas) is a globally distributed, large coastal shark that occurs in marine, estuarine and freshwater habitats.
It has been assessed as near threatened by the IUCN, is caught in recreational and commercial fisheries throughout its range, and shows evidence of recent declines in the Gulf of Mexico. Regional population studies have reported mitochondrial but not nuclear differentiation between the western North and South Atlantic (Karl et al., 2011) and among juvenile C. leucas sampled in river systems across northern Australia (Tillett et al., 2012).

We expanded on these studies by evaluating the global population genetic structure of C. leucas using 12, bi-parentally inherited, nuclear microsatellite loci and a globally distributed set of 470 samples. Our microsatellite data revealed strong genetic differentiation between samples from the western North Atlantic (WNA) and Indo-Pacific (I-P). No population structuring was detected within WNA and Indian Ocean sampling sites.

Fig. 1. Species global distribution indicated in gold shading. Sampling locations with fewer than 10 samples were not included in the population-based differentiation statistical analyses (Fig. 2) but were included in the individual-based analyses (Figs. 3 & 4).
Click for detail!

Notably, however, samples from Fiji demonstrated statistically significant genetic structuring from the remaining locations sampled.

Fig. 2. Charcharhinus leucas genetic differentiation based on population-level statistical analyses. Colored shapes (ovals and square) represent genetically distinct populations. FST values (p = 0.0000) between each population pair are indicated by arrows. Sampling locations (indicated by circles) within each population are not genetically differentiated.
Click for detail!

Assignment testing (GeneClass2) showed evidence of a low-level of first generation migrants from the WNA and western Pacific among the southwest Indian Ocean samples, a surprising finding considering the strongly coastal nature of C. leucas. Finally, parentage analysis of 2 litters suggests that the species may be genetically polyandrous, although this hypothesis will need further testing with more litters.

Conclusions:

Individual and population level analyses are concordant in showing at least 3 genetically distinct populations:

• Western North Atlantic
• Indo-Australia
• Fiji

Fig. 3. pie charts indicate the average proportional membership coefficient of individuals in the 3 distinct lineages inferred from nuclear microsatellite genotypes by the program STRUCTURE. Pie chart sizes are roughly proportional to sample sizes.
Click for detail!

Three 1st generation migrants were identified, indicating contemporary movement from both the Atlantic and Pacific oceans into the Indian Ocean. Complex patterns of migration and population structure require coordinated regional management efforts.
Parentage analyses of 2 litters revealed multiple paternity in both litters.

So there you have it!
This is the result of many years of DNA sampling on Shark Reef whereby so far, we've been able to send more than 70 samples to Mahmood - and counting as there are other, more local aspects we would like to explore.

So, do we have a Fiji endemic?
Probably not at all, because nearby locations like e.g. Tonga and Samoa are very likely to harbor the same Sharks. But from everything we know, Fiji with its robust population of Bull Sharks may well be considered to be the epicenter of this genetic strain, meaning that it would be perfectly acceptable to call this the Fiji Bull Shark - and depending on whether this is a subspecies/race or even an own species: how does Carcharhinus leucas dakuwaqa or Carcharhinus dakuwaqa sound to you!

Anyway, is this mega cool, or what!

79 new Sharks?

Jimmy's Emma - a different species than our Scarface? Great pic by Jim Abernethy.

Not at all!
Trust the journos to parrot the same erroneous information without ever bothering to consult the source! Even the abstract specifies clearly that the analysis comprises approx. 574 Elasmobranchs and that it has identified 38 potentially new species of Sharks and 41 potentially new Rays.
Be it as it may, that's a whole lotta new species - maybe!

The gist?
David has already posted this great review pointing out that if confirmed by further in-depth analysis, the results will have important consequences for conservation, especially for those species that are already classified as threatened with extinction.
Personally, being very much a lumper, I look at these findings with great skepticism - but then again, my taxonomy guru teaches me that the best definition of a species is what a good systematist says it is, so who am I to argue!

But what does that mean for us Shark divers?
Having finally found the time to read through the whole 263 pages, here are the results for some of the most commonly encountered Sharks, in the same order as presented in the paper. It's obviously a subjective selection and readers with a particular interest in other species may find them in the paper that analyzes about half of the species that are currently being recognized.

• Silky, C. falciformis.
  One single species, with Atlantic and Pacific sub-populations.


• Blue, P. glauca.
  One single species, possibly not warranting an independent monotypic genus


• Grey Reef, C. amblyrhynchos.
  Now this is a really interesting one, as the authors are resurrecting the infamous C. wheeleri, or (short-nosed) Blacktail Reef Shark, essentially the Grey Reef from the Red Sea and also the Maldives etc.
  wheeleri can be distinguished by the white upper margin of the first dorsal fin and shorter snout, and by the fact that apparently, it never displays any of the typical agonistic behavior. It was thus once considered to be an own species but then lumped together with was then C. menisorrah (the Grey Reef from the Pacific) into the Indopacific C. amblyrhynchos.
  Here at Shark Reef, we see Grey Reefies with and without white tips and with varying snout lengths, meaning that I continue to remain highly skeptical that these are indeed different species.


• Silvertip, C. albimarginatus.
  One single species with possible sub-populations.


• Galapagos and Dusky, C. galapagensis and obscurus.
  The paper comes to the surprising conclusion that these may well be one and the same species, with the Galapagos merely representing the oceanic form of the Dusky that is confined to continental shelves and adjacent pelagic waters, but with sub-population from the Western North Atlantic and the Gulf of Mexico. Very interesting!


• Oceanic Whitetip, C. longimanus.
  One single species although the samples were not sufficiently representative of its distribution.


• Caribbean Reef, C. perezi.
  Very much unsurprisingly, one single species.


• Blacktip, C. limbatus.
  Latest since the discovery of hybrids with C. tilstoni, the Australian Blacktip, this whole group including C. amblyrhynchoides, the Graceful Shark needs to be re-examined. Limbatus appears be at least two species, the Western Atlantic C. limbatus proper and then C. cf. limbatus (possibly C. pleurotaeniae) from the Indo-Pacific and Eastern Atlantic.
  Yes it's complicated!


• Blacktip Reef, C. melanopterus.
  Possibly two species, one being from the Red Sea.


• Bull, C. leucas.
  Possibly three species: C. leucas from the Western Atlantic, C. cf. leucas 1 from Asia and C. cf. leucas 2 from South Africa.
  This really comes as no surprise in view of the possibly record Bull caught in the Breede River, and as we're always hearing that our animals are substantially bigger than those from the Caribbean.
  But this may not even be the whole story: I hear that Mahmood is finally about to publish his own findings that include the specimens we have collected in Fiji, so keep watching this space!


• Sandbar and Bignose, C. plumbeus and altimus.
  Possibly two species, one Indo-Pacific Sandbar C. cf. plumbeus (possibly C. japonicus) and then one Atlantic Sandbar C. plumbeus that however clusters with all specimens of the morphologically totally distinct Bignose!
  Talk about a taxonomic clusterfuck - literally!


• Reef Whitetip, T. obesus.
  One single species.


• Sicklefin Lemon and Lemon, N. acutidens and brevirostris.
  One single species each.


• Scalloped Hammerhead, S. lewini.
  At least two possible species, S. lewini 1 from the Atlantic and Western Indian Ocean and S. lewini 2 from the Pacific, with possibly further cryptic sub-clusters at species level as e.g. reported here.


• Great Hammerhead, S. mokarran.
  Possibly two species, S. mokarran 1 from the Atlantic and S. mokarran 2 from the Indopacific.


• Tiger, G. cuvier.
  Possibly two species, G. cuvier from the Indopacific and G. cf. cuvier (possibly G. arcticus) from the Atlantic.


• Shortfin and Longfin Mako, I. oxyrinchus and paucus.
  One single species each.


• Great White, C, carcharias.
  One single species, however featuring an Atlantic/Indian Ocean and a Pacific sub-population - but then again, read this about the Mediterranean GWs!


• Zebra, S. fasciatum.
  One single species.


• Whale, R. typus.
  Probably one species.


• Nurse, G. cirratum.
  Probably two species, G. cirratum from the Western Atlentic and then G. cf. cirratum (the Pacific Nurse Shark) from Baja as suggested by Castro.

And of the Rays

• Manta, Manta birostris.
  The authors appear unconvinced of Andrea's resurrection of M. alfredi - but for once, having witnessed the obvious difference both in appearance and behavior between the Pelagic and Reef Mantas, I'm totally sold on the fact that there are at least these two species.


• Spotted Eagle Rays, Aetobatus spp
  Will White has revised the Genus and come up with various species, i.e. the original Spotted Eagle Ray A. narinari from the Western Atlantic, the Whitespotted Eagle Ray A. ocellatus from the Indo-West Pacific, the Pacific Whitespotted Eagle Ray A. laticeps for Baja, the Longheaded Eagle Ray A. flagellum from India and Borneo and finally, an undescribed fifth possible species from Vietnam.

Of course, I remain generally unconvinced.
I'm an avid conchologist and have witnessed how the Cowries, once grouped within the genus Cypraea, have been subdivided into ever more genera, species, sub-species and races, this very much to the detriment of my wallet and to the delight of the traders. There it is business and here, I fear, much of it is excessive scrutiny.

Granted, I probably don't know what I'm talking about.
But to me, if two Sharks look and behave very much the same, let alone interbreed and produce fertile "hybrids" like C. tilstoni and C. limbatus, they are one and the same Shark.
But speciation is of course a gradual process, and the boundaries between species can thus be extremely fuzzy. As a consequence, the threshold of what constitutes a "species" will always be the result of convention rather than the "truth" - meaning that I'm both right and wrong! :)

What I find more compelling are the biogeographic aspects.
Apart from the strict endemics and the truly global pelagic species like the Blue, most Sharks are situated between the two and there exist distinct regional populations that may or may not be considered distinct species.
One such notable region is clearly the Atlantic where there are already a few Sharks featuring corresponding sister species in the Indopacific, like the Nurse/Tawny, the Lemon/Sicklefin and the Caribbean/Grey Reef Sharks. Other such regions are the Middle East, South-East Asia and Australia.

Long story short?
Whatever the ultimate definition of whether those local populations are species, sub-species, races or whatever, those distinct genetic pools warrant further investigation. And alas, they also warrant specific local management and conservation measures, meaning that the task at hand has certainly become even more daunting.

But a Tiger remains a Tiger remains a Tiger!