Saturday, August 11, 2012

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!


Anonymous said...

Good stuff.

But shouldn't that be:-

Whale, 2 species: R. typus and R. typussy with R. typuss the hybrid?


DaShark said...

Aaaah - touché!

Would that be the gentleman adventurer who likes having fish carcasses bounced off his head?

Anonymous said...

I am unable to confirm or deny any such allegation.