Rediscovery of a Lost Shark
Last summer I attended the Sharks International conference in Cairns, Australia. It was an opportunity to catch up with sharky colleagues, and to hear about all the terrific shark research being done around the world. Many of the meeting papers have now been published in a special issue of the journal Marine & Freshwater Research (http://www.publish.csiro.au/nid/126/issue/5632.htm), and I’ll be highlighting a few of them here in the coming weeks.
Every so often a species thought to be extinct is rediscovered, usually “hiding” in a remote part of the world. Few parts areas are as unexplored as the depths of the ocean, so it stands to reason that there would be rediscoveries of marine as well as terrestrial species. Most famous of the marine rediscoveries is certainly that of the coelacanth, the strange, primordial, deep ocean fish that can “walk” on its thick, lobed fins. The coelacanth was believed to have been extinct since the Cretaceous period, 65 million years ago, and had been described only from the fossil record, when one was hauled aboard a South African fishing boat in 1938. (A terrific book about the rediscovery of the coelacanth is “A Fish Caught in Time: The Search for the Coelacanth”, by Samantha Weinberg.)
But I digress. The smoothtooth blacktip shark, Carcharhinus leiodon, is one of the most recent rediscoveries of a lost species. For more than 100 years C. leiodon was known only from a single specimen caught off the coast of Yemen in 1902. The species was placed in the family Carcharhinidae, and given its common name because its teeth lack the serrated edges found in related species. The Carcharhinidae are often called the whaler or requiem sharks, and this group includes many well known species of medium to large live-bearing sharks, such as the tiger shark, the bull shark and the oceanic whitetip. (I love the term requiem sharks, which, though it probably comes from requin, the French word for shark, carries a sort of unintended wistfulness these days with so many shark species in decline.)
One of the most effective ways to determine shark distribution and abundance in many parts of the world is, sadly, to visit the local fish markets. In 2008, researchers from the Shark Conservation Society did just that in Kuwait, where they found 25 smoothtooth blacktip sharks! Had this shark truly disappeared? Many requiem shark species look outwardly similar, so it is likely these animals have been caught all along - though probably always in low numbers - but were never noticed by someone who could identify them as a lost species. Comparison to the single type specimen from 1902, and mitochondrial DNA sequencing, confirmed the identity of these animals as smoothtooth blacktips. DNA analysis showed that C. leiodon is most closely related to a group of whaler sharks that includes the widely distributed blacktip shark (C. limbatus) and grey reef shark (C. amblyrhynchos), and the more localized Australian blacktip shark (C. tilstoni).
The Kuwaiti landing site of these newly discovered animals is nearly 3000 km, as the shark swims, from the Yemeni site where the type specimen was found. Recent surveys of fish markets were also made in Qatar and Abu Dhabi, but the species was not found in those locations. This suggests (very preliminarily) that C. leiodon does not have a widespread distribution, but may occur only in small isolated populations. Such species are particularly susceptible to overfishing and local habitat disruption, with no outside animals to replenish depleted areas. The species is currently listed on the IUCN Red List as Vulnerable, which may seem like an odd status for a fish that hasn’t been seen for a hundred years, but a single specimen is too little data even to declare a species extinct. Now that the species has been “found”, thorough surveys can be made of its conservation status, and that listing revised if warranted.
The paper is: Moore, ABM, White, WT, Ward, RD, Naylor, GJP, and Peirce, R. (2011) Rediscovery and redescription of the smoothtooth blacktip shark, Carcharhinus leiodon (Carcharhinidae), from Kuwait, with notes on its possible conservation status. Marine and Freshwater Research, 2011, 62, 528–539.
It is available at: http://www.publish.csiro.au/?act=view_file&file_id=MF10159.pdf