Many species of shark and ray have taken major hits from human over-hunting (e.g., “finning” and sport-killing) as well as marine environment changes brought about by climate change impacts (e.g., the collapse of many smaller fish species). Understanding how these creatures live out their lives is crucial to helping protect them.
Most sharks and rays are deemed apex predators, as they “sit” at the top of the food chain in which they exist, and thus play a vital role in the maintenance of oceanic ecosystems. But much about these cartilagenous fishes remains unknown or puzzling. For example, the life-cycles and true population numbers of these creatures are not completely understood or known. Further, the genetic/evolutionary relationships between species of shark, or rays, or between sharks and rays, is the subject of much disagreement and debate amongst marine biologists.
To help elucidate these relationships, a team of biologists at the College of Charleston in South Carolina, led by Gavin Naylor, took DNA samples from over 4,200 specimens of shark and ray and sequenced them to determine their relatedness. Of the 4,283 samples, the scientists were able to identify 574 species. But, most surprisingly, they also discovered 79 sequences that potentially represent entirely new species.
Currently, it is estimated that there are about 1200 known species (including both shark and ray species) worldwide. And so, discovering so many new species — even by genetic analysis alone — has come as a shock to many marine biologists.
The discovery may indicate that many or most of these possibly new species are similar in appearance to known species, and so have just been misidentified. As a result, what was described as a single, large population may in fact be two or more populations of closely related but separate species — making all said species members of smaller populations than previously thought.
The discovery of these potentially new species may also mean that many or most are far more critically endangered than supposed.
As an example, Naylor’s analysis revealed that the endangered scalloped hammerhead (Sphyrna lewini) is actually two separate species of hammerhead shark. The scalloped hammerhead is one of those species that have taken a major “hit” (as noted earlier). Thus, given the tendency to lump similar-looking but genetically distinct species together, this finding may indicate that the sustainable population numbers of either species are far worse than estimated.
The team is currently working with the US National Science Foundation to compile a catalog of shark/ray diversity and is assisting the International Union for Conservation of Nature to map the preferred habitats and ranges of all known species of sharks and rays.
“This will have an impact on what is considered endangered and the fragility of different organisms. These are sentinel species of all sorts of other organisms in the sea which are probably undergoing similar or worse kinds of impacts.” [Source: Sci Am]
Other scientists who were informed of the genetic analysis caution that using these new molecular techniques (i.e., gene sequencing from stored specimens) poses certain problems for zoological classification; they allow a more exact comparison of relationships between species, but because the sequences are being “mined” blindly — not knowing where the originals came from or whether any given sample was correctly identified — may result in a distorted estimation of species numbers and even total population numbers.
Naylor acknowledges the importance of using genetic sequencing in combination with other techniques (including in situ sampling and identification).
Sharks and rays are classified under the clade (or superorder) Selachimorpha (or Selachii). The earliest known shark fossils date to over 420 million years ago.
The team recently published their report in the Bulletin of the American Museum of Natural History.
For more infomration, check out the source (SciAm) article for this story: Total of 79 Potentially New Shark Species Found.
- Top Photo: (hammerhead shark) by suneko
- Chart: (global shark catch) Chris huh
- Second Photo: (shark fin soup) Arthur Hungry