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Tag: tiger shark

Have you heard the good news about shark populations? Shark population increases are cause for #OceanOptimism

Posted on February 28, 2018February 28, 2018 By David Shiffman
Conservation, Science

Did you know that some shark populations have declined due to overfishing? Did you know that some once-declined shark populations have recovered? If you’re like my twitter followers, it’s likely that you’ve heard the bad news, but have not heard the good news.

Why does this matter?
It’s important to share bad news so that people know there’s a problem, and that we need to act to solve that problem. However, it’s also important to share good news so that people know that a problem is solvable! This idea was behind the birth of the #OceanOptimism online outreach campaign.

Read More “Have you heard the good news about shark populations? Shark population increases are cause for #OceanOptimism” »

Genetics study reveals 79 potentially new species of sharks and rays: what does it mean for science and conservation?

Posted on July 3, 2012July 3, 2012 By David Shiffman 3 Comments on Genetics study reveals 79 potentially new species of sharks and rays: what does it mean for science and conservation?
Conservation, Science

When Dr. Gavin Naylor and his team started a genetic survey of existing shark and ray species, they didn’t expect the results of their project to make international news.  Their recent paper (which, at over 250 pages and complete with more than 100 figures, is nothing short of epic), however, is too striking to ignore. The results indicate that there may be as many as 79 previously unrecognized cryptic species of sharks and rays.

A cryptic species is defined as a group that looks almost exactly like another, and may even live in the same region, but is genetically distinct. We’ve known that cryptic species of sharks and rays exist for some time, such as manta rays and scalloped hammerhead sharks, but 79 is a lot; as of the paper’s publication, only 1,221 species of sharks and rays were recognized.

According to Dr. Naylor,

“Organisms become genetically differentiated over time through the cumulative effects of mutation and recombination mediated via drift and selection. When they differentiate in isolation they eventually become so different from the parental stock from which they were derived that they can no longer produce fertile offspring when crossed with them.  Some biologists use the point of reproductive inviability as the point at which new species should be recognized…..  For practical purposes we recognize “new species” as being genetically or morphologically distinctive from previously recognized forms.”

The study’s methods, though enormous in scope, were relatively basic. According to Dr. Naylor, the study utilized a technique very familiar to geneticists: “standard DNA extraction, PCR, Sanger sequencing, alignment and analysis of a protein coding mitochondrial  gene”. To achieve the goals of understanding both evolutionary relationships of sharks and rays and parasite host specificity ( where certain parasites associated only with one species), Dr. Naylor and his team obtained and analyzed samples from as many species as they could. The numbers are impressive- 56 of 57 known families of elasmobranchs were represented among the 4,283 samples from 305 species of sharks and 269 species of batoids. In other words, this study included approximately half of all known elasmobranch species, including many that had never been analyzed genetically before. Since 1986, when the project began, samples have been obtained in more than 50 countries, mostly through the team’s own field work!

Read More “Genetics study reveals 79 potentially new species of sharks and rays: what does it mean for science and conservation?” »

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