What Poop, Pee and Dead Skin Can Tell Us About Shark Populations

posted: 07/12/17
by: SharkWeek.com Staff

Much of what we know about shark populations is the result of tissue sampling and tagging. But that's potentially harmful to the shark, and it's not cheap, either. Luckily, scientists have discovered a new method: studying the genetic material that sharks, like us all, leave behind in their day-to-day lives.

Namely their pee, poop and dead skin.

In a study published in October 2016 in the journal Nature Ecology & Evolution, scientists drew findings about whale shark populations from biological material found in just 8 gallons of seawater collected near Qatar. From the diversity found in those samples, they concluded an "effective population size" of around 70,000 sexually active whale-shark females in the Indo-Pacific region (comprising the Indian Ocean, the Pacific Ocean, and the seas between).

How, you ask?

Researchers estimated the mutation rate of the DNA in the samples, and compared it to that of previously obtained whale-shark data. Mutation rate is related to breeding rate, which is related to population size.

The idea of studying populations through environmental DNA is not new; it's been used in studies of fish and birds, for example, in both fresh- and seawater. And there are certainly drawbacks to relying on DNA dispelled in water: In a fluid environment, genetic material degrades quickly and can be transported for miles in ocean currents.

But the eDNA application is new to shark populations, and it's a great alternative to, say, aerial and acoustic detection, given how big -- and deep -- the ocean is, and how greatly dispersed sharks are.

So while it MAY be a little embarrassing to the shark, we're guessing it's preferred to the more traditional -- but invasive or needle-in-a-haystack -- techniques. Sounds like a win-win!


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