Catching sharks can induce labour

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Catching sharks can induce labour

June 12, 2018 - 12:34
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A study about capture-induced birth by pregnant sharks and rays when they are caught shows that the phenomenon is more prevalent than previously thought.

Juvenile spiny dogfish (Squalus acanthias) from Alaska, Prince William Sound

Once in a while, a video surfaces on social media showing dying sharks or rays experiencing capture-induced births, giving birth to their squirming babies on the deck of fishing boats.

Sometimes, the cubs perish unceremoniously on cam; in other cases, they are released into the ocean, upon which they swim away, presumably to a long and happy life.

Really?

For "giving birth," read "abortions" or "premature births."

Kye Adams and his team have been studying the phenomena of capture-induced parturition in elasmobranch species like sharks and rays, looking into why it happens, which species are susceptible and its impact on the population as a whole. The findings of his research have been published in the journal Biological Conservation.

“It’s quite prevalent across a lot of species and also seems to be not well known by both researchers and recreational fishers. [...] They don’t realise these events are abortions, they think they are witnessing a natural birth,” said Adams, a doctoral candidate at University of Wollongong in Australia.

Their research, which involved scouring through scientific records and social media, uncovered several unsettling facts. Eighty-eight species have been observed in capture-induced parturition. The rate varies according to the species; for instance, 2 percent of spinner sharks delivered when they were caught, while for blue stingrays, the proportion was at 85 percent.

Why does it happen?

Reasons for the occurrence could not be positively confirmed. Adams has some theories: the dying mother may prematurely give birth to allow her offspring to escape; she may do so to distract her captors and enable herself to flee; the birth may be the result of the stress of being captured.

Whatever the reason, it is likely that most of these premature pups would not survive, and this has an impact on the future of the species. "Juveniles still have a high probability of dying before they will give a return in the form of offspring," said marine biologist Nicholas Dulvy, from Simon Fraser University in Burnaby, British Columbia.

According to Adams, for critical endangered species like the angel shark and sawfish, "even the loss of a few pups could be pretty concerning."

It is not just fishermen who are responsible for this. Even the scientists who capture sharks to tag them also run the risk of inducing premature births. "Like fishermen, scientists who are catching sharks for research need to know that [capture-induced parturition] happens, and implement strategies to reduce their impact," Adams said.

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