Pregnant Sharks and Rays Abort Offspring When Fished

Pregnant Sharks and Rays Abort Offspring When Fished – Guest post by Kye Adams

Have you ever seen a viral video of a shark or ray giving birth (e.g. River Monsters)? Unfortunately, it turns out these videos have a pretty dark explanation: There’s a fairly high chance the female is actually aborting her pups due to the stress of being caught.

Our new article just published in Biological Conservation  shows that abortion in sharks and rays is a surprisingly common, yet often misinterpreted response to stress. It’s thought that the premature release of pups is a strategy to allow the female to escape more easily if threatened by predators. Alternatively she releases pups if she is attacked by a predator or stranded on a beach to give the pups a chance at survival. Unfortunately it seems that fishing can also trigger this stress response, with pups being induced by most types of fishing including hook and line angling, commercial methods such as long lining, gill-netting and trawling.

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A female Nigerian guitarfish (Rhinobatos annulatus) with pups it aborted after being stranded. Photographer: Kolette Grobler

To date, birth induced by fishing has been observed in 88 different species of sharks and rays, including a number of endangered species such as angel sharks and sawfish. On average 1 in 4 pregnant females are estimated to expel embryos on capture, but for some species, this can be as high as 85%. The study also examined 40 videos of sharks and rays giving birth posted on social media and found that, in most cases, the videos actually showed stress-induced births, including some endangered species.

 Co-author Lachlan (From Fish Thinkers): On a recent research trip there were numerous examples of some species of rays and sharks aborting pups after being trawled up from the depths. Below is some example footage I took showing  a type of electric ray (Tasmanian numbfish, Narcine tasmaniensis) that were aborting their litters after capture…prior to this footage this particular one had already aborted at least 2 pups. 

Although they don’t show maternal care after birth, sharks and rays invest a huge amount of energy into their offspring during development to give them the best start in life. They also have one of the longest gestation periods in the animal kingdom, with an abortion event disrupting a pregnancy of up to two years for some species. However, it is still unknown whether the pups stand any chance of survival when induced by a fishing event, even if they are near term like the spikey dogfish pup pictured below. 

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A near-term spikey dogfish (Squalus megalops) of approximately 24 cm total length that came from a female caught via trawl. Photo: L. Fetterplace

If you do capture a shark or ray that looks like it might be pregnant – and a lot of the time it’s obvious because they’re so fat – there are three general techniques to reduce stress and the chance of causing an abortion:

  • minimise the time the fish spends fighting on the line
  • Do not remove the shark/ray from the water, cut the line close to the mouth (making sure to keep all your limbs)
  • avoid fishing in known reproductive periods and/or areas

One strategy to remove the risk of abortions for the species that are most vulnerable might be seasonal or spatial closures of fishing around pupping or nursery areas to give the females somewhere to pup peacefully.

(Ed: If you would like to read the paper in full and don’t have institutional access to get past the paywall, send us a message and we will happily send through a copy).

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Tasmanian numbfish, Narcine tasmaniensis aborted their pups in large numbers after being caught by trawl. Photo L. Fetterplace

 

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