Australian researchers have found a quarter of pregnant sharks and rays abort their pups when captured, revealing a little-known risk to the survival of the slow-growing animals.

An analysis of recorded instances of sharks and rays either aborting their pups or undergoing a premature birth once captured found 24% of pregnant females across 88 species lost their young. In some species, such as the pelagic stingray, the rate of abortion on capture was 85%.

The research, published in the journal Biological Conservation this week, also examined 40 videos of live births of sharks and rays posted on social media and found that in most cases the videos actually showed a trauma-induced abortion.

It said pregnancy loss through capture-induced abortions was a “largely unreported, often misinterpreted and poorly understood” phenomenon that nonetheless had a “potentially pervasive effect” on population and recovery levels.

Lead researcher Kye Adams, a PhD student from the University of Wollongong, said recreational fishers and marine researchers should be educated about the risk of inducing an abortion when catching a pregnant shark, ray or skates.

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

Because the phenomenon of sharks and rays losing their young when captured is not well known, it is not counted as part of ordinary bycatch monitoring.

About 80% of sharks and rays caught by recreational fishermen in Australia are released back into the water but Adams said just the trauma of being captured could be enough to cause a shark to lose their young.

“We would recommend that if you do catch a pregnant shark or ray – and you can usually tell because they are very fat – the best thing to do is release it without raising it from the water,” he said. “Cut the line as close to the mouth as you can without harming yourself, and don’t take it from the water.”

He also suggested imposing fishing restrictions on the known nursing grounds of species that appear to be particularly affected by capture-induced abortion, such as angel sharks.

The breeding grounds of many protected species, such as sawfish, are already included within marine protected areas.

About 60% of shark and ray species give birth to live young, with gestation periods of up to two years. Adams said that long gestation periods, combined with the slow growth and maturation of many shark and ray species, meant that lost pregnancies potentially had a larger impact on their overall survival.

“They need all the pups they can get,” he said. “For a species like sawfish and angel sharks these abortions could be quite damaging.”

The oldest recorded instance of a shark or ray abortion in a published scientific journal is from 1880, which recounted that: “A female of Squatina, of a considerable size, taken from our net, gave 15 to 20 pups at the time where, due to lack of water, it was [asphyxiated] by the action of the atmosphere on its gills.”

Stress is the most common factor in all the recorded instances of capture-induced parturition, but Adams said there was not enough research available to determine whether the stress was linked to physical trauma, such as being caught on a harpoon or net, or psychological stress.

Most of the recorded instances were associated with the use of trawling or gillnets, but Adams said that’s likely a bias caused by the sampling methods of marine researchers.

“I don’t want to attack recreational fishers for this: it’s equally a problem for researchers like myself who catch sharks and rays to tag them,” he said. “Most fishermen fish because they love fish. So they are not going to want to do things that harm the sharks and rays that they are catching.”