Wednesday, 17 May 2017

Pregnant rays tangled in trawler nets have small, sickly babies

16 May 2017

By Alice Klein

The accidental capture of pregnant rays in fishing trawls harms their unborn babies.

Rays often get tangled up in trawling nets dragged behind boats to catch large volumes of fish. They are usually thrown back into the sea, but being trapped and brought up to the surface can be traumatic — and sometimes fatal.

Those that survive can experience ongoing health problems and have undersized, sickly babies, found Leonardo Guida at Monash University in Melbourne, Australia, and his colleagues.

The researchers collected 19 pregnant southern fiddler rays (Trygonorrhina dumerilii) from Swan Bay in Victoria off the south coast of Australia, and divided them into two groups.

One group was subjected to 8 hours of being dragged in a trawl net, followed by 30 minutes of air exposure in a crate to simulate commercial fishing. The other group served as a control.
Stunted growth

The trawled mothers lost weight and showed signs of stress, and their offspring were born 27 per cent lighter and 12 per cent shorter in length. Examinations of the babies’ blood also indicated that their immunity was reduced.

These effects could have been caused by the release of stress hormones during trawling, says Guida. These hormones may hamper the growth and impair the immune system of a developing fetus, he says.

The findings may have implications for the long-term survival of ray species, many of which are already listed as vulnerable or endangered, adds Guida. Undersized babies with compromised immunity are more vulnerable to predators and pathogens, and may have impaired fertility.

Trawl fishing could also have adverse effects on the offspring of other species unintentionally swept up in nets, such as sharks, says Guida. 

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