Wednesday March 29, 2023


For half a century, industrial tuna fishing vessels have borne scrutiny for catching animals they haven’t meant to: “bycatch,” in fisheries lingo. Purse seiner vessels, which provide most of the world’s canned tuna, have drawn conservationists’ particular ire for their indiscriminate ways. They operate by dropping a massive cylindrical net and cinching it together at the bottom, like a drawstring purse, so that everything above is caught.

Yet in well-regulated regions, purse seining has become less damaging to marine life over time. First, conservationists and regulators focused on ways to avoid killing dolphins, then sea turtles, then sharks. More recently, manta and devil rays (genus Mobula), most species of which the IUCN lists as Endangered, have become part of the bycatch mitigation agenda.

Mobulids, as these rays are collectively called, glide through the upper layers of tropical and subtropical waters, collecting plankton to eat. Mantas, which tend to be larger than devil rays, have a majestic calmness that’s made them popular among divers. They can grow as wide as a giraffe is tall — which makes dealing with them when they arrive on deck no easy task.

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