The term “bycatch” is used to describe fish, or other animals, which are caught unintentionally in a fishery. The Organization for Economic Co-operation and Development (OECD) defines bycatch as “total fishing mortality, excluding that accounted for directly by the retained catch of target species”. While manta and mobula rays are increasingly being fished and targeted for their gill plates in some countries around the world, in many fisheries the resultant bycatch of these large pelagic rays is still seen as worthless and discarded.
Each year it’s likely that many thousands of manta rays and tens of thousands of mobula rays are caught as bycatch in the global hunt for the more desirable species, these captured animals are often dead or dying before they are discarded back into the sea. Each year the world’s fisheries discard 7 million tons of fish, that’s one tenth of the world’s global catch thrown back over the side of the boat… dead!
Destructive Fishing Techniques
Few fishing techniques can target a single species and some of the most destructive forms of fishing, such as drift nets (now illegal in international waters and within many nation’s territorial waters), longlining and gillnetting, are responsible for much of the discarded waste bycatch.
These destructive techniques indiscriminately catch and kill huge numbers of some of our ocean’s most endangered species; from dolphins and whales, to sea turtles, albatrosses and sharks, as well as the manta rays. The oceanic manta ray, and many of the mobula ray species are especially vulnerable to these oceanic fisheries, falling victim to illegal drift nets, gillnets and tuna purse seine fisheries in unknown numbers each year, as they migrate vast distances across the tropical and sub-tropical oceans of the world.
Increasingly, many of the manta and mobula rays fished around the world are now being caught as targeted bycatch, meaning the rays are no longer discarded when captured as bycatch in a fishery which primarily is targeting another, more desirable species. The rays are now being retained because of the increasing demand for their gill plates, which are sold into the Chinese medicinal trade.
The Maldives tuna fishing industry practices some of the most environmentally sustainable fishing anywhere in the world, with all forms of net fishing prohibited, except for the use of small baitfish nets which are used directly to catch small schooling fish for the ‘pole and line’ tuna fishing industry in this country. This ‘pole and line’ tuna fishing technique has long been the mainstay of the local fishery. Consumed locally and exported internationally in great quantities, the Maldives yellow-fin and skipjack tuna fishery guarantees zero percent bycatch, making it one of the most environmentally friendly and sustainable fisheries in the world.
And with no fishing nets blanketing the coral reefs and open seas of this country, large numbers of dolphins, manta rays, whale sharks, sea turtles and sharks can still be seen in this country’s waters. If other nations were to follow this more sustainable approach to fishing the oceans, one of the largest threats to many of the sea’s most endangered species could be dramatically reduced.
As manta rays cannot swim backwards and have to continuously swim forward in order to move water over their gills, they often get entangled in fishing lines and occasionally mooring lines.
As the line catches onto their bodies, gill slits, mouths or cephalic fins, they perform backward rolls and turns attempting to free themselves, unfortunately this often entangles them further. If they are “lucky”, the line will break free and trail out behind the manta, cutting like cheese wire through skin, muscles, and eventually into their vital organs, often causing permanent damage and sometimes death.
Every year divers and snorkelers observe many manta rays still entangled in fishing line, or discarded and broken fishing nets which drift around the world’s oceans “ghost fishing” in countless numbers. These mantas which do encounter divers or snorkelers are the lucky few because they are often able to be cut free, but the unfortunate majority of entangled mantas are destined for a slow and painful death. In countries such as South Africa manta and mobula rays also fall victim to entanglement in shark-nets used to try and reduce shark attacks on humans at some of the busiest recreational beaches.