By Alex Kirby
BBC News Online environment correspondent
Trawling for prawns is hugely wasteful, conservationists say, and threatens other marine creatures with devastation.
Prawns are valuable: The fishery can be destructive (Image: Noaa)
They say prawn trawlers kill 150,000 marine turtles a year, and also large numbers of seahorses.
They want consumers not to buy prawns until supermarkets can prove they have been caught without harming the environment and local communities.
They also argue for an independent, internationally accepted system of certification and monitoring of prawn production.
We badly want EU trawlers to be obliged to operate to EU standards wherever they're fishing
The arguments against the present practice of prawn trawling come from the Environmental Justice Foundation (EJF), a UK-based organisation which tries to link environmental problems, human rights and social need.
It has published a report, Squandering the Seas, which says trawling for prawns (known interchangeably as shrimps), "is threatening ecological integrity and food security around the world".
The report's main findings include:
Steve Trent, EJF's director, said: "This waste, to feed a luxury market here in the UK and other developed nations, is totally unacceptable when so many in poorer countries are going hungry.
trawlers catch up to 20 kilograms of other species for every one kg of prawns they take
they are responsible for one-third of the world's discarded catch, although they produce less than 2% of global seafood
local fish catches can decline sharply in areas where trawlers operate
the trawls cause significant damage to seabed life.
"Just how much is the rest of the world paying for our prawn sandwiches?"
The report says the ratio of bycatch (other species caught accidentally) to prawns is typically 5:1 in temperate seas, and 10:1 in the tropics. But it says in some fisheries the ratio can be 20:1.
Seahorses are under great pressure (Image: Project Seahorse)
Most of the bycatch is simply thrown back into the sea dead or dying, it says. This harms the stocks on which local fishing communities depend, and deprives poor people of a key source of protein.
It says prawn farming is no substitute, with the farmed fish needing to be fed more than twice their own weight in wild-caught fish before they are big enough to sell.
The report says: "Vast areas of mangrove forest have been destroyed to make way for shrimp pond construction, seriously affecting the coastal ecology of many tropical nations."
Often, it says, the trawlers are heavily-subsidised foreign vessels: the European Union (EU) underwrites up to 46% of the costs of trawlers fishing for prawns off Guinea-Bissau in West Africa.
The EU is the world's largest prawn importer: it bought 378,375 tonnes from abroad in 2000.
Within the EU, the UK is the third largest importer. In 2000 it caught 2,100 tonnes of prawns in its own waters, but imported 77,900 tonnes (both fished and farmed) from elsewhere.
Turtles: Victims of the prawn fishery (Image: WPSI/Operation Kachapa/WildAid)
Annabelle Aish of EJF, the report's main author, told BBC News Online: "Prawn trawling often denies local fishermen the right to earn a living and to feed their families.
"The boats discard species that have sustained communities for centuries.
"We badly want EU trawlers to be obliged to operate to EU standards wherever they're fishing.
"That would mean they'd have to use bycatch reduction devices, which really do work."
EJF also wants consumers to avoid buying prawns until supermarkets can prove they have been sustainably caught.
Brendan May, chief executive of the Marine Stewardship Council, told BBC News Online: "There are some good prawn fisheries, but we welcome this report.
"Anything which draws people's attention to the environmental cost of the fish they eat is very helpful."