Use of wrasse to combat parasite
threatens natural stocks, say experts
Robin McKie, science
editor
Saturday 10 June 2017
22.11 BST
Salmon farmers have been accused
of playing dirty by using fish caught in the wild to clean lice from Scottish
fish farms. Marine conservation experts say that shipping tonnes of
English-caught wrasse a year – to tackle lice infestations in salmon pens north
of the border – is endangering natural stocks. English anglers have also warned
wrasse is becoming harder and harder to find in local waters.
However, salmon farmers have
rejected the charge. They say the use of wrasse as a “cleaner” fish is part of
a long-term plan to replace chemicals – which are currently administered to
pens to control lice infestations – with sustainable, biological controls.
Fishermen remain concerned,
nevertheless. “Wrasse play a role in keeping the marine ecosystem in balance,”
said David Mitchell, of the Angling Trust. “We simply do not know what will be
the consequence of removing so many of them from our coastal waters.”
More than 170,000 tonnes of
salmon a year are grown in Scotland at more than 200 marine farms. However, production
is affected by lice infestations that cause lesions and secondary
infections in the fish. Chemicals can control this but pollute water around the
farms. Another solution is provided by wrasse which feed on marine insects.
Many species – such as ballan and goldsinny wrasse – will eat lice that infect
larger fish. As a result wild wrasse are being caught in pots and shipped to
Scotland to tackle sea-lice infestations. One wrasse for every 25 salmon is
used.
But this exploitation of wrasse is
raising concerns. “We are very worried that a large local fishery has developed
rapidly over the past couple of years – with large numbers of wrasse being
taken from local waters – without proper management or any indication of its
sustainability,” said Samuel Stone, of the Marine Conservation Society.
“It is a real concern.”
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