Science sets the minister straight over sea lice on salmon farms
By Derek Evans, Irish Times, Friday 17 May 2013
PROFESSOR Mark Costello, chair of World Register of Marine Species and president of the International Association of Biological Oceanography has written to the Minister for Marine, Simon Coveney, advising him of recent incorrect information in the media regarding whether sea lice from salmon farms can cause problems on wild fish, according to Friends of the Irish Environment (FIE).
In his letter, he explained that while he does “not normally get involved in such debates” he “was surprised at some of the incorrect information about whether sea lice from salmon farms can cause problems on wild fish” and felt it important “that I provide you with best scientific information”.
He points out that salmon lice emanating from farms “have proven difficult to control on farms, especially large farms” and have been “linked to mass fatal parasite infestations on wild salmon and trout in Ireland, Scotland, Norway and Canada”.
While an average of five adult lice per fish generally triggers treatment on farms, “if there are a million fish on the farm with one egg-bearing louse each, the farm may release 500 million lice larva”.
“A key consequence of this,” Costello writes, “is that on large farms, it is possible to keep the number of lice below what is harmful to the farm fish but they may still be producing a lot of lice larvae.
“The current levels of infestation that must be treated under the Irish protocol are five sea lice for most of the year, with two sea lice triggering chemical treatment in the spring.
At the infective stage, sea lice actively search for a host. They swim towards the surface during the day. Surface waters tend to blow towards the shore due to the daytime onshore winds. Thus the sea lice are moved towards the seashore and into estuaries, so they congregate in the path of salmonids migrating to sea.
“Studies in Ireland, Scotland, Norway, and Canada involving computer models and field data on infestations indicate that lice from farms may infest wild fish up to a distance of 30km. Similarly, one may expect farms within 30km of each other to be cross-infecting.
“Like any use of the environment for farming,” Costello concludes, “there can be environmental impacts. It appears that sea lice are the most significant impact of salmon farms generally by virtue of their impact on wild salmonids.”
FIE points out that the Marine Institute and BIM have argued that sea lice are no longer an issue and that the current treatment protocols are adequate.
Commenting on Prof Costello’s letter, Niall Greene of Salmon Watch Ireland, said: “Minister Coveney cannot ignore the mounting evidence that BIM has totally misrepresented the threat posed to wild salmon by sea lice and farmed salmon escapees emanating from the proposed Galway Bay farm.
“It is imperative that he initiates an independent review of all aspects of the proposed project,” Greene said.