Sea Lice get nastier

It’s not an everyday occurrence, anywhere, to find a prominent, highly respected and much awarded professor accusing an ancient university of scandalously misleading the nation, but it happened here in Scotland last month.

The professor’s outburst was prompted by the publication of a study in the publishing arm of the Royal Society, itself a respected institution one would have thought, based on research by an international group of scientists, who suggested that sea lice are responsible for 39 per cent of the mortalities amongst salmon in the Northeast Atlantic Ocean. The press release issued by St Andrews University to accompany publication included

“This high per cent mortality attributable to sea lice was unexpected. The salmon aquaculture industry has long placed a high priority on controlling sea lice on their captive salmon – but these results do emphasise the need for the industry to not only maintain the health of their own stocks, but also to minimise the risk of cross-infection of wild fish.”

It can be read in full by clicking here

A response from the aquaculture industry was to be expected, but the ferocity with which it was delivered perhaps wasn’t. Professor Phil Thomas, the chair of the Scottish Salmon Producers Organisation said

“This story has now been exposed as a scandal – it is a major blunder by the University of St Andrews.  The institution has misled the nation.

“For a prominent Scottish University like St Andrews to behave in this way is inexcusable, whatever its need for publicity. To make these wholly incorrect and unjustifiable claims damages both the scientific reputation of the individuals concerned and the institution.

“But worse, it erodes the already shaky public confidence in science and scientists, and that is ultimately to the detriment of Scotland.”

The researchers did not wither under this fire and did not withdraw the study findings. They did clarify that the study did not actually state that fish farms were the sole source of the sea lice that were killing the wild fish. The inference remained that fish farms could be a contributory cause however.

Fast forward a few weeks and we find Professor Thomas giving evidence to the Rural Affairs, Climate Change and Environment Committee of the Scottish Parliament (RACCE) and returning to his theme. The exchange is worth quoting in some detail

“…..One tricky issue that is often lost in the debate is that there seems to be an assumption that sea lice come from fish farms. Sea lice are already there. For many fish farmers, the most problematic issue is when a run of mature wild fish come in, as they bring in sea lice—there is a sea lice strike on farms. In that situation, there can be rapid increases in sea lice numbers….

The difficulty is that, when wild runs of salmon come in from the sea with heavy infestations of lice, the transfer of lice from the wild salmon to the farmed salmon tends to be a mixture of lice of different stages, including lice that are quite close to mature as well as lice that are at the free swimming stage.”

Nigel Don:  “Up to now, I understood that lice did not transfer except when they were in their first stages, when they are so small that they get out and about—the idea of a bloom was mentioned. However, Phil Thomas is suggesting that mature fish coming  back from the sea bring lice at different stages and that lice at later stages in their development might transfer at that point. That is not what I thought that everybody else had told me. I thought that a mature louse would not transfer. Was I wrong?”

Professor Thomas:  “Without getting too complicated, there are two different types of sea lice, one of which often comes in not on salmonids but on other fish species. It can transfer in a range of ways. However, you are right in thinking that the predominant route of transfer is through the free swimming stage.”

It’s a pity that the RACCE Committee didn’t explore this further, as a few short sentences are barely enough to explain something obviously complicated.

For those of us like myself, a non-scientist member of the public who wants to understand why our wild salmon are disappearing, this conflict is most unhelpful, falling far short of constructive debate. It cannot be helpful to those, like the MSPs on the RACCE Committee, who have to produce a report to the Scottish Parliament, either.

The ways of nature are of course a mystery to most lay people. At the risk of being accused of anthropomorphism it seems to me inherently improbable for a mature sea louse, firmly attached by suction to a returning salmon, travelling  at speed, suddenly to decide to jump ship in the vicinity of a fish farm and make a break for it to another host. For this to happen to such an extent that it would represent a major threat to the farmed fish seems even more unlikely.

Before the recent exchange I had tried to educate myself about sea lice and had learned, as had Nigel Don MSP, that sea lice were a form of tiny marine crustacean that went through a number of changes in their lifecycle, and that only in two or three of these stages were they capable of travelling about. Further reading and discussions with some marine biologists of my acquaintance have only confirmed that this is correct. In their earliest stage as plankton they are propelled by water movements until if successful in finding a host they become anchored to it by a filamentous thread.  In later stages they suck onto the surface of the fish only through being dorso-ventrally flattened.   Although the pre-adult and adult stages are called “mobiles” that word refers to their grazing activity on the host fish and not their ability to swim around at liberty.  They are very weak swimmers and stand more chance of being eaten by big fish than getting aboard them. It has also been shown that mature sea lice only survive in sea water for very brief periods after being separated from the host.

In the final paragraph quoted above Professor Thomas seems to be saying that of the “two types of sea lice” it is the one that infects fish other than salmon that brings in the mature lice. This would rather contradict the earlier statement that the wild salmon rather than those other fish bring them in.

In European waters there are indeed two types of sea louse, Lepeoptheirus salmonis (Leps) and Caligus elongatus (Caligus), the former specific to salmon and the latter usually found on non-salmonids. There seems to be no evidence at all of Leps transferring from wild salmon or salmonids to caged fish. There are apparently some reported instances of Caligus suddenly appearing on caged salmon when

shoals of mackerel, herring, saithe or other shoaling fish swim past (Costello, paper  published by the Royal Society B on 8 July 2009).  Often these fish are attracted into the area by the presence of food and surround the cages.

A useful information resource is at the University of Prince Edward Island (www.upei.ca) where academics partly funded by Canada’s massive fish farming industry are researching how to deal with the threat to caged fish from sea lice. It’s instructive that their work concentrates exclusively on Leps rather than Caligus and I found no reference to sea lice strikes.

This suggests both that “sea lice strikes” if they happen at all do not involve wild salmon and that any that do happen are probably rather minor and do not involve Leps.

Most biologists believe that the primary seat of infection of salmon and sea trout with lice is by juvenile infective stages when the smolts leave the rivers in the Spring to enter into the salty coastal waters for the first time. Before the arrival of fish farms on the aquaculture coast of West Scotland there would always have been some wild salmon and sea trout along the coast to ensure supplies of sea lice larvae to infect them.

Arguably the arrival of fish farms on an industrial scale has changed all that, with enormous populations of mature salmon present all year round in coastal areas. It seems logical to infer a connection between these and the high death rate of wild salmon from sea lice infestation identified in the Royal Society B study.

Whatever the cause there is no dispute over the seriousness of the problem. It is made worse by the fact that sea lice are now developing an immunity to the pesticide that has mainly been used to kill them in recent years, Emamectine Benzoate, otherwise known as SLICE. In a recent talk Dr Mark Fast of the University of Prince Edward Island said

“1999 was the year the aquaculture industry gained what would be its most powerful tool in the fight against sea lice. It’s called SLICE…. It’s an in-feed treatment that, for a time, acted like a silver bullet. It was so effective that as a researcher studying sea lice, I found it difficult to harvest sea lice from salmon in an aquaculture environment. I just couldn’t find them. It worked that well….SLICE’s effectiveness started to seriously wane around 2008. The sea lice were adapting. The previous two summers had been worse than ever. Sea lice were partying even harder than they were in 1999.”

The full talk can be found  by clicking here

Dr Fast predicts that the industry will develop effective vaccines to replace SLICE in seven to ten years and cocktails of other less effective solutions before then, but none of this will directly benefit the native fish.

 

For environmentalists the main worry in all this is for the future of the native salmon and sea trout that are native to Scotland, the wonderful wild creatures that contribute to our national image and that also spearhead the marketing effort of the caged fish industry that may be harming them. There is an urgent need for less invective and more research to find out what is truly going on.

This article is largely the work of two prominent scientists, who prefer not to be named. The image of a sea louse at the top is borrowed from Dr Larry Hammell of UPEI.