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.