Report of the 2005 ICES/NASCO Symposium on Interactions ...

NINA SPECIAL REPORT 34
differences in hydrography could cause changes in sea lice
dispersion that radically altered risks to wild fish.
Differences between emerging dispersion models in
Norway and Scotland were briefly discussed.
Ron Stagg had posed <strong>the</strong> question <strong>of</strong> whe<strong>the</strong>r anyone had
determined <strong>the</strong> impacts <strong>of</strong> sea lice on wild fish
populations. Bengt Finstad attributed this to <strong>the</strong> lack <strong>of</strong>
systematic investigation, a deficiency currently being
addressed through <strong>the</strong> collaborative research project with
industry, recently initiated in <strong>the</strong> Hardangerfjord system.
Tom Cross also appeared to have anticipated <strong>the</strong> question
<strong>of</strong> impacts <strong>of</strong> sea lice on wild fish populations but
explored qualitative changes at <strong>the</strong> genotype and
phenotype level ra<strong>the</strong>r than numerical changes. They
examined impacts <strong>of</strong> diseases associated with farming on
genetic variability <strong>of</strong> sea trout from two systems, <strong>the</strong> Erriff
and <strong>the</strong> Burrishoole. Archived scale samples were
examined and variations at both a locus critical to
immune response (MHC1) and six neutral microsatellite
loci were measured. Two contrasting situations were
found: in <strong>the</strong> Erriff, decreases in genetic variability were
found in both MHC1 and <strong>the</strong> neutral markers. By
contrast, later samples from <strong>the</strong> Burrishoole showed a
recovery in MHC1 variability. Evidence was presented to
show differences between <strong>the</strong> two systems in <strong>the</strong> relative
proportions <strong>of</strong> sea trout to freshwater-resident fish, with
proportionally much higher numbers <strong>of</strong> freshwaterresident
trout in <strong>the</strong> Burrishoole.
Chrys-Ellen Neville presented a paper on <strong>the</strong> effects <strong>of</strong>
fish farm lice on wild pink salmon. Large numbers <strong>of</strong> pink
salmon smolts emigrate through <strong>the</strong> Queen Charlotte
Strait, an area <strong>of</strong> intense Atlantic salmon farming activity.
Data from a recent year class was presented, showing that
adult pink salmon returned in unusually high numbers <strong>the</strong>
following year but it was not possible to conclude
whe<strong>the</strong>r this was due to <strong>the</strong> Provincial Action Plan which
introduced a fallowed migration corridor, or increased
freshwater flow, which could lead to conditions less
favourable to sea lice production, or o<strong>the</strong>r factors.
Ano<strong>the</strong>r session <strong>the</strong>me was sea lice control. Current
health management practices on Scottish salmon farms
were discussed by Graeme Dear. Bacterial problems
were shown to be largely under control due to vaccines,
resulting in major reductions in <strong>the</strong> use <strong>of</strong> antibacterial
compounds. Viral diseases remained a serious concern,
recent ISA outbreaks having largely been controlled only
through rigorous culling. Management measures, in
combination with access to good medicines, have been
critical in reducing sea lice levels on farms, although more
effort is required by some sectors <strong>of</strong> <strong>the</strong> industry. A key
message was <strong>the</strong> threat posed by <strong>the</strong> emergence <strong>of</strong> new
disease challenges, but also flagged up were <strong>the</strong> potential
<strong>of</strong> genetic selection to improve disease resistance, <strong>the</strong>
emerging field <strong>of</strong> nutraceuticals, and <strong>the</strong> continued
importance <strong>of</strong> application <strong>of</strong> best practice to avoid
disease.
Trends in <strong>the</strong> use <strong>of</strong> medicines in <strong>the</strong> Norwegian salmon
farming industry were presented by Kari Grave. This
presentation focused on <strong>the</strong> question <strong>of</strong> whe<strong>the</strong>r <strong>the</strong>
current use <strong>of</strong> antimicrobials and anti-sea lice medicines in
particular posed any threat to wild fish. While it was
concluded that <strong>the</strong>re were no toxicological risks, suboptimal
treatments against sea lice promoted heavy lice
infestations and increased infection pressure on emigrating
Atlantic salmon smolts. At <strong>the</strong> opposite extreme, overreliance
on certain key medicines increased <strong>the</strong> risk <strong>of</strong>
development <strong>of</strong> resistance with consequent welfare
concerns and increased risks to wild fish. Ove Skilbrei
assessed whe<strong>the</strong>r treatment <strong>of</strong> ranched Atlantic salmon
against sea lice with orally administered emamectin
benzoate prior to release affected survival. Survival did
not differ between treatment and control groups released
in May, but <strong>the</strong>re was a two-fold increase in survival in
treated compared with untreated fish released in June.
Moreover, treated fish were almost one third heavier. It
was also concluded that sub-lethal lice levels may affect
growth and, <strong>the</strong>refore, size at spawning and fecundity <strong>of</strong>
wild fish.
The use <strong>of</strong> cleaner wrasse to control sea lice on farmed
fish was reviewed by Per Gunnar Kvenseth. The
presentation informed <strong>the</strong> audience <strong>of</strong> <strong>the</strong> efficacy and
cost-effectiveness <strong>of</strong> using wrasse to control sea lice in
commercial farm situations and <strong>the</strong> recent advances in
breeding <strong>of</strong> ballan wrasse in particular. He concluded that
wrasse should be considered as part <strong>of</strong> an integrated sea
lice management strategy.
Data sharing, trust and cooperation among regulators,
farmers and wild fish interests are <strong>the</strong> foundations
essential to any effective management control strategy.
The achievements <strong>of</strong> <strong>the</strong> Scottish Tripartite Working
Group approach to this were reviewed by Phil Gilmour.
Organisational aspects at national, regional and local levels
were explained. Success was judged in terms <strong>of</strong> <strong>the</strong>
degree <strong>of</strong> consensus that had been achieved, <strong>the</strong> number
<strong>of</strong> Area Management Groups that had been formed and
Area Management Agreements that had been signed.
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