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

NINA SPECIAL REPORT 34
Salmon lice infection <strong>of</strong> running Atlantic
salmon in two Norwegian fjords: effects <strong>of</strong>
hydrography and lice abundance
Peter Andreas Heuch, Jens Christian Holst, Lars Asplin, Bengt
Finstad, Pål A Bjørn and Audun Stien
Research carried out during <strong>the</strong> 1990s identified salmon
lice as a potentially serious population-regulating factor in
Norwegian salmonid stocks. Various management
measures were imposed, amongst <strong>the</strong>m a veterinarian act
in 1997 regulating <strong>the</strong> numbers and stages <strong>of</strong> salmon lice
allowed per individual fish in farms. Through a
comparative study between two major salmon fjords,
Altafjord and Sognefjord, we focused on interactions
between salmon lice and wild and farmed salmonids. In
Altafjord <strong>the</strong> results indicate that salmon lice were never a
problem for migrating post-smolts <strong>of</strong> salmon, while in <strong>the</strong>
Sognefjord <strong>the</strong> conditions have gone from negative before
2002 to good during 2002-2004. This coincides with <strong>the</strong>
fish farming industry’s efforts to reduce <strong>the</strong> salmon lice
production in <strong>the</strong> farms in <strong>the</strong> critical spring period.
Hydrographic-biologic modelling <strong>of</strong> data from Sogn from a
three-year period showed that environmental factors do
not explain <strong>the</strong> reduced infection <strong>of</strong> <strong>the</strong> running salmon
smolts. For sea trout <strong>the</strong> situation seems less positive. A
clear reduction <strong>of</strong> salmon lice infection intensity on sea
trout was not recorded in ei<strong>the</strong>r <strong>the</strong> Altafjord or in <strong>the</strong>
Sognefjord. It is concluded that wild and farmed salmon
can coexist in Norwegian fjords if <strong>the</strong> total amount <strong>of</strong>
salmon lice larvae in <strong>the</strong> fjord is adapted to <strong>the</strong> local
hydrographic conditions and <strong>the</strong> population characteristics
<strong>of</strong> <strong>the</strong> wild salmonids. To ensure precautionary salmon
lice management in Norwegian fjords <strong>the</strong>re is a need for
more knowledge on environmental and biological
parameters, in particular where <strong>the</strong>re are plans for
increasing <strong>the</strong> output <strong>of</strong> farmed fish.
Two-year sea lice larvae plankton survey
Michael J Penston, Ian M Davies and Alain F Zuur
An extensive plankton survey was carried out in <strong>the</strong> Loch
Torridon system, on <strong>the</strong> west coast <strong>of</strong> Scotland, to
investigate sea louse infective pressure. The survey
consisted <strong>of</strong> plankton tows collected weekly at a number
<strong>of</strong> sites within <strong>the</strong> sea loch over a 2-year period, between
2002 and 2004. In total, 884 samples were collected and
8,382 lice larvae were recovered, <strong>of</strong> which 58% were
nauplii and 42% were copepodids. The species <strong>of</strong> <strong>the</strong>
nauplii were not determined, but copepodids were
retained for identification. From <strong>the</strong> 416 samples
containing preserved copepodids, a random selection <strong>of</strong>
102 samples were examined for <strong>the</strong> presence <strong>of</strong>
Lepeoph<strong>the</strong>irus salmonis and Caligus elongatus. The vast
majority <strong>of</strong> <strong>the</strong> copepodids retained were L. salmonis, and
only a few were C. elongatus. During <strong>the</strong> survey, salmon
fish farms in <strong>the</strong> Loch Torridon system completed a
production cycle. Generalised Additive Models (GAMs)
were used to describe <strong>the</strong> distribution <strong>of</strong> lice larvae. The
models suggested an increase in larvae densities during
<strong>the</strong> farm production cycle, followed by a decrease as <strong>the</strong>
farms harvested and were left fallow. Significantly greater
densities <strong>of</strong> copepodids were recovered at <strong>the</strong> surface
than at 2.5 and 5 metre depths. Nauplii showed no
preference for any <strong>of</strong> <strong>the</strong> depths sampled. Densities <strong>of</strong>
sea lice larvae were found to vary considerably, ranging
from 0 to 243 larvae m -3 . This high variability in <strong>the</strong> data
was also indicated in <strong>the</strong> GAM models.
The current state <strong>of</strong> health management in
aquaculture - progress to date and future
challenges
Graeme Dear and Edward Branson
Fish health management has developed from being a ‘new
concept/minor species/green-fingered/let’s try it and see’
aspect <strong>of</strong> aquaculture to one which increasingly utilises <strong>the</strong>
most advanced scientific technology to provide solutions
to health challenges. The current status <strong>of</strong> fish health and
options available to <strong>the</strong> farmer to control pathogens are
described in <strong>the</strong> context <strong>of</strong> a rapidly evolving industry.
The inter-relationship between <strong>the</strong> key parameters <strong>of</strong>
legislation, economics, environment, host, consumer
concerns and veterinary medicines are examined in <strong>the</strong>
context <strong>of</strong> reducing antibiotic use and increasing pressure
to control parasitic and viral diseases such as sea lice,
IPNV and pancreas disease. While vaccine availability and
husbandry methods have advanced to <strong>the</strong> point where
<strong>the</strong>y have reduced, but not eliminated, <strong>the</strong> need for
antibiotics, <strong>the</strong> future challenges revolve around <strong>the</strong>
importance <strong>of</strong> a greater understanding <strong>of</strong> <strong>the</strong> needs <strong>of</strong>
aquaculture healthcare. In an environment which is
increasingly demanding from regulatory, environmental,
retailer, consumer and wider stakeholder interests - it is
important not to forget <strong>the</strong> main purpose <strong>of</strong> <strong>the</strong> subject,
i.e. fish health and welfare. These challenges will be
discussed and key areas identified for veterinary care and
future research and development to assist in <strong>the</strong>
management <strong>of</strong> fish health.
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