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

NINA SPECIAL REPORT 34
fish in <strong>the</strong> catches and, provided that <strong>the</strong> conservation
status <strong>of</strong> local wild salmonid stocks is taken into account,
such a fishery may reduce <strong>the</strong> number <strong>of</strong> escapees, thus
lowering <strong>the</strong> risk <strong>of</strong> introgression with wild salmonid
populations and removing potential sources <strong>of</strong> sea lice,
and provide information on relative abundance <strong>of</strong>
escapees in <strong>the</strong> sea.
A third presentation from Norway described a study, <strong>the</strong>
‘TRACES’ project, that is being conducted in <strong>the</strong>
Hardangerfjord to examine <strong>the</strong> costs and efficiency <strong>of</strong>
identifying and tracing <strong>the</strong> origin <strong>of</strong> farmed salmon. In
2003, a national Committee had been established in
Norway to identify methods to trace <strong>the</strong> origin <strong>of</strong>
escaped farmed salmon and had concluded that no
methods were ready at that time for implementation. Two
methods were, however, identified that merited fur<strong>the</strong>r
investigation: coded-wire tagging and a ‘contingency
approach’ based on <strong>the</strong> characteristics <strong>of</strong> <strong>the</strong> fish. In <strong>the</strong>
‘TRACES’ project, DNA microsatellite markers, single
nucleotide polymorphisms, fatty acid pr<strong>of</strong>iles, trace
element and stable isotope composition were assessed
with regard to <strong>the</strong>ir utility in tracing <strong>the</strong> farm <strong>of</strong> origin <strong>of</strong>
escapes.
A study involving acoustic tracking <strong>of</strong> wild cod found that
<strong>the</strong>y occurred in <strong>the</strong> exit corridors <strong>of</strong> wild salmon smolts
from critically endangered salmon rivers in <strong>the</strong> Bay <strong>of</strong>
Fundy. The authors expressed concern that as field trials
rearing farmed cod are now underway, escapees from cod
farms might behave like <strong>the</strong> wild cod in <strong>the</strong>ir study, and
<strong>the</strong>y could prey on wild salmon smolts. The authors
concluded that <strong>the</strong>re is a need for careful consideration to
cage design and siting so as to avoid interactions with wild
cod and with wild salmon and o<strong>the</strong>r diadromous species.
Sea lice biology
Two posters presented information on sea lice biology.
The first examined <strong>the</strong> infestation success <strong>of</strong> sea lice at
different temperatures ranging from 6 - 16 o C and showed
that lice were infectious for a longer period <strong>of</strong> time at low
temperatures. These data are important in modelling <strong>the</strong>
dispersal and survival <strong>of</strong> free-living lice larvae.
The second presentation examined <strong>the</strong> role <strong>of</strong> freshwater
acidification on <strong>the</strong> sensitivity <strong>of</strong> salmon smolts to sea lice.
Many rivers in sou<strong>the</strong>rn Norway can be periodically
acidified to sub-lethal levels and additionally <strong>the</strong>re are
many fish farms in <strong>the</strong> region. This study concluded that
<strong>the</strong> combined effects <strong>of</strong> moderate acidification in fresh
water and moderate sea lice infestation in sea water can
have <strong>the</strong> same negative effect as higher acidification or
higher lice infestation. The authors concluded that <strong>the</strong>re is
a need, <strong>the</strong>refore, to consider <strong>the</strong> effects <strong>of</strong> multiple
stressors on smolt survival ra<strong>the</strong>r than using single-factor
models.
Stocking programmes
A study from <strong>the</strong> rivers Ulla and Lerez in Spain examined
genetic variation in <strong>the</strong> restored populations. These
populations were close to extinction in <strong>the</strong> 1990s but a
restoration programme involving habitat improvements,
fishery regulations and a supportive breeding programme,
based on native juveniles and returning adults, has been
undertaken since 1995. The study indicated that modern
populations are very similar genetically to those present
prior to stocking, although <strong>the</strong> populations are more
similar today than in <strong>the</strong> past.
The Connecticut River lost its salmon population about
200 years ago due to human activities but a salmon run
has been re-established based mainly on stock from <strong>the</strong>
Penobscot River. The current genetic pr<strong>of</strong>ile <strong>of</strong> salmon in
<strong>the</strong> Connecticut was shown to be very similar to that <strong>of</strong>
its donor population in <strong>the</strong> Penobscot, indicating that <strong>the</strong>
effective number <strong>of</strong> breeders in both rivers has been large
enough to preserve genetic variability and that no genetic
bottlenecks occurred during <strong>the</strong> restoration programme.
The differences that were detected were considered to
be adaptive responses to environmental variation.
A study from <strong>the</strong> Burrishoole River in Ireland analysed
stock and recruitment data for a population receiving
variable, but significant, quantities <strong>of</strong> naturally spawning,
hatchery-origin fish over a thirty-five year period. The
results suggest that <strong>the</strong> hatchery fish had a significant
depressive impact on <strong>the</strong> recipient population <strong>of</strong> about
30% and <strong>the</strong> author concluded that removal, ra<strong>the</strong>r than
addition, <strong>of</strong> hatchery fish may be <strong>the</strong> most effective
strategy to improve productivity and resilience in wild
stocks. In <strong>the</strong> last eight years, hatchery fish were
effectively excluded from spawning in <strong>the</strong> wild and a
significant improvement in freshwater production <strong>of</strong> smolts
was observed.
Aquaculture-free zones
A presentation from Iceland reported on <strong>the</strong> rationale for
<strong>the</strong> establishment <strong>of</strong> aquaculture-free zones in wild
salmon-producing areas to protect valuable salmon angling
fisheries. Salmon farming is not permitted in bays and
fjords with <strong>the</strong> most valuable salmon rivers and in <strong>the</strong>
areas where it is permitted, <strong>the</strong> experience gained will be
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