Wild salmon fisheries and salmon farming

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Wild salmon fisheries and salmon farming

• Alaska wild salmon fisheries
• biocomplexity
• If it is a model of sustainability why is it
  struggling?
• Salmon aquaculture
• Case study Sea lice population declines in
  wild salmon

Ray Troll
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Sockeye salmon life history
MARINE
FRESHWATER
carcasses
Adult sockeye (1-3 years)
spawning
eggs
fry
(1-2 years)
smolts
Anadromy
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The modern fishery

• 2000 drift gillnet boats and 1000 shore based
  set net (limited number of permits, traded like
  stocks)
• Managed for constant escapement in each river
  districtwhen goal is reached, the rest of the
  fish are fair game

• How to decide how many fish to catch each year
  without overharvesting spawners?
• In-season managementadjust fishing
  opportunities as information comes in about
  returns to each river (24hr counting towers)

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The Race for Fish!!!

• All of the fish in Bristol Bay could be caught
  for virtually nothing.
• A set of laws is in place to ensure that they are
  not caught efficiently.
• After Alaskan statehood, harvesting was shifted
  from large corporations to individuals by means
  of restrictions on vessels and gear. (In the
  1970s the number of participants in the fishery
  was limited by introducing a limited entry permit
  system.)
• Fishery participants are in competition with each
  other for a set number of fish
• Thus, it is in the interest of each fisherman to
  invest in a bigger, faster boat with more
  advanced navigation and communication technology
  not because its needed to catch the fish, but
  because its needed to catch the fish before the
  next guy.

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Commercial Sockeye Salmon Catches Since
1883 Bristol Bay, Alaska
biocomplexity
Commercial catch (millions)
Composition
Hilborn et al. 2003
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Warmer winters at Iliamna Lake
170
170
25 May
130
130
Breakup date (days after Jan. 1)
10 May
90
90
50
50
1950
1961
1972
1983
1994
2005
1950
1961
1972
1983
1994
2005
Year
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Trend in body condition of 1 smolts (residual
from length-mass regression)
fat
lean
Data from ADFG
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Increasing tendency for smolts to migrate as
1-year olds (Kvichak River, Alaska)
Data from ADFG
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Bristol Bay salmon are a success story in
sustainable management

• Why??
• Constant escapement
• Withstand pressures to develop some of the
  rivers that support Bristol Bay salmon (dams,
  gold mines, oil production, etc.)
• By maintaining the whole group of river
  districts (and its biocomplexity), the total
  run of salmon available for harvest is buffered
  from environmental changes (climate, landslides,
  missed escapement goals)
• Warming in Iliamana Lake causing a shift from a
  2yr to 1yr juvenile stage
• Major consequences for the productivity of that
  river district
• This was one of the most productive districts in
  the whole bay.what if they had developed the
  rest and just managed this??
• Economic disaster!!!!!

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The emergence of salmon farming
2 500
38 wild
1000s metric tons
1 000
98 wild
0
1980
2001
Eagle et al. 2003
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(No Transcript)
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Concerns with salmon aquaculture

• Feed Conversion
• bioaccumulation
• Pollution
• Escapes
• Disease transfer

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Parasite Sea lice (Lepeophtheirus salmonis)
Host Salmonids (Oncorhynchus and Salmo spp.)
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Pacific salmon life cycle
natal rivers
open ocean
nearshore environment
coastal environment
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Juvenile adult salmon
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Opportunities for parasite transmission
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Add a reservoir host population
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Sea lice year round
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Point source
Constant
Abundance
Single farm raised infection pressure 73 fold
Exceeded ambient levels for 75 km
Position relative to salmon farm
Krkosek et al. 2005
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Farm origin lice induce 5 - 95 mortality in
adjacent pink and chum
Abundance
--------------------
Survival
Krkosek et al. 2006
Position relative to salmon farm
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What we know so far?

• Farms transmit lice to wild salmon
• Lice from farms induce mortality
• Remove farms high wild survival

But the million dollar question is
Does it matter at the population level?
Mortality could be additive () or it could be
compensatory ()
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Population growth rates Unexposed 0.62
Exposed - 1.17
Pink salmon are depressed and declining in region
of salmon aquaculture
4 generations to extirpation?
Krkosek et al. 2007
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What about the rest of the ecosystem?
Salmon
Salmon play an important role in connecting
marine, terrestrial and freshwater ecosystems
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Sea lice

• Increase susceptibility to
• predation ( 4X)
• Predation results in
• transmission of lice to
• predators

Accumulation of sea lice on predatory salmonids?
Connors et al. 2008
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Global assessment of impacts of salmon aquaculture
Survival
/ton farmed salmon/generation
/generation
change
gt 50 reduction in survival at current
production!!!!
Ford and Myers. 2008
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Take Home message

• Preserving biocomplexity can help to ensure the
  biological sustainability of wild salmon
  fisheries

• However, these fisheries must also be
  economically sustainable

• Salmon aquaculture has challenged this
  sustainability
• If we want to ensure the long-term sustainability
  of coastal economies and ecosystems we need to

• recognize that humans are an essential element
  in the biocomplexity of the system

Ray Troll