Salmon and sea-trout ecology in the Moray Firth

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Salmon and sea-trout ecology in the Moray Firth

• John Armstrong
• FRS Freshwater Laboratory
• Pitlochry

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Ecology

• Numbers
• Distribution
• Migration
• Some insight can be gained from information on
  the fisheries, to be discussed later, and fish
  counters

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Ecology

• Migration pathways
• Mortality agents
• Seasonal variation
• Time spent in the Firth
• Inter-annual variation
• Mortality patterns

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Ecology

• Migration pathways
• Mortality agents
• Seasonal variation
• Time spent in the Firth
• Inter-annual variation
• Mortality patterns

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Size-dependent variation in salmon smolt survival

• Does it pay for smolts to be as large as
  possible?
• Does this vary between river and sea migration?

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• The River Conon system is heavily impacted by
  hydro-electric installations
• This provides unique opportunities for studying
  wild salmon

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Smolts

• All fish stocked as eggs and first-feeding fry
  leaving as smolts enter a fish trap

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• 1000-3000 smolts tagged annually with passive
  integrated transponders

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• Passive integrated transponders are
• small, inert internally attached
• relay a unique code when interrogated
• have no battery, but a short range (c. 15cm)

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Smolts

• Returning adults pass across a PIT detector
  installed in a Borland lift fish pass

Adults
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• The detector is integrated with a resisitivity
  fish counter

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Migration in the riverfish tagged above the trap
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Migration in the riverfish tagged above the trap
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Mortality in the river

• Survival decreases with distance travelled
• Survival increases with size at tagging

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Mortality at sea7304 smolts (1998-2001)
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Mortality at sea

• Survival increases with smolt size to a peak and
  then decreases

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Mortality agents

• Sawbill ducks select for smaller smolts
• What predator selects for the larger smolts?

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Planned work

• Migration routes of returning adult salmon
• Consumption of salmon and sea trout by seals
• Relationships between salmon migration and
  dolphin foraging areas

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Collaborators

• Simon McKelvey CADFB
• Alastair Stephen SSE