SALMON

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SALMON IN THE CLASSROOM
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What are Atlantic salmon?

• Atlantic salmon, Salmo salar, are a native
  freshwater fish species.

• Salmon begin their life in freshwater but spend a
  year or more in the sea before returning to
  freshwater to spawn.

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Why is it important to have healthy salmon
stocks?

• Biodiversity

• Angling

• Tourism

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The lifecycle of salmon

• Q What is a life cycle?

A The life cycle or life history of a living
thing is the series of changes it goes through
from the beginning of its life until death.
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Life cycle of salmon
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Spawning

• Spawning is undertaken in the autumn and winter
  as water temperatures fall.

• Spawning takes place where the river bed is made
  up of small stones and pebbles and is silt free.

• The water must be unpolluted.

• The eggs are deposited in a redd which the
  female fish cuts in the river bed with her tail.
  Once the eggs are in the redd she covers them
  over so they are buried out of sight.

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The egg stage

• Salmon produce up to 1700 eggs per kg of body
  weight (a kg is about the same weight as a bag of
  sugar).

• Prior to hatching you can see the fishs eyes
  within the egg the eggs are then described as
  eyed ova.

• The time taken to hatch depends on the water
  temperature the colder the water the longer the
  eggs take to hatch.

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The egg stage

• Sometimes eggs do not survive to hatching and
  turn white and die.
• Can you see the dead eggs in the photo opposite?

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The alevin stage

• When the eggs hatch the young salmon are called
  alevins.

• Alevins do not look for food as they feed from
  their yolk sac.

• To avoid predation and to save energy they remain
  buried in the river bed.

• Once they use up their yolk sac they move into
  the water above to search for food.

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Fry and parr stages

• For the first year of their life the young salmon
  are called fry.

• Once they are over a year old they are known as
  parr.
• Salmon feed mostly on aquatic invertebrates in
  freshwater but they can also feed on terrestrial
  insects that fall into the water.

• The salmon fry and parr are dark coloured to help
  hide them from predators.

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Smolts

• Young salmon stay in their home rivers until they
  develop into smolts. This process is dependent
  upon water temperatures and food availability.
• In southern parts salmon may leave home after 1
  year but in northern areas they may take 5 years!

• The smolt run when these fish migrate
  downstream into the sea is around April-May.

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Where do smolts go?

• Smolts swim along the coast in shoals and then
  move into feeding grounds.

• They head north towards the cold waters of the
  Arctic.

• Smolts that remain in the sea for one winter are
  called grilse and they feed around the Faroes.

• Some smolts travel to feed in waters off
  Greenland. These salmon will stay at sea for two
  or three winters.

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Adult salmon head

• This is the head of a large male salmon just
  prior to spawning time.

• It has developed a kype on its lower jaw.

Q What do you think this is for ?
A It is used as a weapon to fight with other
male salmon to see who spawns with the best
females!
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What happens to salmon after they spawn?

• After salmon have spawned they are are weak and
  tired. They also look thin.
• They are then known as kelts.
• About 90-95 of kelts die after spawning. The
  others may survive to spawn 2 to 4 times.

SPAWNING
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How do people study salmon populations?
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Electro-fishing

• Electro-fishing is used to stun the fish so they
  can be captured without harming them.

• Using electro-fishing equipment all the fish can
  be captured in a known area.

• This allows the number, growth rates and health
  of the fish population to be examined.

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Fish tagging

• Fish are often tagged to help in experiments and
  studies.

• The fish in the top photo is having a tag
  injected under the skin near its eye. This does
  not harm the fish but means that biologists can
  recognise it in later years.

• Can you see the yellow tag beside the fishs eye?

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Testing water quality

• Clean, well-oxygenated water is needed for
  healthy salmon.

• By testing a sample it is possible to examine if
  the water is polluted.

• The equipment in the photo was set up to test the
  waters acidity, as acidic conditions can stop
  salmon from hatching. It is powered by a solar
  panel.

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Fish traps

• Fish traps are often used to capture fish
  entering burns to spawn. This allows biologists
  to assess whether enough fish have returned to
  the river.

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Scale reading
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What problems face the salmon?
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Pollution problems

• Severe pollution will kill fish.

• Large amounts of silt entering a river may
  suffocate eggs and alevins buried under the
  gravel.

• Even if pollution does not kill the fish it may
  kill the invertebrates which salmon feed on
  leaving them to starve.

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Access to spawning grounds

• If salmon are not able to get to where theyd
  like to spawn, their whole lifecycle may suffer.

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Parasites and disease

• Parasites and disease may kill large numbers of
  fish, in particular when fish congregate in high
  densities below falls or at the mouth of a river.
• This photo shows a sea louse on a salmon that was
  caught by a netsman. These parasites can cause
  problems to both juvenile and adult salmon.

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Question

• Q What problems can these animals pose to salmon?

A
Erosion Bank collapse Lack of cover Silt input
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Question
Who could have eaten this fish?
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Answer
A Seal!
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Otter kill

• This fish was killed by an otter.

• Although it had only eaten a small part of this
  fish when the photo was taken the otter actually
  returned the following 3 days until it had
  devoured the lot!

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Can you think of any other problems that salmon
might face?
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How can people help salmon?
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Deciduous tree planting

• If few natural deciduous trees exist near the
  water courses then it may be desirable to plant
  more.

• The trees will

• Provide shelter cover

• Stabilise bank sides

• Increase number of invertebrates

More bigger salmon!
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Bank side fencing

• The erection of fencing to keep farm animals away
  from the water edge is beneficial.

• As you can see in the photo, a fence has been
  erected so that bankside vegetation can recover
  from overgrazing.

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Fish passes around obstructions

• Fish passes can be created to allow salmon access
  to suitable spawning areas upstream.

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Poor instream habitat

• In this watercourse, the farmer had dredged and
  straightened the burn over a number of years. He
  did this to make it easy for water to drain
  quickly away from his fields.

• The burn was not suitable for salmon any more as
  spawning beds were silted up and little suitable
  habitat for parr existed.

• It was felt that something had to be done!

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Better instream habitat

• This is the same burn after tonnes of rocks were
  carefully added by hand.

• The careful addition of rocks actually helps the
  water to drain away quickly!

• The little weirs and dams that were created
  provide more suitable salmon habitat.

• A far healthier salmon population is now found in
  this burn.

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Stocking

• To help salmon survive in areas where spawning is
  a problem, some groups undertake stocking.

• Stocking involves rearing salmon eggs in a
  hatchery until they reach fry or parr stage.

• The reared fish are fed until they are returned
  to the wild.

• Survival rates are higher in the hatchery than in
  the wild

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• Thank you for your attention!
• Now you will hear about how you are going to help
  salmon!