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SFCC Introduction to salmon scale reading; Terminology and Common Scale Patterns


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Introduction to Salmon Scale Reading

Here is part 1 of 2 featuring terminology and common scale patterns.

Developed with thanks to The Tweed Foundation

Published in: Science
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SFCC Introduction to salmon scale reading; Terminology and Common Scale Patterns

  1. 1. Introduction to Salmon Scale Reading • Terminology • Common scale patterns • “Problem” scales • Erosion • Spawning marks • Smolts.
  2. 2. Salmon Scale Reading • Terminology and the parts of a scale
  3. 3. This is the worn, posterior, protruding part of the scale Visible on the outside of the fish under the Epidermis, which covers it. This is anterior, embedded part, the “root” of a scale. This is the part that is read. These “rings” are the growth circuli, that are laid down as the scale gets bigger as the fish grows.
  4. 4. At the centre of the scale is the “Focus”, the original, small, scale formed towards the end of the fish’s first Summer Focus
  5. 5. Scales can come off fish, and in the resulting gap, “Replacement” scales are grown. These do not show the growth pattern of the fish before they themselves formed and so cannot give the complete history of a fish. Replacement scale
  6. 6. On adult salmon scales there are two phases of growth shown – the River stage when the fish was a Fry and Parr in fresh water and the Marine stage when it was living in the sea. The transition between the two should be very obvious – the sea has much better feeding TRANSITION
  7. 7. Readings “inside” the transition give data on the freshwater phase and show how old the fish was when it smolted. River Age Sea Age
  8. 8. Winter Bands form when the growth circuli are closer together because the fish & its scales are growing more slowly in colder conditions. Note how narrow the first Summer band is – just a couple of circuli between the Focus and the first Winter band.
  9. 9. This fish therefore smolted after two Winters in fresh water. The Marine phase is read in the same way – counting the tight bands of circuli that show Winter (closed) growth.
  10. 10. Focus River zone First summer at sea. Widely spaced circuli. Winter band of narrow-spaced circuli. Second summer at sea. Marine Stage / SEA AGE Transition from river to sea.
  11. 11. This fish therefore had two Summers and one Winter in the sea – so it is a Grilse : . 1+ ( 1 Sea-winter + Summer growth afterwards ) A “Winter” indicates a full year’s growth as it marks the end of full year, “+” means part of a year’s growth after the last Winter And as it had two Winters in the river, it is a :- 2 .1+ The .between the two numbers is the transition between the river stage and the sea stage
  12. 12. The most common range of patterns likely to be read from Tweed fish.
  13. 13. River Age: 1 2 2 . ( The .shows that the number is before the transition to the sea) 2 River Winters, with a straight and abrupt transition from river to sea
  14. 14. River Age: Run out 1 1 + . One River Winter and a gradual transition to marine growth, “Run Out”
  15. 15. Juvenile 21 River Age: Run out 1 2 2 + . or 2ro . Two River Winters and Run –out:
  16. 16. A “Summer Grilse” – with 1Sea Winter, and Open, plus, growth right to the the edge 1SW . 1 + + O Open (“Summer”) growth at the edge Sea Age:
  17. 17. Growth Checks: the main problem in scale reading This is not a Winter band, it is a growth “Check”. It is weaker than a Winter band – it is narrower and is not continuous 1st Sea-Winter (.1) Open, Summer Growth (+) ?
  18. 18. s An “Autumn Grilse” – with 1 Sea Winter, open, plus growth and then Closing growth at the edge 1SW . 1 + + Closing growth at the edge cl Sea Age:
  19. 19. The same pattern, but as this fish was caught in Spring, the two Winter bands of closed growth represent two full years = a Spring Salmon, .2 This is why the date a fish is caught is important 1SW 2SW
  20. 20. Three closed bands, but without a date could be an Autumn Salmon ( . 2+cl ) or a Spring Salmon ( .3)