Introduction to Salmon Scale Reading Here is part 2 of 2 featuring 'problem scales', erosion, spawning marks and smolts. Developed with thanks to The Tweed Foundation

1. Introduction to Salmon Scale Reading
• “Problem” scales
• Erosion
• Spawning marks
• Smolts.

2. Not all scales conform to these simple patterns
• Two examples of “problem” scales.

3. Where is there a
winter?
18 /08 /2006
3lb, 50cm.

4. 26 /09 /2007
5lb, 59cm.
Split winter - (Winter checks )
- Where’s the actual Winter band?
?
?
?

5. Erosion
• When salmon return to fresh water they
stop feeding
• To provide energy, material is reabsorbed
from body tissues, including the roots of
the scales
• The degree of erosion can show how long
a fish has been in fresh water – but some
can occur at sea after feeding stops.

6. 29 /09 /2007
4.5lb 61cm
This means this fish has been in fresh water for some time.
Half of the edge of this scale has been eroded away
1SW
2SW

7. 29 /09 /2007
10lb 74 cm
This 70% eroded scale
shows that this fish probably
entered the river as a Spring
Salmon, though caught in
September,
1SW
2SW

8. 100% erosion makes
this scale impossible
to read fully. the scale
is no longer complete
to the edge
10 /11 /2007
14lb 86cm.
1SW
2SW

9. When scale reading, Erosion is the first thing to look for and assess as it
tells you whether you are dealing with a fish newly in the river and
therefore directly reflecting the part of the season during which it was
caught (Spring, Summer or Autumn) or whether it is from earlier in the
year – e.g. a Spring or Summer fish caught in Autumn and is not
therefore reflecting the time at which it was caught.

10. Spawning marks
• If a fish spawns in the river and returns to
the sea to recondition, evidence of
spawning remains on its scales.

11. 04 /09 /2007
9.25 lb 72cm.
The spawning mark
(SM) is the old eroded
edge, with new marine
growth beyond it
The SM has replaced the old edge of the scale: it could have been open or closed or
a full winter band at the end. All that is definite is that there was summer growth
before it, which is denoted as “+”
. 1.
1SW
+
+
SM
SM. ++

12. Smolts
• Scales can be collected from smolts and
read in the same way as other life cycle
stages

13. 16 April 2007
131mm
2+ . With a lot of + growth (= “run-out” on the adult scale)

14. 16 April 2007
127mm
2. With no + growth (or very little) but average smolt length

15. 16 April 2007
101mm
2. With no + growth (or very little) but a small smolt

16. 11 April 2007
85mm
1+. :with a lot of+ growth but a very small smolt

17. Warning
We should remember that information should
be read from the image not that we should
force information onto the image to match
what we would expect for a given size of
fish or time of year.
Always be aware of which way information is
actually flowing – it should be from the
screen, not to it.
It is better to have an “unreadable” category
rather than have forced interpretations in
your data.