Introduction to Salmon Scale Reading
• “Problem” scales
• Erosion
• Spawning marks
• Smolts.
Not all scales conform to these simple patterns
• Two examples of “problem” scales.
Where is there a
winter?
18 /08 /2006
3lb, 50cm.
26 /09 /2007
5lb, 59cm.
Split winter - (Winter checks )
- Where’s the actual Winter band?
?
?
?
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.
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
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
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
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.
Spawning marks
• If a fish spawns in the river and returns to the sea to recondition, evidence of spawning remains on its scales.
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. ++
Smolts
• Scales can be collected from smolts and read in the same way as other life cycle stages
16 April 2007 131mm
2+ . With a lot of + growth (= “run-out” on the adult scale)
16 April 2007 127mm
2. With no + growth (or very little) but average smolt length
16 April 2007 101mm
2. With no + growth (or very little) but a small smolt
11 April 2007 85mm
1+. :with a lot of+ growth but a very small smolt
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.
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