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.