This document discusses the importance of scale reading for understanding salmon fisheries management on the River Tweed. Scale reading allows analysis of catch composition and trends over time. It shows which stocks and age classes are being caught each year and how catches depend on particular age groups. Scale reading data is collected and analyzed to understand geographical and temporal patterns. This helps assess current stock status by comparing to long-term trends. An example shows how scale reading revealed cycles in low spring salmon catches were linked to fewer fish of a particular age class five years prior, related to poor spawning conditions. Scale reading provides important insights for fisheries management.

1. SCALE READING FOR FUN & PROFIT

2. WHY DO WE READ SCALES ON THE TWEED ?
INPUT 2D: ANALYSE THE CATCH COMPOSITION AND TRENDS OF EACH
STOCK OF SALMON
Rationale: Historic records show how the sizes and run timings of the fish have varied greatly
over the years and give the context for assessing the present day situation. Establishing long-
term trends shows if there are large-scale changes that cannot be countered, though could be
managed. Variation outside known parameters from the past could be a warning sign of
problems
Analysis of catches from year to year for their composition shows which stocks (and areas of
the catchment) are producing the fish that support the fisheries and how the ages and sizes of
fish can change
To understand what is going on

3. AN IMPORTANT PART OF THE TWEED FISHERIES MANAGEMENT PLAN
Policy 2D.2 - Monitor Catch Composition
(a) Continue collection of salmon scales from rod fisheries along the course of the main river and the
larger tributaries and the netting station at Paxton and add the readings to the scales database
(b) Use this database to analyse scale readings to show :-
( i) Geographical and temporal patterns and age structures
( ii) Lengths and weights of fish in relation to area, time of year and age
(iii) The different stocks and age classes of fish being caught. This shows how dependent catches are
on particular ages of fish and how success or failure of particular spawning or smolt years can
be reflected in the catches of the resultant adults.
(iv) Whether high or low catch years are related through generational cycles i.e. whether they are
spaced at intervals of common salmon or grilse ages
( c ) Develop and improve expertise in scale reading through collaboration and co-operation with scale-
reading personnel in Trusts and Agencies
( i)Work to ensure consistency of scale reading interpretation throughout the country
( ii)Analyse Tweed scale reading results with those from other rivers to find differences and
similarities.

4. Scale Reading for Understanding: Example 1 – Tweed Spring Salmon
MIDDLE TWEED: Catches < 1st July
0
500
1000
1500
2000
2500
3000
1970 1973 1976 1979 1982 1985 1988 1991 1994 1997 2000 2003 2006
The change back
from Spring to
Autumn phase was
in 1968 when half
the catches were
again caught in
Autumn.
1998: Spring Salmon “Catch & Release” policy begins
Five yearly patterns of low catches could be seen in the Spring Salmon
catches: but what is the significance of five years, if any ?

5. Scale reading showed that five years is the commonest age of Spring Salmon
TWEED : Percent Spring Salmon that are 2.2
0
10
20
30
40
50
60
70
80
90
100
1970 1973 1976 1979 1982 1985 1988 1991 1994 1997 2000 2003 2006
PERCENT
Low catches reflected lower than usual proportions of five-year old fish:
The cycles of low Spring catches can be traced back to 1982 – so did anything
special happen five years before, in 1977?

6. This is what happened in 1977!
PEAK FLOWS AT LINDEAN, LOWER ETTRICK
0
100
200
300
400
500
600
1962 1967 1972 1977 1982 1987 1992
October November December
Peak flow of 560cumecs on the 31st
October, 1977, the largest ever
recorded on the Ettrick & right in
the middle of the Spring Salmon
spawning season on the most
important tributary
BEFORE THE 1st of JULY
1st JULY to 31st AUGUST
1st SEPTEMBER ONWARDS
RADIO-TRACKING RESULTS - Salmon tagged in the estuary :-

7. Scale reading therefore showed:
1) The five yearly low catches were linked, five years being the age of a
cohort
2) That because so many Spring Salmon were the same age (5 yrs), one low
catch year could lead to another. Too few fish of different ages (4 & 6 yrs
old to “fill the gaps” – and fish of different ages might well spawn in
different areas of the Ettrick (see next slide)
3) Therefore that such low catches indicated when stocks were too low to
fully recruit the next generation i.e. showed when Conservation Limits
were not being met.
4) That reduced catches could therefore be due to past problems, even 20
years before, and not to any immediate cause.

8. FRY LENGTH CATEGORIES (5mm)
UPLAND, COLD: “room” for two cohorts of parr before smolting
TOP OF
ETTRICK
BOTTOM
OF
ETTRICK
AVERAGE FRY LENGTH AVERAGE PARR LENGTH
AVERAGE SMOLT LENGTH
LOWLAND WARM: “room” for only one cohort of parr before smolting
3.2 come from
this zone
1.2 come from
this zone
2.2 come from
this zone
AVERAGE
LENGTHS
OF FRY
AND PARR
IN THE
ETTRICK
WATER
FROM TOP
TO
BOTTOM
6 year olds
5 year olds
4 year olds

9. Scale Reading for Understanding: Example 2 – Sea-trout (Next)