Deconstructing Tweed Sea-trout

by scale reading

Length frequencies of angling samples of Tweed Sea-trout

FIRST TIME SPAWNERS

REPEAT SPAWNERS

UNIMODAL

BIMODAL

1) Caught on the R. Till

2) Caught on the Tweed

upstream of the R. Till

The common sizes of Sea-trout caught on the Tweed are

the uncommon ones on the Till. Why?

TILL: Sea-trout sizes and ages (first time spawners only)

TILL: Small (40-50 cms)

1 Sea-winter early

summer (April & May)

Sea-troutTILL: Larger (55cms+)

2 Sea-winter Spring Sea-

trout. The summer fish that

follow on are much the same

size

UPPER TWEED FISH: Almost all 1Sea-

winter Summer and Autumn caught fish –but

larger than the Till’s because return July to

November rather than in April and May

UPPER TWEED :

Sea-trout sizes and ages

(first time spawners only)

MIDDLE TWEED FISH: Almost all 1Sea-

winter Summer fish –but, again, larger than

the Till’s because return July to September

rather than April and May

MIDDLE TWEED :

Sea-trout sizes and ages

(first time spawners only)

More small fish than for the Upper Tweed

These differences between

Upper and Middle Tweed

may well be due to the latter

catching fish from the R.

Ettrick which turn in to that

tributary and do not go on to

the upper river.

SCALE EROSION: often overlooked as data

Catching fresh

Catching stale

TILL: The source of the smaller Sea-trout

TILL: Small (40-50 cms)

1 Sea-winter early

summer Sea-trout

The Whitling of the Till

“... Is the whitling taken in any streams in this part of the country except the Till?

.....Not in Northumberland, that I am aware of, but it is caught in the Whitadder...

(Oliver, S., 1834 : Scenes and Recollections of Fly-fishing in Northumberland)

The

College

Burn

THE COLLEGE BURN: Whitling Home Ground

Bowmont Water

River Till

Hethpool Linns Not passable by Salmon

TWEED

The Cheviot

The College Burn

THE COLLEGE BURN: Whitling Home Ground

Their different behaviour means the opportunity to study them in their home area as a

biological unit

Only around

The Cheviot

are adult Sea-

trout electric-

fished in small

hill burns from

June onwards

20th June 1997:

Right up in the hills, but still silvery

By August & September, completely brown

“The herds have a curious way of poaching here, as well as in the College and other

small burns about the neighbourhood.

They go with a heavy mallet, and having driven the trout under the large stones they

strike the stone a smart blow. The jar somehow stuns the trout and they are easily picked

up.

This is said to be a very destructive method of poaching, but I have never seen it in

operation.”

(Francis, F., 1874 : By Lake and River: An Angler’s Rambles in the North of England and Scotland)

Their very tight size-range is obvious, the only outliers being fish of 280-300mm that are Blacktail

(=Finnock) spawners, fish that return to fresh water in the same year that they smolted

79.7% of them are between 380 and 460mm (15” to 18”)

50% of them are from 400 to 440mm (15½” to 17¼”) – half

the population within 40mm (1½”) of each other in size.

I was out yesterday morning below Ford, and out of the seven that I caught, there

were only two that were less than fourteen inches (360mm), and each of these

measured a foot (300mm) ”

(Oliver, S., 1834 : Scenes and Recollections of Fly-fishing in Northumberland)

There is no doubt that some Whitling spawn as Blacktails: not only were a few

found during the sampling work (photo), scales read from “normal” fish showed

that they had spawned during their first post-smolt Winter, instead of staying in the

sea like the majority (the “spawning mark” is indicated by the red arrow – on

“normal” fish this is where the First Sea-winter Band is found)

Only 9% return to spawn for a second time (Orange)

1.7% for a third time (Green)

TABLE A: COLLEGE BURN WHITLING: Population Characteristics

Smolt ages S1 S2 S3 S4

0 77.7% 21.7% 0.5%

Winters at sea before first return 0SW* 1SW 2SW 3SW

3.0% 97.0% 0 0

Repeat Adult Spawnings (1) 1sm 2sm 3sm 4sm

9.3% 1.7% * *

* Fish that return to the river in the same year that they smolted, "Blacktails"

(1) Fish that return to spawn for a second or third time

TABLE A: COLLEGE BURN WHITLING: Population Characteristics

Total ages 3yrs 4yrs 5yrs 6yrs

71.6% 23.3% 5.1% 0

Life histories 2.1+ 3.1+ 2.1+sm+ Other

69.9% 18.2% 5.1% 6.8%

Size Range <349mm 350-99 400-49 450-99 >500mm

0.62% 20.00% 59.38% 17.54% 2.46%

Sex ratio Male Female

29.15% 70.85%

The origins of Sea-trout caught in Tweed river (Paxton) and estuary (Gardo)

nets

Tillmouth, R.

Tweed

16lb Sea-trout,

18th June 2007

Tillmouth, R.

Tweed

16lb Sea-trout,

18th June 2007

Upper Tweed 1993-11-11

20lbs 6 oz

Date of Capture lbs oz Age Date of Capture lbs oz Age

1963.07.06 15 8 2.3+ 1963.07.17 14 0 2.2+

1963.07.08 10 4 2.2+ 1963.07.17 14 0 2.3+

1963.07.08 12 0 3.2+ 1963.07.26 16 10 2.2+

1963.07.08 13 0 3.2+ 1963.07.27 15 8 2.3+

1963.07.08 17 0 2.2+ 1963.08.05 17 3 2.2+

1963.07.16 21 0 2.2+ 1963.08.28 16 0 2.2+

1963.07.16 23 8 2.2+ 1963.09.06 18 0 2.2+

1963.07.17 12 0 2.2+

I.J.R. Hynd, The Salmon & Trout Magazine, Sept. 1964