Talk provided at the Institute of Fisheries Management (IFM) / Scottish Fisheries Co-ordination Centre (SFCC) workshop on scale reading, held at The Tweed Foundation, 26/03/2015.

1. ANDY WALKER

2. SOME PROBLEMS OF INTERPRETATION
• Multiple provenances influence growth
• Missing centres – early life lost
• ‘Run-out’ or an extra year in fresh water?
• ‘Finnock’ checks - or annuli?
• Scale erosion - losing years?
• Defining ‘spawning marks?’

4. Manual on Sea Trout Ageing, Digital Scale
Reading and Growth Methodology Jan-2011 (edited by R.
Poole)
This publication was prepared by the CSTP Workshop on chaired by
Dr. Russell Poole and held in the Marine Institute, Newport, Co. Mayo,
Ireland from 24-28 May 2010.
This illustrated manual of best practice and scale images is intended as
a guide to standard protocols for sampling sea trout scales, and age and
growth determination from scales, as used in the Celtic Sea Trout
Project. The CSTP and the workshop were part funded by the Interreg
IVA Ireland and Wales Cross-Border programme.

6. Ist sea
winter
SCOTTISH EAST
COAST NORTH
OF TWEED
TYPICAL R. EARN 1kg
MAIDEN SEA TROUT
aged 2.1+
2 parr
years

8. RIVER SPEY NETS SEA
TROUT 24 May1976
46cm 4.1+
56cm 2.1+3SM+
(run-out?)

9. Missing
centre
Spawning
marks (5)
AN OLD
SPEY SEA
TROUT

10. R.GRANDE
SEA TROUT
Feb 1997
66cm 11lbs
3.2+sm+
With run-
out?

11. RIO GRANDE
FEB 1997
SEA TROUT
82cm 17.5 lbs
3.1+2sm+?

12. • Profusion of freshwater lochs, all very
nutrient-deficient
• Some reached by sea trout and salmon
• Others only have brown trout
• Old smolts and moderate marine growth
• No sign of lice problem

13. READING SEA TROUT SCALES
• Build up knowledge of the normal pattern of growth and
migration from realistic sampling and marking studies
• Use examples of trout of “known age”(probably tag recaps)
• “Easier” readings help show where winters are expected
• Back-calculations allow mean length at ages, but older fish
with scale erosion may give poor results
• Repeat some readings for consistency

14. SMOLT AGE OF SEA TROUT
Place Region Method Years N Smolt Age
Annan* Solway Rd,Net 81,82,98,99 1239 1.9
Nith Solway Rd 80,81 436 2.1
Etive West Rd 90 29 2.1
Ayrshire Clyde Rd 81,82 335 2.1
Tweed* East Net 81-83,90-92 2450 2.2
Tay* East Net 81 78 2.2
Earn East Rd,El. 80-86,90-92 2205 2.3
Ythan* N.East Rd,Net 91,93 45 2.3
Cree/Fleet Solway Rd 81 37 2.4
Esks N.East Rd,Net 90,91 107 2.4
Don N.East Rd 90,91 48 2.4
N Skye N.West Rd 79,80,90,92 255 2.4
Mull West Rd 82,84 85 2.4
Dee* N.East Net 84 873 2.5
Spey* Mor.Firth Net 76 608 2.5
SpeyMFSTP Mor.Firth Rd,El. 2003-10 147 2.5
Ullapool N.West Rd 97,98 85 2.5
Dundonnell N.West Rd,Fyke 97,98 165 2.6
Shieldaig N.West El,Tp 92-99 110 2.6
S Uist O.Hebrid. Rd 94 25 2.6
Inverie* West Net 80,82 177 2.6
Laxford N.West Rd,Net 91,95 59 2.7
S Skye N.West Rd,Net 84,90-92 140 2.7
Eachaig Clyde Rd,Net 91,98,00 201 2.7
Clair/Coulin N.West Rd,Net,Tp 84,91-96 265 2.8
R Shiel West Rd,Net 90-93 99 2.9
S Harris O.Hebrid. Rd,Net 82,84,96 199 3.0
Hope North Rd 2000-01 147 3.2
Gruinards N.West Rd 78,90-93 124 3.2
Ewe Syst. N.West Rd,El,Net 84,90-98 3330 3.2
R Ewe N.West Rd,Net 90,91,97 406 3.2
Squod N.West El,Tp 90-97 100 3.2
Maree N.West Rd,Net,Tp 91-98 384 3.3
Lomond Clyde Rd 81 44 3.5
Hope North Rd 90-92 1225 3.6
*Commercial nets,
Rod, Research Seine,
Fyke net, or Trap
Electrofishing
VALUE OF BIG SCALE
COLLECTIONS

15. SCOTTISH SEA TROUT MEAN LENGTH (MM) AT SEA AGE (WINTERS)
(Numbers in brackets)
SEA AGE
PLACE YEARS 0+ 1+ 2+ 3+ 4+ 5+ 6+ 7+ 8+ 9+ 10+ 11+
Annan* 81,82,98,99 328(52) 394(906) 440(238) 498(35) 560(8)
Nith 80,81 337(9) 438(304) 506(115) 557(7) 610(1)
Cree/Fleet 81 335(2) 373(26) 451(8) 630(1)
Tweed* 81-83,90-92 414(37) 470(1967) 552(425) 570(50) 623(8)
Tay* 81 360(3) 425(48) 459(18) 500(9) 500(3)
Earn 80-86,90-92,03 326(97 437(1555) 492(423) 535(105) 585(105) 598(4) 713(2)
Esks 90,91 245(100) 417(3) 588(4)
Dee* 84 408(728) 446(103) 507(30) 520(8) 618(2) 605(1) 650(1)
Don 90,91 254(38) 404(10)
Ythan* 91,93 260(11) 429(32) 545(2)
Spey* 76,90,91,03-10 291(13) 448(425) 497(109) 543(37) 595(16) 590(7) 630(2)
Hope 90-92 308(53) 366(694) 424(289) 485(93) 517(32) 539(21) 564(6) 595(2) 635(2)
Hope 2001-02 402(63) 441(52 490(16) 539(7) 573(3)
Hope 90-91 308(53) 369(757) 427(341) 486(109) 521(39) 543(24) 564(6) 595(2) 635(2)
Laxford 91,95 242(48) 378(6) 395(3) 434(2)
Ullapoolletc 97,98 196(96) 287(14) 354(9) 415(1)
Dundonnell 97,98 201(128) 368(29) 381(5) 523(3)
Gruinards 90-98 225(99) 326(17) 388(7) 550(1)
Ewe System 1980 280(33) 340(321) 406(305) 457(169) 513(140) 554(78) 576(40) 607(18) 619(10) 690(3) 650(3) 668(2)
Ewe System 90-99 245(275) 304(437) 366(232) 409(70) 430(27) 462(9) 510(4) 586(1)
R Ewe 90,91,97 236(113) 294(231) 359(52) 406(6) 481(2) 508(1) 500(1)
Maree 91-98 248(114) 314(128) 370(97) 410(28) 435(13) 524(3) 531(1)
Clair/Coulin 91-98 257(48) 320(78) 366(83) 409(36) 416(12) 416(5) 505(2) 586(1)
Squod 90-97 258(36) 332(45) 399(17) 420(1) 500(1)
Shieldaig 92-99 268(76) 302(27) 361(5) 468(1) 368(1)
S Harris 82,84,96 291(53) 377(105) 411(31) 558(2) 483(5) 533(2) 680(1)
S Uist 94 425(4) 512(17) 580(3) 558(1)
N Skye 79,80,90,92 273(163) 361(85) 438(4) 505(2) 510(1)
S Skye 84,90-92 287(93) 369(41) 371(2) 530(4)
Etive 90 170(29)
Inverie* 80,82 278(9) 393(62) 467(56) 549(24) 606(15) 633(6) 690(3) 600(1) 62(1)
R Shiel 90-93 236(80) 307(10) 428(8) 452(1)
Mull 82,84 302(5) 408(57) 513(17) 530(2) 627(3) 540(1)
Eachaig 91,98,00 242(70) 381(76) 429(32) 462(13) 549(3) 608(5) 622(2)
Lomond 81 362(17) 457(16) 529(7) 550(3) 580(1)
Ayrshire 81,82 298(149) 428(141) 488(39) 543(3) 650(1) 615(2)
*Commercial nets

16. SEA GROWTH OF
SEA TROUT – based on
long-term scale
collections (AFW)
• Length and weight data
from anglers have to be
reliable
• Too few scales are a
problem (10-15 needed)

17. Decline in frequency with sea age
Based on long-term
scale collections