ANDY WALKER

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?’

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.

Ist sea

winter

SCOTTISH EAST

COAST NORTH

OF TWEED

TYPICAL R. EARN 1kg

MAIDEN SEA TROUT

aged 2.1+

2 parr

years

RIVER SPEY NETS SEA

TROUT 24 May1976

46cm 4.1+

56cm 2.1+3SM+

(run-out?)

Missing

centre

Spawning

marks (5)

AN OLD

SPEY SEA

TROUT

R.GRANDE

SEA TROUT

Feb 1997

66cm 11lbs

3.2+sm+

With run-

out?

RIO GRANDE

FEB 1997

SEA TROUT

82cm 17.5 lbs

3.1+2sm+?

• 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

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

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

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

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)

Decline in frequency with sea age

Based on long-term

scale collections