CM_2001_P_28.pdf (332.9Kb)

1 International Council for

the Exploration of the Sea

CM 2001/P:28

Theme Session: Quality and Precision of Basic Data Underlying Fish Stock Assessment

2000 ICES COORDINATED ACOUSTIC SURVEY OF ICES DIVISIONS IIIa, IVa, IVb AND Via (NORTH)

E J Simmonds¹, B V Svendsen², E Torstensen², P G Fernandes¹, D G Reid¹, A S Couperus⁵, K-J Staehr³, C Zimmermann⁶ and E Götze⁴

1FRS Marine Laboratory, PO Box 101, Victoria Road, Torry, Aberdeen, AB11 9DB, Scotland, UK

2Institute of Marine Research, Bergen, Norway

3Danish Institute for Fisheries Research, The North Sea Centre, Hirtshals, Denmark

4Inst Fischereitechnik, Hamburg

5RIVO, Ijmuiden, The Netherlands

6Inst Seefischerei, Hamburg

ABSTRACT

Six surveys were carried out during late June and July covering most of the continental shelf north of 54^oN in the North Sea and to the west of Scotland to a northern limit of 62^oN. The eastern edge of the survey area was bounded by the Norwegian and Danish coasts, and to the west by the shelf edge between 200 and 400 m depth. The surveys are reported individually in the report of the planning group for herring surveys, and a combined report has been prepared from the data from all surveys. The combined survey results provide spatial distributions of herring abundance by number and biomass at age by statistical rectangle; and distributions of mean weight and fraction mature at age.

INTRODUCTION

Six surveys were carried out during late June and July covering most of the continental shelf north of 54^oN in the North Sea and 56^oN to the west of Scotland to a northern limit of 62^oN.

The eastern edge of the survey area is bounded by the Norwegian, Danish and German coasts, and to the west by the shelf edge at approximately 200 m depth. The surveys are reported individually in appendices Ia-f of the report of the planning group for herring surveys (ICES, 2001). The vessels, areas and dates of cruises are given below and in Figure 1:

Scotia 4-24 July 58-62N 4W-2E

Kings Cross 7-26 July 56- 60N 10-3W

Tridens 19-14 July 54 30-58N 4W-3E

GO Sars 27 June -18 July 57-62N 2W-8E

Dana 26 June - 7 July 56/57N 6E-12E

W Herwig 23 June - 14 July 54-57N 3E-8E

2

maturity stage and mean weights at age are calculated as weighted means of individual survey estimates by ICES statistical rectangle. The weighting applied is proportional to the survey track for each vessel that has covered each statistical rectangle. The data has been combined and estimates of North Sea autumn spawning herring, Western Baltic spring spawning herring, and West of Scotland (VIa_north) herring are shown in Tables 4.1.1a-c.

METHODS

The acoustic surveys were carried out using Simrad EK500 or EY500 38 kHz sounder echo-integrator with transducers mounted on the hull, drop keel and towed bodies. Further data analysis was carried out using BI500, Echoview and Echoann software. The survey track was selected to cover the area giving a basic sampling intensity over the whole area based on the limits of herring densities found in previous years. A transect spacing of 15 nautical miles was used in most parts of the area with the exception of some relatively high density sections east of Orkney, east and west of Shetland, and in the Skaggerak where short additional transects were carried out at 7.5 nm spacing.

The following target strength values have been used to analyse the data:

herring TS = 20 log L - 71.2 dB sprat TS = 20 log L -71.2 dB gadoids TS = 20 log L - 67.5 dB mackerel TS = 21.7 log L - 84.9 dB Combined Acoustic Survey Results

The estimates of North Sea Spawning Stock Biomass (SSB) are 1.7 million tonnes and 8,750 millions herring (Table 1). The North Sea survey is consistent with previous years, giving a total adult mortality of about 0.4 over the last two years, which is similar to the estimates from the assessment (0.5). The SSB rose from 1999 to 2000. The survey also shows exceptional numbers of 1 ring herring (the 1998 year class) in the North Sea, which is consistent with the observation of an exceptionally large year class observed in the MIK and IBTS surveys (ICES, 2000). The acoustic survey indicates that the abundance of this year class is four times the preceding (1997) year class. The numbers and biomass of adult autumn spawning herring can be seen in Figure 2, the numbers at ages 1, 2 and 3+ rings in are given in Figure 3. The spatial distribution of mean weight at age 1 and 2 ring, and fraction mature at 2 and 3 ring, are given in Figure 4. These show considerable spatial trend which is observed each year, with larger more mature fish found in the North and smaller less mature fish found in the south and particularly the eastern North Sea. The relative spatial distributions of adult and juvenile autumn spawning herring can be seen in Figures 5 and 6 respectively. The contours on these figures have been set to contain 10% of the abundance within each contour.

The estimates of Western Baltic spring spawning herring SSB are 190,000 tonnes and 2,000 millions and show a similar pattern to previous years, with a slight increase in SSB over 1999 (Table 2). The numbers and biomass of adult autumn spawning herring can be seen in Figures 7 along with the numbers at ages 1, 2 and 3+ rings. The spatial distribution of mean weight at age 1 and 2 ring, and fraction mature at 2 and 3 ring are given in Figure 8.

The relative spatial distributions of adult and juvenile autumn spawning herring can be seen in Figure 9. The contours on these figures have been set to contain 10% of the abundance within each contour.

3

fish, and shows the high 1995 year class again this year. Total adult mortality shows low mortality (0.14) which is consistent with the 2000 assessment that the stock is lightly exploited (ICES, 2000). The spatial distributions can be seen in the same figures for the North Sea.

REFERENCES

ICES. 2000. Report of the Herring Assessment Working Group for the Area South of 62^°N.

ICES CM 2000/ACFM:10.

ICES. 2001. Report of the planning group for herring surveys. ICES CM 2001/G:02.

Total numbers and biomass of North Sea autumn spawning herring in the area surveyed in the acoustic surveys July 2000, with mean weights and fraction mature by winter ring.

North Sea Numbers (millions)

Biomass Tonnes * 10⁶

Maturity (fraction)

mean weight (g)

0 7570.6 39.2 0.00 5

1 24514.1 1139.6 0.00 46

2 2773.3 326.1 0.66 118

3 1995.9 360.2 0.96 180

4 2871.0 626.6 1.00 218

5 923.5 214.4 1.00 232

6 442.8 115.4 1.00 261

7 243.9 71.9 1.00 295

8 111.5 33.5 1.00 300

9+ 91.9 25.8 1.00 280

Immature 33127.0 1231.1

Mature 8411.5 1682.4

Total 41538.5 2952.8

Total numbers and biomass of Western Baltic spring spawning herring in the area surveyed in the acoustic surveys July 2000, with mean weights and fraction mature by winter ring.

Baltic Numbers

(millions)

Biomass Tonnes * 10⁶

Maturity (fraction)

mean weight (g)

0 0.0 0.0 0.00

1 1509.2 61.4 0.00 40.7

2 1891.1 138.1 0.42 73.1

3 673.6 68.8 0.80 102.2

4 363.9 45.3 1.00 124.4

5 185.7 25.1 1.00 135.4

6 55.6 10.0 1.00 179.2

7 6.9 1.4 1.00 208.8

8 9.6 1.3 1.00 135.2

9+ 0.0 0.0 1.00 0

Immature 2736.0 155.2

Mature 1959.5 196.2

Total 4695.5 351.5

Total numbers and biomass of autumn spawning of West of Scotland herring in the area surveyed in the acoustic surveys July 2000, with mean weights and fraction mature by winter ring.

West Scot Numbers (millions)

Biomass Tonnes * 10⁶

Maturity (fraction)

mean weight (g)

0 0.0 0.0 0.00

1 447.6 27.8 0.00 62

2 316.2 44.6 0.45 141

3 337.1 58.3 0.92 173

4 899.5 164.6 1.00 183

5 393.4 76.4 1.00 194

6 247.6 50.5 1.00 204

7 199.5 42.2 1.00 211

8 95.0 21.1 1.00 222

9+ 65.0 15.0 1.00 230

Immature 648.7 55.5

Mature 2352.0 444.9

Total 3000.8 500.5

Estimates of North Sea autumn spawners (millions) at age from acoustic surveys, 1984-2000. For 1984-1986 the estimates are the sum of those from the Division IVa summer survey, the Division IVb autumn survey, and the Divisions IVc, VIId winter survey. The 1987 to 2000 estimates are from the summer survey in Divisions IVa,b and IIIa excluding estimates of Division IIIa/Baltic spring spawners. For 1999 and 2000 the Kattegat was excluded from the results because it was not surveyed. The 1996 to 1999 surveys have been revised due to changes in methods for calculating mean weight and proportion adult.

Numbers (millions)

Year 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000

Age (ring)

1 551 726 1,639 13,736 6,431 6,333 6,249 3,182 6,351 10,399 3,646 4,202 6,198 9,416 4,449 6,542 24,514 2 3,194 2,789 3,206 4,303 4,202 3,726 2,971 2,834 4,179 3,710 3,280 3,799 4,557 6,363 5,747 2,945 2,773 3 1,005 1,433 1,637 955 1,732 3,751 3,530 1,501 1,633 1,855 957 2,056 2,824 3,287 2,520 4,364 1,996

4 394 323 833 657 528 1,612 3,370 2,102 1,397 909 429 656 1,087 1,696 1,625 1,036 2,871

5 158 113 135 368 349 488 1,349 1,984 1,510 795 363 272 311.0 692.1 982.4 470.1 923.5

6 44 41 36 77 174 281 395 748 1,311 788 321 175 98.7 259.2 445.2 289.5 442.8

7 52 17 24 38 43 120 211 262 474 546 238 135 82.8 78.6 170.3 128.9 243.9

8 39 23 6 11 23 44 134 112 155 178 220 110 132.9 78.3 45.2 51.6 111.5

9+ 41 19 8 20 14 22 43 56 163 116 132 84 206.0 158.3 121.4 82.7 91.9

Total 5,478 5,484 7,542 20,165 13,496 16,377 18,262 12,781 17,173 19,326 13,003 11,220 18,786 22,028 16,104 15,910 35,521

Z(2+/3+) 0.92 0.57 1.02 0.81 0.11 0.11 0.57 0.37 0.74 1.21 0.53 0.43 0.40 0.76 0.60 0.34

Smoothed

Z(2+/3+) 0.78 0.70 0.82 0.46 0.13 0.32 0.44 0.53 0.92 0.91 0.57 0.45 0.50 0.91 0.46 0.22

SSB

(‘000 t) 807 697 942 817 897 1,637 2,174 1,874 1,545 1,216 1,035 1,082 1446.2 1,780 1,792 1,501 1,682

Numbers of Western Baltic Spring Spawning herring at age (winter rings) from acoustic surveys 1991 to 2000.

AGE 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2 1864 2092 2768 413 1887 1005 715 1682 1142.9 1121 3 1927 1799 1274 935 1022 247 787 901 522.7 765.5

4 866 1593 598 501 1270 141 166 282 134.8 183.2

5 350 556 434 239 255 119 67 111 28.3 39.8

6 88 197 154 186 174 37 69 51 2.8 30.3

7 72 122 63 62 39 20 80 31 1.5 2.1

8 10 20 13 34 21 13 77 53 0.7 9.6

Numbers at age and SSB of West of Scotland Autumn Spawning herring at age (winter rings) from acoustic surveys 1987, 1991 to 2000.

Age 1987 1991 1992 1993 1994 1995 1996 1997^# 1998 1999 2000

1 249 100 338 312 74 310 2 760 494 150 441 240 41 220 792 320 1 221 700 487 000 447600 2 578 400 294 484 503 430 750 270 542 080 1103 400 576 460 641 860 794 630 293 900 316200 3 551 100 327 902 210 980 681 170 607 720 473 220 802 530 286 170 666 780 1 265 800 337 100 4 353 100 367 830 258 090 653 050 285 610 450 270 329 110 167 040 471 070 393 800 899 500 5 752 600 488 288 414 750 544 000 306 760 152 970 95 360 66 100 179 050 280 700 393 400 6 111 600 176 348 240 110 865 150 268 130 187 100 60 600 49 520 79 270 126 400 247 600

7 48 100 98 741 105 670 284 110 406 840 169 080 77 380 16 280 28 050 78 900 199 500

8 15 900 89 830 56 710 151 730 173 740 236 540 78 190 28 990 13 850 25 200 95 000

9+ 6 500 58 043 63 440 156 180 131 880 201 500 114 810 24 440 36 770 32 300 65 000

SSB: 273 000^* 452 000 351 460 866 190 533 740 452 120 370300 140 910 375 890 419 500 444 900

Figure 1. Survey area layouts and dates for all participating vessels in the 2000 North Sea and west of Scotland herring acoustic survey. Shaded areas indicate areas of overlap.

-14 -12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12 14

LONGITUDE 53

54 55 56 57 58 59 60 61 62

Scotia 05-26/7/00

G.O.Sars 30/6-18/7/00 Charter

07-26/7/00

Tridens 26/6-14/7/00

W. Herwig 23/6-14/7/00

24/6-5/7/00 Dana

LATITUDE

Figure 2. Numbers and biomass (upper and lower value) of mature autumn spawning herring from combined acoustic surveys in June July 2000.

-10 -8 -6 -4 -2 0 2 4 6 8 10 12

54 55 56 57 58 59 60 61

0.0 0.0 0.0

7.3 24.1 186.4 1.9

8.5 12.3 21.1 107.0 79.8 0.0 0.0 0.0

0.0 43.3 188.2 45.5 100.4 0.0 0.0 0.3 0.0

2.3 14.9 13.3 52.3 0.0 108.6 185.7 74.8 3.2 0.0 0.5 0.1

0.0 30.9 10.2 9.1 7.7 0.0 3.4 48.8 31.1 0.6 0.4 8.1 0.0

0.0 36.3 17.0 15.1 2.9 0.0 8.3 7.7 59.3 45.9 17.0 0.0 3.9 0.0 0.0 0.1 0.2 0.0

28.3 19.1 20.9 5.5 0.0 0.9 4.2 6.6 35.9 31.0 0.0 0.0 0.0 0.0 0.0 0.1 0.2 1.2 0.0

40.3 25.9 1.7 0.0 0.0 0.3 0.4 0.4 12.9 1.4 0.0 0.0 0.0 0.0 0.5 0.5 1.3 1.3 1.2 0.0

40.2 5.8 0.0 0.0 0.6 0.4 3.7 1.3 0.0 0.0 0.0 0.0 0.5 0.5 1.3 0.3 0.0 0.1

56.7 29.0 12.5 0.0 0.9 0.2 1.1 10.4 5.7 3.2 0.0 0.0 0.0 0.0 0.0 0.1 0.0

0.0 7.2 0.0 0.0 0.1 0.0 0.3 4.5 12.4 0.7 0.0 0.0 0.0 0.0 0.1 0.0

10.1 0.0 0.1 12.2 0.5 0.0 0.0 0.0 0.0

3.2 6.9 6.5 0.0 0.0 0.0 0.0 0.0 0.0 0.0

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

28 92 712 7

38 54 95 482 305 0 0 0

0 195 969 205 453 0 0 2 0

12 77 76 228 0 532 837 337 15 0 4 1

0 160 58 52 39 0 26 312 190 4 2 42 0

0 188 98 86 16 0 63 59 373 280 104 0 20 0 0 2 2 0

144 98 117 32 0 7 33 50 225 189 0 0 0 0 0 1 2 13 0

205 132 9 0 0 3 4 4 81 9 0 0 0 0 7 7 15 15 13 0

204 32 0 0 5 4 23 9 0 0 0 0 7 7 15 4 0 1

289 161 68 0 8 2 9 77 43 24 0 0 0 0 0 1 0

0 38 0 0 1 0 3 33 93 5 0 0 0 0 1 0

64 0 1 77 3 0 0 0 0

20 44 41 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0

Figure 3. Numbers at ages 1, 2 3+ ring (upper middle and lower value) of autumn spawning herring from combined acoustic surveys in June July 2000.

-10 -8 -6 -4 -2 0 2 4 6 8 10 12

54 55 56 57 58 59 60 61

0.0 0.0 0.0

27.1 89.9 695.5 7.2

34.4 49.5 86.2 436.7 297.8 0.0 0.0 0.0

0.0 176.7 758.6 185.6 409.8 0.0 0.0 2.8 0.5

12.0 76.3 63.3 209.3 0.0 439.4 758.1 305.5 13.3 0.0 5.4 0.9

0.0 158.6 48.8 43.1 34.1 0.0 5.9 171.7 123.2 2.5 1.7 32.8 0.2

0.0 186.2 80.9 71.6 13.6 0.0 14.4 13.5 218.5 181.7 67.3 0.0 16.0 0.0 0.2 0.3 0.1 0.0

144.4 97.4 101.5 25.6 0.0 1.9 10.7 11.5 132.4 122.7 0.0 0.0 0.0 0.0 0.0 0.2 0.4 2.8 0.0

205.1 131.7 8.7 0.0 0.0 1.7 2.1 2.3 59.7 6.3 0.0 0.0 1.6 1.0 0.2 0.2 2.6 2.6 2.8 0.0

204.6 30.4 0.0 0.0 3.0 2.1 17.1 6.3 0.0 0.0 0.0 0.0 0.2 0.2 2.6 0.6 0.0 0.0

289.0 150.7 56.7 0.0 1.7 0.4 2.0 30.2 16.7 9.4 0.0 0.0 0.0 0.0 0.0 0.0 0.0

0.0 37.0 0.0 0.0 0.2 0.0 0.6 13.0 36.3 2.1 0.0 0.0 0.0 0.0 0.0 0.0

75.5 0.0 0.6 91.4 3.8 0.0 0.0 0.0 0.0

23.8 52.0 49.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

0.7 2.4 18.3 0.2

3.3 4.7 9.3 47.0 7.8 0.0 0.0 0.0

0.0 19.0 217.3 20.0 44.1 0.0 0.0 7.9 1.4

0.4 2.7 31.3 20.0 0.0 95.9 81.5 32.9 1.4 0.0 15.4 2.6

0.0 5.6 20.9 21.3 10.6 0.0 23.5 153.6 68.9 1.4 0.5 10.3 0.1

0.0 6.6 42.8 35.3 6.7 0.0 57.5 53.9 165.7 101.6 37.7 0.0 5.0 0.0 0.3 2.6 3.7 0.0

1.4 2.4 41.3 24.5 0.0 6.7 30.7 45.7 99.9 68.6 31.0 12.8 4.2 0.0 0.0 1.7 3.4 21.1 0.0

2.0 1.3 1.2 0.0 0.0 5.6 7.2 7.9 174.3 18.3 15.7 3.5 37.3 22.7 12.9 12.9 24.9 24.9 21.1 0.7

2.0 4.1 0.0 0.0 10.2 7.2 50.0 18.3 0.0 0.0 0.0 0.0 12.9 12.9 24.9 6.2 0.7 1.4

2.8 20.6 37.0 0.0 27.1 6.0 32.1 96.3 53.4 30.0 0.0 0.2 0.0 0.9 0.7 1.4 0.3

0.0 1.9 0.2 0.0 2.9 0.0 10.0 41.4 115.6 6.6 0.0 0.0 0.0 1.3 1.4 0.7

34.3 0.0 0.3 41.5 1.7 0.0 0.0 0.0 0.5

10.8 23.6 22.3 0.0 0.0 0.1 0.0 0.0 0.0 0.0

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

0 0 1 0

0 1 1 6 1 0 0 0

0 2 31 2 5 0 0 7 1

0 0 1 2 0 21 10 4 0 0 13 2

0 0 0 0 0 0 95 283 10 0 0 0 1

0 0 57 1 0 0 232 217 221 15 6 0 0 86 5 29 112 0

0 0 35 337 0 72 702 201 131 10 1523 629 53 18 2 19 39 435 0

0 0 0 0 0 164 209 231 134 14 376 83 307 187 341 344 924 924 435 316

0 0 0 0 298 209 38 14 0 14 0 0 515 453 924 231 316 633

0 0 3 0 425 93 503 127 70 40 43 48 106 217 316 633 158

0 0 13 0 45 0 156 55 153 9 0 237 3 679 633 316

50 0 0 60 2 4 435 341 427

16 34 32 0 0 0 98 205 11 100

0 154 3118 0 111 35 196 0 0

0 0 0 0 88 10 1 4 16

Figure 4. Mean weight at ages 1, 2 ring (upper left and right value) and fraction mature at ages 2, 3 ring (lower left and right values) of autumn spawning herring from combined acoustic surveys in June July 2000.

+ + +

0.93 0.93 0.93 0.93

0.97 0.97 0.97 0.97 0.93 + + +

+ 0.97 0.97 0.97 0.97 + + 0.14 0.14

0.41 0.41 0.49 0.93 + 0.97 0.97 0.97 0.97 + 0.14 0.14

+ 0.41 0.49 0.49 0.57 + 0.85 0.92 0.97 0.97 0.9 0.9 0.03

+ 0.41 0.46 0.49 0.49 + 0.85 0.85 0.93 0.97 0.97 + 0.9 + 0.03 0.5 0.5 +

0.62 0.45 0.41 0.29 + 0.81 0.72 0.85 0.93 0.97 0 0 0 + + 0.5 0.5 0.5 +

0.62 0.62 0.58 + + 0.39 0.39 0.39 0.12 0.12 0 0 0 0 0.5 0.5 0.5 0.5 0.5 0.5

0.62 0.58 + + 0.39 0.39 0.12 0.12 + 0 + + 0.5 0.5 0.5 0.5 0.5 0.5

0.62 0.58 0.35 + 0.23 0.23 0.23 0.5 0.5 0.5 0.3 0.3 + 0.3 0.5 0.5 0.5

+ 0.59 0.2 + 0.23 + 0.23 0.5 0.5 0.5 0.3 + + 0.3 0.5 0.5

0.13 + 0.13 0.13 0.13 + + + 0.3

0.13 0.13 0.13 + + 0.62 + + + +

+ + + + 0.3 + + + +

+ + + + + + + + +

-10 -8 -6 -4 -2 0 2 4 6 8 10 12

54 55 56 57 58 59 60 61

149 149 149 149

158 158 159 159 149 + + +

+ 159 140 159 159 + + 98 98

157 157 146 157 + 143 159 159 159 + 98 98

+ 157 146 146 148 + 116 127 135 135 158 158 84

+ 157 141 146 146 + 116 116 129 135 135 + 158 + 83 83 81 +

158 157 130 120 + 114 110 116 129 135 86 86 82 + + 83 83 82 +

158 158 152 + + 87 87 87 100 100 78 78 70 70 80 80 78 78 82 73

158 152 + + 87 87 100 100 + 42 + + 80 80 78 78 73 73

158 152 132 + 89 89 89 103 103 103 81 81 + 81 73 73 73

+ 153 106 + 89 + 89 103 103 103 81 + + 81 73 73

92 + 92 92 92 + + + 81

92 92 92 + + 126 + + + +

+ + + + 81 + + + +

+ + + + + + + + +

94 94 94 94

88 88 88 88 94 + + +

+ 88 83 88 88 + + 80 80

+ + 87 88 + 77 88 88 88 + 80 80

+ + 87 87 87 + 66 67 82 82 60 60 80

+ + 62 87 87 + 66 66 68 82 82 + 60 64 73 50 45 +

+ + 76 60 + 54 50 65 68 82 45 45 49 64 61 50 50 45 +

+ + + + + 48 48 48 73 73 58 58 58 58 48 48 48 48 45 39

+ + + + 48 48 73 73 + 37 + + 49 48 48 48 39 39

+ + 81 + 50 50 50 68 68 68 35 35 35 35 39 39 39

+ + 58 + 50 + 50 68 68 68 35 35 34 35 39 39

52 + 52 52 52 35 35 35 35

52 52 52 + + 35 35 35 35 35

+ 43 43 + 35 35 35 + 35

+ + + + 35 35 35 34 34

+ + +

1 1 1 1

1 1 1 1 1 + + +

+ 1 1 1 1 + + 0.3 0.3

0.92 0.92 0.88 1 + 1 1 1 1 + 0.3 0.3

+ 0.92 0.88 0.88 0.93 + 1 1 1 1 1 1 +

+ 0.92 0.87 0.88 0.88 + 1 1 1 1 1 + 1 + + 0.85 0.85 +

0.94 0.93 0.83 0.77 + 1 1 1 1 1 + + + + + 0.85 0.85 0.85 +

0.94 0.94 0.95 + + 0.42 0.42 0.42 1 1 + + 0 0 0.85 0.85 0.85 0.85 0.85 +

0.94 0.95 + + 0.42 0.42 1 1 + + + + 0.85 0.85 0.85 0.85 + +

0.94 0.95 0.88 + 0.7 0.7 0.7 0.96 0.96 0.96 + + + + + + +

+ 0.95 + + 0.7 + 0.7 0.96 0.96 0.96 + + + + + +

0.51 + 0.51 0.51 0.51 1 + + +

0.51 0.51 0.51 + + + + + + +

+ + + + + + + + +

+ + + + + + + + +

Figure 5. Relative spatial distribution of mature autumn spawning herring from combined acoustic surveys in June July 2000. 10% of the population is contained within each contour. Contour colour indicated density.

-10 -8 -6 -4 -2 0 2 4 6 8 10 12

54 55 56 57 58 59 60 61

Figure 6. Relative spatial distribution of juvenile autumn spawning herring from combined acoustic surveys in June July 2000. 10% of the population is contained within each contour. Contour colour indicated density.

-10 -8 -6 -4 -2 0 2 4 6 8 10 12

54 55 56 57 58 59 60 61

Figure 7. Numbers and biomass (upper and lower value left panel) of mature Western Baltic spring spawning herring, numbers at ages 1, 2 3+

ring (upper middle and lower value from right panel) of Western Baltic spring spawning herring from combined acoustic surveys in June July 2000.

2 4 6 8 10 12

55 56 57 58 59 60

0 0 0

0 27 5

0 53 9

0 0 1

0 0 6 1 17 19 0

0 3 0 2 0 11 23 117 0

0 0 32 19 48 37 187 187 117 6

0 0 0 0 37 37 187 47 6 12

0 0 0 0 0 6 12 3

0 0 0 0 0 12 6

0 0 0 0 0

0 0 0 0 0 0

0 23 4

0 45 8

0 0 4

0 0 38 7 18 39 0

0 0 0 9 1 12 24 161 0

0 0 91 56 98 68 180 180 161 29

0 0 0 0 68 68 180 45 29 58

0 0 0 0 0 29 58 15

0 0 0 0 0 58 29

0 0 0 0 0

0 0 0 0 0 0

0 0 0

0 0 0

0 0 0

0 0 0 0 4 13 0

0 0 0 0 0 3 6 55 0

0 0 0 0 16 16 51 51 55 109

0 0 0 0 16 16 51 13 109 218

0 0 0 0 0 109 218 54

0 0 0 0 0 218 109

0 0 0 0 0

0 0 0 0 0 0

2 4 6 8 10 12

55 56 57 58 59 60

0 0 0

0 3 1

0 6 1

0 0 0

0 0 1 0 3 3 0

0 0 0 0 0 2 3 18 0

0 0 0 0 7 6 28 28 18 1

0 0 0 0 6 6 28 7 1 3

0 0 0 0 0 1 3 1

0 0 0 0 0 3 1

0 0 0 0 0

0 0 0 0 0 0

0 21 4

0 41 7

0 0 0

0 0 4 1 25 37 0

0 3 0 1 0 17 33 188 0

0 0 28 17 76 68 263 263 188 20

0 0 0 0 68 68 263 66 20 40

0 0 0 0 0 20 40 10

0 0 0 0 0 40 20

0 0 0 0 0

0 0 0 0 0 0

Figure 8. Mean weight at ages 1, 2 ring (upper left and right value) and fraction mature at ages 2, 3 ring (lower left and right values) of autumn spawning herring from combined acoustic surveys in June July 2000.

+ + +

+ 0.14 0.14

+ 0.14 0.14

+ + 0.03

+ + 0 0.03 0.5 0.5 +

+ + + 0 0.01 0.5 0.5 0.5 +

+ + 0 0 0.35 0.5 0.5 0.5 0.5 0.5

+ 0 + + 0.5 0.5 0.5 0.5 0.5 0.5

+ + + + + 0.5 0.5 0.5

+ + + + + 0.5 0.5

+ + + + +

+ + + + + +

2 4 6 8 10 12

55 56 57 58 59 60

+ 98 98

+ 98 98

+ + 84

+ + 77 83 75 72 +

+ + + 77 72 75 75 73 +

+ + 70 70 72 72 76 76 73 62

+ 42 + + 72 72 76 76 62 62

+ + + + + 62 62 62

+ + + + + 62 62

+ + + + +

+ + + + + +

+ + +

+ + +

+ + +

+ + + + 52 48 +

+ + + + + 52 52 47 +

+ + + + 53 53 48 48 47 38

+ + + + 53 53 48 48 38 38

+ + + + + 38 38 38

+ + + + + 38 38

+ + + + +

+ + + + + +

+ + +

+ 0.3 0.3

+ 0.3 0.3

+ + 0.22

+ + 0.33 0.2 0.85 0.85 +

+ 1 + 0.33 0.61 0.85 0.85 0.85 +

+ + 0 0 0.8 0.85 0.85 0.85 0.85 0.85

+ + + + 0.85 0.85 0.85 0.85 0.85 0.85

+ + + + + 0.85 0.85 0.85

+ + + + + 0.85 0.85

+ + + + +

+ + + + + +

Figure 9. Relative distribution of numbers of mature (left panel) and juvenile (right panel) Western Baltic spring spawning herring, from combined acoustic surveys in June July 2000.

2 4 6 8 10 12

55 56 57 58 59 60 61

2 4 6 8 10 12

55 56 57 58 59 60 61