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(1)International Council for the Exploration of the Sea. CM2002/G02 Addendum. 2001 ICES COORDINATED ACOUSTIC SURVEY OF ICES DIVISIONS IIIa, IVa, IVb AND Via (NORTH) E J Simmonds1, D G Reid1, E Torstensen2, K-J Staehr , C. Zimmermann4 S Jansen4 E Götze6, and A S Couperus5 3. 1. FRS Marine Laboratory, PO Box 101, Victoria Road, Torry, Aberdeen, AB11 9DB, Scotland, UK 2 Institute of Marine Research, Bergen, Norway 3 Danish Institute for Fisheries Research, The North Sea Centre, Hirtshals, Denmark 4 Inst Seefischerei, Hamburg 5 RIVO, Ijmuiden, The Netherlands 6 Inst Fischereitechnik, Hamburg ABSTRACT Six surveys were carried out during late June and July covering most of the continental shelf north of 54oN in the North Sea and to the west of Scotland to a northern limit of 62oN. 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 54oN in the North Sea and 56oN to the west of Scotland to a northern limit of 62oN. 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, 2002). The vessels, areas and dates of cruises are given below and in Figure 1:. Vessel RV Taits M. Sars Scotia Tridens Solea Dana. Dates 10-30 July 29 June – 24 July 3 July – 23 July 25 June – 20 July 29 June – 20 July 30 June – 11 July. Area Surveyed 56- 60N, 4 - 10 W 57- 6130 N, 2 - 8 E 58- 6130 N, 4 W - 2 E 54 30 - 58 N, west of 3 E 54 - 57 N, east of 3 E North of 57 N, east of 6 E. Days 21 27 21 26 22 13. The data has been combined to provide an overall estimate. Estimates of numbers at age, maturity stage and mean weights at age are calculated as weighted means of individual 1.

(2) 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 (VIanorth) herring are shown in Tables 1-3. 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 either BI500, Echoview or 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 sprat gadoids mackerel. TS = 20 log L - 71.2 dB TS = 20 log L -71.2 dB TS = 20 log L - 67.5 dB TS = 21.7 log L - 84.9 dB. A part of the area comprising the five ICES rectangles 45E7, 45E8, 45E9, 45F0 & 45F1 from 4°W to 2°E and latitude 58° to 58°30’ N was not surveyed in 2001 (Fig. 1). While this is not a critical part of the area, an analysis of historical data (1989-2000) indicated that it could contribute up to 5% to the total biomass of the combined survey. On previous occasions, unsurveyed areas were thought to contribute less than 1% of the total and were, therefore, ignored. This year there is therefore the potential for the unsurveyed area to cause bias and so it was deemed important to fill in the area with an estimate of abundance. However, as there is no established method for filling in missing in data, the following three options were examined: 1. An average proportion of abundance in the missing area relative to that of the whole area. In this area the average biomass over the 12-year period is 4.6% of the total biomass. Applying the same proportion gives an estimate for the missing area of 154,000 t in 2001. 2. A median factor of the mean density in the area to the mean density derived from adjacent connecting rectangles (5 north, 5 south and one to the east) over the 12-year period. The median density factor is 1.18 which gives an estimate for the missing area of 211,000 t in 2001. 3. A linear interpolated value from the adjacent 4 connecting rectangles in 2001. This is similar to a kriging estimate for the missing data when the data is on a regular grid. This method gives an estimate for the missing area of 178,000t in 2001. Option 3 lies almost exactly half way between the other two options so has been chosen as a good compromise. This result contributes an additional 5.5% to the overall North Sea abundance for the remaining fully surveyed area. The increases in immature and mature proportions are similar in magnitude at 5.5 and 5.6% respectively. Combined Acoustic Survey Results 2.

(3) The estimates of North Sea SSB are 2.4 million tonnes and 15,000 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 2 years, which is similar to the estimates from the assessment, (0.45). The SSB in the 2001 survey is seen to be rising from 1.7 million tonnes in 2000 (Table 4) to 2.6 million tonnes in 2001. The survey also shows the exceptional numbers of 2 ring herring in 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 2001) and the acoustic survey in 2000. The acoustic survey indicates that the abundance of this year class is still 4 times the preceding (1997) year class (Table 4), which is consistent with the 2000 survey. The system for combining surveys was developed in 1997 recently the historic survey series was entered into the same system. The original surveys were combined with equal weight, later they were weighted by the survey effort. There are small changes to the series due to these differences in the analysis. In addition a calibration error of 9% was found in the Scottish survey following the change in transducer with the new vessel 3 years ago. The new series has been tested in the assessment and there are small differences in the results, an increase of 3% in SSB and a reduction of 2.5% in terminal f for ages 2-6wr. These are not significant changes in a management context. The estimates of Western Baltic spring spawning herring SSB are 100,000 tonnes and 774 millions (Table 2) and show a reduction compared with previous years, with a decrease in SSB from 2000 (Table 5). The West of Scotland survey gives estimates of SSB are 359,000 tonnes and 2,100 millions (Table .3), and shows the high 1995 year class again this year (Table 6), total adult mortality shows higher mortality (0.5) but the mean mortality over the last 3 years has been 0.3 this is consistent with the 2001 assessment that the stock is lightly exploited (ICES 2001). The spatial distributions of the abundance (numbers and biomass) of autumn spawning herring are shown in Figures 2. The distribution of numbers by age are shown in figures 3 for 1 ring, 2 ring and 3+ ring autumn spawning herring. The survey provides estimates of maturity and weight at age, the mean weight at age for 1 and 2 ring herring along with the proportion mature for 2 and 3 ring herring are shown in Figure 4. The spatial distribution of mature and immature autumn spawning herring is shown in Figures 5 & 6 respectively. The spatial distributions of the abundance (numbers and biomass) of Western Baltic spring spawning herring are shown in Figures 7. The distribution of numbers by age are shown in Figures 8 for 1 ring, 2 ring and 3+ ring. The mean weight at age for 1 and 2 ring herring along with the proportion mature for 2 and 3 ring herring are shown in Figure 9. The spatial distribution of mature and immature Western Baltic spring spawning herring is shown in Figures 10 & 11 respectively. REFERENCES ICES. 2001. Report of the Herring Assessment Working Group for the Area South of 62˚N. ICES CM 2000/ACFM:10. ICES. 2002. Report of the planning group for herring surveys. ICES CM 2002/G:02. 3.

(4) TABLE 1 Total numbers and biomass of North Sea autumn spawning herring in the area surveyed in the acoustic surveys July 2001, with mean weights, mean lengths and fraction mature by winter ring. Age (wr) 0 1 2 3 4 5 6 7 8 9+ Immature Mature Total. Numbers Biomass Maturity weight(g) length (cm) 14052.7 113.0 0.00 8 10.6 6837.1 343.0 0.00 50 18.4 12290.5 1561.6 0.77 127 24.1 3082.8 499.1 0.92 162 25.9 1461.9 298.9 1.00 204 27.8 1676.1 381.5 1.00 228 28.7 449.6 106.8 1.00 237 29.0 169.6 43.2 1.00 255 29.7 97.7 27.9 1.00 286 30.6 58.9 17.3 1.00 294 31.6 23979.0 770.1 16197.8 2622.1 40176.8 3392.2. TABLE 2 Total numbers and biomass of Western Baltic spring spawning herring in the area surveyed in the acoustic surveys July 2001, with mean weights, mean length and fraction mature by winter ring. Age (wr) Numbers Biomass Maturity weight(g) length (cm) 0 0.0 0.0 0.00 1 65.5 3.5 0.10 54 19.3 2 641.2 55.6 0.33 87 22.0 3 452.3 51.2 0.52 113.2 23.8 4 153.1 21.5 1.00 140.5 25.2 5 96.4 17.9 1.00 185.2 27.3 6 37.6 6.9 1.00 182.6 27.6 7 23.0 4.8 1.00 206.3 28.4 8 8.5 1.9 1.00 222.2 30.0 9+ 3.4 0.8 1.00 238.8 30.5 Immature 707.0 64.4 Mature 774.0 99.6 Total 1481.0 164.0. TABLE 3 Total numbers and biomass of autumn spawning of West of Scotland herring in the area surveyed in the acoustic surveys July 2001, with mean weights, mean lengths and fraction mature by winter ring. Age (wr) 0 1 2 3 4 5 6 7 8 9+ Immature Mature Total. Numbers Biomass Maturity weight(g) length (cm) 70.3 0.2 0.00 3 7.5 313.1 19.6 0.00 62 19.2 1062.7 139.8 0.93 132 24.3 217.7 37.1 0.99 170 26.4 172.8 32.8 1.00 190 27.3 437.5 86.7 1.00 198 27.7 132.6 28.1 1.00 212 28.2 102.8 22.6 1.00 220 28.6 52.4 12.3 1.00 236 29.2 34.7 8.8 1.00 254 29.9 462.2 28.8 2134.3 359.2 2596.5 388.0.

(5) TABLE 4. 44. 158. 394. 1,005. 3,194. 551. 1984. 17. 41. 113. 323. 1,433. 2,789. 726. 1985. 6. 24. 36. 135. 833. 1,637. 3,206. 38. 77. 368. 657. 955. 4,303. 1,639 13,736. 1986. 11. 23. 43. 174. 349. 528. 1,732. 4,202. 6,431. 1988. 44. 120. 281. 488. 1,612. 3,751. 3,726. 6,333. 1989. 134. 211. 395. 1,349. 3,370. 3,530. 2,971. 6,249. 1990. 112. 262. 748. 1,984. 2,102. 1,501. 2,834. 3,182. 1991. 155. 474. 1,311. 1,510. 1,397. 1,633. 4,179. 6,351. 1992. 178. 546. 788. 795. 909. 1,855. 3,710. 10,399. 1993. 220. 238. 321. 363. 429. 957. 3,280. 3,646. 1994. 110. 135. 175. 272. 656. 2,056. 3,799. 4,202. 1995. 132.9. 82.8. 98.7. 311.0. 1,087. 2,824. 4,557. 6,198. 1996. 78.3. 78.6. 259.2. 692.1. 1,696. 3,287. 6,363. 9,416. 1997. 45.2. 170.3. 445.2. 982.4. 1,625. 2,520. 5,747. 4,449. 1998. 54.3. 138.6. 313.6. 506.4. 1,116. 4,725. 3,078. 5,087. 1999. 120.4. 266.4. 482.5. 1,006. 3,139. 2,156. 2,922. 24,735. 2000. 97.7. 169.6. 449.6. 1,676. 1,462. 3,083. 12,290. 6,837. 2001. Numbers (millions). 52 23. 26,124. 39. 34,928. 0.37. 58.9. 15,107. 0.34. 0.45. 97.2. 16,104. 0.60. 0.22. 2,622. 87.2. 22,028. 0.76. 0.46. 1,833. 121.4 18,786. 0.40. 0.91. 1,534. 158.3 11,220. 0.43. 0.50. 1,792. 206.0 13,003. 0.53. 0.45. 1,780. 84 19,326. 1.21. 0.57. 1446.2. 132 17,173. 0.74. 0.91. 1,082. 116 12,781. 0.37. 0.92. 1,035. 163 18,262. 0.57. 0.53. 1,216. 56 7,542 20,165 13,496 16,377. 0.11. 0.44. 1,545. 43. 0.11. 0.32. 1,874. 22. 0.81. 0.13. 2,174. 14. 1.02. 0.46. 1,637. 20. 0.57. 0.82. 897. 8. 0.92. 0.70. 817. 19. 0.78. 942. 41. 697. 5,484. 807. 5,478. 1987. Estimates of North Sea autumn spawners (millions) at age from acoustic surveys, 1984-2001. 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 2001 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. Estimates in 2000 and 1999 modified following checks in historic series.. Year Age (ring) 1 2 3 4 5 6 7 8 9+ Total Z(2+/3+) Smoothed Z(2+/3+) SSB (‘000 t).

(6) TABLE 5 Numbers of Western Baltic Spring Spawning herring at age (winter rings) from acoustic surveys 1991 to 2001. AGE 2 3 4 5 6 7 8. 1991. 1992. 1993. 1994. 1995. 1996. 1997. 1998. 1999. 2000. 2001. 1864 1927 866 350 88 72 10. 2092 1799 1593 556 197 122 20. 2768 1274 598 434 154 63 13. 413 935 501 239 186 62 34. 1887 1022 1270 255 174 39 21. 1005 247 141 119 37 20 13. 715 787 166 67 69 80 77. 1682 901 282 111 51 31 53. 1143 522.7 134.8 28.3 2.8 1.5 0.7. 1891.1 673.6 363.9 185.7 55.6 6.9 9.6. 641.2 452.3 153.1 96.4 37.6 23.0 11.9. TABLE 6 Numbers at age and SSB of West of Scotland Autumn Spawning herring at age (winter rings) from acoustic surveys 1987, 1991 to 2001. Values in 1999 modified following checks in historic data. Age 1 2 3 4 5 6 7 8 9+ SSB. 1987 249.1 578.4 551.1 353.1 752.6 111.6 48.1 15.9 6.5 273.0. 1991 338.3 294.5 327.9 367.8 488.3 176.3 98.7 89.8 58.0 452.0. 1992 74.3 503.4 211.0 258.1 414.8 240.1 105.7 56.7 63.4 351.5. 1993 2.8 750.3 681.2 653.1 544.0 865.2 284.1 151.7 156.2 866.2. 1994 494.2 542.1 607.7 285.6 306.8 268.1 406.8 173.7 131.9 533.7. 1995 441.2 1103 473.2 450.3 153.0 187.1 169.1 236.5 201.5 452.1. 1996 41.2 576.5 802.5 329.1 95.4 60.6 77.4 78.2 114.8 370.3. 1997 792.3 641.9 286.2 167.0 66.1 49.5 16.3 29.0 24.4 140.9. 1998 1221 794.6 666.8 471.1 179.1 79.3 28.1 13.9 36.8 375.9. 1999 534.2 322.4 1388 432.0 308.0 138.7 86.5 27.6 35.4 419.5. 2000 447.6 316.2 337.1 899.5 393.4 247.6 199.5 95.0 65.0 460.2. 2001 313.1 1062 217.7 172.8 437.5 132.6 102.8 52.4 34.7 359.2.

(7) 63 62 61 60 59 58 57 56 55 54 53 -14. -12. -8. MFV Taits 10-30/7/01. -10. -6. -4. -2. Scotia 03-23/7/01. 2. 4. 6. 8. 29/6-20/7/01. Solea. 29/623/7/01. Michael Sars. Tridens 25/6-20/7/01. 0. 12. Dana 01/7-11/7/01. 10. 14. Figure 1. Survey area layouts and dates for all participating vessels in the 2001 acoustic survey of the North Sea and adjacent areas. Shaded areas indicate areas of overlap..

(8) 62. 61. 60. 59. 58. 57. 56. 55. 54. 53 -10. 0 0 143 26. 311 55. 334 47. 33 5. 38 7. 422 66. 1435 240. 55 11. 34 7. 359 60. 1533 2565 1090 254 425 185. 168 32. 7 1. 0 0. 10 2. 132 25. 616 55. 31 2. 7 1. 2 0. 7 1. 30 3. 75 8. 0 0. 0 0. 2 0. 16 2. 10 1. 28 4. 13 2. 6 1. 0 0. 19 2. 51 13. 131 24 412 72 483 72 108 20. 9 1. 31 2. 58 15. 0 0 367 67 1 0 228 35. 195 18. 55 3. 259 67. 38 7 0 0 1386 175. 159 21. 220 14. 443 115. 225 43 100 13 163 19 253 31. 126 5. 179 46. 0 0 63 9 0 0 307 38. 103 5. 229 11. 0 0. 105 20 41 5 759 90. 93 6. 23 2. 0 0. 0 0 50 7 111 10. 115 12. 71 4. 37 3. 154 24 127 11. 398 42. 85 4. 0 0. 25 2. 84 16 185 24 387 41. 101 4. 0 0. 233 18. 328 45 132 4. 196 9. 18 1. 34 3. 128 24 58 2. 0 0. 4 0. 17 1. 15 3 0 0. 107 11. 382 15. 27 1. 0 0. 163 17. 0 0. 233 18. 99 13. 65 7. 731 80. 49 4. 40 8 112 4. 272 30. 45 3. 43 8 16 2. 63 4. 4 0. 53 2. 29 6. 27 1. 42 2. 133 5. 27 1. 116 22 0 0. 74 3. 1 0. 12 1. 19 4 0 0. 248 10. 2 0. 13 0. 164 26. 0 0. 9 0. 53 2. 152 29. 523 57. 783 85. 0 0. 27 1. 23 4. 970 106. 43 4. 57 2. 12. 27 1. 237 15. 282 26. 9 0. 27 1. 10. 53 2. 60 2. 275 17. 27 1. 8. 0 0. 26 1. 0 0. 1 0. 0 0. 172 7. 0 0. 177 7. 366 14. 86 12. 190 7. 31 1. 7 1. 2 0. 0 0. 0 0. 84 3. 0 0. 1 0. 0 0. 0 0. 3 0. 0 0. 6. 13 1. 4. 229 7. 2. 6 0. 0. 11 1. -2. 165 11. -4. 5 1. -6. 1 0. -8. Figure 2 Abundance of Autumn spawning herring from combined acoustic survey July 2001. Numbers (millions) (upper figure), and biomass (thousands of tonnes) (lower figure).

(9) 62. 61. 60. 59. 58. 57. 56. 55. 54. 53 -10. 0 3 12 0 8 36 0 3 16 0 4 19 0 0 1. 0 23 105 0 7 33 0 20 96 0 27 125 0 1 4. -8. 0 0 0 0 15 69 23 239 67 7 77 15 0 5 24 40 28 97 140 25 0. 0 0 0 0 18 87 7 83 64 14 144 27 0 0 0 2 11 4 0 0 0 10 2 0. -6. 0 40 185 0 52 11 0 45 4 70 48 9 0 0 0. 0 0 0 0 7 31 1 92 8 0 37 3. -4. 0 0 0 0 44 87 1 166 201 0 0 0 0 0 0. 0 0 0 1 180 131 0 81 62 1 247 165 0 0 0 9 141 14 33 71 7 57 1 0. 0 0 0 0 0 0. 0 1 57 0 0 0 4 0 175 2 3 956 1600 575 962 0 2 20 869 12 564 0 0 275 293 58 129 2 0 348 12 133 27 34 1 1146 136 207 91 82 19 574 205 103 83 130 37 1 275 0 75 111 6 1 46 0 13 27 48 0 14 0 1 60 179 1 55 0 3 26 209 0 64 0 3 0 5 1 10 6 71 0 0 0 6 0 0. -2. 0. 0 1 50 0 9 434 1 621 468 0 224 135 0 8 26 0 13 43 0 29 79 19 156 78 38 282 77 16 116 32 53 170 49 189 605 176 135 104 43 0 0 0 0 0 0 229 0 0 0 5 253 0 31 101 0 2 7 0 0 0 0 2 5 0 39 129 46 51 62 11 82 22 10 76 21 143 456 133 102 326 95 20 16 7 0 0 0 0 0 0 6 5 2. 2. 0 2 5 0 1 2 0 2 5 26 4 1 306 217 92 128 31 36 92 1 0 0 0 0 0 0 0 0 0 0 153 488 142 0 0 0 0 0 0. 0 0 1 0 0 0 0 0 0 34 17 24 14 7 10 3 2 5 103 1 0 194 2 0. 2 0 0 1 0 0 3 0 0. 4. 0 0 0 0 1 5 0 3 10 0 11 17 1 4 6 4 3 8 126 0 0 100 1 0 382 0 0 248 0 0 9 0 0 27 0 0 190 0 0 84 0 0 0 0 0. 4 8 7 169 26 24 84 1 0 4 0 0 74 0 0 2 0 0 9 0 0 176 1 0 0 0 0. 6. 46 10 0 66 5 0 18 0 0 42 0 0 1 0 0 57 0 0 172 0 0 31 0 0. 23 8 0 18 5 0 0 0 0 4 0 0 132 1 0 0 0 0 1 0 0 366 0 0. 8. 13 4 0 31 12 2 217 11 1 0 0 0. 27 0 0. 19 7 0 25 9 0 31 16 2 8 4 1. 10. 30 7 0 175 33 25 175 33 25 24 2 0 24 2 0. 24 2 0 48 5 0 48 5 0 48 5 0. 12. 12 1 0 24 2 0. Figure 3 Numbers (millions) of Autumn spawning herring from combined acoustic survey July 2001. 1 ring (upper figure), 2 ring (centre figure), 3+ (lower figure).

(10) 62. 61. 60. 59. 58. 57. 56. 55. 54. + + + +. + + + +. 93 99 93 99 + 172 + 172 93 99 93 99 93 99 + 172 + 172 + 172 + + + +. + + + + 7 23 + 122. + + + + 7 23 + 122. 14 35 33 125. 92 95 91 92 91 92 91 93 90 97 95 143 138147 138147 138148 + 156. + + + +. + + + +. 7 23 14 35 14 35 + 122 33 125 33 125. 7 23 + 122. + + + +. 93 98 93 97 91 92 91 92 91 92 90 97 90 142 90 142 138147 138147 138147 + 156. 93 98 93 98 93 97 92 97 85 97 88 94 90 97 + 143 + 143 90 142 90 141 90 134 138141 + 156. 93 97 81 97 88 97 90 97 90 97 17 100 26 36 90 142 98 130 + 149 + 156 + 156 59 84 61 125. 7 21 + 122. + + + +. 58 99 69 98 78 97 87 97 90 97 49 78 26 36 2 21 93 112 94 120 99 129 99 150 + 156 60 108 61 125 101107. 93 98 94 99 94 100 + 143 74 131 74 131. + + + + + + + +. 57 99 69 98 71 98 69 98 71 93 61 79 33 35 33 35 20 16 39 112 43 120 74 109 74 105 61 118 60 121 63 115 63 115 70 107. 93 98 95 99 94 100 94 100 + 143 85 131 74 131 74 131 93 98 93 98 95 100 95 100 92 100 + 143 + 143 85 129 85 129 55 127. 0 + 41 52. 6 9 76 96. 6 9 76 96. 6 9 76 96. 6 9 71 88. 6 + 74 112. 6 9 28 86. 67 98 67 98 67 98 0 + 0 + 74 101 74 101 74 101 62 109 50 81. 0 + 39 53. + + 39 +. 20 16 15 + 6 + 8 9 6 9 6 9 43 106 50 110 66 113 63 104 74 104 71 88. 4 + 31 71. 4 + 31 71. 0 + 43 58. + + 39 +. + + + +. 0 + 43 56. 0 + 39 53. + + + +. 0 + 45 57. 0 + 39 53. 93 98 93 98 95 100 + 143 + 143 85 129. + + + +. 0 + 39 53. 6 9 28 86. 67 98 67 98 67 98 74 101 74 101 74 101. + + + +. + + + +. 6 + 6 + 5 9 6 9 6 9 46 111 61 113 44 100 74 104 28 86. 4 + 31 71. 67 97 67 97 79 107 79 107. + + 39 +. 93 98 93 98 93 98 56 100 + 143 + 143 + 143 55 123. 34 82 56 81. 0 + 39 53. 6 9 28 86. 4 + 31 71. 0 + 39 53. 6 9 28 86. + + + +. 0 + 39 53. + + 39 +. 12. 6 9 28 86. 93 98 93 98 86 98 + 143 + 143 59 134. + + + +. 0 + 39 53. 0 + 39 53. 10. 6 9 28 86. 67 97 67 97 79 107 79 107. 0 + 39 53. + + + +. 77 100 77 100 67 97 70 99 70 99 79 107. + + 39 +. 34 82 56 81. 0 + 39 53. 4 + 31 71. 0 + 39 53. + + 39 +. + + + +. + + 39 +. + + 39 +. + + + +. 0 + 39 53. 0 + 39 53. + + + +. 0 + 39 53. + + + +. 100100 100100 57 114 57 114. + + 39 +. + + 39 +. + + + +. + + 39 +. + + + +. + + + +. + + + +. 2. 100100 100100 77 100 30 87 30 87 70 99. 0. + + 39 +. + + + +. -2. 8. 6 9 28 86. 34 82 56 81. -6. 6. 4 + 31 71. -8. 4. + + + +. -4. 93 98 93 98 67 100 67 100 + 143 + 143 59 106 59 106. 53 -10. Figure 4 Mean weight & maturity of Autumn spawning herring from combined acoustic survey July 2001. Fraction mature (upper) 2 ring (left), 3 ring (right), mean weights (lower) 1 ring (left), 2 ring (right), 0 indicates measured fraction mature, + indicates surveyed with zero abundance, blank unsurveyed rectangle..

(11) 62. 61. 60. 59. 58. 57. 56. 55. 54. 53 -10. -8. -6. -4. -2. 0. 2. 4. 6. Figure 5 Abundance of mature autumn spawning herring from combined acoustic survey July 2001. Numbers of herring,. 8. 10. 12.

(12) 62. 61. 60. 59. 58. 57. 56. 55. 54. 53 -10 -8 -6 -4 -2 0 2 4 6 Figure 6 Abundance of immature autumn spawning herring from combined acoustic survey July 2001. Numbers of herring,.. 8. 10. 12.

(13) 61. 60. 59. 58. 57. 56. 55. 0 0. 10 2. 2 0. 0 0. 0 0. 3 0. 0 0. 11 2. 0 0. 9 2. 1 0. 23 4. 0 0. 0 0. 53 8. 48 8. 0 0. 54 6. 21 3. 23 3. 3 0. 9 1. 9 1. 15 2. 62 9. 0 0. 0 0. 2 0. 1 0. 213 31. 39 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. 36 4. 54 5. 24 2. 48 5. 114 10. 26 3. 28 3. 31 3. 114 10. 32 2. 17 2. 16 2. 21 2. 8 1. 32 2. 63 4. 0 0. 0 0. 0 0. 0 0. 32 2. 63 4. 16 1. 0 0. 0 0. 0 0. 0 0. 63 4. 32 2. 0 0. 0 0. 0 0. 0 0. 0 0. 0 0. 0 0. 0 0. 0 0. 0 0. 2. 4. 6. 8. 10. 12. Figure 7 Numbers (millions) (upper =) and biomass (thousands of tommes) (lower) of Western Baltic spring spawning herring from combined acoustic survey July 2001.. 61. 60. 59. 58. 57. 56. 55. 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0. 0 2 8 0 1 2 0 2 8 0 0 0 0 35 19 0 9 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0. 2. 0 0 2 0 0 0 0 0 1 0 22 31 0 9 12 0 4 5 0 2 0 0 0 0. 0 0 0 0 2 9 0 5 18 0 11 37 0 9 13 0 6 9 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0. 4. 0 17 45 0 59 154 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0. 0 13 25 0 6 10 0 0 0 0 0 0 0 0 0 0 0 0. 6. 1 14 10 1 12 16 1 10 10 0 0 0. 0 9 17 0 5 10 0 0 0 0 0 0 0 0 0 0 0 0. 8. 1 21 14 1 28 19 1 14 16 0 3 4. 0 23 30 4 49 61 4 49 61 5 18 9 5 18 9. 10. 5 18 9 10 35 18 10 35 18 10 35 18. 2 9 5 5 18 9. 12. Figure 8 Numbers (millions) of Western Baltic spring spawning herring from combined acoustic survey July 2001. 1 ring (upper figure), 2 ring (centre figure), 3+ (lower figure).

(14) 61. 60. 59. 58. 57. 56. 55. + + + +. 7 23 + 122. 7 23 + 122. + + + +. + + + +. 7 23 + 122. + + + +. 14 35 + 125. + + + +. 7 23 14 35 14 35 + 122 + 125 + 125. + + + +. + + + +. 26 36 + 125. 7 21 + 122. + + + +. 49 78 26 36 + 108 + 125. 2 21 + 107. 61 + 61 + 33 35 33 35 20 16 + 121 + 121 + 115 + 115 + 107. 36 69 75 91. 36 69 53 76. 36 69 75 91. 36 69 75 91. 36 69 51 75. + + + +. + + + +. 0 + + 81. 0 + + 52. 20 16 29 36 + 106 42 98. 35 67 42 86. 33 53 80 93. 36 69 80 89. 36 69 51 75. 36 69 52 64. + + + +. + + + +. + + + +. + + + +. + + + +. 33 69 42 83. 36 69 42 85. 29 69 80 82. 36 69 80 89. 36 69 52 64. 36 69 52 64. + + + +. + + + +. + + + +. + + + +. + + + +. + + + +. + + + +. 36 69 52 64. 36 69 52 64. 36 69 52 64. + + + +. + + + +. + + + +. + + + +. + + + +. + + + +. 36 69 52 64. 36 69 52 64. + + + +. + + + +. + + + +. + + + +. + + + +. + + + +. + + + +. + + + +. + + + +. + + + +. + + + +. + + + +. 2 4 6 8 10 12 Figure 9 Mean weight & maturity of Western Baltic spring spawning herring from combined acoustic survey July 2001. Fraction mature (upper) 2 ring (left), 3 ring (right), mean weights (lower) 1 ring (left), 2 ring (right), 0 indicates measured fraction mature, + indicates surveyed with zero abundance, blank unsurveyed rectangle. 61. 60. 59. 58. 57. 56. 55. 2. 4. 6. 8. 10. 12. Figure 10 Abundance of mature Western Baltic spring spawning herring from combined acoustic survey July 2001. Numbers of herring,..

(15) 61. 60. 59. 58. 57. 56. 55. 2. 4. 6. 8. 10. 12. Figure 11 Abundance of immature Western Baltic spring spawning herring from combined acoustic survey July 2001. Numbers of herring,..

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