Translation Series No.1211

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7 197 ` It has already bee/I .:stated -that the present investigations of the fishing intensity and the strength of the stock are based only on the salmon fishery in the main basin of the Baltic Sea. Therefore, we must restrict oursellies to a part of the stock on account of the limited.data. Slich' a delimitation can bè carried .out when one considers the immigration of the young salmon from the Gulf of Bothnia as recruitment and all losses except natural mortality and loases through fishing as spawning migration. The recruitment is taken care of through the divers values of the stock density. The figures that are obtained for the spawning migration com- prise all salMon that emigrate from the main basin. This part of the stock, however, becomes subject to shore and river fishery, so that only a certain percentage of the spawning migrants actually reaches the spawning grounds. These events, however, are of no interest to us, Since only an unimportant . fraction of Balm.= survives spawning and returns to the Baltic Sea, all spawning migrants are counted from the beginning as defdnite losses. 7.2: Lbsses in the eXploited stock yew e.(a.ss In the above chapters it has been shown that a-ye-eta-es—set becomes eiploited for the first time during the fall of the second year in the Baltic Sea. One has therefore to distinguish between an undisturbed stage and an exploited phase. Since the fishing season commences in the fall of each year,.the - transition-between the two sections Occurs rather suddenly. During the first phase, losses are caused only by natural causes (enemies, sickness,lack of food), later the losses through fishing are added. Finally, a Part of the salmon migrate in order to spawn and - thus leave the exploited phase. At this time there are-three different causes that work logether_and lead to a reduction of the stock. The total'of
• - 1 98- the stock losses are composed of the waste by fishing, the natural mortality and the losses caused by the spawning mration. 7.2.1. Total mortality Beverton and Holt (1957) have, among other things, described the losses in a stock of fish with the aid of a differential equation. According to this the number of fish that is lost from the stock in the time t is proportional to the total mortality Z and the number N of the fish present. obtain dN = dt Through solving the differential quotient and integration we W - t W The mortality . thus follows the law of exponential dependence. N is proportional to t, when t increases arithmetically, N decreases geo- metrically. Z . is called the exponential coefficient of the total losses. Equation (1). thus gives the number of survivors at the time t. . The nuiber of the dead is then N o _ N t= N o _ oe -Zt . • N o -'r t D0 (1 e t) With the aid of - (1) and . the values available, one can now calculate the total mortality 11- = 0. e ln 1.4 = Zt ln -D = Z:t N t (1 ) (2) (3) [ p. 347]
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FISHERIES RESEARCH BOARD OF CANADA
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sos-2cto—lo-31 DEPARTMENTOFTHESEC
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• 6.1. Previous investigations 17
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-5-. and Kerr very much later menti
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treated as a quality, a special pop
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• -9-- per cent). Furthermore, th
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• - 11 - fishery, mentions the gr
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• - 13 - in LiepUva. These voyage
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• 1948/49 545 1949/50 730 1950/51
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• 2.2.1. River fishing - 16- The
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- 18- are 50 norsels, 60 to 80 cm l
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• nets give better results is onl
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• • G Fig. 4. End buoy for salm
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• with • Total length (cm) Mout
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• • - 25- of Bothnia. In the fa
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• • - 27- increase the catch. S
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• of • fishing representsavalue
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• to lower figures than in the fa
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• • Umfang = Cire umference - 3
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• - 35 - and nape corresponds to
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• • / 100 50 Selektion Selectio
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- 39 - In Table 9 have been calcula
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. Table 10. Number of salmon per 10
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• Table 11. Number of salmon per.
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• - 45 - cza-ci, es When consider
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- 47 - If We examine once more the
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- 49 - German fishermen work during
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• - 51 - is true, have to be corr
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Table 16. Seasonal yields of the fi
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Table 17. Monthly average weights o
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- 57 - In February and March hardly
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• Table 20. Additional catch of c
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• 100 50 60 100 cm Totallarle . 2
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• subject to an error of ± o.op9
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cycle) during the second . period o
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• their third year. , Recruitment
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50 r-■ 2 / bet; 56cm = 1 fis 1 li
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• - 71 - ovary that has already b
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5 - 73 - April 1960 the diameter of
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- 75 - oocytes can be demonstrated
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. ineftlerer Mean OocytendurcArness
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- 79 - furnish the energy fer the s
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' 1741 salmon, which were.caught be
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• - 83- the series of measurement
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- 85 - the relative amount of eggs
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- 87 - The calculation of a formula
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- 89 - area of distribution is form
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- 91 - as percentages of thé recov
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Table 22. The recapture of tagged s
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• II> Three conclusions can be dr
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• 6 65- 64 - 62-. 61 - 6 . 5 . 59
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• - 99 - fish. The tagging does n
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- 101 - tagging experiments'that sa
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- 103- Renne Bank in about 60 m dep
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• 9:1 0 a) el-4 o (XI -P CNI 4- o
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14,3 14,3 30,7 31,3 27,7 6,0 15,0 1
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Table 26. Catches of salmon in the
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- 111 - between Hela and Kahlberg r
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• - 113- 5 .. Age and growth of t
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cm 100 80 60 40 - 1 15- customarily
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found can be used for the recalcula
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v 0 00 0 I I - 119- of the scales.
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- 121 - The interpretation of the y
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• - 1 23 - the age groups 2.B to
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• L s - L c r s 0.85 Smolt Ls = l
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5.3. The'age composition of the Ger
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-129- with shares in the catch of o
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"ervoct. Yeer-Le- -e-t. '4.y-c.1*.e
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1955 1 2 3 4 23 3 61 506 7 3 135 21
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- 135 - yeAy-ctt4 thé explanation
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• • _ Table 33. The composition
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Table 34. Composition by age of cat
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- 141 - yeAy-cle..es Table 35. The
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- 143 - • U7,) tdL comparablenece
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• whereas the present data .(1957
Page 151 and 152: Sin% 0,1 2,8 37,0 96,8 100,0 - 147-
Page 153 and 154: • - 149 - these results 38 per ce
Page 155 and 156: • • Number of salmon J. en1967
Page 157 and 158: 4. number 50 e" • ); e e , lot nb
Page 159 and 160: they take account of the annual cha
Page 161 and 162: • -157- and in the stock are bein
Page 163 and 164: Table 43. Mean lengths of age group
Page 165 and 166: • - 161 - of these catches has be
Page 167 and 168: - 163 - of enolt in Fig. 36. From a
Page 169 and 170: --165 - increase'in weight is more
Page 171 and 172: • rl -P b..0 -e nzi -ri r-1 gl a)
Page 173 and 174: - 169 - CLA‘s set of smolt of 193
Page 175 and 176: Year's sets of smolt CILS present 7
Page 177 and 178: - 173 - necessary to follow the gro
Page 179 and 180: - 175 - • been ascertained from t
Page 181 and 182: (after K. A. Pyefinch 1955). — 17
Page 183 and 184: • gadids and sticklebacks (after
Page 185 and 186: - 181 - especially decisive in, the
Page 187 and 188: 6.3.1. Seasonal fluctuations 36,9 2
Page 189 and 190: • Number of Months Gear salmon in
Page 191 and 192: MagerdW hing 40 , 20 Filling of Sto
Page 193 and 194: Deep could be examined. - 188 - Chr
Page 195 and 196: - 190 - salmon . switch over to the
Page 197 and 198: • - 192 - recognizable after seve
Page 199 and 200: - 194 - amount of food. Under-consi
Page 201: - 196- expenditure, composition in
Page 205 and 206: NUmber of salmon per Z Weigh- Seaso
Page 207 and 208: • 'Table 55. Values of the total
Page 209 and 210: - 204 experiment were about 40 per
Page 211 and 212: - 206- strength of the stock N pert
Page 213 and 214: • N„ Z o = cf„ (M1- T) -- In
Page 215 and 216: — 210— the coefficient for the
Page 217 and 218: - 212- In a further paper Piggins (
Page 219 and 220: - 214- shifted and the fOod supply
Page 221 and 222: - 216 - concerns the yield of captu
Page 223 and 224: nachafter 00 04 0,3 0,4 2 1 0,5 6 9
Page 225 and 226: • 1. (5 100 000) (4 250 000) 4 25
Page 227 and 228: • •em.ilts - 222 - in an error
Page 229 and 230: • - 224- BRANDT, A. y. , 1959: Fa
Page 231 and 232: - 226 - Paw, T. H., 1938: Fluctuati
Page 233 and 234: - 228- PETERSEN, C. G. .11, and Orr
Page 235 and 236: Table I. Captures per unit effort w
Page 237 and 238: Table II. Captures per unit effort
Page 239 and 240: • Yea.r Sweden Continuation Table
Page 241 and 242: Table VI. Ratio between fork le . B
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