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Fluctuations in the Great Fisheries of Northern Europe Viewed In

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Fluctuations in the Great Fisheries of Northern Europe Viewed In CONSEIL PERMANENT INTERNATlONAL POUR 1,'EXPLORATION DE LA MER RAPPORTS ET PROCRS-VERBAUX -- VOLUME ?(X FLUCTUATIONS IN THE GREAT FISHERIES OF NORTHERN EUROPE VIEWED IN THE LIGHT OF BIOLOGICAL RESEARCH BY JOHAN HJORT WITH 3 PLrlTES EN COMMISSION CHEZ ANDR. FRED. H0ST & FILS COPENHllGUE .iVI<Il, 1!I1,1 COPPNHAGUE - IMPRIYERlR BIANCO LTJNO CONTENTS Page INTRODUCTION .................................................................... 3 Fluctuations in the yield a characteristic feature of all great fisheries ................. 3 Norwegian Cod fisheries ........................................................... 3 Norwegian herring fishery ................................................... 4 Popular attempts to explain the fluctuations ........................................ 4 The theory of migration as a cause of the fluctuations ............................... 4 Probable extent of migration essentially reduced by scientific investigation ............. 6 Investigations as to the distribution of the fish in the Norwegian Sea ................. G Principal species only found on the coastal banlrs in spawning time ................... 7 A considerable portion of the stoclr annually taken by the fishery .................... 9 Preliminary irlvestigations as to the .cod fishery in northern Norwegian waters, 1900-. l903 9 Melhods of age determination adopt.ed in the investigations .......................... l0 Representative biological or vital statistics .......................................... 10 CHAPTER I The Herring Stock in' Norwegian coastal waters ....................................... 14 Norwegian Herring Fisheries ....................................................... 14 Popular classification of the different varieties ....................................... 16 Size of the herring. and determination of age by means of measurcmcnt .............. l6 The Scalcs of the herring as a means of determining the age and growth of the fish ... 18 Average size of the herring at different ages ........................................ 19 Growth at different seasons of the year ............................................. 19 The small herring and fishery for same ............................................. 20 The fat herring and fishery for same ......................: ........................ 21 Year class 1904 among fat herring ................................................. 22 Year class 1904 arnong large herring and spring herring .............................. 24 Comparison of different samples as a means of checking results ....................... 28 Recruiting of the spawning shoals from those of the Cat herring ...................... 32 Recapitulation. Slretch of the natural history of the herring ......................... 35 The fluctuations of the herring fishery .............................................. 37 Assortment of fat herring ......................................................... 39 I~luctuationsin the fat herring fishery .............................................. 39 Fluctuations in the weight of spring herring ........................................ 40 Fluctuations in the yield of the spring herring fishery ............................... 41 CHAPTER I1 The Stoclc of Herring in the North Sea and Skagerrak ................................. 44 The Herring fishery in the Norlh Sea. Yicld ....................................... 44 Drift nets and Lrawl ..............................................................45 Seasonal variation of llle fishery ................................................... 46 Difference of opinion as to lhe migratio~~sand race of the herring .................... 47 Heinclre's classification of thc races of herring ....................................... 49 Mixture of Races in the North Sea ................................................ 60 Mixture of races in tlie norther~~~nostpart of the KorLl~ Sea ......................... 61 Broch's investigations as to mixture of races ........................................ 53 International studies as to age and growth ......................................... 54 Gcograpliical tlistriblltion of the rlibercnl agc groul)~................................ 56 Page Distribution of thc youngest year classes ........................................... 57 Comparison of the distribution of the youngest year classcs with the currenls in Lhe North Sea 60 Composition in point of age of herring shoals of older age classes . Difficulty of investigation 62 Different types of corriposition in point of age ...................................... 62 Numerical relation of the year classes .in different parts of tlir Yortl.1 Sra ............. 66 Slragerralr and Kattegat ........................................................... 71 Variations in age composition from year to year .................................... 72 Occurrence of the rich year classes concurrent with rich yield in the fisheries (in 1911 and 1912) 80 CHAPTER 111 The cod. its spawning. migrations and size ............................................ 81. Geographical distribution of the Gadoid species ...................................... 81 Norwegian Cod Fisheries .......................................................... 83 The skrei fisheries ................................................................ 84 Old slrrei grounds ................................................................. -85 Distribution of the floating egg .................................................... 85 Egg investigations off Lofoten. in 1913 ............................................. 88 International invesligations as to the spawning places of the cot1 ..................... 89 Size of the skrei .................................................................. 91 Comparison of various slrrei samples ................................................92 Migrations of the skrei ............................................................ 98 Percentage of fish recaptured ......................................................104 Mipations ........................................................................ 104 Comparative size of slrrei and Fin~narlrfish in 1913 .................................105 Marlring experiments in Finmarlren in 1.913 .........................................10G Other instances of migration noted .................................................106 Younger stages of cod .............................................................108 Passive movemenls and distribution of the young cod ...............................110 Distribution of the youngest bottom stages .........................................110 Marking of small cod .............................................................111 Finmarlr codling, "Loddefisk" ......................................................113 Migrations of capelan shoals towards the Finmarlr coast .............................113 Size of the Finmarlr fish .......................................................... 114 Size of the Finmark fish in different years .......................................... 116 Variation in size of the Finmarlr fish in one and the same year ...................... 117 CHAPTER IV The &ock of Cod; its composition with regard to age .................................121 Age and growth of the cod ........................................................ 121 Damas' scale investigations .........................................................122 Examples of different growth in different waters .................................... 124 Sund's methodical investigations as the utility of the scales in the study of growth .... 124 Growth and age of young cod .....................................................129 Growth and age of the loddefislr ...................................................130 Age and growth of the slrrei ....................................................... 136 Similarity of composition between slrrei and Finmarlr fish in 1913 .................... 1.37 The year class 1904 ...............................................................138 Relation betwecn size and weight of the cod ........................................ 141 Whole weight of the cod ..........................................................141 Weight of gutted cod .............................................................143 VlTeight of the dried fish ...........................................................145 Cured weight of Fin~narlrfish for the years 1908-1913 .............................. 147 Rich yield of the Finmarlr fishery in the years 1910-1913 ........................... 150 Fluctuatioris of the fishery in Iormer years .......................................... 151 1901-1903 ....................................................................... 151 1904-1909 .......................................................................154 Periodical variations in the average size of Lhe slrrSei................................. 166 The periodical fluctuations, renewal and mortality of the slirei ........................ 158 Longevity of the skrei . Mortality among the stoclr .................................158 Majority of slzrei between 7 and 10 years old ....................................... 159 Number of spawning years per fish .................................................169 Oldest slrrei .......................................................................I60 Average longevity of the slrrei determined by the fishery? ............................ 160 Renewal of l.he stoclr affected by lhe fishery? ......................................
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