— 25 — APPENDIX A: PETTERSSON 



The accomodation ot these periods to the annual hydrographie periodicity is not 

 more incongruous than is the wellknown fact, that the animals of the dry land, f inst. 

 the migratory birds, have adjusted their migrations and physiologic functions to the 

 predominant climatic conditions. 



The south-fish is an inhabitant of the Atlantic water proper and appears in greatest The South- 

 number at the flooding of this water. The mackerel, the hake, the Belone belong to '^^''^^ 

 this category. 



The question whether the sardine and other fish-species only found in the southern Migrations 

 North Sea extend their wanderings through the Channel into the Atlantic must be left '" 'J'^ ^"""i"" 



^ " . North Sea 



to the future to solve. In any case the most important fishmigrations are those under- 

 taken within the southern North Sea itself 



Dutch investigations have shown, that both flatfish and shellfish of this region 

 undertake seasonal wanderings between the continental shoals and the Dogger bank. As 

 already stated the North Sea south of Dogger forms hydrographically a semi-isolated 

 area. Recent Dutch' observations show, that this is the case in a biologic sense too. 



North of Dogger where the interchange of water by the way north of Scotland and Migrations 

 the Shetlands takes place on a large scale between the Atlantic and the North Sea, the '"'Î'TO''^'"" 



, . ^ ^ North Sea 



migration both of South-fish and North-fish seems to attain far greater dimensions. 



As an illustration of this the experiences of Professer Henking in his study of the 

 hake may be quoted. The hake is a typical South-fish, which to the fisheries of Spain 

 and France is of the greatest importance. In our hits, it arrives towards the end of 

 summer with the setting in of the Atlantic water and disappears again in winter. 

 Henking says^: 



"The hake is remarkable in this regard , that the difi"erence in quantity caught 

 during summer and during winter is surpassed by no other known species. During 

 winter (November — April) the total catch averages 2 pounds, while in summer the daily 

 catch averages 100 pounds. 



Appendix F contains an account of the appearance in the North Sea and Atlantic 

 of this fish. The mackerel too must be considered a South-fish although its predatory 

 habits and strong swimming capacity bring its rovings tar beyond the compass of the 

 Atlantic water proper. 



So fir the influence of hydrographie periodicity on fishery conditions may be con- 

 sidered as proved. The hydrographie periodicity, however, is subject to disturbances 

 chiefly appearant in the retardation of its maximum from autumn to winter. In what 

 manner do these disturbances aff'ect the fishery conditions? The full answer to this 

 question which practically is of vital importance will not be at hand for years yet to 

 come. Summarizing the experience of these two years we should say, that to the 



1 H. C. Redeke, Vangststatistieken van hoUandsche Stoomtrawlers 1903— -1904. Mededeelingen over 

 Visscherij, Nr. 130, Oktober 1904. Dr. Redeke says (I.e. p. 217): 



«Zoo blijkt uit dit statistisch onderzoek, en hierop zoudc ik ten slotte nog even de aandaclit willen 

 vestigen, dat, gelijk reeds menige andere waarneming ons leerde, het /.uidelijk deel van de Noordzee een 

 min of meer zelfetandig gebied vormt. Hoewel er in het noorden geen zichtbare grenzen bestaan, lieeft dit 

 gebied toch zijn eigen vischwereld, zijn eigen bodem-tauna, zijn eigen plankton, kortom zijn eigen levende 

 natuur, waarin slechts zelden zwervelingen uit het noorden indringen». 



2 Henking; Die Befischung der Nordsee etc. 1. c. S. 5 and 6. 



Appendix A J 



