The occurrence and distribution of the eggs, larvae and various age-groups of the food-fishes in the North Sea
Appendix E of Rapports et Proces-Verbaux des Reunions Vol. 3.
The first condition for a right understanding of the habits and habitats of the food- fishes of the sea, and in general, of the production of the sea as regards useful fishes, is an exact knowledge of the occurrence and distribution of these food-fishes at all the various stages of their life, from the egg on to the adult mature form. The plaice is the most important, ground-dwelling food-fish of the North Sea. In the interests of the sea- fisheries we wish to know, under what conditions the plaice lives in the North Sea, how it nourishes itself and reproduces its kind, whether an overfishing of the stock is going on, if it is a stationary or migratory fish in the North Sea, and whether, according to the answer to this question, an influx from other seas is occurring to compensate for the fish removed or not, and whether finally, fixed protective legislation at certain regions of the North Sea has a possible prospect of good results or not. In order to settle these and many other points, we must of necessity first investigate and determine above all possibility of objection, the following facts. Where and when does the plaice spawn? Where and in what relative amounts are the free-swimming eggs and the planktonic larvæ hatched from them? When and at what size is the metamorphosis of the plaice-larvæ complete and does their life on the bottom begin? Where are these youngest bottom-stages of the plaice to be found, how fast do they grow there, and what size do these young plaice reach at the end of their first year? Where do they live and how large are they in the second, third and following years of their life? At what size and in what year of their life, do the plaice become usable for a rational fishery,-at which age are they mature for the first time, and where do they frequent at that time and in the following years of their maturity? How old can a plaice in the North Sea become in general and — in connection therewith — through how many years can they, by production of eggs, contribute to the maintenance of the stock ? Do the plaice make regular migrations in the course of the year from one part of the sea to another, how far do such migrations extend and do the older plaice travel further than the younger? and so on.