The study of the fish populations of European waters developed chiefly in the Scandinavian countries and in Great Britain largely as a result of the economic importance of the fisheries to these countries. Outstanding discoveries include the facts that some year-classes are fifty or sixty times as abundant as others, that such wide fluctuations characterize most of the important commercial species, that even when fish are abundant there are wide fluctuations in availability due to hydrographic conditions, and that great fluctuations in abundance also characterize the fauna of the sea bottom. Demonstration of considerably increased mortality due to fishing has led to action designed to prevent overfishing. The International Council for the Exploration of the Sea, has contributed materially towards the study of these problems and in initiating international action to meet situations uncovered. An important feature of the study of populations has been the recognition and description of .local races-more or less discrete populations having separate spawning areas and characterized by average differences in certain morphological characters such as numbers of vertebrae, of scales and of fin-rays. The discovery that the age of fish and certain characteristics of their life histories could be read from the scales has been basic to many phases of population work. The organization of statistics, especially those on an international scale, has also been an indispensable tool in population studies. The understanding of populations and of the factors affecting them has reached the stage where in some species fishing probabilities have been attempted with considerable success. |
