Comportement de l'espèce “Salmo trutta” dans le bassin de la Seine. Suite et fin

Abstract

Since a certain time, it is observed, in the spring, in Low Seine, that Salmonidae are coming together. These concentrations concern yearling subjects. Besides, a certain number of adult fisches, marked in Ile de France in 1961-1962-1963, have been captured downstream very far from their introduction point. Because of the investments supported by fishmen for restocking the rivers as well with immediately catchable trouts than with fry and young trouts, it became necessary to try to understand the reasons of the runnings down that has been recorded and to calculate their importance. These investigations have been carried out by a systematic marking of the fishes organized on the whole of the four great hydrographic Regions of the River Seine :— Bassin of the Upper Marne ;— Bassins of the Upper Seine and Upper Aube ;— Bassin of the Upper Aisne. On the 31th October 1967, on 30.030 marked subjects, 3.138 have been caught and recorded. On these 3.138 subjects, 3.049 had not left the Bassin into which they had been introduced. The general mark-returns percentage, reaches 10,15% and the percentage of the distant returns is 3,06‰ The highest returns percentage is this of the Upper Bassin of the River Aisne, where, locally, 34,80% of the marked fishes have been captured. But it can be noted a running down rate in Lower Seine and in the sea of 2,94‰ for the Upper Marne; 2,20‰ for the River Aube and the Upper Seine and 4,71‰ for the Ile de France. The highest removing is this of a trout introduced in Ardennes Country and which has been caught at Dunkerque Harbourgh after a travel of 805 kilometers, 530 of wihch made in fresh water. Investigations by marking have been completed by biometrical studies carried out on samples drawn of Lower Seine, at the time of the big concentrations of the winter end. A certain number of constatations derives from it :— There are groups of fishes which are inclined to run down-stream, more than the others— The exotic peninsular (Danish) stocks gives a higher rate of migratories than the native continental stocks.— Some fishes have irregular removings, either upstream or downstream, to search a more propicious environment.— The breeders are going more or less far to search proper spawning places.— The native populations are very sedentary, if they lives in a stable and inviolate environment.— The concentrations of fishes in Low-Seine includes, vith the same silverwhite skin :— Salmo trutta fario ;— Salmo trutta gairdneri ;— and Salmo salar.But, it is not possible, to make a discrimination between Salmo trutta fario (dulcaquicola) ; and Salmo trutta fario (marina). The migrator fishes of the species changes their skin at the time of the physiological motivation and it can be found all the possible links between the sea-trout and the streamtrout.