Freshets and Fish
streams, Atlantic salmon, salmon, entrance, estuary, trout, turbulence, migration
Journal or Book Title
Transactions of the American Fisheries Society
The action of freshets on the runs of fishes in streams has been long known to man,but has never been scientifically studied.Angling for Atlantic salmon in the Margaree River, Cape Breton, was found to be dependent uponentrance of the fish from the sea which required heavy freshets. These freshets in 1935 made anabrupt transformation in fish present and in angling. In comparison with the neighbouringCheticamp River, the tendency of the fish to enter chiefly late in the season, months after theyhad appeared on the coast, has been related to the difficulty for the salmon to enter through thestrongly tidal estuary mouth until heavy rains come in the fall.Experiments with sharp, but not large artificial freshets in the Moser River, Nova Scotia, gavedouble the expected number of both salmon and brook trout entering from the sea and gave goodangling when the temperature was not too high. There is evidence that at all stages salmonrespond more or less to freshets by ascent of streams. Ascent occurs chiefly as the freshet issubsiding. Descent of salmon at all stages occurs with freshets but chiefly at the height of thefreshet.The phenomenon is a general one and is probably not confined to fishes. In essence, it is theresponse of the organisms to displacement over the solid substratum by the fluid medium. In thefish, it is part of the rheotactic response, effected through sight, contact with the bottom and possibly the action of turbulences on the lateral line organs. Freshets effect migration of fishthrough such a stimulus to ascent, through carrying the fish downstream, and through breakingup the 'homes' of the individual fish.