Habitat Availability and Carrying Capacity in the French Part of the Rhine for Atlantic Salmon (Salmo Salar L.)

A survey of potential spawning grounds and rearing habitats for Atlantic salmon was conducted in the French part of the Rhine Basin in Alsace, using a macro-habitat description method. Aerial photography was used for the Rhine whereas tributaries were described from a canoe. 113 ha of rearing habitat and 6 ha of spawning grounds were recorded, of which about half were in the I11 catchment and half in the Old Rhine between France and Germany. Their carrying capacity was evaluated on the basis of stocking tests. Parr densities at the end of the summer ranged from 0 to 26 0+ parr per 100 m2 of suitable habitat with unfed fry and from 5 to 70 with feeding fry (4-5 cm). The overall carrying capacity of the French part of the Rhine for Atlantic salmon is estimated at 344 100 yearling parr for the whole area. The carrying capacity would enable a production of 56 000 to 112 000 smolts, of which 70%are one year-old and 30% two-year-olds. Mortality through hydroelectric turbines during downstream migration was estimated at 20% of the smolt run. On a basis of a 2% return rate at the eventual stage of the reintroduction period, 900 to 1700 adults would return each year to the area. Recommendations are made to protect and restore vanishing running waters needed for salmonids.