Fish have traditionally been released to improve sports fishing in rivers or to compensate for reduced fish production. More recently, the focus has been on maintaining and replenishing vulnerable stocks. Today, fish are released for a number of reasons: when required by the authorities as a condition in connection with hydropower and other developments along river systems; on a voluntary basis to replenish stocks and improve sports fishing; and to restock rivers or rebuild weak stocks.
The Norwegian Scientific Advisory Committee for Atlantic Salmon Management surveyed releases in 236 Norwegian salmon rivers to evaluate their effectiveness in achieving spawning stock targets. Their report states that in the period from 2005 to 2009 an average of nearly eight million fish and eyed eggs per year were released/planted in the rivers.
Egg planting was the most commonly used method (65 % of the total number), followed by the release of fry (16 %), fingerlings (14 %) and smolt (5 %).
Each year the authorities require the release of roughly 1 850 000 salmon fry and smolt, and also require planting of eyed eggs in certain rivers. The corresponding figures for sea trout are substantially lower: fewer than 150 000 fry, fingerlings and smolt and roughly 50 000 eyed eggs.
More than 1.5 million salmonids a year are released/planted in Norwegian rivers on a voluntary basis. Of these, roughly 1.3 million are Atlantic salmon and 240 000 are sea trout. Usually, early life stages are used: eyed eggs, fry and smolt.
Fish releases are regulated by Norwegian legislation. The Act relating to salmonids and freshwater fish contains provisions on the release of fish, and the Food Act also governs the production, transport and release of fish. The Norwegian Food Safety Authority administers relevant regulations, which deal with disease control, transporting wild fish, and more.
A risk-based inspection and enforcement system for health-related issues is required at all aquaculture facilities, including stock enhancement facilities and gene banks. Inspections must be carried out by a fish health biologist or veterinary surgeon, and the frequency of inspections varies with the number of fish at the facility and number of rivers where they are to be released.