Human activity has brought about changes in many waters. When, for example, the natural reproduction of fish has declined due to a lack of spawning grounds, recovery measures must be taken to restore fish stocks. Fish stocks are supplemented by both stocking and the restoration of habitats.
The purpose of stocking measures taken by Metsähallitus is to either improve the likelihood of catches in a specific fishing destination or to build up fish and crayfish stocks.
The so-called "stock and fish" destinations controlled by Metsähallitus are annually stocked with approximately 60 000 kg of catch-sized fish. Most of these fish are rainbow trout and trout, but some waters are also stocked with grayling. The fish planted into the "stock and fish" waters are there purely for the purposes of fishing and these plantings do not aim to cultivate naturally reproducing fish stocks.
However, in terms of surface area, the stock and fish destinations make up only a small portion of the fishing waters and fisheries management activities controlled by Metsähallitus. In addition to the fry stocking of traditional salmonids, trap and lure fishing waters are also stocked with fry-sized whitefish, grayling and pike-perch. In Upper Lapland, Arctic char specimens caught in natural waters may be transferred to other water areas to bolster fish stocks where needed.
Metsähallitus has conducted licensed transfer plantings of indigenous noble crayfish almost annually with the purpose of restoring noble crayfish stocks that have been decimated by the crayfish pest or creating completely new stocks in new water areas. Metsähallitus does not stock waters with signal crayfish, as it is an invasive species.
The crayfishing season begins each year at the end of July and ends at the end of October. The preconditions for crayfishing arrangements are laid out in the Fishing Act and Decree.
Metsähallitus uses methods such as exploratory fishing and exploratory crayfishing to determine the state of the fishing waters it controls. The most essential methods of exploratory fishing are net fishing and electrofishing. Sometimes lure fishing tackle is also used for these purposes. The state of crayfish stocks, especially noble crayfish (Astacus astacus) stocks, is surveyed with exploratory fishing conducted using crayfish traps.
The purpose of exploratory fishing is to discover how widely a species has spread, what the relationships between different species are, what the current state of fish stocks is and how they are developing. These days important information on the state of fish species and fish stocks is also received in the form of catch feedback, which fishers can submit via the free Tuikki.fi fishing log.
The success of stocking activities and the development of the stocks are monitored via exploratory crayfishing. The catch feedback collected from these fishing tests and also from crayfishers themselves allows Metsähallitus to scale crayfishing to a sustainable level at each crayfishing destination.