Benefit: Viable populations
The benefits of nursery habitats are perhaps best described in terms of viable populations. Here we present some economically important species, but the same habitats function as nursery habitats for many other species as well, and thus maintain biodiversity and a functioning food chain.
The Atlantic salmon (Salmo salar) reproduces naturally only in two Rivers in Finland, Tornionjoki and Simojoki. In both rivers the number of smolts has increased since 1980s. In Tornionjoki the growth has been nearly exponential, in 25 years the number of smolts has increased by more than 20-fold. In Simojoki number of smolts has doubled since 1980s. In 2013 there were about 1.5 million smolts in Tornionjoki and 35 000 smolts in Simojoki.
The water quality in Tornionjoki is better than in Simojoki which partly explains why the number of smolts is higher there. Other factors that have an effect on the number of smolts are, for example, free access from the sea to the upstream rapids, stable fluctuation of the water flow and regulation of fishing.
The density of grouse species and the share of chicks are assessed separately in every county. The graph below presents the maximum and minimum density in every year. Most often the maximum density of willow grouse (Lagopus lagopus) was observed in northern Finland in Lapland, Oulu and Kainuu regions. Miminum density of willow grouse has been zero in every year. The species is very scarce in southern Finland.
The maximum density of hazel grouse (Tetrastes bonasia) has been highest in southern and central Finland. In Lapland the species is quite rare. Black grouse (Tetrao tetrix) has been most common in northern parts of central Finland, in Otrobothnia and in Kainuu. It isalso quite rare in Lapland. The density of capercaillie (Tetrao urogallus) is at its highest in a fairly large area, ranging from coastal Ostrobothnia in the west to eastern Finland, northern Karelia and Kainuu. The species is fairly rare in southwestern Finland.
Hazel grouse and black grouse are the most common grouse species. Their maximum density was in 2014 approximately 10 individuals / km2 of forest land. The density of capercaillie was smaller, ca. 5 individuals / km2. The density of willow grouse has decreased considerably during the past decade. The maximum density in 2014 was only 1.6 individuals / km2.
Metsäkanalinnut. Tilastotietokannat. Game and Fisheries Research Institute. [In Finnish]
- Updated (03.10.2017)