Many species of fish undertake migrations on a regular basis. Several fish are strongly depend on open rivers to reach their breeding grounds, such as salmon and sturgeon, while others just use the brackish delta water in their juvenile phase, like herring. Open deltas- which provide free fish migration from sea to source are therefore vital for many fish species.
Migration takes place on time scales ranging from daily to annual, and with distances ranging from a few meters to thousands of kilometres. The purpose of migration usually relates to either feeding or breeding. In some cases the reason for migration is still unknown.
Types of Migration
Fish that migrate between salt and fresh water are defined as 'diadromous fish'. These include the anadromous species, migrating from the sea to fresh water for spawning, and the catadromous species, spawning in the sea and migrating towards freshwater as a juvenile. Species such as salmon, sturgeon, lampreys and various Cyprinids all have anadromous migration patterns, while Eels have catadromous migration patterns.
Migration problems and solutions
There are several factors that cause migration problems such as:
- artificial barriers, dams, sluices and weirs
- green energy power turbines
- intensive fishery
- habitat loss and fragmentation
Because of habitat loss and fragmentation a decline of habitat quality for fish and the isolation of populations of the fish stock have been noted. These problems will intensify taking with anticipated increasing pressures from flood management, renewable energy generation, and agriculture. These pressures are essential for European development and will go ahead. The Living North Sea project seeks to address these pressures and proposes measures on how best to restore good ecological conditions for migratory fish in the North Sea region. By looking at the problems in a international way we will be able to prioritize important areas for key species and make recommendations for local solutions.
For more information about fish migration: http://en.wikipedia.org/wiki/Fish_migration