Sea lamprey

Sea lamprey(Petromyzon marinus) is a very special fish species. The species has been around for over 400 million years but is now at risk of disappearing completely in Sweden. There are documented specimens that have grown to over one meter in length and weighed over two kilos. As adults, sea lampreys are parasites on larger fish, but also whales and seals. Using their special jaws, they suck on their prey, scrape out a wound and suck blood and body fluids.

The species spawns in pairs, and both parents die after spawning

Small obstacles become big barriers
In Sweden, sea lamprey occur along the west coast and rarely in the southern Baltic Sea along the coasts of Skåne and Blekinge. The country’s largest spawning population is found in River Ätran.
They spawn in the same environments as salmon, but unlike salmon and trout, for example, sea lampreys cannot jump, which makes most fish ladders obstacles.

Very unusual life cycle
The sea lamprey spawns in fast-flowing streams with gravel bottoms during July-August. The male digs a spawning pit by moving stones with his mouth. The species spawns in pairs, and both parents die after spawning. The eggs hatch after 10-12 days. The newly hatched larvae, called line eels, burrow into soft bottoms where they filter algae and decomposed plant material for 5-8 years. At metamorphosis, when they are 11-20 cm long, they turn into adults and migrate to the sea the following summer.

Improvement for the endangered species
The sea lamprey has been hit hard by hydropower development and migration barriers, which make it difficult for the fish to reach their spawning grounds. Channelization and pollution have also reduced the population. The sharp decline of large fish in the sea has meant that there are few fish to parasitize on, which also has a very negative impact on the species. Despite the ban on fishing, more efforts are needed to save the species, such as improving habitats and strengthening protection.

The Improve Aquatic LIFE project has a particular focus on sea lamprey as the situation for the species is considered very serious. By removing migration barriers, creating fishways and restoring habitats such as backwaters and sandbanks in a number of key areas, it is hoped that the species will remain and increase in Swedish waters.