Sea lamprey

Sea lamprey(Petromyzon marinus) is a very special fish species. The species has existed for over 400 million years but is now at risk of disappearing completely from 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 specialized jaws, they attach to their host, scrape open a wound and feed on 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 is rarely found in the southern Baltic Sea along the coasts of Skåne and Blekinge. The country’s largest breeding population is found in River Ätran.
They spawn in the same environment as salmon, but unlike salmon and trout, for example, sea lampreys cannot jump, which makes most fish ladders impassable barriers.

Very unusual life cycle
Sea lampreys spawn in fast-flowing rivers 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 ammocoetes, burrow into soft sediment where they filter algae and decomposed plant material for 5-8 years. At metamorphosis, when they are 11-20 cm long, they transform into adults and migrate to the sea the following summer.

Improving conditions for the endangered species
The sea lamprey has been severely affected by hydropower development and migration barriers, which hinder the fish to reach their spawning grounds. River channelization and pollution have also reduced the population. The drastic decline of large fish in the sea has meant that there are few fish to parasitize on, negatively impacting the species further. Despite  fishing beeing prohibited, more efforts are needed to save the species, such as improving habitats and stronger 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, the hope is that the species will remain and increase in Swedish waters.