Petromyzon marinus (Linnaeus 1758), Sea lamprey (Petromyzontidae)

Author: Ronald Fricke, Germany

1. Description of the habitat/autecology of the species

The sea lamprey Petromyzon marinus is an anadromously long distance migrating species. Adults enter freshwater habitats in late winter or spring and migrate upstream to their spawning sites that consist of gravel areas with isolated larger pebbles or rocks and adjacent clean sandy areas, where they spawn from June to July. After spawning, the adults normally die. The larvae stay near the spawning site for 2-5 years and bury in the sand, where they feed on micro-organisms and detritus. After metamorphosis, they migrate downstream to the sea, where they live parasitic on fish and mammal species, sucking blood and feeding on skin and musculature (Fricke, 1987: 39). An anticoagulant substance prevents the blood of the prey from clotting (Holcik, 1986). In the ocean, sea lampreys are found from inshore to deep waters, either on rock bottom where they can attach with their sucking disk, or parasitic on their prey (Froese & Pauly, 2005). The species occurs regularly in the whole Baltic Sea catchment area, though it is very rare in the northern parts, and spawning has not yet been observed there. The species reaches a maximum total length of 120 cm, a maximum weight of 2.5 kg, and an individual age of up to 9 years.

2. Distribution (past and present)

The species is distributed throughout the HELCOM area, but is very rare in most areas. Probably it was more common in the past. However, in the Baltic Proper and the Gulfs it has been very rare in most areas, at least since the early 1800s. Along the German coast the species occurs more often, and even attacks on bathing people are documented seldom, but regularly. In Sweden the sea lamprey usually will be found along the west cost, but even in Öresund and in the southern Baltic Sea it is a very rare, occasional visitor. In the river Råån which flows in to Öresund, spawning has been documented, latest in 2003. The northernmost catch has been got north of Umeå (river Rickleån, 1965). Finnish fishermen have caught this species less than 20 times within the last 200 years.

3. Importance (sub-regional, Baltic Sea-wide, global)

According to the definition in HELCOM (2007), the species is considered of local importance in the Baltic Sea region.

4. Status of threat/decline

The species is threatened and its populations have significantly declined throughout the Baltic Sea. In the HELCOM area, it is classified as endangered (EN) according to IUCN criteria, and as a HELCOM high priority species (HELCOM, 2007). The species is listed as critically endangered (CR) in Germany, and as endangered (EN) in Lithuania, Poland, Russia, and Sweden. It is also included on the OSPAR list (Anonymous, 2004), and on Annexes II and V of the EU Habitats Directive.

5. Threat/decline factors

There are several threat factors: eutrophication in the spawning habitats also outside the Baltic Sea area (since larvae survive only on well oxygenated sand bottoms), construction of weirs and dams in rivers, outside the HELCOM area also fisheries (sea lamprey as target species, e.g. in Portugal, France), and fisheries on sea lamprey's prey species (large fish). The species is considered as rare and highly sensitive to human activities, but not as a keystone species.

6. Options for improvement

Measures for protection of sea lamprey should mainly include the improvement of the situation along the migration routes, mainly in fresh water habitats and at the (potential) spawning sites. Eutrophication of potential spawning sites should be avoided. Fisheries on sea lampreys should be forbidden and it is already forbidden in Sweden. There is no target fishery on sea lampreys in the Baltic Sea and sea lampreys do not spawn in the Baltic Sea proper. Anyhow, obligatory discarding as a by-catch rule could be considered.

7. References

Anonymous 2004. 2004 Initial OSPAR List of Threatened and/or Declining Species and Habitats (References number 2004-06). OSPAR Convention on the Protection of the Marine Environment of the North-east Atlantic, Meeting of the OSPAR Commission (OSPAR), Reykjavik, 28 June-1 July 2004.

Fricke R. 1987. Deutsche Meeresfische. Bestimmungsbuch.  Hamburg (DJN), 219 pp.

Froese, R. & Pauly, D. (eds) 2005. FishBase. Available in: www.fishbase.org, version (11/2005).

HELCOM 2007. HELCOM Red list of threatened and declining species of lampreys and fish of the Baltic Sea. Baltic Sea Environmental Proceedings, No. 109, 40 pp.  Available in: http://www.helcom.fi/stc/files/Publications/Proceedings/bsep109.pdf

Holcik, J. (Ed) 1986. The freshwater fishes of Europe, Vol. 1, Part I Petromyzontiformes, edited by Juraj Holcik, with contributions by Pier Giorgio Bianco, Martin W. Hardisty, and Claude B. Renaud. AULA-Verlag. Wiesbaden.