Densities and biomass of larval sea lamprey populations (Petromyzon marinus Linnaeus, 1758) in north-western Spain and data comparisons with other European regions

Although the sea lamprey, Petromyzon marinus Linnaeus, 1758, is a threatened species in Europe, available data on the condition and dynamics of its populations are very limited. Thus, electrofishing surveys were conducted annually between 2007 and 2011, so as to study the status and trends of larval populations of P. marinus in north-western Spain. In addition, data from other European regions were compiled. The density and biomass (mean +/- standard error) of ammocoetes in selected areas of larval habitat in north-western Spain were 11.0 +/- 1.44 individuals m(-2) and 15.1 +/- 2.64 g m(-2), and showed signs of a population increase during the study period. However, conservation status of P. marinus was not considered favourable because of several factors, such as the widespread presence of obstacles (restriction of migration and habitat availability), along with some cases of organic pollution. Results and available data suggest that the largest populations of P. marinus as well as the main fisheries are located throughout the south-western areas of Europe (north-central Portugal, north-north-west of Spain and west-south-west of France). Signs of population increases were also registered in other European regions; however, more data are needed to confirm whether this trend has any relevance to a possible overall recovery.