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

Abstract

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 AE standard error) of ammocoetes in selected areas of larval habitat in north-western Spain were 11.0 AE 1.44 individuals m À2 and 15.1 AE 2.64 g m À2 , 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.

Upstream migration of the anadromous sea lamprey (Petromyzon marinusLinnaeus, 1758) in a highly impounded river: Impact of low‐head obstacles and fisheries

“…This study was carried out in the River Ulla (in north‐west Spain; total length 132 km, catchment area 2803 km 2 ). The length accessible for diadromous species in the main channel of the river is 80 km, limited by the presence of a dam for hydroelectric production (UTM: 29 T 561986E 4742078 N), which is the first impassable barrier for diadromous species (Silva, Vieira‐Lanero, et al, ; Figure ). There are also 45 low‐head obstacles of variable size in the accessible section of the river (Figure ; Table S1), 20 of which are pesqueiras – artificial obstructions constructed for lamprey fishing (Figure ).…”

“…The anadromous sea lamprey ( Petromyzon marinus Linnaeus, 1758; Figure ), present on both sides of the North Atlantic, can be considered representative of the threatened anadromous lampreys, which are all affected by the same threats (Maitland, Renaud, Quintella, Close, & Docker, ; Silva, Barca, & Cobo, ). European populations of P. marinus have suffered a significant decline during the second half of the 20 th century through overfishing, habitat loss and degradation, physical barriers to migration, and pollution (Maitland et al, ; OSPAR, ), and future trends remain unclear (OSPAR, ; Silva, Vieira‐Lanero, Barca, & Cobo, ). As a result, in Europe P. marinus receives conservation protection through the Bern Convention and the European Habitats Directive (Council of the European Communities, ), as a species requiring the designation of ‘special areas of conservation’ (SACs).…”

“…The main European populations and fisheries of P. marinus are located in the north west of the Iberian Peninsula and in south‐west France (Silva, Vieira‐Lanero, et al, ). In the Iberian Peninsula, as is common in Europe, there is a high level of habitat fragmentation owing to the presence of low‐head obstacles.…”

Length‐based assessment of larval lamprey population structure at differing spatial scales

“…Harvey and Cowx () proposed HD assessment of larval lamprey (ammocoete) populations in streams in terms of presence or absence, abundance and demographic structure at index sampling sites. Although this framework was suggested as an ‘initial statement’ intended to open discussion and experimental study, it has been used largely unchanged in many subsequent catchment‐wide studies (Nunn, Harvey, Noble, & Cowx, ; Silva, Vieira‐Lanero, Barca, & Cobo, ; Watt, Ravenscroft, & Seed, ). The value of the approach is reflected in its continued application under the Common Standards Monitoring Guidance for Freshwater Habitats and Species (Joint Nature Conservation Committee (JNCC), ) as the approved method for assessing lamprey populations at designated sites across the UK.…”

“…Harvey and Cowx (2003) proposed HD assessment of larval lamprey (ammocoete) populations in streams in terms of presence or absence, abundance and demographic structure at index sampling sites. Although this framework was suggested as an 'initial statement' intended to open discussion and experimental study, it has been used largely unchanged in many subsequent catchmentwide studies (Nunn, Harvey, Noble, & Cowx, 2008;Silva, Vieira-Lanero, Barca, & Cobo, 2017;Watt, Ravenscroft, & Seed, 2008).…”