Sergio Silva

Downstream migration and hematophagous feeding of newly metamorphosed sea lampreys (Petromyzon marinus Linnaeus, 1758)

The metamorphosis of sea lamprey (Petromyzon marinus Linnaeus, 1758) allows young postmetamorphic individuals to migrate to the sea and start the hematophagous feeding. However, the information about this phase is very limited, especially for European populations. Herein, we provide for the first time a comprehensive study on the phenology of downstream migration, the timing and location of first feeding and the prey species in the River Ulla and its estuary (NW Spain). Results show that downstream migration occurs between October and May with a peak in March. At least for a part of the postmetamorphic lampreys this migration stops for several months when they reach the estuary, where lampreys find shelter and abundant food, before moving to coastal waters. Hematophagous feeding in the estuary allows postmetamorphics to increase their total length and weight exponentially. Our results also suggest that part of the postmetamorphics (10–30%) start the hematophagous feeding in the river, with a special affinity for anadromous species, probably because of their larger size.

The haematophagous feeding stage of anadromous populations of sea lamprey Petromyzon marinus : low host selectivity and wide range of habitats

Limited information is available regarding habitat use and host species of the haematophagous feeding stage of the anadromous sea lamprey Petromyzon marinus Linnaeus, 1758, due to the difficulties in capturing feeding lampreys and wounded hosts. The aim of this study is to provide new records of P. marinus feeding on host species and to review the available information in this regard to better know the ecology and distribution of sea lamprey during this stage. Thus, new records of P. marinus individuals or wounds on 23 species of fishes and cetaceans are provided. Nineteen of these species were described for the first time as hosts of P. marinus. As a result, an updated list of 54 host species is provided. They belong to diverse taxonomic groups and exhibit different morphological, physiological and ecological patterns. The attacks were located from fresh and brackish waters to open sea. The results suggest that the marine distribution of P. marinus is mainly related to coastal areas with part of the population widely dispersed in offshore areas. This remarkable capacity of inhabiting a broad range of aquatic ecosystems and exploiting different host species could have favoured the dispersal ability and evolutionary success of sea lamprey.

Haematophagous feeding of newly metamorphosed European sea lampreys Petromyzon marinus on strictly freshwater species.

Approximately 6% of the freshwater living northern straight-mouth nase Pseudochondrostoma duriense in two Spanish rivers had attached post-metamorphic sea lamprey Petromyzon marinus. Minimum prey size was 16·1 cm fork length and 56·3 g mass. The condition factor of attacked P. duriense was 16% lower than that of unattacked conspecifics.

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±2.64g 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.