Sea lamprey (Petromyzon marinus L.) spawning migration in the Vouga river basin (Portugal): poaching impact, preferential resting sites and spawning grounds

Abstract

Historical spawning grounds for sea lampreys (Petromyzon marinus L.) in most Portuguese river basins are becoming inaccessible due to the construction of impassable dams and/or weirs. Studies like the one described in this paper are particularly important in areas like the Vouga river basin, where there is a considerable fishing effort from both professional fishermen and poachers. In fact, for management and conservation purposes, it is important to clarify several aspects of the sea lamprey spawning run in this particular watershed. Therefore, a total of 30 radio tagged, migrating sea lampreys were released in the River Vouga and some of its main tributaries during 2004 and 2005. Results from the tracking sessions were used to determine the effect of poaching on the spawners' population and the characteristics of the resting sites used during the upstream movement. The rivers' stretches were also characterized according to the type of substrate present in the riverbed and flow type, in order to determine its aptitude to constitute appropriate spawning habitats for sea lampreys. We have identified in the upstream stretches of River Vouga, and in the tributary River Caima, characteristics that are particularly suitable for the construction of nests by the spawners. Presence of larvae provided evidence that spawners migrated into the River Vouga's upper reaches. However, abundance and age class diversity appeared to be higher downstream of Sernada and Carvoeiro weirs, corroborating the telemetry data which suggested difficulty in passing these obstacles during low precipitation years. In the River Caima, migration was most predictable, which might be related to daily water releases from a small hydropower dam at dusk, that stimulated the lampreys to resume migration. Poaching has had a considerable negative effect on the success of the tagged lampreys' migration: 76% of the animals released during 2005 were captured.

Population ecology of the sea lamprey (Petromyzon marinus) as an invasive species in the Laurentian Great Lakes and an imperiled species in Europe

“…The spawning migration ranges from September to March along the east coast of North America (Beamish 1980); begins in December, peaks in February-March, and ends with spawning in April-June in Southwestern Europe Portuguese rivers (Almeida et al 2000;Rev Fish Biol Fisheries (2016) 26:509-535 511 Oliveira et al 2004); and begins in February, continues through May-June, and ends with spawning between the end of May and early July in the Northwestern Europe Severn River, Britain (Hardisty 1986). Upstream spawning migration is triggered by flow variation and temperature, so increased migratory activity in periods of high discharge is likely a behavior adopted by sea lampreys to overcome difficult passage stretches to reach upstream spawning areas (Almeida et al 2002a;Andrade et al 2007;Binder et al 2010). Regulated increased river discharge at night (i.e.…”

“…In Southwestern Europe, the sea lamprey is economically valuable, and supports commercial fisheries in major river systems, but is vulnerable to reductions in suitable essential habitats. Conservation measures to rehabilitate sea lamprey habitat and to manage for sustained commercial exploitation have been proposed (Almeida and Quintella 2002;Andrade et al 2007). Further, conservation plans for sea lamprey should include projections of the geographic distribution of the sea lamprey in response to global climate change, with priority given to restoring suitable basins in Portugal (Lassalle et al 2008).…”

Sea LampreyPetromyzon marinusBiology and Management Across Their Native and Invasive Ranges: Promoting Conservation by Knowledge Transfer

“…Adults return from the sea to freshwater 145 between March and December when temperatures are between 10 and 19 C, with earlier migrations tending to occur at lower latitudes (Beamish, 1980;Malmqvist, 1980a;Andrade et al, 2007;Beaulaton et al, 2008). The adults are capable of migrating hundreds of kilometers 150 upstream into freshwater to find suitable spawning habitat, during which they do not feed (Beamish, 1980;Hardisty and Potter, 1971b); thus, migration, gonad maturation and spawning rely on energy reserves developed in the marine life phase (Beamish, 1980;Hansen et al, 155 2016).…”

“…These obstructions severely fragment their habitats and thus can strongly restrict the riverine habitats available 225 to spawning adults (Lucas et al, 2009), as well as impede the downstream movement of larvae/juveniles (Nunn and Cowx, 2012;Hogg et al, 2013). The blockage of migratory routes can thus significantly affect the lifetime fitness of P. marinus, impacting their population growth 230 and distribution, spawning success and recruitment, and affecting their vulnerability to fishing and predators (Andrade et al, 2007;Klamath River Expert Panel, 2010;Mateus et al, 2012). The passage of river lamprey Lampetra fluviatilis over 235 anthropogenic barriers has received some attention in Europe in recent years (Masters et al, 2006;Lucas et al, 2009;Kemp et al, 2011;Russon et al, 2011;Foulds and Lucas, 2013) and this literature might be informative for P. marinus, although some caution is suggested given the 240 larger body sizes of the latter.…”

“…In France reported annual catches include 58 tons from the River Loire in 1989 and 355 a mean of 8.5 tons per year from the River Adour between 1986 and 2004 (Beaulaton et al, 2008). In the Minho River and Tagus River, Portugal, annual catches can be as high as 120,000-160,000 and 10,000-15,000 individuals respectively (Suıssas, 2010), with high exploi-360 tation and illegal fishing considered as a major threat to population sustainability and conservation (Andrade et al, 2007;Mateus et al, 2012).…”