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