THE ANADROMOUS SEA LAMPREY IN PORTUGAL: BIOLOGY AND CONSERVATION PERSPECTIVES

The sea lamprey is a species with high economic value in Portugal. During the spawning migration they are most active at night, and attain a ground speed that varies between 0.84 km h-1 and 1.5 km h-1. The duration of the larval stage in Portuguese rivers is between four and nine years and metamorphosis occurs from autumn to winter, with a peak in October-November. Larval distribution is strongly dependent upon sediment, especially particle size composition. Smaller individuals (20 mm < TL ≤ 60 mm) are commonly found on silty sand bottoms. Ammocoetes with a total length of 60 mm to 140 mm prefer a more heterogeneous substrate, where gravel and silt seem to make an identical contribution to sediment composition (gravel-silty-sand). The larger ammocoetes (140 mm < TL ≤ 200 mm) clearly prefer more coarse sediments, substrates composed of sand or gravelly sand. The major constituents of the microphagous diet of the ammocoetes are microalgae belonging to the class Bacillariophyceae. Overfishing and habitat destruction are the two major threats to the conservation of the sea lamprey in Portugal. 4