Portuguese Red List: Vulnerable (VU).
The anadromous sea lamprey is a semelparous species (a single reproductive episode before death), with a freshwater larval phase and a post-metamorphic marine phase. Spawning migration to continental waters begins in December and peaks between February and March, with spawning occurring between April and June in river stretches with sand, gravel and pebbles bottoms. Larvae (ammocoetes) live 3 to 7 years burrowed in fine sediment deposits of rivers and streams in freshwater, in shallow areas with weak currents. Sea lamprey larvae are filter feeders, while the adults are parasitic feeders. Adults stop feeding when the spawning migration begins. The sea lamprey is a native species, occurring in the main Portuguese river basins north of Sado and in the Guadiana basin. Main threats include the loss of river continuity, poaching and overfishing.
Portuguese Red List: Endangered (EN).
The allis shad is a pelagic species that occupies the water column during its period in marine habitat and feeds on plankton. The adults stop feeding during the spawning migration, which begins in February and lasts until June, taking place in shallow waters over gravel substrate. Allis shad are predominantly semelparous. Downstream migration to the estuaries occurs in the autumn and the juveniles enter oceanic waters before completing their first year of life. This species occurs in the Minho, Lima, Cávado, Douro, Vouga, Mondego, Tejo and Guadiana river basins. The main threats to the allis shad are the loss of river continuity that prevent the fish to reach spawning and/or feeding areas, alongside with overfishing.
Portuguese Red List: Vulnerable (VU)
The twaite shad is a pelagic species that feeds on plankton but may occasionally feed on smaller fishes. Unlike the allis shad, this is a predominantly iteroparous species (reproduction occurs several times in life). The preferred spawning habitat also differs, as the twaite shad remains downstream, in the lower section of rivers. Adults stop feeding during spawning migration, which takes place between February and the beginning of summer, with juveniles migrating towards the sea in the autumn. Twaite shad occurs in the Minho, Lima, Cávado, Douro, Vouga, Mondego, Tejo, Sado, Mira and Guadiana river basins. The main threats to this species are the loss of longitudinal connectivity within river basins that prevents fish to reach spawning and/or feeding areas, alongside with overfishing.
Portuguese Red List: Critically Endangered (CR).
Salmo trutta has two distinct ecotypes: the anadromous form – sea trout – and the resident form, potamodromous – river trout. In Portugal, the species is present in the river basins of the north and center of the country, specifically between the Minho and Mondego basins, which represents the southern limit of its distribution. Juveniles migrate to the ocean, where they complete their growth and reach sexual maturity, subsequently returning to rivers to reproduce. The spawning habitat is characterized by sections of well-oxygenated and cold water, moderate to strong currents, low levels of pollutants, and coarse substrate (gravel and pebbles). Migration to the sea occurs between March and May. Reproductive migration begins between mid-summer and early autumn, with spawning occurring between November and February in more upstream areas. Upon completion of the reproductive cycle, some individuals return to the sea, and may spawn again during their lifetime. The species is of territorial nature. Its diet consists of benthic invertebrates, insect larvae, and mollusks and larger trout may feed on fish. The primary threats to sea trout populations include the loss of river connectivity due to dam and weir construction, pollution, the introduction of invasive species, overfishing, and inadequate fishing regulations.