Mature adults ascend rivers during spring and early summer (Ref. 35387, 88186) when water temperature ranges from 10-18°C (Ref. 88184) and gather in small groups (Ref. 5504). Behavioural experiments suggest that mature sea lampreys can smell the presence of ammocoetes and use this as a guide to functional spawning grounds (Ref. 88714). Spawning occurs in fast-flowing highly oxygenated areas with gravel, pebbles and sand bottoms (Ref. 12324). Females release small eggs (< 1 mm diameter) in nests exclusively built by males, which have been observed to reach the spawning grounds first (Ref. 5504, 12324, 51442). Spawning takes place mostly during sunny days, when water temperature is at least 15°C (Ref. 88171). Ammocoetes hatch after 7-14 days (41851, 88186). Successful hatching requires water temperatures of 15-25°C (Ref. 88715). Ammocoetes develop in freshwater and migrate to the sea after metamorphosis (Ref. 5504). Also Ref. 30578, 51442.
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