At least one stock of Atlantic herring spawns in every month of the year. Each spawns at a different time and place (spring, summer, autumn, and winter herrings). Greenland populations spawn in of water, while North Sea (bank) herrings spawn at down to in autumn. Eggs are laid on the sea bed, on rock, stones, gravel, sand or beds of algae. Females may deposit from 20,000 to 40,000 eggs, according to age and size, averaging about 30,000. In sexually mature herring, the genital organs grow before spawning, reaching about one-fifth of its total weight.