Capelin have two spawning modes. Many populations spawn on shallow subtidal gravel and sand at depths of a few metres to tens of metres. Others spawn demersally in the intertidal zone, riding a wave onto the beach, releasing eggs and milt among the gravel, and being carried back by the backwash. The eggs adhere to the gravel and develop in the sediment.
The event is compressed and conspicuous. Beaches turn silver for a few days, seabirds and whales gather offshore, and in Newfoundland the arrival is known as the capelin roll and has long been harvested with dip nets and buckets. Mortality among spawners is heavy, and many fish are stranded above the waterline.
Capelin matter far beyond their own biology. They are the main energy conduit between plankton and larger predators in several North Atlantic ecosystems, and the timing of the roll interacts with cod condition, seabird breeding success and whale distribution. Whether recent shifts in capelin timing and abundance are driven mainly by warming, by predation, or by fishing is contested, and the Newfoundland stock has not returned to earlier levels.