Predators of Pacific herring are whales (grey), dolphins, birds (gulls), seals, Stellar sea lions, larger fish (shark, dogfish, salmon, cod, halibut) and of course, humans. Planktivores, herring feed on phytoplankton, euphausids, also copepods, mysids, amphipods and zoea of crabs mainly by filter feeding. Clupea pallasi is sometimes referred to as a keystone species.
Spawning seasons vary by geographic region, anytime from December to July depending on the latitude. In Alaska herring can be found spawning in late March and can continue through mid-July depending on the location.
The eggs of Pacific herring are 1 to 1.5 mm in diameter, pale, amber and translucent. Eggs exhibit adhesive qualities and when deposited by females on intertidal and subtidal vegetation (kelp, seaweed, eelgrass, spruce boughs) stick to the substrate in large masses. Males then pass over the eggs, releasing milt to fertilize them.