Pacific herring (Clupea harengus pallasi) are winter–spring spawners which exhibit a south to north latitudinal dine in spawning time. In the eastern Pacific, major spawning populations are concentrated near San Francisco, in Puget Sound, and along the coasts of British Columbia and southeastern Alaska. In the Bering Sea, herring spawn in Alaska and along the Kamchatka Peninsula. In the western Pacific, herring spawn in the Sea of Okhotsk and the Japan Sea. Atlantic herring (Clupea harengus harengus) consist of both winter–spring and summer–autumn spawning groups characterized in the northeast Atlantic by oceanic, shelf, and coastal populations. The oceanic group are large migratory fish spawning off the coasts of Norway and Iceland. The shelf group includes the various locally migratory North Sea populations adjacent to the British Isles. The coastal groups consist of smaller fish restricted to the Baltic and White seas. In the northwest Atlantic, spawning occurs from northern Labrador to Virginia with spring spawners predominating in the north and fall spawners in the south. Herring typically congregate near their spawning grounds for several weeks to months prior to spawning. Temperature is one of the factors that determine when spawning occurs. The Atlantic herring exhibits sexual dimorphism in the spawning act with only the female interacting with the spawning substrate. Both sexes of the Pacific herring make physical contact with the substrate on which the adhesive eggs are deposited. Spawning grounds are located in high-energy environments, either nearshore for spring spawners or in tidally active areas for fall spawners. Spawn is deposited on marine vegetation or on bottom substrate, such as gravel, which is free from silting. The eggs are tolerant to temperatures in the range of 5–14 °C and salinities in the range of 3–33‰. Egg mortality results mostly from suffocation due to high egg densities and silting, predation, and, in intertidal spawn, from stresses imposed by exposure to air and from egg loss by wave action.