HERRING: Lifecycle

[John Pierce]

SIZE: 5 to 12"

EGGS
Between February and April, depending on location, herring congregate in huge numbers to spawn along the coastal shores. The females lay their sticky eggs (avg 20,000) on seaweed, sea grass, or rough rocks. The males spread their sperm, turning large swaths of the ocean into a characteristic turquoise blue color. Depending on the intensity and size of the spawning population, spawning activity lasts 2 to 4 days. A spawn event can stretch over many kilometers of shoreline, ~5,285 km (or 18 %) of British Columbia's extensive 29,500 km coastline have been classified as herring spawning habitat. Of this, an estimated 300 to 600 kilometres, or about 1.8 % of BC's total shoreline length, is intensively utilized by herring spawners in a typical season.

LARVAE
The fertilized eggs take between 10 to 14 days to hatch and the tiny (5.5-7.5 mm) larvae drift with the coastal currents. After another 10 to 14 days, when the larvae (now about 10 mm in length) use up their yolk sac, they begin to feed on phytoplankton and the smallest zooplankton, such as the larvae of barnacles. The herring larvae remain in near shore waters close to their spawning grounds in the protective cover of shallow water habitats. Usually the older herring have left the spawning grounds by the time the eggs hatch. Sometimes, when spawning is drawn out over a long time or there is a second wave of spawning on the same spawning ground, adult herring might feed on herring larvae.

JUVENILES
After 2 to 3 months the larvae develop into juveniles. During the summer of their first year, the juveniles form schools in shallow bays, inlets, and channels. At this stage herring are the ideal food for a host of predators including fish (such as perch, salmon, and dogfish), mammals (such as seals), and birds (such as gulls, cormorants, and diving ducks). It is estimated that only one herring out of 10,000 eggs reaches adulthood.

FINGERLINGS
By fall, juvenile herring are fingerlings, meaning they are about the size of fingers. These juveniles have developed scales and working fins and resemble the adults in appearance.  Technically, the juvenile stage lasts until the fish is fully grown, sexually mature, and interacting with other adult fish.  At this time, the juveniles move into deeper water where they are spatially separate from the adults. After 2 to 3 years, they emerge as mature herring and then join other schools of adult herring.

ADULTS
Herring mature at 3 to 4 years of age and grow to 25 - 45 cm in length. In Southern Alaska and British Columbia, they can reach an age of 8 years; in the Bering Sea the maximum recorded age is 19 years!  Recently, a shift to younger ages and smaller sizes of only about 20-25 cm has been observed [link to TEK on herring size] in British Columbia and southern Alaska. Although some mixing occurs between schools, tagging studies show that most Pacific herring remain in the same school for years. Adult herring live in huge schools of many millions of fish and forage in the open coastal and offshore waters. Observations over the last century indicate a change in herring populations and their behavior. Up until recent decades, some schools tended to stay in particular large bays. These "resident" or "homesteader" stocks are largely extirpated. Historical documents record the huge extent of some herring schools. For instance in 1893 in the Strait of Georgia, "a small tug passed for three hours through a continuous mass of migrating herring in the month of June".