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Wildlife Spotlight: Pacific Herring

Herring
Pacific herring. Photo: NOAA

By Cori Hach

Each spring in the Gulf of the Farallones Marine Sanctuary, schools of Pacific herring return to their natal waters to spawn.  Journeying back from the open ocean, they linger for days or weeks in the coastal waters outside Bodega Bay before entering and congregating in the shallow inter-tidal zone. 

It’s not completely clear how a school makes decisions about when and where to begin spawning.  Salinity levels are a factor, as is temperature.  Herring usually select calm and protected areas with vegetated or rocky terrain where the eggs will be secure as they mature.

Whatever the trigger, at some point the moment is ripe!  Thousands upon thousands of narrow, silvery fish swirling and circling among each other, each obeying the same internal cue—this is the time, this is the place. 

The males release milt, which can remain fertile in the water for about three hours.  A pheromone in the milky substances compels the females to begin extruding.  Making pass after pass, creating layer after layer, the females deposit adhesive eggs onto underwater substrate.  Each female carries tens of thousands of eggs—up to 50,000 in a large fish. 

The spawning assembly can last up to a week for large schools, and when it ends the adult herring depart the bay immediately.  They leave behind a swath of shoreline coated with millions of fertilized eggs which will hatch about ten days later.

Ecology and Life Cycle

The annual spawning ritual is important for many marine animals besides the herring themselves. Herring are an important forage species for larger marine life all year round, but they create a bona fide smorgasbord during spawning. Gulls, cormorants, pelicans, sea lions, harbor seals, and various fish take their fill from the concentrated throng of spawners.  Predation of the eggs, especially by seabirds, is also high. 

Those eggs that do survive to the larval stage hatch with a yolk-sac attached to provide nourishment as they develop.  Once the yolk-sac is depleted, the larval herring has to start finding its own food, primarily the eggs and larvae of even smaller organisms.  Eventually, juvenile herring trade the protected waters of the bay for the open ocean. 

Herring are sexually mature by age three, and from then on they return to their home bay annually to spawn.  Juvenile herring tend to stay closer to shore during the remainder of the year, whereas adults disperse further out into the ocean.  Some herring live up to ten or eleven years and grow up to eighteen inches, but most live between six and eight years and grow to about eleven inches.

Herring Fishery

Herring in the Gulf of the Farallones Marine Sanctuary face constant peril from predation; that’s why the natural survival rate is so low. Outside the sanctuary, though, herring may face a different sort of obstacle entirely—fishermen.  Neighboring San Francisco Bay, for example, is one of the nation’s largest urban commercial fisheries. 

Adult herring are a low-value fish, processed into meal for pet food and poultry feed.  Herring eggs (roe), on the other hand, can be extremely valuable.  Called “kazunoko”, the roe are a traditional Japanese holiday gift. 

At the peak of the California industry in 1979, fishermen could make up to $4,000 per ton from herring.  Now, however, kazunoko has slid from a luxury item to an everyday food in Japan, and during the 2006-07 herring season, fishermen made only $560 per ton for the same product. 

A different method of harvesting the roe was designed by some inventive scuba divers.  Instead of catching adult herring and extracting the roe from the females, fronds of giant kelp are dangled underneath rafts placed in the midst of a spawning event.  Once the female herring deposit several layers of eggs on the kelp, the fronds are gathered and exported.  This roe-on-kelp, called “komochi kombu”, is also a popular Japanese delicacy and is even more valuable per pound than plain roe. 

Every winter you can see the Herring fishing boats come into San Francisco Bay.