Pacific Herring

Fascinating facts about the Pacific Herring

• A single Pacific herring female can dump up to 20,000 eggs in one spawning bout, yet only about one of every ten thousand eggs survives to adulthood, showing how a tiny splash of life fuels entire coastal food webs.
• When a school spawns, the egg density can reach 6,000,000 eggs per square meter, creating a floating blanket of future fish that feeds countless predators in just a few hours.
• The species can grow to 45 cm (18 in) and weigh as much as 550 g (19 oz), but most adults are closer to 33 cm (13 in), a size that lets them slip through the nets of predators and fishermen alike.
• Pacific herring were fished for oil and fertilizer from the 1880s until 1966, and the overall fishery collapsed in 1993; today the fish are slowly returning to harvestable numbers in places like San Francisco Bay and Humboldt Bay.
• Named after naturalist Peter Simon Pallas, these herring hide their silvery bodies with guanine crystals that act like tiny mirrors, making them nearly invisible in dim water and helping them evade the many predators that rely on them for food.

At a glance

About the Pacific Herring

The Pacific herring (Clupea pallasii) glints like a moving ribbon of silver as it darts through the temperate waters of the North American Pacific coast and northeast Asia. Its bluish-green back fades into silver-white sides, a camouflage born of microscopic guanine crystals that reflect the surrounding light. A single mid-body dorsal fin and a deeply forked caudal fin give it a sleek, laterally compressed silhouette, while large, easily removable ventral scales and a scaleless head set it apart from its herring relatives. Adults typically reach 33 cm (13 in) and 550 g (19 oz), though exceptional individuals can grow to 45 cm (18 in). Beneath the bony, oily flesh lies a suite of adaptations: a tooth-less jaw punctuated only by occasional vomerine teeth, an unusual retinal structure that enables filter-feeding in dim light, and a complex nerve-gas bladder system that powers rapid vertical maneuvers. Each winter, schools of herring migrate from the open ocean into sheltered bays, San Francisco, Richardson, Tomales, Humboldt, and farther north to Sitka Sound, where they congregate over eelgrass and seaweed. A single female can lay up to 20 000 eggs, releasing a dense cloud that can reach six million eggs per square meter, yet only one adult emerges for every ten thousand eggs due to relentless predation. The fertilized spheres, 1.2–1.5 mm in diameter, incubate for about ten days at 10 °C before hatching into vulnerable larvae. This prodigious productivity makes Pacific herring a keystone species, linking planktonic producers to a myriad of predators, while its surprising ability to spawn repeatedly across years ensures its presence in the food web year after year.

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