The Pacific herring (Clupea pallasii) is a remarkable species of fish that holds significant ecological importance in the Pacific Ocean environments of North America and northeast Asia. Its silvery appearance, unspined fins, and deeply forked caudal fin distinguish it from other species within the herring family. Pacific herring can be found along the California coast, ranging from Baja California up to Alaska and the Bering Sea. In Asia, their distribution extends south to Japan, Korea, and China. As a keystone species, the Pacific herring exhibits high productivity and plays a critical role in the interactions between various predators and prey.
Pacific herring exhibit variable spawning seasons, often occurring in the early part of the year within intertidal and sub-tidal environments. They commonly spawn on eelgrass, seaweed, or other submerged vegetation. What makes them unique is that they do not die after spawning and can breed in successive years. This reproductive strategy contributes to their high productivity and population sustainability. While the Pacific herring fishery collapsed in 1993, it has been gradually recovering in several North American stock areas, paving the way for future commercial viability.
The Pacific herring showcases distinct physical features. It possesses a bluish-green back and silver-white sides and bellies, providing effective camouflage in its surroundings. The silvery coloration results from guanine crystals embedded in their laterals. This species has a single dorsal fin positioned mid-body and a deeply forked tail-fin. Its body is laterally compressed, with ventral scales that protrude in a serrated fashion. Notably, Pacific herring lack scales on their heads and gills, making their scales large and easy to extract.
Measuring up to 45 centimeters in exceptional cases, Pacific herring typically reach a length closer to 33 centimeters. They can weigh up to 550 grams. Internally, their flesh is oily and their bones are quite bony. Unlike some other fish species, Pacific herring lack teeth on their jawline but have teeth on the vomer bone. Their unique retinal morphology allows them to engage in filter feeding, even in extremely dim lighting environments. Furthermore, their complex nerve receptor system design facilitates rapid vertical motion through the connection to the gas bladder.
Pacific herring prefer sheltered bays and estuaries for spawning. Along the American Pacific Coast, notable spawning locations include San Francisco Bay, Richardson Bay, Tomales Bay, and Humboldt Bay. Adult males and females migrate from the open ocean to these areas, usually between November and December. The precise triggers for spawning are not fully understood, but both males and females gradually transition from deeper channels to shallower intertidal or sub-tidal waters. They exhibit a preference for submerged vegetation, particularly eelgrass, as a substrate for egg deposition.
During spawning, a single female Pacific herring can lay up to 20,000 eggs. However, the survival rate of the resulting juveniles is relatively low, with approximately one adult herring per ten thousand eggs reaching maturity due to predation by various other species. The spawning process is thought to be initiated by the male's release of milt, which contains a pheromone stimulating the female to begin oviposition. This collective behavior often leads to intense spawning events, with egg densities reaching up to 6,000,000 eggs per square meter.
The fertilized spherical eggs, measuring 1.2 to 1.5 millimeters in diameter, incubate for approximately ten days in estuarine waters with temperatures around 10 degrees Celsius. During this vulnerable stage, both eggs and juveniles face significant predation pressure.
Historically, Pacific herring has been a valuable resource due to its productive nature and significant biomass. However, overfishing has caused the collapse of the North American Pacific herring fishery in 1993. Since then, active management by North American resource managers has been gradually enabling the recovery of Pacific herring populations. Harvestable numbers have started to reappear in various North American fisheries, including San Francisco Bay, Richardson Bay, Tomales Bay, Sitka Sound, Half Moon Bay, and Humboldt Bay.
Currently, commercial harvesting of Pacific herring primarily focuses on bait and roe. Past commercial uses included fish oil and fish meal. Efforts are being made to ensure sustainable fishing practices, taking into account the importance of maintaining balanced ecosystems and the long-term viability of Pacific herring populations.
Pacific herring's designation as a keystone species reflects its critical role in maintaining ecological balance and supporting the health of marine ecosystems. As a primary forage fish, it serves as a vital food source for numerous predators, including marine mammals, seabirds, and larger fish species. Additionally, herring play a crucial role in nutrient cycling, transferring energy and nutrients from lower trophic levels to higher trophic levels.
By contributing to the stability and productivity of the Pacific Ocean environment, Pacific herring helps sustain the diversity and abundance of other species. Protecting and managing the populations of this keystone species is essential for maintaining the overall health and resilience of marine ecosystems.