Pacific Herring, Clupea pallasii

Pacific Herring, Clupea pallasii. Fish caught from within San Francisco Bay, San Francisco, California, January 2021. Length: 10 cm (3.9 cm). Catch, photograph and identification courtesy of Vince Golder, Santa Cruz, California.

The Pacific Herring, Clupea pallasii, is a member of the Herring or Clupeidia Family, that known in Mexico as el arenque del Pacifico. There are two living global members of the genus Clupea Sardinops, one of which is found in Mexican waters, this species from the Pacific Ocean.

The Pacific Herring has a slender elongated compressed fusiform body with a depth that is 18% to 22% of standard length. They are bluish-green dorsally, silvery on their sides, and white ventrally. They have a relatively small oblique mouth that opens at the front and terminates before their eyes. Their anal fin has 12 to 23 spines; their caudal fin is forked; their dorsal fin is located mid-body with no spines and has 13 to 21 rays; and, their pelvic fins are under the dorsal fin. They are covered with large scales.

The Pacific Herring is a pelagic coastal schooling species that are found in brackish and marine waters in large schools on the surface in the surf zone at depths up to 250 m (820 feet). They reach a maximum length of 46 cm (18 inches) and can weigh up to 550 grams (1 lb 3 oz). They feed on phytoplankton and zooplankton in nutrient-rich waters associated with oceanic upwelling possessing the unusual ability to filter-feed in dim-lighting environments and can make rapid vertical migrations; young fish feed on zooplankton such as copepods. Reproduction is oviparous with batch fecundities of each female being up to 20,000 eggs. The adults migrate from the open ocean to spawn in sheltered bays and estuary environments, commonly on eelgrass, seaweed or other submerged vegetation. The larvae metamorphose into juveniles in two to three months and the juveniles remain in coastal waters for two to three years. They rely on their silvery color for camouflage to avoid predation, however their eggs and juveniles are subject to heavy predation and 10,000 eggs will produce only one adult. They have life spans of up to 19 years in northern latitudes.

In Mexican waters the Pacific Herring is found in the Pacific Ocean but has a very limited distribution being reported to be found along the west coast of the northern Baja Peninsula.  Recently these populations have significantly declined with fish being smaller in stature with shorter life spans which is attributed to global warming and rising water temperatures and loss of eelgrass habitat.

The Pacific Herring is similar to the Pacific Sardine, Sardinops sagax (a row of black spots mid body; pelvic fin under the rear of the dorsal fin).

From a conservation perspective the Pacific Herring is currently considered to be of Data Deficient. Pacific Herring are currently harvested commercially at a level of 400,000 tons per year on at the global level with fish primarily caught via purse seines. They are utilized for sushi, bait and roe but their meat is very oily and they are very bony. The seasonal collection of Herring Roe has been a time-honored traditional practice among the natives of Pacific Coast of Alaska and Canada for centuries. Herring Roe (called Kazunoko) emerged as a significant market in Japan in the 1960s with majority being collected in Alaskan waters. This demand took a dramatic downturn in 2023 due to overfishing, depleted stocks, and loss of eelgrass habitats. They are considered to be an essential component of the oceans life cycle providing a food source for birds, fish, invertebrates and marine mammals.