Herring Fishery: The California Herring Fishery - An example of success and sustainability

Article from Outdoor California Magazine [Sep-Oct 2001, Vol. 62 no. 5]

By Diana Watters and Eric Larson

San Francisco Bay is at the center of the fifth largest metropolitan area in America, with a population of 6.6 million people, major ports for shipping and commercial fishing, and a variety of industries. San Francisco Bay also provides habitat for a diverse assemblage of fish and wildlife species despite its urbanization and accompanying human impacts.

One of the great natural wonders of San Francisco Bay is the annual return of California's largest spawning population of Pacific herring, which use the Bay as a breeding ground and nursery. The annual return of Pacific herring to San Francisco Bay supports a commercial fishery which is considered to be one of the last urban fisheries in America. The San Francisco Bay herring fishery, along with commercial fisheries for herring in Tomales Bay, Humboldt Bay, and the Crescent City Harbor Area, are closely managed by the California Department of Fish and Game (DFG). In fact, this fishery has been nationally recognized as one of the five best state managed fisheries in the country.

San Francisco Bay herring schools range in size from less than 10 tons of fish to tens of thousands of tons. One of the largest schools ever measured by DFG biologists was 15 miles in length and stretched from Bluff Point on the Tiburon Peninsula, through Racoon Strait, across to the San Francisco city waterfront and all the way down to Hunter's Point.

Prior to spawning, herring typically hold in deeper portions of the Bay for up to two weeks, while their gonads (ovaries and testes) ripen or mature. During this stage, a school will travel with the tidal currents, which can move at speeds of four knots or more. The schools will also grow in size as more individuals join up.

Most spawning occurs in the intertidal and shallow subtidal areas of the central part of San Francisco Bay between the Richmond-San Rafael bridge in the north to Candlestick Point in the south. As the school ripens, it begins to move into shallower water. Male scouts leave the school and move in to shallow water to find suitable spawning areas. As they do, they release milt into the water, cuing the rest of the school to follow and begin spawning. There are other cues, which in combination, are thought to induce spawning. One is the reduced salinity that rainfall brings, the other is the differences in tide heights depending on the phases of the moon. San Francisco Bay herring tend to spawn around the quarter moon, when the difference in height between high and low tides is least extreme, and currents are less pronounced. This makes it easier for the fish to spawn at a chosen site, by reducing both the amount of energy required to fight the current and the amount of eggs and milt swept away by the current.

While the males release milt into the water, the females swim with their bellies near suitable substrates and release up to 45,000 sticky eggs that adhere to the surface of the chosen substrate. For San Francisco Bay herring, suitable substrates include natural and manmade structures that are relatively siltfree, such as eelgrass and the red algae Gracilaria, rocks, shells, pier pilings, jetties, and boat bottoms.

A small spawn, involving a few tons of fish, can go unnoticed and be over in a single tide. Large spawns, however, are truly spectacular. Spawns of larger magnitude can go on for several days and cover miles of shoreline. The water turns milky with milt. When exposed at low tide, the fertilized eggs (embryos) can be seen blanketing the shoreline and structures such as pier pilings, giving them a pale golden color.

Schools of Pacific herring that move into the state's northern bays to spawn provide an important food source for other animals including invertebrates, fish, birds and mammals - which feed on the deposited embryos - as well as the spawning adults. A feeding frenzy often commences and can last for days following the completion of a spawning event. At the water's surface, large numbers of gulls, cormorants, pelicans and other marine birds, as well as California sea lions and harbor seals, can be seen feasting on herring and herring embryos. The scene is anything but quiet, with sea lions barking and gulls calling and fighting over fish. Beneath the water's surface, a variety of fish and invertebrate species also feed on the herring bounty.

Surviving embryos will hatch in about 10 days into larvae, which will then metamorphose into juvenile herring. They will spend spring and summer feeding and growing in San Francisco Bay before migrating to the open ocean to feed and grow some more. By the time they are two years of age, many, but not all, herring are sexually mature and return to the Bay to spawn. It is believed that all Pacific herring are sexually mature by age three and will return each year thereafter to spawn.

Because Pacific herring are relatively short-lived (maximum age is nine for San Francisco Bay herring) the success (or survival) of each year's cohort (or crop) of new fish has a large influence on determining the size of the population. A single highly successful cohort will dramatically increase population size while two or more poor cohorts drive the population size down quickly. A variety of environmental factors, that are not well understood, play a role in determining cohort success. These include Bay and ocean productivity (food), salinity, Delta flows, and temperature. Herring abundance is closely tied to Bay and ocean productivity, which, in turn, affects the abundance of zooplankton, a main food source for herring. Because of the close ties to environmental conditions, Pacific herring tend to fluctuate widely in abundance from year to year.

Since 1973, San Francisco Bay's herring population has supported one of the state's most valuable fisheries, often ranking among the top three in dollar value. The fishery provides two types of roe (egg) products which are traditional delicacies in Japan. The largest part of the fishery is for the egg skeins or sacks from the females which are called "kazunoko". For this product, herring are caught by means of anchored gill nets placed in the water in a manner that catches the fish as they move in to spawn. It is at this point that the eggs are at their ripest. The egg skeins are later removed from the females and processed in a salt water brine while the male and female bodies are processed for animal feed and human consumption.

The second roe product is called kazunoko kombu, or eggs-on-kelp. In this fishery, the stipes of giant kelp are suspended from constructed rafts which are moved by the fisherman to potential spawning locations within San Francisco Bay. Following the spawn, the kelp fronds with the egg deposits, often several layers thick, are removed from the water and processed in a salt water brine for the market. This carefully managed and highly regulated fishery is also considered to be one of the DFG's commercial fishery success stories.

The overall health and condition of California's Pacific herring population is closely monitored by the DFG. Annual population assessments are conducted by the DFG's Pacific Herring Research Project and include both hydroacoustic surveys of herring schools and surveys of the egg deposition associated with spawning events. Together, these surveys are used to estimate the season's spawning biomass. The DFG also collects samples of herring from each school to determine their condition and the age structure of the population. The catch quota is set annually at no more than 20 percent (typically 15 percent or less) of the previous season's spawning biomass estimate. This harvest rate takes into consideration oceanic conditions, population size and structure, and the importance of Pacific herring as a food fish for other species. The quota itself is set each year by the Fish and Game Commission based on the DFG's recommendations. The fishery restrictions and catch limits are strictly enforced.

The California commercial herring fishery is a limited-entry fishery. For San Francisco Bay there are some 415 permit holders. These permittees are divided into three fishing groups or platoons. Each platoon is allowed to fish only during specified periods of time, thus limiting congestion on the water and conflict with other users of the Bay.

It is possible for the fishery to catch the quota in a very short period of time, sometimes in less than 24 hours. The DFG's Pacific Herring Fishery Management Team closely monitors the catch and can quickly close the fishery to prevent the established quota from being exceeded. Gill nets are restricted in mesh size and length and must be tended at all times to avoid lost nets and incidental catches.

The San Francisco Bay herring fishery is truly a sight to behold. While much of the actual fishing activity occurs during nighttime hours, there is still plenty of fishing that takes place throughout the day. Many of the Bay Area's ferry boat commuters have seen this fishing activity firsthand from their morning and evening boat-side views, but all are invited to the Central San Francisco Bay's shoreline during the months of December and January, and at times through mid-March to see the Bay's Pacific herring fishery first hand.

Diana Watters is an associate marine biologist and project leader for the DFG's Marine Region Pacific Herring Research Project.

Eric Larson, contributor to this article, is a Senior biologist supervisor for the DFG's Marine Region and is the research and fishery manager for the state's Commercial Pacific herring fishery.