Pacific herring (Clupea pallasii) are a vital component of the marine food web and are a keystone/indicator species in Washington. These highly abundant, prolific fish are prey for a wide variety of birds, fish and marine mammals. Herring spawn for the first time at age two or three throughout Puget Sound at specific locations between early January and mid-June, depending on the stock. Eggs are deposited mainly on marine vegetation in the intertidal and shallow subtidal zone, with spawning activity sometimes creating “white water” from the cloud of released milt.
Herring stocks are defined by spawning grounds and spawn timing. Up to 21 stocks spawn annually inside Puget Sound; two additional stocks spawn on the Washington coast in Willapa Bay and Grays Harbor. Several genetic studies (see history of stock identification section of 2012 stock status report for details) have indicated that the Cherry Point and Squaxin Pass herring stocks can be differentiated, but all other sampled stocks in Puget Sound have not exhibited genetic divergence from each other. The observed lack of differentiation among other genetically sampled herring stocks from Puget Sound (Quartermaster Harbor, Port Gamble, Kilisut Harbor, Skagit Bay, Fidalgo Bay, and Semiahmoo Bay) suggests sufficient gene flow among populations, particularly those with similar spawn timing, that would reduce genetic divergence. With the exception of Cherry Point and possibly Squaxin Pass herring, Puget Sound herring stocks may be part of a metapopulation. Research conducted by WDFW’s Marine Toxic Contaminants group using herring as one of its monitoring species has indicated a life history/geographic separation between samples taken at from different herring stocks in Puget Sound. While it is important to protect all documented herring spawning grounds it may be more meaningful to examine abundance trends on a larger scale than the individual stock level.
Tagging of adult herring on their spawning grounds in the 1950’s from the Port Orchard-Port Madison, Quilcene Bay, and Holmes Harbor stocks documented significant migration of at least some of each of these stocks to offshore feeding grounds. For each tagged stock at least one recovery was made on Swiftsure Bank (off southwest tip of Vancouver Island) or the west coast of Vancouver Island in the summer, in addition to tag returns at or near their tagging site. There were also tag returns for each tagged stock from the Canadian reduction fishery in the southeast Vancouver Island region, which occurred mostly from October to January. These tag results suggest a summer outmigration, followed by a fall movement back toward the lower Strait of Georgia and return to the spawning grounds. It is most likely that Puget Sound herring stocks consist of a combination of “migratory” and “resident” fish. It is also probable that many stocks consist of both migratory and resident individuals.
Stock assessment of Puget Sound herring is based on estimates of the spawning biomass, which is the estimated tonnage of spawning (adult) herring in a given year; it does not include juvenile fish abundance. Two methods have been used by WDFW since the 1970s to provide quantitative estimates of herring spawning biomass: spawn deposition surveys and acoustic/trawl surveys. Prior to 1996, the spawning biomass for the 10-12 larger Puget Sound stocks typically was assessed by both methods each year while the smaller 6-8 stocks were surveyed by spawn deposition surveys only on a 3-year rotational basis. Beginning in 1996, duplicate assessment coverage was reduced and assessment for all known herring stocks has been attempted annually by at least one method.
Spawn deposition surveys provide a direct estimate of herring spawning biomass. Marine vegetation on spawning grounds is sampled for location of spawn deposition and spawn density, and those data are converted to an estimate of spawning escapement. These surveys are generally conducted weekly during a stock’s spawning season to document cumulative spawn deposition.
Acoustic/trawl surveys are conducted on prespawner holding areas early in, or prior to, the spawning season when abundance is peaking. This method utilizes computer interfaced echosounding equipment that produces real-time estimates of total fish abundance, which are apportioned to herring biomass based on trawl catch data. The weighted data from all trawl samples for each stock are pooled and extrapolated to the final spawning biomass estimate from spawn deposition surveys. Analyses of the trawl-caught samples provide the basis for detailed stock indices such as biomass age composition, annual survival rates, and recruitment. Due to WDFW budget reductions, herring stock assessment using acoustic/trawl surveys was eliminated in 2009, and currently only spawn deposition surveys are being conducted.
- Adam Lindquist
- Roy Clark
- Paul Clarke
- Kris Costello
- Mark Millard
- George Peterson
- Don Velasquez