Category: Species Status Reports
Published: September 2019
Publication number: FPT 19-07
Author(s): Todd Sandell, Adam Lindquist, Phill Dionne, and Dayv Lowry
This is the sixth edition of the Washington Department of Fish and Wildlife’s report on Pacific herring stock status. As in the 2012 edition, data collected from spawning ground surveys were used and geographic coverage is limited to greater Puget Sound (also referred to as the southern Salish Sea; SSS). In this report we revised our traditional stock status review method to reduce the influence of extreme values in any particular survey year and end the practice of using inputed values for years with missing data.
In the current report stock status was determined by comparing the four-year mean, rather than the two year mean, of estimated abundance with the previous 25-year mean abundance. (This reduces the influence of an abundance estimate from any single year on our understanding of recent stock status, minimizing status volatility, and brings assessment in alignment with the periodicity of these reports). We also base the mean abundance estimates for each stock only on years for which data are available, rather than using mean imputation for years in which data are unavailable, as in past reports. This practice added apparent stability in abundance over periods for which, in reality, no assessment of stock status could be made. Furthermore, we apply consistent, numerical stock status evaluation criteria and revised categories to include an “Increasing” status to reflect the large increases of abundance observed for some stocks. The new status categories are decribed in the Stock Status section on page 19. In the table of historic stock status (Table ES1), the new evaluation and status assignment criteria are used for each four year period, establishing new status time trends.
Using the new evaluation and status assignment criteria, the status category of 7 stocks has worsened, 12 stocks have the same classification, and 2 stocks have improved in the four years since 2012. The number of stocks classified as Increasing or Healthy have decreased from 5 to 4 (Table ES1). Cumulative abundance of the Other Stocks Complex remained relatively stable (Figure ES1) over the past four years. For the 2013-16 period the aggregate of SSS herring stocks is considered Healthy (total estimated spawning biomass is 110% of the 25 year mean). While this metric is the traditional model of assessment, it obscures several important trends. Stability of the total herring spawning biomass is driven entirely by large increases in the Quilcene Bay (Hood Canal) stock, which has increased 224% over the past four years and now makes up over half of all the SSS spawning herring biomass. If Hood Canal stocks are excluded from the Other Stocks Complex, the aggregate biomass of the remaining stocks has decreased and would now be categorized as Declining.
By basin, South and Central Puget Sound stock aggregates (Table ES1, Figure ES3) have changed from Declining to Critical, with four individual stocks (Purdy, Wollochet Bay, Quartermaster Harbor, and Port Orchard-Port Madison) having no spawn detected in 2016. The Whidbey Basin stock aggregate has also been changed from Healthy to Depressed. The Strait of Juan de Fuca and Hood Canal stock aggregates continue with the same status from 2012, with Strait of Juan de Fuca being Critical and Hood Canal categorized as Increasing. Northern stocks have been changed from Depressed to Healthy, due mainly to robust years at Semiahmoo and Samish/Portage Bays.
The genetically distinct Squaxin Pass stock is considered Depressed at this time (51% below 25 year mean), due in part to changing the sampling methodology (see the Squaxin Pass section for more information). The Cherry Point stock also shows no signs of recovery from its low level of abundance; spawning biomass in 2016 was again an all-time low (the stock has now declined over 96% from the initial estimate made in 1973). However, by basin the northern stocks (excluding the Cherry Point stock) aggregate spawning biomass is classified as Healthy partially because the Cherry Point Stock has been Critical for so many years that the rolling 25-year mean now fails to capture historic biomass peaks.
Commercial herring fisheries in the SSS have experienced several major shifts since the start of the last century, as described in detail by Trumble (1983) and Williams (1959), and summarized in a previous Washington state stock status report (Stick and Lindquist 2009). At present, the “sport bait” herring fishery continues to be the only commercial herring fishery still operating in Puget Sound, providing bait for sport salmon and groundfish fisheries. The sport bait fishery mostly targets 1+ to 2+ year old (juvenile) herring assumed to be an aggregate of stocks within the region. Almost all harvest in recent years has been taken by non-tribal fishers using relatively small (maximum length of 200 feet) lampara seines, with a small portion of landings captured via dip bag net gear. This fishery has a harvest guideline of less than 10% of the cumulative adult herring spawning biomass (SB) estimate of stocks that spawn in South/Central Puget Sound, Hood Canal, and the Whidbey Basin (Bargmann, 1998; Day, 1998), but usually only achieves 2-6% of the SB because of market conditions and processing/holding capacities (Stick et al., 2014). Fishing activity is primarily in South/Central Puget Sound. Hood Canal has been closed to all commercial herring fishing since 2004 due to concerns about the impacts of low dissolved oxygen and elevated summer temperatures on fish health and abundance, and several other areas are closed year round or seasonally to minimize harvest of spawning adults (Figure 7). Since the commercial harvest seasons depicted in Figure 7 were developed, additional spawning areas have been identified. To protect the herring spawning in these newly documented areas, the Department may consider modifications to the commercial seasons.
Stock status throughout the SSS is influenced by a variety of natural and anthropic factors, including habitat availability, predation intensity, and water quality. Efforts to comprehensively assess and evaluate stressors that might be mitigated by management actions is currently underway. Ensuring long-term persistence of herring stocks is key to food web and ecosystem health, and is a primary goal of the Department’s Marine Fish Science Unit.