Herring Highway

What Are Herring?

Pacific herring (Clupea palasii) are a critical component of trophic cascades of northeast Pacific ecosystems. Herring shoal in large numbers in specific areas before spawning along sweeping reaches of the Salish sea nearshore during the first months of winter into spring (Stick et al., 2014, Sandell et al., 2019, Keister 2020).

Image 2: Adult herring with eggs on Eelgrass, Pulali Point, Hood Canal, Washington, 8 March 2020. Photo by Anne Shaffer and CWI.

Spawning

Herring spawning in the Salish Sea begins in January and in some areas continues until June. The majority of spawning occurs almost simultaneously across hundreds of miles in March. Spawning begins with a broadcast release of sperm by males, also called ‘white water’ due to the striking coloration when observed from the air that occurs concomitantly with females laying eggs on eelgrass (Zostera spp) and seaweeds (primarily Gracilaria and Sargassum spp).

Image 3: Herring 'white water' British Colombia. Pacific Wild https://pacificwild.org/

Spawning Events

A single herring spawn event can cover tens of miles of shoreline of the Salish Sea, and provides significant nutrient resources that herald the beginning of spring. These events are critical food resources for thousands of migrating sea ducks, gulls, eagles, marine mammals, and fish (Sandell et al. 2019, Fox et al., 2015, 2018). The majority of spawning events from British Columbia, Canada and Washington occur within a few weeks.

Image 4: Herring eggs laid on Eelgrass (Zostera spp) and seaweed (Sargassum spp) in Hood Canal, Washington. Photo by Dave Parks and CWI.

Hatching Herring Highway

Herring larvae hatch from eggs roughly two weeks after spawning occurs, filling the Salish Sea as a fundamental component of the first annual zooplankton blooms that are the basis for our coastal food chain. Slide 1/3

Image 5: Hatching herring larvae. Photo by Anne Shaffer and CWI.

Herring Highway Continued

Slide 2/3

Image 6: Zooplankton biomass in the Salish Sea over multiple herring spawning seasons (Sandell in prep., figure by Julie Keister, University of Washington)

Herring Highway Continued

Slide 3/3

Image 7: Average density (#/m ³ ) for 2015 (primarily March - September) of all larval fish (including herring) in seven basins of the Salish Sea. Figure from Stonecipher et al. 2016.

Juvenile Herring

Mere months after hatching, juvenile herring form dense migrating schools along reaches of the Salish sea, and are seasonally the most abundant fish along shorelines including the San Juan Islands and Strait of Juan de Fuca (Miller et al., 1980, Simenstad et al., 1977, 1988, Shaffer 2019, 2020; Shaffer et al., 2023), literally filling, and fueling, the Salish Sea ecosystem. During June and through summer, herring larvae/juveniles migrate off natal spawning beds and then intersect with the migrations of juvenile salmon emigrating to the nearshore from natal rivers. This finely tuned intersection of these two groups of fish is the first of a lifelong and fascinating nexus of multiple migration pathways, and critical and complex ecosystem interactions (Shaffer et al., 2019, 2020; Shaffer et al., 2023). These dramatic and large juvenile herring migrations are also important culturally for native peoples (Butler et al 2019).

Image 8: Juvenile salmon smolts preying on large shoals of young-of-the-year herring, Strait of Juan de Fuca. Photo by Anne Shaffer and CWI.

Pressures

Historically, commercial fisheries in the southern Salish Sea targeted adult herring shoals primarily for the sac roe and reduction fisheries. Currently a much smaller scale bait fishery, targeting juvenile herring, continues to the present (Sandell et al., 2019). Resource management research to date therefore has focused on changes in trends of distribution and abundance of herring spawning stocks, spawn and spawning locations (Stick et al 2014, Sandell et al., 2019). Little is known about the density and movement of larval or juvenile herring, despite the important role these fish play in fueling the Salish Sea ecosystem.

Image 9: Herring fishing boats. Pacific Wild https://pacificwild.org/

Herring larvae are particularly vulnerable to ecosystem stressors including water quality (Welsh 2015), temperature, and acidity (see Francis and Lowry, 2018 for discussion). Stormwater and road runoff conveyance are ubiquitous on our regions' shorelines, and route large volumes of extremely toxic water to herring larvae precisely where herring larvae are growing and hatching (Harding et al., 2020).

Image 10: Uncontrolled upland stormwater runoff and outfall along a marine shoreline.

Photo by David E. Hess

Herring Numbers

Herring numbers in the B.C. and U.S. zones of the Salish Sea declined significantly over the last twenty years, coinciding with a collapse of the Salish Sea ecosystem and declining populations of the higher trophic levels that depend on them, including marine birds, salmon, and subsequently, southern resident killer whales (SRKW) (Stick et al., 2014, Francis et al., 2018). Losses have been broadly attributed to overfishing, nonpoint and point source impacts to water quality, oil spills, and habitat losses (Francis et al., 2018). There is very little known about the status of and specific impact factors to vulnerable larval and juvenile herring, including their distribution trajectory in the Salish Sea, their patterns of movement, or exposure pathways along the shoreline.

Image 10: Herring stock status Washington state Salish Sea (Sandell et al., 2019)

Why Does It Matter?

It is clear why this matters. Food availability for Southern Resident Killer Whales (SRKW) has been identified as the top risk factor for continued survival (WDFW 2020, Figure 10). Resident Orca are big, fish-eating whales and they need big salmon. Big salmon,-in particular Chinook and coho- in turn need abundant, healthy forage fish. Juvenile Chinook and coho-the most vulnerable of salmon stages- need juvenile forage fish, of which juvenile herring in nearshore areas are a critical component (Duffy et al., 2010, Shaffer et al., 2019, 2020). So what drives the presence of these larval and juvenile herring throughout the Salish Sea? Are these juvenile shoals linked? How far do they migrate? In a nutshell, we don’t know.

Image 11: Southern resident killer whale feeding on salmon in the Salish Sea. Photo by American Rivers.

Migrating Larval / Juvenile Herring: Ecosystem Drivers, and Stressors

We do know that wind driven surface currents are drivers of herring larvae, post larval, and juvenile migration within the inland B.C. Salish Sea (Snauffer et al., 2014). But this is only one region of a very large and linked system. The localized, detailed mechanistic relationships between physical forcing processes of local wind and current patterns, as well as the temporal and geographic linkages of impact factors and juvenile herring presence/distribution of the Salish Sea, are not known. Without a detailed understanding of the migration drivers of this juvenile ‘herring highway’, it’s impossible to identify and prioritize ecosystem and local-scale impactors to these large and important groups of vulnerable young fish as they migrate thru the Salish Sea. Further, climate change driven changes of wind and surface current patterns that drive larval distribution are inevitable, but not understood. Changes/disruption in seasonal wind and surface current patterns, wave climate, water quality and habitat impediments relative to seasonal distribution of herring larvae, post larvae, and juvenile herring, are also critical to understand how juvenile herring support our salmon stocks in a changing world. These gaps in understanding fundamental physical and biological linkages of our marine system impede us from defining and implementing the most effective on the ground conservation and restoration solutions. And so we must address them.

Image 12: Juvenile herring ‘breaking’ to avoid predators lurking beyond the outer edge of a razor thin kelp bed along the San Juan Islands. Photo by Anne Shaffer and CWI.

How to Get Involved!

As CWI and our partners continue to work to get these important information gaps addressed we offer this story map to visually illustrate temporal and geographic linkages of these remarkable systems, how we as humans interact with them, and how we can conserve them. We hope you will join us.

 https://coastalwatershedinstitute.org/