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Kelp/Salmon/Forage Fish Dynamics and Cross-Ecosystem Trophic Subsidies: The Interconnected Engine of Our Cold Water North East Pacific Coastal Ecosystems

Overview: Seasonal Dynamics of Three Guilds and How They Intersect

Nearshore systems are a critical migration corridor of our cold water coastal ecosystems — seasonally dynamic and nutrient-limited, particularly during summer and fall/winter months (Newton 2021). Three guilds drive interconnected seasonal cycles across these zones: kelp forests, forage fish, and juvenile salmon.

Kelp forests are a dominant and foundational feature of our nearshore region, providing both habitat and food resources that alter the physical environment of temperate oceans (Pfister et al. 2018). Overstory kelp, including bull kelp (Nereocystis luetkeana), and giant kelp (Macrocystis integrifolia) are seasonally dominant features of our shoreline. Both are  highly productive, seasonally highly variable due to annual growth patterns, and found only in shallow nearshore zones. Understory perennial species of kelp (including Pterygophora spp.) persist through winter, providing year-round structure. Overstory kelp forests are seasonal — growing up to 25 cm (about 10 inches) a day through spring and summer, declining in fall and winter — and are a driver of patterns in fish and zooplankton presence throughout the year (Shaffer and Parks 1994; Shaffer et al. 2020, 2023; Holbrook et al. 1990; Villegas et al. 2019). *UNDERSTORY* kelp forests are also essential habitat for herring spawning, which occurs on eelgrass and understory kelp. *NOTE* that herring don’t spawn on overstory kelp, including bull kelp.

Forage fish are the dominant fish guild of our nearshore region (Frick et al. 2022). Pacific herring (Clupea pallasii), surf smelt (Hypomesus pretiosus), and Pacific sand lance (Ammodytes hexapterus) feed on zooplankton and are foundational to nearshore food webs. Each species has a distinct seasonal life history tied to nearshore zones — herring spawn on understory algae and eelgrass in late winter/early spring; sand lance and surf smelt spawn along very specific grain size intertidal beaches primarily in fall/winter and spring/ summer, respectively. Juvenile and adults of all three species migrate along nearshore in large numbers during spring and summer, and are critical prey for outmigrating salmon.

Juvenile salmon recruit to nearshore kelp zones during spring outmigration, still fragile and not yet ready for the open ocean. As kelp grows to overstory status seasonally, and young of the year forage fish  migrate off natal beds, young of the year salmon arrive to the nearshore and meet forage fish, heralding their phylogenic shift — transitioning from invertebrate prey to forage fish.  CWI research has revealed that 78% of salmon-forage fish interactions occur in association with kelp, and 100% of observed predation events were in kelp zones (Shaffer et al. 2023).  These ‘intersections’ peak in June and July, the height of kelp growth and summer forage fish migration (Shaffer et al. 2023). In these studies, herring and sand lance were the most important forage fish for juvenile salmon; predation of herring is a direct indicator that the phylogenic shift is underway.

Links to videos of these brilliant feeding interactions are provided on the ‘Resources’ page of this website.

These three guilds are physically and seasonally linked to each other and to broader hydrodynamic and water quality processes. Disrupting any one of these connections disrupts the system as a whole.

Cross-Ecosystem Trophic Subsidies Initiative

Coastal ecosystems are sustained by seasonal pulses of nutrients and energy that move across ecosystem boundaries — from ocean to shore, from spawning bed to kelp forest, from returning salmon to the nearshore zone. These cross-ecosystem trophic subsidies are the engine that drives productivity in cold water coastal systems of the northeast Pacific. CWI’s research documents three critical subsidy pathways:

  1. Forage fish, including herring spawning, trophic subsidies for outmigrating salmon
  2. Forage fish, including juvenile herring, trophic subsidies to kelp forests
  3. Salmon trophic subsidies to nearshore coastal zones
1)      Herring Spawning and Juvenile Salmon: A Critical Connection

Herring spawning is a critical component of intertidal and terrestrial coastal systems. Spawning occurs in intense pulses through late winter and early spring, depositing eggs and sperm along intertidal and shallow subtidal coastal zones. This provides a critical injection of protein, fats, and nutrients to the coastal zone at the time of year when the nearshore is at its lowest seasonal productivity. Research has documented that herring eggs and larvae provide essential nutrients that subsidize beach wrack and coastal carnivores (Fox 2013; Fox et al. 2018).

 
2)      The Forage Fish–Salmon Link

Herring spawning occurs at the very beginning of salmon outmigration. Chum, coho, and Chinook outmigrants recruit to coastal zones just after herring spawning, depending first on invertebrates and later on fish larvae for their diet (Bax et al. 1978, 1983). Fox and Aldridge (2000) documented that upon hatching, the majority of herring egg sac larvae stay in the vicinity of hatching. CWI research defines the linkages between herring spawning and hatching, zooplankton composition, and salmon presence and behavior along spawning zones — including over and understory kelp forests — capturing the first critical cross-ecosystem relationships of a life-long association between herring and salmon, the cornerstones of our cold water ecosystems.

 
3)      Salmon homecoming-feeding the forage fish nearshore

In fall, adult chum, pink, coho, and Chinook return to coastal zones in large numbers. In many areas, salmon returns are substantial, resulting in rafts of carcasses along river deltas, shorelines, and lower river reaches. These carcasses deliver a pulse of high protein, fats, and amino acids to the coastal zone precisely as light levels decrease and plankton resources dwindle — completing the nutrient cycle that began with herring spawning in winter. CWI research examines how this detrital subsidy links adult salmon fall migration to zooplankton composition and the forage fish populations that recruit to nearshore zones for spawning just weeks later (Shaffer et al. 2019, 2020, 2023, 2024).

Figure 1. The nearshore engine. The nearshore engine, seasonal cycle of cross-ecosystem trophic subsidies. From winter herring spawning that fuels outmigrating juvenile salmon, through summer juvenile herring migration subsidizing kelp forest zones, to fall adult salmon homecoming delivering a critical pulse of nutrients back to the nearshore coastal system. These interconnected seasonal cycles are the engine of our cold water coastal ecosystems across the northeast Pacific. Illustration reprinted from Avila et al. (2026) CWI all rights reserved

CWI’s Research Approach

CWI’s research is ongoing. Contact us for details and to collaborate.

References 

    • Avila, A.M., Shaffer, J.A., Parks, D., Byrnestrong, A., Christiansen, N., 2026. Field techniques to study dynamics of juvenile salmon, forage fish, and plankton in kelp forests. Pacific Salmon Foundation. https://doi.org/10.48689/4eb55a19-3f24-4707-ac14-d7f9d8363855
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    • Bax, N.J., Salo, E.O., Snyder, B.P., Simenstad, C.A. and Kinney, W.J., 1978. Salmonid outmigration studies in Hood Canal. Univ. of Washington. FRIUW-7819.
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    • Bax, N.J., 1983. The early marine migration of juvenile chum salmon (Oncorhynchus keta) through Hood Canal — its variability and consequences. University of Washington.
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    • Fox, C.H., 2013. Pacific herring and salmon: ecological interactions across the land-sea interface (Doctoral dissertation). University of Victoria.
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    • Fox, C.J. and Aldridge, J.N., 2000. Hydrographic circulation and the dispersal of yolk-sac herring (Clupea harengus) larvae in the Blackwater Estuary. Journal of the Marine Biological Association of the United Kingdom, 80(5), pp.921–928.
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    • Fox, C.H., El-Sabaawi, R., Paquet, P.C. and Reimchen, T.E., 2014. Pacific herring Clupea pallasii and wrack macrophytes subsidize semi-terrestrial detritivores. Marine Ecology Progress Series, 495, pp.49–64.
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    • Fox, C.H., Paquet, P.C. and Reimchen, T.E., 2015. Novel species interactions: American black bears respond to Pacific herring spawn. BMC Ecology, 15, pp.1–18.
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    • Fox, C.H., Paquet, P.C. and Reimchen, T.E., 2018. Pacific herring spawn events influence nearshore subtidal and intertidal species. Marine Ecology Progress Series, 595, pp.157–169.
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    • Frick, K.E., Kagley, A.N., Fresh, K.L., Samhouri, J.F., Ward, L.S., Stapleton, J.T. and Shelton, A.O., 2022. Spatiotemporal variation in distribution, size, and relative abundance within a Salish Sea nearshore forage fish community. Marine and Coastal Fisheries, 14(2), p.e10202.
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    • Holbrook, S.J., Carr, M.H., Schmitt, R.J. and Coyer, J.A., 1990. Effect of giant kelp on local abundance of reef fishes: the importance of ontogenetic resource requirements. Bulletin of Marine Science, 47, pp.104–114.
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    • Newton, J., 2021. Eutrophication in marine waters. In: Encyclopedia of Puget Sound. https://www.eopugetsound.org/science-review/section-5-eutrophication-marinewaters
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    • Pfister, C.A., Berry, H.D. and Mumford, T., 2018. The dynamics of kelp forests in the northeast Pacific Ocean and the relationship with environmental drivers. Journal of Ecology, 106(4), pp.1520–1533.
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    • Shaffer, J.A. and Parks, D.S., 1994. Seasonal variations in and observations of landslide impacts on the algal composition of a Puget Sound nearshore kelp forest. Botanica Marina, 37, pp.315–323.
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    • Shaffer, A., Parks, D., Schoen, E.R. and Beauchamp, D., 2019. Salmon, forage fish, and kelp. Frontiers in Ecology and the Environment, 17(5), pp.258–258.
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    • Shaffer, J.A., Munsch, S.H. and Cordell, J.R., 2020. Kelp forest zooplankton, forage fishes, and juvenile salmonids of the northeast Pacific nearshore. Marine and Coastal Fisheries, 12(1), pp.4–20.
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    • Shaffer, A., Gross, J., Black, M., Kalagher, A. and Juanes, F., 2023. Dynamics of juvenile salmon and forage fishes in nearshore kelp forests. Aquatic Conservation: Marine and Freshwater Ecosystems, 33(8), pp.822–832.
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    • Shaffer, J.A., ByrneStrong, A., Parks, D. and Pype, C., 2024. Field techniques to study dynamics of juvenile salmon and forage fish and plankton in kelp forests. Coastal Watershed Institute Technical Report CWI 072024:1. ISSN 2643-9697.
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    • Shaffer, A., Parks, D., Maucieri, D.G., Oxborrow, B., Juanes, F., Qualley, J., Avila, A. and ByrneStrong, A.,. Herring spawning provides cross-ecosystem trophic support through zooplankton subsidies for out-migrating juvenile salmon. (in review).
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  • Villegas, M., Laudien, J., Sielfeld, W. and Arntz, W., 2019. Effect of foresting barren ground with Macrocystis pyrifera on the occurrence of coastal fishes off northern Chile. Journal of Applied Phycology, 31, pp.2145–2157.