The foodscape – (re) connecting salmon to the productive capacity of their watersheds

By Gabriel J. Rossi, J. Ryan Bellmore, Jonathan B. Armstrong, Carson Jeffres, Sean M. Naman, Stephanie M. Carlson, Theodore E. Grantham, Matthew J. Kaylor,Seth White, Jacob Katz, Mary E. Power

In 1927, the famous ecologist Charles Elton (when he was 27 years old) set the stage for the modern ecological study when he published his great treatise “Animal Ecology.” In it, he penned: “Food is the burning question in animal society, and the whole structure and activities of the community are dependent upon questions of food-supply” (Elton 1927). This sentiment is older than modern science of course – it reflects millennia of human history where people tracked great animal migrations and observed relationships between animals and their environment. And yet, oddly, this sentiment failed to take root in the last century of salmon research and management. For over a hundred years or so, salmon managers focused on a litany of strategies for recovering salmon: hatchery production, harvest quotas, managing streamflow below dams, improving physical habitat, and fish passage. In that same hundred years, we watched salmon populations continue down a seemingly inexorable path to extinction. Here in California, we are experiencing a second year of complete closure of the salmon fishery and numerous salmon populations are on the brink of extinction. And yet recently there has been a reawakening to what Charles Elton recognized 96 years ago – and what Indigenous stewards from Europe to Asia have known for millennia before: that ‘food’ is at the heart of ecological resilience and also of the relationship between humans and other biota (e.g. Quaempts et al 2018). Simply put, we are unlikely to recover robust salmon populations without recovering the dynamic food webs that sustain them (Naiman et al. 2012, Bellmore et al. 2022, Rossi et al. 2024).

Throughout their lives, mobile consumers like salmon track fluctuating resources across heterogeneous landscapes to grow and survive. Many species of salmon emerge and rear in small streams before moving into mainstem rivers, backwaters, or lakes. They may cross inundated floodplains and off-channel habitats, or rear in estuaries and saltwater sloughs, before finally moving to the near-marine environments and open ocean (Figure 1). In these networks, the abundance and accessibility of food and the costs and benefits of foraging vary among habitats and through time, providing a shifting mosaic of growth opportunities for salmon. A “foodscape” depicts this dynamic mosaic of food abundance, food accessibility, and environmental conditions that contribute to the spatial and temporal variation of fish growth in rivers and, consequently, to their life histories (Rossi et al. 2024, Figure 2).

**Figure 1.** Salmon are iconic mobile foragers. As they grow from eggs laid in freshwater streams to adults in the ocean, salmon can make use of virtually all of the freshwater, estuarine and marine habitats they can physically access. However, each habitat differs in timing and extent of food abundance, food accessibility, and environmental conditions that contribute to growth. This shifting mosaic can be expressed as a foodscape (Figure 2). Figure 1 is reused here, with permission, from CalTrout et al. (2024).

Recent work by our team focused on watersheds from Alaska to California highlights the central role of foodscapes in salmon resilience and recovery (Rossi et al. 2024). Foodscape thinking expands our view of watershed management to consider sources, phenology, and pathways of key food resources (see also Rossi et al. 2022 or Wipfli and Baxter 2010). Foodscape thinking rightfully focuses our attention on the conditions that allow salmon (and other mobile consumers) to persist by tracking and exploiting riverscape feeding opportunities. Also, foodscape thinking is fun (see: The Foodscape as Song). Like every aspect of salmon habitat, the foodscape has been (and continues to be) altered, simplified, and often severed. But unlike work focused on fish passage, water quality, or instream flow, we are just beginning to realize the challenges and opportunities for recovering and maintaining healthy, functional foodscapes for salmon.

The central question of foodscape restoration is: how have the multi-scale processes affecting food abundance, food accessibility, and physiological environment for foraging been degraded? And how can these same processes be recovered? More focused questions follow, such as: are there important trophic pathways (pathways that transform a photon of light to a calorie of salmon!) that have been impaired and can restored or replicated?. And, how might consumers track resources across the landscape (or riverscape) if the foodscape was healthy? In relatively intact watersheds, tackling these questions can illuminate key trophic pathways and spatiotemporal patterns of foraging and growth potential that support fish populations (e.g., Bellmore et al. 2022), which can inform planning and climate vulnerability assessments (e.g., Wade et al. 2017). In heavily impacted river systems, foodscapes can provide a novel lens to consider how alternative restoration actions such as hydrologically reconnecting floodplain wetlands to stream channels can promote diverse growth opportunities for fish (e.g., Cordoleani et al. 2022, see also [California Salmon Strategy]. Ultimately, foodscape thinking reveals opportunities to find new, productive tools that can move the needle on salmon population abundance, diversity, and resilience – opening new possibilities for watershed stewardship and optimism during a time of ecological crisis.

**Figure 2.** The foodscape considers movement of animals across landscapes or riverscapes, *and* the spatial and temporal dynamics and drivers of growth across that same mosaic. A diversity of life histories allow salmon to capitalize in asynchronous growth potential across the riverscape.

Gabriel J. Rossi, Stephanie M. Carlson, and Theodore E. Grantham are affiliated with the Berkeley Freshwater group in the Department of Environmental Science, Policy, and Management, and Mary E. Power (senior author) is an emeritus faculty member in the Department of Integrative Biology at the University of California, Berkeley. J. Ryan Bellmore is affiliated with the Forest Service Pacific Northwest Research Station in Juneau, Alaska. Jonathan B. Armstrong and Seth White are affiliated with the Department of Fisheries, Wildlife, and Conservation Sciences, and Seth White is also associated with the Oregon Hatchery Research Center at Oregon State University in Corvallis, Oregon. Carson Jeffres is affiliated with the University of California, Davis, Center for Watershed Sciences. Sean M. Naman is affiliated with the Freshwater Ecosystems Section for Fisheries and Oceans Canada in Cultus Lake, British Columbia. Jacob Katz is affiliated with the non-profit California Trout in Woodland, California. Matthew J. Kaylor is also associated with the Columbia River Inter-Tribal Fish Commission in Portland, Oregon.

Further Reading

Elton, C. S. 1927. Animal ecology. Reprinted 2001. University of Chicago Press, Chicago.

Bellmore, J. R., J. B. Fellman, E. Hood, M. R. Dunkle, and R. T. Edwards. 2022. A melting cryosphere constrains fish growth by synchronizing the seasonal phenology of river food webs. Global Change Biology 28:4807–4818.

California Trout, Stillwater Sciences, Applied River Sciences, and U.C. Berkeley. 2024. Eel River Restoration and Conservation Plan—Phase 1: Planning—of the Eel River Watershed Restoration and Conservation Program. Prepared for California Department of Fish and Wildlife. June 2024.

Cordoleani, F., Holmes E., Bell-Tilcock M., Johnson R.C., Jefres C. 2022. Variability in foodscapes and fish growth across a habitat mosaic: implications for management and ecosystem restoration. Ecological Indicators 136:108681

Naiman, R. J., J. R. Alldredge, D. A. Beauchamp, and others. 2012. Developing a broader scientific foundation for river restoration: Columbia River food webs. Proc. Natl. Acad. Sci. U. S. A. 109: 21201–21207. doi:10.1073/pnas.1213408109

Rossi, G. J., M. E. Power, S. M. Carlson, and T. E. Grantham. 2022. Seasonal growth potential of Oncorhynchus mykissin streams with contrasting prey phenology and streamflow. Ecosphere 13 (9) e4211.

Rossi, G.J.,Bellmore, J.R., Armstrong J.B., Jeffres, C., Naman, S.M., Carlson, S.M.,Grantham, T.E., Kaylor, J.M., White, S., Katz, J., Power, M.E. 2024. Foodscapes for Salmon and Other MobileConsumers in River Networks. In Press. Bioscience. dx.org/10.1093/biosci/biae064.

Wade, A.A., Hand, B.K., Kovach, R.P., Luikart, G., Whited, D.C. and Muhlfeld, C.C., 2017. Accounting for adaptive capacity and uncertainty in assessments of species’ climate‐change vulnerability. Conservation Biology, 31(1), pp.136-149.

Wipfli, M. S., and C. V. Baxter. 2010. Linking Ecosystems, Food Webs, and Fish Production: Subsidies in Salmonid Watersheds. Fisheries 35:373–387.