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Estuaries, Climate Change, and Native Fish

Status
Ongoing

Salmon and other anadromous fish need freshwater, estuary, and marine habitats to complete their life cycle. Estuaries are unique environments with productivity driven by the daily ebb and flow of the tides. Functional estuaries with tidally inundated channels provide critical nursery habitat for juvenile salmon and steelhead, as well as other culturally and commercially important species.

Pacific salmon are anadromous fish, meaning they move between freshwater and marine environments to complete their life cycle. Estuaries provide a critical transition from fresh to salt water for out-migrating smolts (the sea-going juvenile stage), as well as for returning adults as they prepare to migrate upstream to spawn and then die in freshwater streams. The habitat needs of juvenile fish in freshwater environments are well studied, but their use of estuaries is less understood. Our work seeks to explore how juvenile fish use estuary habitats, as well as the implications of disturbances such as climate change, invasive species like five-spine green crabs, and human infrastructure, particularly tide gates on habitat availability. This research will contribute to more comprehensive and holistic management of Pacific salmon that links freshwater, estuary, and marine environments.

Bar chart of the generalized proportion of time spent in freshwater, estuary, and marine environments for six species of Pacific salmon. Masu salmon, an Asian species, spend over 40 percent of their time in freshwater, between 5 and 10 percent in the estuary, and the remaining approximately 50 percent in marine environments. Sockeye salmon spend 40 percent of their life in freshwater, about 5 percent in the estuary, and over 55 percent in the marine environment.

Pacific salmon are anadromous, requiring habitats spanning freshwater, estuary, and marine environments to survive and complete their life cycle. Many species spend the smallest proportion of their life history in freshwater settings, where most research into habitat connectivity has been concentrated (from Flitcroft et al. 2019).

Drawing of a five-spine green crab. These crabs have a carapace about the size of the palm of your hand and are olive-green mottled with black.

Five-spine green crabs are an invasive species along the Pacific coast of the United States and Canada. USDA Forest Service artwork by Kathryn Ronnenberg.

Salmon may experience the effects of global climate change differently depending on where they are in a stream network. We hypothesize that sea-level rise, as projected by the International Panel on Climate Change, will submerge existing complex habitats found in estuaries. The critical elements of current estuarine habitats may not be able to easily shift farther upstream owing to topography and human development. We have developed tools for mapping salmonid habitat changes under different scenarios of sea-level rise.

Five-spine green crabs (Carcinus maenas), also known as European green crabs, are an invasive crab that destroys eel grass habitats, a key environment for native estuarine species and a nursery for marine species. These crabs are also linked to climate change. They are now surviving and successfully reproducing in habitats north of the historically warmer waters where they were originally found. As a result, the crabs are now invading and establishing populations in Oregon, Washington, and British Columbia, Canada. By trapping these crabs, scientists can evaluate their population status and determine recruitment over time. 

Extremely high tides, known as king tides, hint at how far up the future high-tide line may move in the estuaries of coastal Oregon and

 elsewhere. For example, low tide exposes mudflats and tidal channels bordered by shoreline vegetation along Willanch Creek in Coos Bay, Oregon. With an extreme high tide, however, the water rises above the usual tideline to submerge the bases and roots of shrubs and trees that cannot survive repeated or sustained inundation. 

Two photos of Willanch Creek, Coos Bay, Oregon. The view taken at low tide shows exposed, intertidal mudflats and tidal channels bordered by shoreline vegetation of marsh grass, shrubs, and ash and spruce trees. In the second photo, an extreme high tide has flooded not only the tidal channel and marsh vegetation, but also shrubs and trees that stand on higher ground.

Willanch Creek, Coos Bay, Oregon, at low tide (left) and extreme high tide (right). USDA Forest Service photos by Rebecca Flitcroft.

Sea-level rise may expand habitat complexity in some low-lying and undeveloped estuaries on the Oregon coast. However, most estuaries are naturally constrained by the slopes of the Oregon Coast Range. They are also often surrounded by development, including levees and diking that constrains the ability of salt marshes to expand upstream and into floodplain areas. 

Map graphic demonstrating fractal dimension (FD) as a measure of salmonid habitat availability in estuaries along the Oregon Coast. As FD decreases, so does the complexity of the estuarine channels, and thus the potential to provide habitat for juvenile salmonids. Five maps display modeled scenarios with varying levels of sea-level rise: 1.5 meters, with FD = 2.30; 2 meters, with FD = 2.22; 2.5 meters, with FD = 2.09; 3 meters, with FD = 1.31; and 4 meters, with FD = 1.28.

Patterns of tidal inundation associated with changes in sea level may result in changes to estuary vegetation communities and patterns of tidal channels that serve as key rearing environments for native salmonids. In the Salmon River Estuary on the Oregon Coast, different amounts and sinuosity of edge habitats are associated with different tidal heights, resulting in variation in the amount and type of habitats for rearing salmonids.

By trapping five-spine green crabs at Salmon River Estuary, we have discovered that this crab can develop self-supporting populations even in a small system with limited crab habitat.

Photo of a black-mesh, rectangular Fukui crab trap containing seven invasive five-spine green crabs in the left and center, with two native Dungeness crabs to the right. Five-spine green crabs are smaller, with a carapace about the size of the palm of your hand, and olive-green mottled with black; in contrast, full-grown Dungeness crabs are roughly twice that size or larger, and a dull orange.

Invasive five-spine green crabs in the left and center of a Fukui crab trap, with native Dungeness crabs to the right, at Salmon River Estuary, Oregon. Five-spine green crabs alter estuary habitat for native species and thrive in estuary environments that have become warmer as the climate changes. USDA Forest Service photo by Rebecca Flitcroft.

Understanding how estuaries in rain-dominated areas are likely to be affected by climate change is key to managing these habitats essential for Pacific salmon.

Information about the implications of climate change on coastal-draining streams can help guide conservation, preservation, and landward-migration planning in lowland areas.

Ongoing monitoring of five-spine green crabs could lead to future eradication efforts at Salmon River, where the estuary is small enough for extensive crab removal.

Project Contact

Collaborators

  • Oregon State University

  • Environmental Protection Agency

  •  TerrainWorks

  • U.S. Geological Survey

  • 4CAST

  • Oregon Coast Aquarium

Publications

External Publications

  • Flitcroft, R.L. 2018. Seasonal fish abundance at tide-gate locations in the Coos River Estuary. Piscatorial Press Newsletter of the Oregon Chapter, American Fisheries Society. Summer 2018, p. 6.

Last updated June 11, 2024
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