Modeling Fish on the Move

By: Marguerite Huber

How many places have you lived? Why did you move? Personally, I have lived in eight different places because of school and jobs. Other people move to find better opportunities, like housing or a place to raise their children.

Fish are sometimes forced to move as well. But, unlike you and I, fish cannot just get up and move across towns, states, and countries. They have to move across their own river networks to maximize survival.

For fish, the availability of sufficient spawning and rearing habitats can strongly influence the productivity of an entire river network. Fish also move based on certain environmental drivers like warming temperatures, and human activities such as land development, building of dams, and changes in stream channels, which can contribute to water pollution or alter fish habitat. Additionally, fish are affected by their interactions with other species. When different species interact, they can compete for resources or have a predator-prey relationship.

The Willamette river network, color-coded to show which of the 3 primary environmental conditions are currently most limiting habitat suitability for Chinook salmon, a species of high management concern.

The Willamette river network, color-coded to show which of the 3 primary environmental conditions are currently most limiting habitat suitability for Chinook salmon, a species of high management concern.

To fully understand fish in their changing environment, EPA researchers created a model that simulates groups of fish in river landscapes. This model helps determine how fish populations reproduce, move, and survive in response to both environmental drivers and species interactions. It is designed to help EPA assess the impacts of land development on fish assemblages, and better understand how these impacts may be intensified by climate change.

The researchers studied how Chinook salmon (Oncorhynchus tshawytscha) respond to steepness of the stream channel, flow, and temperature in the Willamette River basin of Oregon. This region is important to study because it is expected to experience substantial rises in human population and water demand over the next 50 years. The model, which can be applied to any watershed, helped create a map of the salmon’s abundance and distribution in the Willamette River basin. To capture species interaction, scientists also modeled the abundance of another fish, the northern pikeminnow (Ptychocheilus oregonensis), a native predator and competitor of Chinook salmon.

Afterwards, researchers modeled both species together, accounting for projected effects of competition and predation. They found that species interactions and temperature affect both Chinook salmon and northern pikeminnow. The results show species distributions throughout the basin and their projected responses to future stressors such as climate change, water consumption, and hydropower management.

Not only will EPA’s model help construct a map of fish on the move, but it will help inform the science used to develop water quality regulations and trading, help prioritize restoration, and advise management decisions.

About the Author: Marguerite Huber is a Student Contractor with EPA’s Science Communications Team

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