Each year, millions of fish migrate thousands of miles from freshwater to the ocean to feed and grow, returning to freshwater to spawn. Throughout this journey, many species encounter barriers that prevent them from reaching their destination. So, what are these barriers and what can we do about them?
Fish barriers are natural or man-made structures that prevent fish and other aquatic organisms from moving upstream. Common fish barriers include culverts, dams, tide gates, flood gates, along with ecological challenges (flow variations, excess sediment, poor water quality, and elevated water temperature). For years, scientists have pondered the positive and negative effects of engineered barriers on aquatic wildlife and habitat. Additionally, fish barriers may contribute to habitat fragmentation, breaking apart the aquatic ecosystems fish and aquatic organisms need for survival. Without a passage from the ocean to their native habitat, anadromous fish cannot return to their natal grounds to spawn, deterring the species from building a sustainable population. Altering habitat connectivity may inhibit species from escaping predation and finding food, further depleting populations of fish. Other negative consequences of barriers include slowed stream flows, habitat alteration, and temperature fluctuations.
On the other hand, fish barriers can sometimes benefit native species by preventing nonnative aquatic organisms from moving upstream. This protects native aquatic organisms and fish against predators, disease, hybridization, and competition for food, thus mitigating threats to their survival. They can also create wetlands upstream of undersized culverts.
How is Herrera Helping to Improve Fish Migration?
Herrera’s fisheries biologists and ecologists develop creative and integrated management solutions for fish barriers across Puget Sound. Many of these efforts are in response to a federal court injunction imposed in 2013, requiring Washington State to remove all state-owned culverts that block habitat for salmon and steelhead by 2030.
With this, Herrera’s scientists conduct stream surveys and fish population studies and evaluate mitigation and restoration opportunities. Herrera also performs smolt behavior studies, electrofishing, spawning surveys, and habitat assessments to evaluate the direct and indirect impacts of proposed actions on fish and other aquatic species. Our team of wetland scientists can assess wetland impacts associated with removal and provide innovative strategies for permit compliance.
In addition, Herrera’s team of engineers develop preliminary hydraulic designs (PHDs). These initial reports inform culvert design and include a description of the watershed, an assessment of fish and wildlife use, and geomorphic analysis on sediment passage and processes. Hydrologic modeling is also included to show the amount of water in the system during different modeled events, such as flooding, as well as existing and proposed conditions before and after barrier correction.
Finally, Herrera’s team maximizes ecological functions and benefits by offering expertise in river reach analysis, delineation of channel migration zones, design of engineered log jams, and investigation of sediment erosion, transport, and deposition. Through these efforts, Herrera aims to improve aquatic habitats for a more resilient ecosystem.