Comparison of Salmon Migration Systems

Question

Dams provide electricity, flood control, recreation and transportation, as well as water for domestic and agricultural use. However, dams also change the way rivers function and may interfere with the life cycles of salmon, steelhead, and other animals. They are barriers to juvenile salmon migrating to the ocean and an obstacle as adult fish return to the streams where they were born to spawn.

Dams affect the way water moves down a river by changing the amount and timing of flow, as well as the water's temperature and chemical characteristics. Because dams transform the upstream habitats from rivers into lakes, they change the amount and location of available habitat and significantly alter the salmon’s interaction with predators and competitors.

For salmon to thrive, it is important to provide safe, swift passage past dams for juveniles traveling to the ocean and for adults migrating back to their spawning grounds. There are many types of passage that can help the fish get past the dams, depending on factors such a dam’s age, size, location, and purpose. Sometimes passage facilities are added many years after a dam is built. These are the most common types of fish passages.

Answer 1

Comparison of Salmon Migration Systems in Relation to Dams

1. Barriers Created by Dams:

• Obstacle to Migration:
  • Dams disrupt the natural migratory routes of salmon and steelhead, impeding both juvenile fish as they journey downstream to the ocean and adult fish returning upstream to spawn. This disruption can lead to decreased fish populations over time.

2. Alteration of River Dynamics:

• Flow Changes:
  • Dams modify the natural flow of rivers. They can alter the timing (seasonality) and volume of water flow, which affects spawning conditions and habitat availability.
• Temperature and Chemistry:
  • The water retained by dams typically becomes warmer and may have different chemical compositions compared to natural river water. This alteration can affect fish physiology, behavior, and health.

3. Change in Habitat:

• Transforming Rivers into Lakes:
  • Upstream habitats can shift from flowing river systems to still lakes, which impacts the availability and quality of habitats for salmon. The introduction of predators and competition in these new habitats can further complicate salmon survival.
• Habitat Availability:
  • Dams can reduce the quantity and quality of spawning and rearing habitats, leading to increased competition and predation risks for juvenile salmon.

4. Fish Passage Solutions:

• Types of Fish Passage:
  • Various solutions have been developed to help salmon navigate past dams, with choices depending on the dam's characteristics:
    • Fish Ladders: These are structures that allow fish to swim upstream by providing a series of ascending pools.
    • Fish Gates and Bypass Channels: These constructs enable fish to travel around dams, often through specially designed channels that mimic natural river flow.
    • Lift Systems: Mechanical systems that literally lift fish over dams, ensuring safe passage.
    • Screening Systems: Barriers and screens that prevent juvenile fish from being drawn into turbines or other harmful infrastructure.

5. Implementation Variability:

• Dependent on Various Factors:
  • The effectiveness of fish passages is influenced by factors such as dam age, size, location, and operational purpose. Older dams may not have been designed with fish passage in mind, leading to retrofitting challenges.
• Implementation Timeline:
  • Often, fish passage solutions are integrated long after a dam is constructed, necessitating ongoing adaptation and innovation to resolve the ecological challenges posed by existing infrastructure.

Conclusion

The presence of dams can significantly impact salmon migration and overall ecosystem dynamics. While they serve vital human interests such as energy production and flood control, priority must also be given to fish passage solutions that aim to restore and maintain healthy salmon populations. These efforts require a collaborative approach between engineers, ecologists, and policymakers to balance human needs with ecological sustainability.