A fish fence is a barrier placed in water to manage aquatic populations by blocking, guiding, or enclosing them, similar to how a land fence contains livestock. These structures range from simple setups to advanced systems, with designs adapted to specific environmental conditions and fish species.
Primary Functions of Fish Fences
The most direct use of a fish fence is for containment in aquaculture. Fish farming operations use nets or other barriers to enclose an area, such as a coastal bay. This prevents farmed stock like salmon or tilapia from escaping, which protects the farmer’s investment and avoids ecological disruption from non-native species.
Fences are also used for exclusion to protect fish or specific habitats. Power plants and irrigation channels install screens over their water intakes to prevent fish from being drawn into machinery. In conservation, fences can block the advance of invasive species, such as carp, from overwhelming native ecosystems.
Another function is guidance, where fences direct the movement of fish toward a specific point. For example, V-shaped fences can funnel migrating salmon into a trap box, allowing scientists to count them, assess their health, and collect genetic samples. These “counting fences” are used to monitor population trends and inform conservation efforts.
Common Types and Materials
Physical barriers are the most prevalent form of fish fence, constructed from materials suited to the location and goal. Traditional fences in coastal regions are built with wooden poles and netting. Industrial applications use durable materials like metal grates, rebar, or high-strength polymer netting. The design of any physical fence includes a mesh or gap size small enough to block the target fish without trapping smaller organisms.
Beyond solid structures, non-physical barriers have been developed to manage fish movement. These systems deter rather than physically block fish. One example is the BioAcoustic Fish Fence (BAFF), which combines a bubble curtain with underwater sounds that fish find repellent. This “wall of sound” can guide fish away from dangerous areas without a physical obstruction.
Design and Placement Considerations
The placement and engineering of a fish fence are determined by the local environment. A fence in a fast-flowing river must be built to withstand water pressure and floating debris. In contrast, a fence in a calm lake faces less force but may require features that prevent it from sinking into soft sediment.
Understanding the behavior of the target fish species is another design factor. For fish that are strong swimmers and leapers, like adult salmon, a fence must be tall enough to prevent them from jumping over it. For species that live near the bottom, the fence must be securely anchored to prevent them from burrowing underneath.
Designers must also consider the broader environmental context. A fence should be constructed to minimize its impact on non-target species and the surrounding habitat. The structure should not significantly alter water flow or cause sediment buildup in ways that could damage the local ecosystem.