Semi-automated system for capturing and removing invasive carp during seasonal migrations

Many invasive fish conduct seasonal migrations, which create opportunities for large-scale removal. However, labor costs, cumbersome logistics, and environmental conditions (water depth, current, etc.) often make such efforts not feasible. We tested a semi-autonomous system for removing invasive common carp during spawning migrations in a natural stream (20 m wide, 1.5 m deep) over two migration seasons. A low-voltage, vertical deterrence and guidance system (DGS) was used to block the migrating carp and direct them into a large enclosure near shore. Additional electrodes placed in the enclosure created a sweeping electric field to push the carp towards one end and aggregate them over partially submerged conveyors that removed the carp from the water. Passive integrated transponder (PIT) tags and antennas were used to monitor carp behavior and removal efficacy. Each year, spawning migration lasted approximately two months and removal efforts occurred on 19 (year 1) and 21 (year 2) days. The DGS blocked over 90% of the carp and directed them into our trap. In year 1, 56% of the migrating carp were removed, and 68% were removed in year 2 (23,500 carp removed overall). In the final iteration of the system, a crew of three was able to conduct the removal, primarily by operating control systems on shore. Similar systems could be used for other invasive fish in larger and deeper environments where direct human labor is problematic. Such systems could also be used for native species to help them navigate passageways or to deflect them from entrainment areas.