Field test of an electric deterrence and guidance system during a natural spawning migration of invasive common carp

Non-physical deterrence and guidance technologies are sought after for management of invasive fish, but they have rarely been tested in the field during natural fish migrations. We tested the efficacy of a semi-portable deterrence and guidance system (DGS) that used vertical electrodes producing low-voltage electric field to deter the upstream spawning migration of common carp (Cyprinus carpio Linnaeus, 1758) and direct them into a trap (5 m by 25 m enclosure with a net) in a natural stream. The behavior of carp was monitored using Passive Integrated Transponder (PIT) tags and antennas. The migration began on 7 April 2019, when water temperature was 5 degrees C and lasted through May 2019. Performance of the DGS was evaluated during three separate periods, between which the DGS was briefly deactivated. During the first period (4/7-4/19), 559 unique carp challenged the DGS. Of those, 10 were able to cross the DGS (98.2% efficacy), 234 (41.8%) were directed into the trap and 54 were captured. The mean number of days each carp was detected at the DGS was 2.6. During the second period (4/25-5/7), 562 unique PIT carp challenged the DGS. Of those, 24 were able to cross it (95.8% efficacy), 241 (42.9%) were directed into the trap and 148 were captured. Mean time at the DGS was 5.6 days. During the third period (5/7-5/15), 147 PIT carp challenged the DGS and 2 were able to cross it (98.6% efficiency). The mean time at the DGS was 5.5 days. Due to decreasing numbers of carp during the third period, we did not attempt to direct them into the trap for removal. Stream discharge during our test exceeded the 11-year average by 2-3 times; the floodplain was periodically flooded, and it is possible that some carp migrated around the DGS rather than through it. Overall, our results suggest that DGS that generate mild, electric field can be useful in deterring seasonal migrations of common carp and facilitating new removal strategies. The semi-portable nature of the system and low site-engineering requirements allow for rapid deployments and targeted applications during seasonal migrations.