Graduated-Field, Electric Barrier Technology for Invasive Fishes: Successes, Challenges and Innovations

Various technologies have been developed and tested in efforts to limit the spread of invasive species or to achieve fish guidance and conservation.  Historic attempts to block or guide fish movements with electricity used alternating current (AC) for deterrence. This paper examines some innovative approaches to fish guidance that combine new developments in the use of electric fields and barriers to direct and/or block fish movements.  These include: (1) the ability to use and control pulsed DC waveforms; (2) the capacity to remotely monitor and adjust operational settings and output levels; (3) the implementation of safeguards to minimize potentials for human or animal interactions with deterrence fields; and (4) the ability to design Graduated Field Fish Barriers (GFFBs) as well as non-graduated, more abrupt deterrence fields where conditions warrant.  This paper reviews the efficiencies of GFFBs and other bottom-mounted electric guidance arrays (which can be up to 100% effective) from results published in the peer-reviewed literature.  Published accounts primarily address deployments aimed at blocking movements of invasive fish species (e.g. common carp in Minnesota lakes; Asian carp in the Chicago Sanitary and Ship Canal) or for conservation and guidance of desirable species to or away from specific aquatic environments. Currently, there are 47 GFFB arrays in use around the world for various fish guidance, deterrence, retention and/or conservation needs.  This paper outlines “the lessons learned” in applying electric barrier technology for fish guidance.  It addresses the technology’s successes, its limitations and challenges, and the design modifications that have been necessary to enhance the effectiveness of systems currently in use.  Whereas fish guidance and/or deterrence barriers have been largely successful for upstream-moving species, only limited success has been achieved in attempts to influence downstream-moving fish.  Accordingly, we discuss a new but untested concept for guiding downstream-moving fish:  an angled array of horizontal or vertical electrodes (that could be used in combination with other technologies) to induce movement away from specific aquatic locations before fish become incapacitated by the electric field.