SARF071: Preliminary tests of the behavioural responses of seals to electric fields in seawater

Start Date: 01/03/2010
End Date: 30/11/2010
Main Contractor(s): Sea Mammal Research Unit, University of St Andrews
Other Sponsor(s):  

Objectives

As a preliminary study the project has only one objective:  To determine if low intensity electric fields have the potential to act as seal deterrents in marine fish cages

 

Summary

As a preliminary study the project has only one objective:  To determine if low intensity electric fields have the potential to act as seal deterrents in marine fish cages

Protecting caged fish from attacks by seals is a major concern for the salmon farming industry. To date this has relied on acoustic deterrents with questionable/variable degrees of success, barrier netting which is difficult to maintain or direct killing of seals which has only short term benefits in terms of reduced predation and significant long term costs in terms of the public image of marine aquaculture.  The industry therefore needs a system of net defence that is reliable, effective, easily maintained and operated and benign or at worst, non-lethal to seals.

Recent developments have shown that seals may respond to electric fields at strengths significantly lower than those which cause behavioural responses in salmonid fish.   A useable freshwater deterrence system has been developed and tested in the US and Canada on both captive and wild, free ranging seals and sea lions with promising results.    

In sea water the electric field is rapidly dissipated, so there is little chance that such systems could be developed into area exclusion devices for marine fish farm sites.  However, it should be possible to produce local electric fields within a few centimetres of a net wall with deterrent capabilities that could be developed into a system for preventing direct attacks on net cages.  At present we simply do not know if seals would be deterred by the sorts of field strengths that could be practically generated at the net wall without affecting fish behaviour.

The project has clearly demonstrated that seals can be prevented from entering a small area using low voltage, short duration pulsed electric fields. This method therefore has clear potential as a net defence method. Approximate power requirements have been given however these vary widely since power is determined by the square of the voltage difference. Improved predictions of the power requirement require an improved understanding of

  • · which parameters of the electric field control the response of the seal;
  • · the observed difference between the single adult and the juveniles tested;
  • · whether a single polarity electrode configuration is more efficient; and
  • · the responses of the seals to electric fields that are intermittent and the potential for longer term learned responses.

Proposed future work to test the effectiveness and practicality of such a system will include

studies of:

  • · Electrical conditions need to deter seals using the single polarity electrode configuration.
  • · The behaviour of seals of different sizes and increased sample sizes to determine the extent of inter animal and size related variation in response level.
  • · The effects of different electrode geometries, e.g. trials using areas of netting with woven in electrodes of various pitches