Ineffectiveness of light emitting diodes as underwater deterrents for Long-tailed Ducks Clangula hyemalis

Abstract

Gillnet bycatch accounts for over 400,000 bird mortalities worldwide every year, affectinga wide variety of species, especially those birds that dive when foraging. Technologicalsolutions to improve gillnet visibility or deter birds from approaching nets, such as LEDlights, are essential for aiding diving birds to perceive nets as a hazard. Designing suchsolutions requires obtaining visual and behavioural ecology information from species toassess their ability to see the warning devices, and to examine their behavioural responsesto them. Seaducks, particularly Long-tailed DucksClangula hyemalis,have high bycatchmortality rates. We examined the visualfields of four Long-tailed Ducks to understandtheir three-dimensional view around the head. The visualfield characteristics of thisspecies indicate a reliance on visual guidance for foraging associated with their capture ofvaried, mobile prey in their generalist diet. We subsequently conducted dive tank trials totest the effectiveness of 12 different LED treatments as visual deterrents to the underwaterforaging behaviour of 8 Long-tailed Ducks. During each trial, ducks were offered foodrewards from a specific underwater location in a dive tank, having the choice of whether totake the food or not. At the same time, they were exposed to either one LED light or thecontrol (no light) to determine whether the presence of each light affected the foragingsuccess rate of dives compared to the control. Exposure of ducks to all 13 treatmentcombinations was randomised over the trial period. White lights with an increasingflashrate were shown to have a significant positive effect on foraging success, and likely acted asa visual attractant, rather than as a deterrent. No light treatment significantly reduced theforaging success of ducks. LED lights did not inhibit the feeding of Long-tailed Ducks. Suchlights may be ineffective as underwater visual deterrents when deployed on gillnets, whilewhiteflashing lights may make foraging sites more attractive to Long-tailed Ducks.