Assessing the importance of net colour as a seabird bycatch mitigation measure in gillnet fishing
To ascertain if net colour is a potential mitigation measure through improving visibility of nets, we tested the ability of little penguins to differentiate between three different coloured netting materials (green, clear and orange) under controlled conditions. The study involved a repeated-measures design with penguins exposed to a number of experimental treatments (variously coloured mono-filament threads creating a gillnet mimic) and a control without the threads (no gillnet mimic). The gillnet mimic was made up of single-strand monofilament nylon of 0.5 mm diameter, similar to that used to construct most gillnets, and configured as a series of vertical lines 25 mm apart stretched tightly across a stainless steel frame. Results demonstrated that orange coloured monofilament lines resulted in low collision rates of little penguins compared to clear and green coloured monofilament lines. Collision rates were not only high with the clear and green coloured monofilament lines, but we also found that little penguins persisted to swim through the clear and green monofilament lines after collision. These behaviours confirm previously observed patterns within gillnet seabird bycatch species, that there is a cognitive failure in identifying the danger of a hazard. We conclude that gillnets constructed of orange-coloured materials may reduce the bycatch of penguins and other seabirds in surface or shallow-set gillnet fisheries, but further studies are required to assess the effect of gillnet colour on catch of target species.