Assessing the importance of net colour as a seabird bycatch mitigation measure in gillnet fishing

Abstract

1. Gillnets are used widely in fisheries throughout the world and known to cause the death of thousands of seabirds each year. Currently few practical or technical options are available to fishers for preventing seabird mortalities.2. The ability of little penguins (Eudyptula minor) to differentiate between different coloured netting materials was tested under controlled conditions to ascertain if changes in gillnet colour could facilitate a potential mitigation measure by improving visibility of nets.3. The study involved a repeated-measures design with penguins exposed to variously coloured mono-filament threads creating a gillnet mimic. The gillnet mimic was made up of gillnet material configured as a series of vertical lines 25 mm apart stretched tightly across a stainless steel frame that measured 1160 mm × 1540 mm and divided into two equal panel areas. The panels were placed in a large tank within an enclosure that housed 25 penguins. Penguins were able to readily access the tank and swim freely. The frame was always introduced into the tank with one panel containing a gillnet mimic, and the other panel left empty as a control.4. Gillnet filament colours tested were clear, green and orange. Orange coloured monofilament lines resulted in lower collision rates (5.5%), while clear and green monofilament lines resulted in higher rates of collision (35.9% and 30.8%, respectively). 5. These results suggest that orange-coloured lines were more apparent to the birds. Constructing nets of orange-coloured material may be effective in reducing bycatch in gillnets set in shallow waters and high light levels where seabirds are able to identify fine colour differences.6. Further testing under experimental conditions, accompanied with at-sea trials to verify effectiveness in varied light conditions is warranted, together with an assessment of the effect of gillnet colour on catch efficiency of target species.

High mortality of adult female Magellanic penguins by gillnet fisheries in southern Brazil

“…Another possible explanation could be a lack of enforcement since there is a general pattern of over‐exploitation of several fishing resources which led some of them to be at risk of commercial unviability (Haimovici & Cardoso, ). An alternative with the potential to decrease bycatch is modifications in the net such as increasing its visibility without a significant reduction in its efficiency to catch target species (Hanamseth, Baker, Sherwen, Hindell, & Lea, ; Martin & Crawford, ). However, there is a clear lack of proper management measures or enforcement in the study area, as several threatened marine megafauna species are killed annually in high numbers and most of the fishing resources are over‐exploited (Haimovici & Cardoso, ).…”

“…Another possible explanation could be a lack of enforcement since there is a general pattern of over-exploitation of several fishing resources which led some of them to be at risk of commercial unviability (Haimovici & Cardoso, 2016). An alternative with the potential to decrease bycatch is modifications in the net such as increasing its visibility without a significant reduction in its efficiency to catch target species (Hanamseth, Baker, Sherwen, Hindell, & Lea, 2018;Martin & Crawford, 2015).…”

“Feelings and Fitness” Not “Feelings or Fitness”–The Raison d'être of Conservation Welfare, Which Aligns Conservation and Animal Welfare Objectives

“…Increasingly, this kind of information and a focus on animals' mental experiences is guiding habitat design [e.g., ( 133 , 207 )] and the evolution of zoo policies and guidelines ( 116 ), ZAA's Animal Welfare Position Statement ( 205 ) and is being given greater weight in conservation decision-making in the zoo community [e.g., Periera ( 208 ) “Tiger returned to SF zoo after transfer to Sacramento made her homesick”; Anon ( 209 ) “Zoo pays tribute to much-loved lions”; Johnston ( 210 ) “Auckland zoo puts down ‘unhappy and agitated' gibbon”]. Individual zoo organizations, and increasingly the zoo community as a whole, are showing leadership in this regard, and there is great potential for zoo biologists and welfare scientists to collaborate more closely with their field research colleagues to optimize policies and practices to better achieve both welfare and conservation goals more broadly [e.g., ( 211 , 212 )].…”

Efficacy of Time-Area Fishing Restrictions and Gear-Switching as Solutions for Reducing Seabird Bycatch in Gillnet Fisheries

“…Gear modifications and gear handling practices have been effective at reducing seabird bycatch for active fishing gears, such as longlines and trawls, based on the ability to observe interactions between birds and gear components during fishing activities (Croxall 2008;Bull 2009;Anderson et al 2011;Løkkeborg 2011). Such technical measures have not generally been successful when applied to passive gears, including gillnets, because bycatch events typically occur when the gear is untended or underwater where interactions cannot be directly observed (Almeida et al 2017;Hanamseth et al 2017;Field et al 2019;Cantlay et al 2020). Similarly, fleet communication programs designed to reduce bycatch rely on real-time, or near real-time, observations and information sharing to avoid bycatch hotspots (Gilman et al 2006;O'Keefe and DeCelles 2013;Bethoney et al 2013a) and are not feasible for untended passive gears.…”