Reducing bycatch in gillnets: A sensory ecology perspective

Abstract

a b s t r a c tSensory capacities and perceptual challenges faced by gillnet bycatch taxa result from fundamental physiological limits on vision and constraints arising within underwater environments. To reduce bycatch in birds, sea turtles, pinnipeds and blue-water fishes, individuals must be alerted to the presence of nets using visual cues. Cetaceans will benefit but they also require warning with cues detected through echolocation. Characteristics of a visual warning stimulus must accommodate the restricted visual capacities of bycatch species and the need to maintain vision in a dark adapted state when foraging. These requirements can be provided by a single type of visual warning stimulus: panels containing a pattern of low spatial frequency and high internal contrast. These are likely to be detectable across a range of underwater light environments by all bycatch prone taxa, but are unlikely to reduce the catch of target fish species. Such panels should also be readily detectable by cetaceans using echolocation. Use of sound signals to warn about the presence of gillnets is not recommended because of the poor sound localisation abilities of bycatch taxa, cetaceans excepted. These warning panels should be effective as a mitigation measure for all bycatch species, relatively easy to deploy and of low cost.

Physiology in the service of fisheries science: Why thinking mechanistically matters

“…Such an approach requires exploitable physiological and behavioral differences between target and nontarget species that allow gear modifications to deter the latter but not the former, lest target catches decline (Southwood et al 2008;Brill et al 2009;Wang et al 2010). Understanding the sensory abilities of fisheries resources (e.g., Horodysky et al 2008a, b) and bycatch species is the critical first step to develop potential technologies (Southwood et al 2008;Martin and Crawford 2015); these can then be tested with field gear modification trials and generate new hypotheses that can be addressed in the laboratory Mooney et al 2007). Similar strategies have been used to test synthetic alternatives to the use of species of concern as bait (e.g., Magel et al 2007).…”

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

“…chlorophyll content) but is influenced by its viewing angle (Cocking, Double, Milburn, & Brando, 2008;Johnsen, 2002Johnsen, , 2003Johnsen & Sosik, 2003). This affects the perceptive capabilities of freshwater and marine species at any given time, as they not only move between media (air and water) but some species also travel rapidly to depths (Martin & Crawford, 2015) and across the latitudes, especially for several migratory species. This affects the perceptive capabilities of freshwater and marine species at any given time, as they not only move between media (air and water) but some species also travel rapidly to depths (Martin & Crawford, 2015) and across the latitudes, especially for several migratory species.…”

“…Birds nest in colonies along coastal, inshore and offshore islands of southern Australia and New Zealand, and typically forage within 30 km of their colonies. Most bycatch species, including little penguins, appear to be captured in gillnets as the nets are not clearly visible to them (Martin & Crawford, 2015). Most bycatch species, including little penguins, appear to be captured in gillnets as the nets are not clearly visible to them (Martin & Crawford, 2015).…”

Tangled and drowned: a global review of penguin bycatch in fisheries

“…Penguin entanglements in gillnets are almost inevitable given their pursuit diving foraging behaviour and the virtual invisibility of modern monofilament nylon netting when deployed underwater (Martin & Crawford 2015). Bycatch mortality in gillnets has been recorded in Magellanic, Humboldt, Galápagos, African, northern rockhopper, little, Fiordland and yellow-eyed penguins.…”

“…Some measures have shown promise, including thicker, white meshes in the upper sections of driftnets and the use of acoustic 'pingers' to deter auks (Melvin et al 1999). Recent research has proposed the deployment of black and white panels to alert birds to gillnets (Martin & Crawford 2015), and tests of LED lights clipped along the headline of gillnets have reduced turtle (Wang et al 2013, Ortiz et al 2016 and seabird (Mangel et al unpubl. data) bycatch.…”