Use of biodegradable driftnets to prevent ghost fishing: physical properties and fishing performance for yellow croaker

Abstract

When synthetic non-biodegradable fishing nets are lost, abandoned or discarded at sea, they may continue to catch fish and other animals for a long period of time. This phenomenon is known as 'ghost fishing'. Biodegradable fishing nets, on the other hand, are intended to degrade or decompose after a certain period of time under water and thereby lose their ghost fishing capacity more quickly than conventional gear. A biodegradable net material, a blend of 82% polybutylene succinate (PBS) and 18% polybutylene adipate-co-terephthalate (PBAT), was developed. We examined the physical properties and degradability of the biodegradable monofilament, and compared the fishing performance of driftnets made of conventional nylon and of the biodegradable material. When dry, conventional nylon monofilament exhibited a greater breaking strength and elongation than biodegradable monofilament of the same diameter. When wet, the biodegradable monofilament exhibited a stiffness of c. 1.5-fold than nylon monofilament. This suggests that a net made of the less flexible biodegradable monofilament would have lower fishing efficiency than conventional nets. The fishing performance comparisons between the biodegradable and conventional nylon nets, however, revealed similar catch rates for yellow croaker Larimichthys polyactis. Biodegradable monofilament started to degrade after 24 months in seawater by marine organisms. We conclude that biodegradable netting may become a feasible alternative to conventional nylon netting and can contribute to reducing the duration of ghost fishing. Nonetheless, there remain many uncertainties, challenges and knowledge gaps that have to be solved before we are able to draw firm conclusions about the overall benefits of these materials in driftnet fisheries.

Biodegradable fishing gear: part of the solution to ghost fishing and marine pollution

“…Furthermore, the experimental netting had a significantly lower catch rate of unwanted juvenile yellow croaker, supporting improved catch levels of adult age classes of this target species. Kim et al's (2016) findings are encouraging, contributing to a small but growing body of literature on the use of weaker and degradable gear to reduce ghost fishing. Many critical questions remain.…”

“…Kim et al (2016) developed a new synthetic material for monofilament twine of gillnets and assessed its breaking strength, amount of time to begin degrading and fishing efficiency relative to the conventional nylon twine used in the Korean coastal yellow croaker Larimichthys polyactis benthopelagic gillnet fishery. Ghost fishing is thought to be most problematic in gillnets and other passive fishing gears, where the capture process relies on the movement of organisms into the gear (Matsuoka, Nakashima & Nagasawa, 2005;Gilman et al, 2013).…”

“…Ghost fishing is thought to be most problematic in gillnets and other passive fishing gears, where the capture process relies on the movement of organisms into the gear (Matsuoka, Nakashima & Nagasawa, 2005;Gilman et al, 2013). Kim et al (2016) found that the experimental twine began to be degraded by microbes after 2 years in seawater. Conventional gillnets made of nylon monofilament can take decades to degrade (Carr et al, 1985).…”

Biodegradable nets are not a panacea, but can contribute to addressing the ghost fishing problem

“…ALDFG raises a number of issues, including stock depletion for species targeted by the fishery, mortality to non-target species, which in some cases are species of conservation concern (Derraik, 2002;Wilcox et al, 2015), hazards to other vessels due to fouling of propellers or fishing gear, and costs for removal that are imposed on public agencies or other bodies (Macfadyen et al, 2009). Kim et al (2016) explore biodegradable polymers as a possible solution to the issue, for passive fishing gear such as gillnets and trammel nets. These nets had only slightly lower catch rates than conventional nylon nets in field tests, and yet they showed clear signs of degradation within 2 years of introduction to salt water.…”

“…While it is commendable that Kim et al (2016) have developed a nylon substitute for fishing gear that degrades back to the monomer, and eventually the elemental level, leaving no plastic residue in the environment, there are a number of significant issues with the solution they propose, even for ALDFG in the Korean croaker fishery they use as a pilot study. First, the time required for the gear to degrade is likely far longer than the time it effectively fishes.…”