Can biodegradable materials reduce plastic pollution without decreasing catch efficiency in longline fishery?

Longlining is a widely used fishing method. All types of longlines consist of three components: a mainline, hooks and snood connecting the hooks to the mainline. During longline fishing, some of the snoods are often lost at sea. Longline fisheries use mainly synthetic materials such as spun polyester, twisted polyester and twisted nylon (polyamide 6) for mainlines and usually monofilament nylon snoods. Loss of these components at sea is posing a threat to the marine food web as they degrade, creating nano- and microplastic pollution and releasing toxic substances. Biodegradable plastics as replacement for conventional plastics have the advantage that they are fully degraded by naturally occurring microorganisms.

While biodegradable plastics can be considered as more environmentally friendly, these materials have so far shown lower performance when applied to fishing gears. For example, results from earlier experiments showed lower catch efficiency in gillnet fisheries and lower tensile strength of biodegradable plastics compared of traditionally used plastic materials. Further tests in longline fisheries are important as the adoption of biodegradable plastics in fisheries depends on their ability to match the performance of the conventional plastics.

This study is the first to quantify the snood loss rate in a coastal longline fishery. Further, it investigated the initial catch efficiency and snood loss risk of biodegradable polybutylene succinate co-adipate-co-terephthalate (PBSAT). This study was performed in the coastal longline fishery in Northern Norway targeting haddock and cod and tested monofilament PBSAT snoods of different thicknesses against monofilament nylon material. Results showed no statistically significant difference in either catch efficiency or snood loss risk between PBSAT and nylon. Because the risk of snood loss was not significantly higher with PBSAT when compared to nylon, the need for replacement of snoods did not increase either.

The coastal longline fishery usually uses longline sets with 10.000–30.000 snood lines, and the estimated snood loss risk when using conventional nylon material was 4.66%, showing that 466 to 1380 snoods can be lost at sea during each single deployment when using nylon snood lines. The results of this study suggest a viable biodegradable replacement material for nylon in coastal longline fisheries. Despite these positive preliminary results, further research is needed to test the long-term performance of PBSAT, as the difference in tensile strength between PBSAT and nylon can increase over time, potentially impacting catch efficiency. Another possible barrier for the adoption of PBSAT is its higher production cost. This problem may be overcome if the production of PBSAT is scaled up and the material becomes subsequently less expensive.

Research team: Kristine Cerbulea, Eduardo Grimaldo (a,b), Bent Herrmann (a,b,c), Roger B. Larsen (a), Jure Brčić (d), Jørgen Vollstad (b)

(a) UiT Norges Arktiske Universitet, Tromsø, Norge
(b) SINTEF Ocean, Trondheim, Norway
(c) DTU Aqua, Institutt for Akvatiske Ressurser, Hirtshals, Denmark d Split Universitet, Fakultetet for marin (d) forskning, Kroatia

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This article is a summary of the research article Can biodegradable materials reduce plastic pollution without decreasing catch efficiency in longline fishery?