Biodegradable nets | Resistance and Durability

Are biodegradable fishing nets a secure alternative?

In order to evaluate the potential of the selected biodegradable resin (PBSAT) as an alternative to nylon monofilament or others for the production of biodegradable fishing nets, different laboratory tests related to its mechanical strength and biodegradability were carried out by the University of Minho. The results are promising since there seem to be an adequate balance between the expected mechanical strength and the biodegradation of PBSAT, in a marine environment.

The introduction of biodegradable materials in the fishing industry is promising, considering the negative impacts resulting from the fishing activity such as marine pollution and ghost fishing produced by fishing gear usually discarded or lost during the activity. The implementation of new solutions more adapted to the marine environment and the consequent protection of marine species is increasingly urgent and essential, considering that marine life is related to various ecosystem services at an environmental, social, and economic level.

In order to study the mechanical strength of PBSAT, tensile tests were carried out on dozens of nets of mesh made out of this material, before and after being used in experimental fishing campaigns. The results indicate some strength variability after use and exposure of the material to adverse and marine conditions, however without compromising the mechanical efficiency, proving to be favourable for the case study. The evaluation processes of mechanical and biological degradation in the laboratory were carried out through different tests, including characterization by scanning electron microscopy, which allowed the assessment of the surface morphology and the chemical composition of the material. The biodegradability test was also carried out in the laboratory by measuring the dissolved oxygen demand in seawater (BOD), which essentially allows the study of the material's biodegradation processes by aerobic organisms, under submerged marine conditions. The material, for the different monofilament diameters, showed different degradation signs such as delamination, mechanical abrasion, variation of the section geometry, and diameter reduction of the monofilament. Regarding the BOD test, the results showed a decrease in dissolved oxygen in the sample and therefore, a potential positive indicator of biodegradability in the marine environment. In situIn situ, other tests are also underway to study the long-term mechanical and biodegradation behaviour in real conditions, which will last for at least 2 years, the necessary time for the material to be biodegraded. For this, analyses of scanning electron microscopy, mechanical strength, and weight loss are carried out periodically to assess the evolution of the material with the exposure time to the real conditions of use.

Our relationship with fishing activity is already quite ancient, with the first records of the use of fishing nets being found back in 8300 years BC. Since then, various materials have been used for fishing nets production, from natural materials such as cotton, silk, wool, and hemp to plastics, like nylon. Nylon has been the most used since the mid-1940s because of its high durability and fishing efficiency. However, nylon is a material that presents a high resistance to degradation, and even when degraded, contributes to the problem of microplastic proliferation, continuing to present not only serious environmental and social risks but also economic impacts.

The E-Redes project is a pilot study promoted by the Municipality, in partnership with the municipal company Esposende Ambiente, the University of Minho, and the Environmental Association - Rio Neiva, which aims at promoting the use of biodegradable nets and, at the same time, collect, quantify and monitor the marine litter arriving at the beaches of the municipality.

In this way, the Municipality of Esposende is contributing to the fulfilment of the Sustainable Development Goals (SDGs) of the UN 2030 Agenda, namely SDG 12 - Sustainable Production and Consumption, SDG14 - Protect Marine Life, and SDG 17 – Partnerships for the Implementation of the Sustainability Goals.