Gillnet is one of the most important fishing gears in Norway. Cod, saithe, Greenland halibut, angelfish, and lumpfish are the most important species for these fisheries. In 2012, the cod quota was distributed as follows: approx. 93,000 tonnes for the gear group fishing with gillnets, approx. 76,000 tonnes for trawl, approx. 58,000 tonnes for Danish seine, approx. 40,000 for autoline, and approx. 25,000 tonnes to others. However, it is estimated that the number of lost gillnets per year is approx. 13.900. Today, Norway and South Korea are the only countries in the world that have a program for systematic clean-up of lost fishing gear from the most intensively fishing areas. The Norwegian Directorate of Fisheries has since 1983 retrieved approx. 20,450 lost gillnets, and a considerable number of other fishing gear. The cleaning operation is very demanding due to the operation depth (500-1000m), strong currents areas, and the uncertainty associated with the accuracy of the positions of the lost nets. Therefore, in parallel with the clean-up program, research in recent years has focused on developing methods and techniques to reduce the number of lost nets, location of lost gears, and assess the possibility of using biodegradable materials. Biodegradable gillnets (that degrades in water and CO2) have been developed in recent years by S-ENPOL (earlier owned by Samsung Fine Chemicals Co. Ltd.) and are now a commercial product used in several gillnet fisheries in South Korea.
This project has carried out the following tasks: i) Degradation tests in the sea. In these tests, we put samples of degradable and nylon monofilaments, as well as degradable and nylon nets in the sea, both in Trondheim and in Tromsø. The test was conducted for two years and the samples were analysed for tensile strength and elongation at break every three months. ii) Degradation experiments in lab focusing on studying changes in polymers in the material and quantifying any detached particles to the seawater. iii) Fishing trials. Biodegradable PBSAT gillnets have been tested in the fisheries for Greenland halibut (May-Jun. 2016), saithe (Oct.-Dec. 2016, 2017 and 2018) and cod (Jan.-Mar. 2017 and 2018). The experiments were conducted in commercial fishing grounds and under commercial fishing conditions. iv) UV degradation test.
The project has developed degradable gillnets. Fishing experiments on cod, saithe and Greenland halibut show that bio gillnets still have poorer fishing efficiency than traditional nylon gillnets. Lower fishing efficiency can make fishermen prefer traditional nylon gillnets rather than bio gillnets because they have a higher fishing efficiency. Degradation tests in the sea show approx. 26% reduction in breaking strength in PBSAT nets after approx. 25 months in the sea (cold water), while the samples from bio-nets used in one fishing season (max. 3 months) showed approx. the same reduction in breaking strength. Daily use and wear of the gillnets accelerates the degradation process. Controlled laboratory tests at 20 °C also show approx. 20% degradation after 12 months exposure in seawater. No fragmentation has been recorded, i.e. microplastic formation. UV degradation tests where we exposed biodegradable material to UV-radiation showed that PBSAT monofilaments degrade faster than nylon monofilaments, thus demonstrating a stronger reduction in mechanical strength and material integrity. In addition, PBSAT is changing its chemical structure more significantly during degradation compared to nylon. UV degradation tests showed detached particles.
This project has focused on developing biodegradable gillnets for Norwegian fishing and has focused on quantifying the catch efficiency, degradation rate and possible formation of microplastic in seawater. Much of the results from these studies have already been published in international journals. Some tests are still running and several publications on the subject are expected in the future.
It is recommended further studies of catching modes and this requires new fishing experiments and new analyses of data. It is proposed to continue the project and complete the work where we study the degradation process of the biomaterial. Today this experiment has lasted for 18 months but was designed and planned to last 36 months.
A large problem of using gillnet in commercial fishing is that the fishermen lose considerable amounts of gillnets. The Norwegian Environment Agency (2018) has estimated that approx. 13000 gillnets are lost per year. Lost gillnets give the fishermen an alternative loss in the form of lost catches by ghost fishing. It is therefore strongly recommended to carry out a bio-economic analysis of gillnet fishing and estimate the value of lost resources due to ghost fishing mortality. It is recommended to investigate how the use of bio gillnets (and thus the reduction of plastic pollution and ghost fishing) can be implemented in Norway.
Lost, abandoned, and/or discarded fishing gear (LADFG) is an internationally recognized problem that causes unwanted ghost fishing; pollution of the marine foodweb with plastics; alterations to the benthic environment; and a variety of costs related to clean-up operations and impacts on business activities. In response to this problem, a large number of international organizations and agreements now focus on LADFG, and numerous national and local-level initiatives have been implemented around the world.
To date, Norway is the only country in the world that has a program for the systematic annual retrieving of LADFG from the most intensively fished areas. Since this program started the total number of retrieved gillnets has reached 18,300 nets (approx. 494 km). The retrieving operations are however highly demanding because of operation depth (500-1000m), strong currents in the areas, and the uncertainties associated with the accuracy of the lost gear's position.
In the last decade, a large number of R&D projects with biodegradable EnPol gillnets to reduce the impact of ghost fishing have been carried out by Samsung Fine Chemicals and research institutions in Korea. These gears have been tested in 13 different fisheries, and include gillnetting and potting for round, flatfish, shrimps, octopus and crabs, eels. The results of these experiments have shown that the fishing efficiency of these gears is similar to those made of synthetic fibres (nylon, polyethylene and polypropylene). Currently 21 kind of fishing gears have been developed and a total of 370 Korean coastal vessels are using biodegradable fishing gears on a regular basis.
This project brings togheter Korean and Norwegian institutions to develop biodegradable gillnets for the most important deep-water gillnet fisheries in Norway. The main objective is to develop bio-degradable gillnets as a responsible fisheries management measure for reducing ghost fishing and pollution of plastics in the environment.