Evaluation of the use of netting and biodegradable materials in drifting FAD construction in the WCPO

Drifting Fish Aggregating Devices (dFAD) are widely used in purse seine tuna fisheries globally and are often lost or abandoned which can lead to marine pollution, entanglement of sensitive species and habitat damage. This study, which is an update from a recent scientific paper by Escalle et al. (2023), used data collected by fishery observers to investigate materials and designs used in dFAD construction over the last 13 years in the Western and Central Pacific Ocean. Results indicated that apart from bamboo, which is commonly used in dFAD rafts with other synthetic materials for buoyancy, very few natural materials are used. In the 2011–2023 period, dFADs are dominated by a mix of synthetic and natural (categories (cat.) II, IIb, III, IV and IVb; 57%); artificial (cat. V; 33%); or completely natural (cat. I; 9%) materials. However, several materials recorded by observers could either be synthetic or natural (e.g., cords, ropes, canvas, netting, sacks and bags) and additional information on their biodegradable nature is needed. The median depth of dFAD appendages was 50m, but information on their design is currently lacking due to the difficulties in observing them. Most dFADs used netting of various mesh sizes in some aspect of their construction. A trend in dFADs without netting (8% in 2011–2019 and 12% in 2020–2023), as well as a slight decrease in the mesh size is identified since 2020. Currently a transition towards more environmentally friendly dFAD designs is being promoted through CMM 2019-01 and CMM 2021-01, including banning netting by 2024 and encouraging the use of natural materials, with scientific trials of biodegradable dFADs underway. However, the low observer coverage in 2020–2023 due to the COVID-19 pandemic, which has hopefully passed, has reduced the information available to investigate dFAD materials and designs and may have influenced the changes noted in this paper for the last few years. Additional years with higher observer coverage are therefore needed to confirm, or infirm, these trends. Nevertheless, this paper provides important baseline data to detect and monitor future changes in dFAD construction and materials in response to CMMs. It also highlights limitations to data collected by observers that will need to be improved to better monitor these changes.

- Note that limited information on dFAD designs and materials are available from 2020 to 2023, due to low observer coverage, as well as the need for additional data fields or more systematic data to be recorded to adequately assess the designs, materials and type of dFADs deployed in the WCPO. - Note that materials used in dFADs in the WCPO have been dominated by artificial (cat. V; 33%), or a mix of synthetic and natural (cat. II, IIb, III, IV and IVb; 57.6%) and entangling materials, with variability among fleets, with the limited use of biodegradable dFADs (cat. I, II and IIb; 22.7%). - Note that, even with the information currently available, a trend in use of dFADs without netting (from 7.7% to 12.2%) and use of smaller mesh sizes in the rafts (from 7.0 to 6.4 cm) and appendages (from 8.1 to 6.9 cm) can be detected since 2020, compared to 2011–2019. - Note that further studies are needed to quantify the effectiveness and the entanglement frequency of Species of Special Interest (SSI) in the WCPO on common dFAD designs, but also on new low entanglement risk, non-entangling and biodegradable dFADs. - Continue to promote the reduced use of plastics, entangling and non-biodegradable materials in the construction of dFADs in the WCPO to help reduce marine pollution and ecosystem impacts and support on-going research activities and at-sea trials of biodegradable and non-entangling dFAD design options in the WCPO.