Lost fishing gear at a global scale : amounts, sources and solutions

Abandoned, lost or otherwise discarded fishing gear (ALDFG) represents a consequential amount of marine debris, with serious adverse socioeconomic and environmental impacts to sustainable fisheries and livelihoods, food security and marine ecosystems. Once introduced to the marine environment, ALDFG injures and kills a variety of marine wildlife, results in losses of fishing gear and catch, presents hazards to navigation and safety at sea, damages fragile marine environments, and is expensive and challenging to recover and clean-up. With most modern fishing gear comprised of highly durable and resilient plastic materials, ALDFG can persist in the marine environment for years to decades, exacerbating its potential for prolonged impacts.

To inform global ALDFG prevention and reduction efforts, this thesis answers critical questions about total amounts and sources of ALDFG in the world's oceans and identifies effective ALDFG solutions. The thesis presents estimates for ALDFG that can be used as baselines from which to monitor and measure the effectiveness of ALDFG interventions, and to support targeted development and implementation of solutions at scale. Gear loss causes and drivers are identified, which can be used to aid fishers, managers, policy makers and NGOs with fishing gear risk assessments and to tailor sustainable solutions to prevent and reduce ALDFG at source. A review of historic and ongoing work to prevent and mitigate ALDFG highlights successful interventions available for replication and adaptation.

This thesis employs a range of methodologies, which include: examination of efforts by global experts and organizations to build evidence around and combat ALDFG; a comprehensive ALDFG literature review and meta-analysis; and interviews with fishers from seven countries around the world (Belize, Iceland, Indonesia, Morocco, New Zealand, Peru and the United States of America) representing five major fishing gear types (gillnets, purse seine nets, trawl nets, longlines and pots and traps).

The thesis begins with a background of the ALDFG issue and highlights the importance of evidence gathering to inform sustainable solutions, from local to global scales. It summarises innovative approaches to ALDFG data collection and gear retrieval efforts, opportunities to fill data gaps and how to raise awareness of this important topic. Following this overview, it discusses major challenges around the creation of global ALDFG estimates, including costs and consequences of misinformation and the importance of visiting primary sources to ensure sound data collection and dissemination.

Pressures and drivers of gear losses are then explored through a case study of Australian and Indonesian fishers in the Arafura Sea. Major drivers of fishing gear losses reported by these fishers included lack of fisheries enforcement, pressures arising from illegal, unreported and unregulated fishing activities, and overcrowding and overcapacity. This regional case study shares valuable lessons learnt which are broadly applicable on a global scale, including the critical role that effective fisheries management plays in preventing the pressures and drivers that eventually result in ALDFG.

Scaling up from this regional case study to a global examination of ALDFG, the thesis presents results from a global literature review and meta-analysis. This meta-analysis used quantitative data from published ALDFG studies between 1975 - 2017 to create the first synthetic, statistically robust global ALDFG estimates, estimating that 5.7% of all fishing nets, 8.6% of all traps and 29% of all lines are lost around the world each year. Estimates are also provided for specific, sub-gear types operating across various environmental conditions, and basic causes of gear losses are additionally explored across studies.

The thesis subsequently examines the causes of gear losses that are common to most major fishing gear types employed around the world through systematic global fisher interviews. Fishers were asked about why they lose gear, and what they view as effective mechanisms for preventing gear losses. Data from the interviews revealed that bad weather, interactions with wildlife, snagging gear on a bottom obstruction, and gear conflicts and interactions with other fishers and vessels are the primary causes of gear losses, across all gear types. Operational and behavioural characteristics such as gear type, vessel length, and the party responsible to pay for gear repairs and replacements also significantly influence gear losses. Fisher interviews emphasize the importance of regular gear maintenance, training crew in gear management, reducing active gear interactions with wildlife, improving access to port reception facilities for end of life gear, reducing fishing effort, and targeting ALDFG education and stewardship programs toward lower income fisheries and countries.

The final data chapter provides updated global ALDFG estimates. These estimates use data gleaned directly from global fisher interviews and reflect gear losses according to most current and best available global fishing effort estimates. These estimates represent the largest international survey of fishers around gear losses, and account for influences from vessel size and gears contacting the seafloor. The estimates predict that nearly 2% of all fishing gear, comprising 2,963 km² of gillnets, 75,049 km² of purse seine nets, 218 km² of trawl nets, 739,583 km of longline mainlines, and over 25 million pots and traps are lost to the ocean annually.

In summary, this body of research presents the first global, statistically rigorous estimates for total amounts of ALDFG entering the world's oceans annually to provide topical, relevant baselines of the magnitude of this serious environmental and socioeconomic issue. The thesis also provides insights into why and how gear becomes lost, including major pressures and drivers behind gear losses, and highlights the critical importance of good fisheries management to effectively prevent gear losses at source. Better understanding how much, where and why fishing gear losses occur, as well as effective prevention and reduction measures ultimately contributes to more sustainable fisheries and a cleaner, healthier marine environment whilst ensuring food security into the future.