Brailing of tuna onboard vessel Dolores, 2008. Credit: Siosifa Fukofuka (SPC)
Understanding the impact of modern fishing techniques on the tuna fishery is critical to ensure the sustainability of the Western and Central Pacific Ocean (WCPO) tuna fishery – the largest in the world, accounting for 55% of the total tropical tuna catch and providing up to 98% of government revenue for some Pacific Island nations.
Multiple agreements have been signed by Pacific Island countries and territories to maintain the sustainability of this important ocean resource. However, the advent of fish aggregating devices (FADs) and their impact on fishing efficiency over the past 20 years has added a largely unknown factor to the management required to maintain the sustainability of this key fishery into the future.
Researchers from the Pacific Community’s Oceanic Fisheries Programme and the Australian Research Council Centre of Excellence for Climate Extremes have recently published two papers that reveal for the first time the trajectories and potential impact these FADs may have on fisheries and Pacific Island nations. They used a combination of records from captains and scientific observers, FAD tracking data, ocean models and cutting edge simulation methods.
“Between 30,000–65,000 FADs are released every year in this region but we have very little understanding of where they end up, how they are being used, and the impact they have on coastal areas and the overall catch of the fishery,” said Dr Lauriane Escalle, a fisheries scientist at SPC.
“While we know FADs make fishing more efficient, allowing fishing vessels to use less fuel and reduce fishing effort, there are unanswered questions around potential overfishing, impacts on bycatch species, ghost fishing and reef damage caused by FADs washing up on coral reefs and islands,” she added.
Aside from catch data and ocean models, modern FADs themselves played an important role in helping the researchers get their answers.
FADs work because ocean going species, such as tuna, tend to aggregate around floating objects. Why they do this is still not fully understood but fishers have long known this fact and have taken advantage of it by releasing bamboo rafts into the ocean – the world’s first FADs. Over time, commercial fishers added old ropes and nets to slow the drift of the FADS through the ocean.
Today, FADs are high-tech buoys with solar powered devices that record the position, scan the ocean below to estimate the number of aggregated fish, and transmit this information to vessels via satellite. This technology opened the door to detailed observations of FAD life history while they drift across the Pacific Ocean.
Combining this real-world information with catch data and cutting-edge simulations based on ocean models allowed the researchers to examine the dynamics of FAD connectivity and to test various hypotheses explaining the high number of FADs being beached in some areas. This key information could significantly assist in the management of the Western and Central Pacific Ocean tuna fishery and the exclusive economic zones within it.
The studies found that:
- more than 2000 FADs wash up on beaches and coral reefs every year;
- up to 6000 FADs found on in the WCPO had drifted in from another fishery in the Eastern Pacific Ocean, which has different management systems;
- FADs spent more time in the exclusive economic zones of Tuvalu and Solomon Islands than any other part of the fishery;
- the highest number of FAD beaching events occurred in Solomon Islands, Papua New Guinea and Tuvalu. This was more the result of ocean currents than where the FADs were deployed, making management of this issue more difficult; and
- Kiribati, located along the equator, experienced a high number of FADs drifting through their waters, alongside significant levels of beaching, as a result of where fishers deployed FADs.
Results from these studies will help to manage tuna resources effectively, through measures on the number and location of FAD deployments, the use of biodegradable FADs, programmes to recover lost FADs before they reach sensitive areas, and more research on the impact of FADs on tuna and bycatch populations.
“Access to this unique regional database of FAD tracking data by fishing companies and managers allowed us to not only validate ocean models, but also to test different deployment hypotheses using millions of virtual FADs,” said Dr Joe Scutt Phillips, another fisheries scientist at SPC.
“This method allows us to look back in time and make good estimates of the movement and impact of FADs from before tracking programmes, as well as examine their potential impact on tuna behaviour,” he added.
“This collaboration among fishing companies, regional management organisations and researchers has resulted in an extraordinary amount of useful data that will go a long way towards helping Pacific Island nations and fisheries managers maintain the sustainability of this valuable USD 6 billion a year industry. It’s a great example of managers, industry and researchers working together for the benefit of all,” he concluded.