Whether it’s sold as sushi or steak or in other forms, tuna is valuable: In fact, tuna caught by longline fishing vessels worldwide is worth more than $8 billion a year. These boats use fishing lines stretching up to 60 miles with thousands of baited hooks, which unfortunately also catch nontargeted (bycatch) species, including endangered turtles, sharks, rays, and seabirds.
To help track these longliners’ catch—and the impact they have on the ocean—many regional fisheries management organizations (RFMOs) require observers on board, but most do so only for 5% of fishing trips. Although these observers provide critical information to fishery managers and scientists on what longliners catch and where they fish, two new scientific papers find that the current level of coverage in the Pacific Ocean tuna longline fisheries is insufficient to provide accurate and representative data. They recommend that observer coverage be increased to at least 20% across the fleet. RFMOs and their members should heed this call and commit to increasing longline observer coverage and to developing comprehensive electronic monitoring (EM) programs.
The first paper, published in the journal Environmental Science and Pollution Research and authored by scientists from Shanghai Ocean University and the University of Maine, used observer data from 103 tuna longline vessels fishing in the Pacific Ocean from 2010 to 2019 to model what would happen if observer coverage increased from the 5% requirement. Their models showed that increasing observer coverage would lead not only to more accurate catch estimates for targeted fish stocks, but also to better bycatch estimates, which are essential for sustainably managing these fisheries. Across all species, the accuracy of catch estimates would increase by an average of 50% with higher observer coverage, the researchers found.
The second study was carried out by scientific staff from the Inter-American Tropical Tuna Commission (IATTC), the RFMO that manages the tuna fisheries in the Eastern Pacific Ocean. They looked at whether the data that observers collect on longliners in the region is representative of the overall activities of the fleet, and whether the information allows for reliable estimates of catch of tuna and bycatch species. The scientists analyzed available data from 2016 to 2018 for four fleets that made up a significant proportion of the overall longline fishing catch during those years.
This analysis found that the observer data for three of the four fleets was not geographically representative of the overall fishing effort and that two of the fleets had observers on board only during the second half of each year studied, even though their fleets were fishing year-round. The paper also found that catch estimates that came from such low levels of observer coverage significantly underestimated the catch of yellowfin and bigeye tunas compared with numbers reported by the fishing countries. In some cases, observed catch versus reported catch differed by nearly 70%. The IATTC scientific staff concluded that observer coverage needs to be increased to at least 20% to accurately monitor tuna catch—and should in fact be much higher to precisely estimate capture of bycatch species.
Taken together, these studies add to the growing evidence that the current RFMO observer coverage requirements are insufficient to properly manage the tuna longline fleet. Fortunately, EM—which consists of a system of sensors and cameras placed on board a vessel to collect independent information—can boost that coverage by enabling monitoring of more vessels and increasing the amount of data available for fisheries managers and scientists. The tuna RFMOs have already begun the process of designing EM programs, and these new scientific papers reinforce why all stakeholders should commit to implementing robust EM programs and working toward full observer coverage of the tuna longline fleets.
Jamie Gibbon is a manager with The Pew Charitable Trusts’ international fisheries project.
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