March 16, 2023 — The following was released by the Western Pacific Regional Fishery Management Council:
The Council’s Scientific and Statistical Committee (SSC) yesterday reviewed a 2023 study that found the Phoenix Islands Protected Area (PIPA) and other large oceanic no-take marine protected areas (MPAs) do not have discernible conservation benefits for Pacific skipjack and bigeye tuna.
The paper published in Frontiers in Marine Science was led by world-renowned tuna expert Dr. John Hampton of the Pacific Community (SPC) and a team of tuna scientists and oceanographers. The authors evaluated the estimated population and fishery changes for these two commercially important tunas in the PIPA and a series of large hypothetical MPAs, making up approximately 33% of the Western and Central Pacific Ocean (WCPO).
“Skipjack and bigeye tuna have a wide distribution in tropical and sub-tropical waters of the Pacific, and are capable of spawning anywhere the water temperature is greater than about 25 °C,” said Hampton. “Their larvae drift in the surface water currents, and as they grow, they are able to move widely throughout the region. So closing off one part of the area does not offer much, if any, protection to species like this.” He added, “When areas like the PIPA are closed to fishing, we tend to see the vessels that would have fished there simply move their activities to adjacent areas, which again limits their conservation effectiveness.”
SSC member Ray Hilborn also presented research findings suggesting the 2016 expansion of the Papahānaumokuākea Marine National Monument (PMNM) in the Northwestern Hawaiian Islands did not lead to significant localized increases in tuna. Hilborn’s analyses counter claims made in a study published in Science in October 2022. The claim was based on higher tuna catch rates outside the expansion area after 2016. Hilborn revealed catch rates were already higher in areas immediately outside the new monument border prior to its designation.
Proponents for the PIPA and the PMNM believe a theorized “spillover effect” from these MPAs would have a significant conservation benefit and increase tuna abundance directly surrounding the MPA. This benefit was never realized in either case, according to Hampton and Hilborn.
Hampton and Hilborn pointed out yellowfin tuna abundance, according to a comprehensive population assessment, was increasing prior to the PMNM expansion and continued afterwards. Proportional increases in tuna catch rates, relative to earlier years, were not higher in the potential spillover area. Hampton noted the paper published in Science made no reference to the amount of tuna caught inside the expansion area, nor did it reference tuna stock assessments.
The SSC concurred with the two scientists’ findings. PIPA, unlike the PMNM, had significant levels of industrial tuna fishing, and its closure did not render much of a conservation benefit or spillover effect. The SSC lamented the difficulty of correcting published work that promotes large MPAs. “There is a need to elevate issues raised in these presentations within the global community,” Hilborn said.
SSC Informs Domestic and International Bigeye Tuna Management
The SSC reviewed a framework to establish multi-year allocation limits for bigeye tuna from American Samoa, Guam, and the Commonwealth of the Northern Mariana Islands (CNMI). The new framework may remove requirements for annual catch limits in the territories from the Council’s Pelagic Fishery Ecosystem Plan.
The Western and Central Pacific Fisheries Commission (WPCFC), that manages the tuna stock internationally, does not require catch limits for Small Island Developing States and Participating Territories. However, the Council conservatively recommended catch limits for the territories when the WCPO bigeye tuna stock was considered to be experiencing overfishing in 2014. New data revealed in 2017 the stock was not overfished, nor experiencing overfishing.
The Council is considering taking action to specify multi-year territorial bigeye tuna catch and/or allocation limits at its meeting during the last week of March. The SSC determined that the bigeye tuna stock was healthy and any potential impacts of the Hawai‘i-based U.S. longline fishery would be minimal.
“We can all agree, based on the science available, that the options presented to the Council do not pose any significant conservation risk to tuna stocks,” said Steve Martell, SSC member.
The SSC also discussed the scientific requirements for revising a WCPFC tropical tuna measure, and supporting longline management workshops. The Council hosted a workshop in November 2022 with the Marshall Islands Marine Resources Authority (MIMRA) to improve international management of tropical tuna longline fisheries. A second workshop is planned for April 2023.
The scientific needs include analyses of future fishing levels on the bigeye tuna stock and methods to convert tuna catch into units of fishing days. The Council and MIMRA’s next workshop will explore using “zone-based management” for longline vessels on the high seas and within the national waters of the United States or other nations. SSC members referred to zone-based management of tunas by Pacific Island countries that comprise the Parties to the Nauru Agreement, and recommended investigating existing tools.
“If linear programming tools have already been developed to convert catch to fishing days based on vessel sizes, we should certainly consider utilizing them for the Hawai’i fishery,” according to SSC member Milani Chaloupka.
SSC members plan to develop alternatives to manage the U.S. longline fleet before the WCPFC hosts its longline management workshops this summer.
The SSC also discussed the international working groups’ progress to improve understanding of life history characteristics for key North Pacific billfish species. The group was formed to address a need for coordinated billfish biological sampling across nations and fisheries to improve stock assessments. To enhance regional outreach, the SSC recommended the working group inform the WCPFC Scientific Committee of its research. The SSC also requested periodic updates from the NMFS PIFSC Life History Program for billfish and other pelagic species of interest to the committee.