By Victor Restrepo & Laurent Dagorn
Working to improve the sustainability of tuna fisheries requires the development and implementation of verifiable, science-based practices, commitments and international management measures. A scientific foundation is essential to inform these management decisions – without it, debates about fisheries management are simply campaign-driven and made to fit the respective agendas of varying interest groups. Over the past year, much attention has deservedly been given to the bigeye tuna fishery in the Western and Central Pacific region, what we know and don’t know about the potentially perilous situation there. As marine scientists, it’s our job to collect and analyze data to find answers to these unknowns.
Since 2011, the International Seafood Sustainability Foundation (ISSF) has conducted seven at-sea research cruises – almost all of which took place on working fishing vessels. These voyages are built on scientific research and aimed at finding techniques and procedures that would result in more selective fishing in purse seine fisheries, which means catching only what a vessel sets out to catch. Our focus on these research cruises is twofold: reducing the incidental catch of non-tuna species (also called bycatch, such as sharks) and better understanding and prediction of the catch composition of small bigeye tuna, a species currently overfished in the Western and Central Pacific Ocean.
While some NGO campaigns refer to purse seine-caught bigeye tuna as a bycatch species, this open water fish is actually a target catch in these fisheries. Bigeye are caught and sold by purse seine vessels and other gear types in the same manner as skipjack and yellowfin, the other two tuna species targeted by large purse seiners. Thinking of bigeye only as bycatch can lead to a loss of detailed catch information and, subsequently, indirect and insufficient management measures. Simply put, bigeye cannot truly be lumped together in the same basket with all non-target species. Bigeye catches by all fishing gears – primarily longline and purse seine, but also handline and pole-and-line – need to be monitored and managed directly, just like their yellowfin and skipjack counterparts. The more we know about these catches, the better the Western and Central Pacific Fisheries Commission (WCPFC) – the relevant regional fishery management organization (RFMO) – can manage them.
Last year, ISSF was fortunate enough to collaborate with Albacora, one of the world’s leading purse seine fishing companies, in sending scientists on an at-sea research-fishing trip in the central Pacific Ocean. A main objective of the cruise was the use of acoustic echo-sounders to better understand species composition when fishing on floating objects, also known as fish aggregating devices (FADs). Scientists deployed on-board echo sounders with three different frequencies aimed at determining the “target strength” for each of the three target tuna species – in other words, a tool with the potential to improve a fisher’s ability to assess the amount of small bigeye tuna aggregating at floating objects before setting their nets on that floating object or FAD. The central equatorial Pacific is an ideal place for this research because bigeye tuna is very common in this geographic area and because bigeye catches are especially high there for both longline and purse seine fisheries. Most importantly, this research took place in-situ, that is, at-sea, in a real situation, as opposed to a controlled laboratory setting.
We won’t summarize all of the cruise findings here, but we want to highlight one that we find most valuable. On this fishing trip, there were sets made that resulted in almost only bigeye, and there were sets that resulted in almost only skipjack, as well as mixed sets with a wide range of bigeye-skipjack and yellowfin combinations. In statistical analyses, we refer to this data as data with ‘high contrast.’ High contrast data are critical to a study’s ability to meet the rigors of the scientific method. And they are ideal in terms of science. How can we determine each species’ unique target strength, for example, if each species was not well represented during our analyses? Had all the sets been mixed – say 80% skipjack and 20% bigeye – the situation would not have been nearly as meaningful and impactful in scientific terms.
While it was disappointing to see a lack of action by WCPFC to better protect the Western and Central Pacific bigeye tuna stock last year, it only underscores the urgent need to continue our study. And it is impossible do so in a real-life setting without going onboard a working commercial vessel. The bycatch project cruises in the Central Pacific have been a series of great moments for marine science that would not have happened without the collaboration from industry participants. Like our collaborators before them, by allowing scientists to conduct experiments during that trip onboard their vessel ALBATUN TRES, Albacora created a pathway for us to record and disseminate information that could not have been done strictly in lab. We encourage and welcome other industry participants to help on the water in any way they can. Only then can we hope to improve data collection, learn new techniques and, ultimately, move the needle on protecting vulnerable species.
Victor Restrepo is Chair of the ISSF Scientific Advisory Committee. Previously, he worked with the International Commission for the Conservation of Atlantic Tunas (ICCAT). Dr. Restrepo holds a PhD in Population Dynamics from the University of Miami, as well as a BSc in Marine Science and Biology from the University of Miami.
Laurent Dagorn is member of the ISSF Scientific Advisory Committee and a Senior Scientist working for the Institut de Recherche pour le Développement in France. Dr. Dagorn coordinated two major EU funded projects on FADs. Dr. Dagorn holds a PhD in Fisheries Science from the ENSA Rennes (France), as well as an accreditation to supervise research (university degree for Senior Scientists) from the University of Perpignan.
Copyright © 2015 by Marine Science Today, a publication of Marine Science Today LLC.