High tech, complex science and deep knowledge: assessing WCPO tuna populations

Detailed scientific assessments are conducted regularly to calculate how well tuna populations are coping with fishing and changes in the oceanic environment.

They are rigorous and exhaustive: it takes a full year to assess one species. The results form the basis for the management of the tuna fisheries in the Western and Central Pacific Ocean (WCPO). Scientists of the Division of Fisheries, Aquaculture and Marine Ecosystems (FAME) at the Pacific Community (SPC) conduct assessments on the four commercially important tuna albacore, bigeye, skipjack and yellowfin and on other important species, such as swordfish, striped marlin, and several sharks.

Each of the tuna is assessed every three years, and the other species every four or five years.

The WCPFC uses the highly technical assessments to make formal statements about the status of each species, and to make management decisions aimed at keeping tuna populations and tuna fishing sustainable for many generations. Decisions encompass fishing rules, including limits, to protect the viability of the tuna species, and rules to protect the environment and other species.

The assessment reports and data files are available to everyone. SPC also publishes an overview that gives an excellent summary of the status of the tuna populations. It includes some other matters researched. The most recent overview, for 2019, included the effects of fishing on marlin stocks, some endangered species of sharks, the effects of El Nio Southern Oscillation (ENSO) and the potential impact of the climate on fisheries.

Determining how healthy the populations are, and whether they are being overfished, involves a team of people with a range of skills. A scientific committee decides which species will be assessed, what modelling approaches to use, and what particular inputs should be used to account for uncertainty. Others involved are:

• fisheries biologists, who provide information on age, growth, and reproduction of species
• ecosystem scientists, who collect and analyse primary tagging data (relying on input from commercial and subsistence fishers when they capture tagged fish)
• oceanographers and climate scientists, who provide data on whats happening in the ocean environment and climate, what may be changing and why
• statisticians, who design how the sampling is done, and who process the collected data to make sure it is representative of the population being modelled
• stock assessment scientists, who combine all the data collected into a sophisticated statistical model that estimates the current abundance of the stock, and compares it with historical data and trends to calculate its sustainability.

SPCs research shows that all four tuna in the WCPO are in a healthy state, and that none of them are being overfished. The status of tuna in the region is much better than for any other ocean basin.