SPC conducts ongoing research on fish-stock levels.
Graham Pilling explains SPC’s role in conducting stock assessments on the four major tuna species in the Western and Central Pacific, and how that feeds into decisions made by the WCPFC (1.39 mins).
Hear SPC’s Andrew Hunt, who collects data for the Oceanic Fisheries Management Project (OFMP2), explain how that data feeds into stock assessment (32 secs).
Current status of tuna stocks
FFA describes the status of tuna stocks annually in a report-card format, and publishes the report cards and related documents on its website.
The Tuna Fishery Report Card 2019 contains the most recent assessment of the status of major tuna species. The abundance of a species is estimated against a benchmark called a target reference point (TRP), which is a desirable level of stock to maintain the healthy functioning of the environment and the sustainability of fishing.
- Skipjack tuna is not overfished, and overfishing is not occurring. The stock is above the TRP. An improved model will be used in the next assessment.
- South Pacific albacore tuna is not overfished, and overfishing is not occurring. Although no assessment of the stock was scheduled for 2019, it was estimated to be above the TRP (which was agreed in December 2018). However, fishing effort and catch need to be reduced if the fishery is to remain viable.
- Yellowfin tuna is not overfished, and overfishing is not occurring, according to the last assessment, which was made in 2017. A target reference point is being developed for yellowfin.
- Bigeye tuna is not overfished, and overfishing is not occurring, according to the latest assessment, which was made in 2017. Bigeye was previously believed to be overfished. But new knowledge about the biology of bigeye tuna in the Western Pacific Ocean has led to a change in the way the stock is assessed, and bigeye is no longer believed to be depleted. The SPC’s Oceanic Fisheries Programme Manager, Dr John Hampton, explains the change and what it means (3.29 mins).
For further details see:
- Tuna Fisheries Assessment Report No. 18
- Individual assessment reports for bigeye (2017), South Pacific albacore (2018), skipjack (2019), and yellowfin (2017) tuna.
Models used to help assess tuna stocks
Estimating tuna populations in the Western and Central Pacific Ocean is a challenge. Tuna are always on the move, driven by ocean currents, changes in the availability of their prey, and other processes that vary naturally. They are continuously being born, growing and dying of natural causes in ways that are not well understood.
Tuna are caught by fishing fleets that record and report their catches with varying degrees of accuracy. Sampling is limited to a tiny fraction of this commercial catch, and is often not representative of the tuna population at large.
Not only must the numbers and weight of each species be estimated, but these values have to be compared with the population size that would produce the maximum yield in the future. SPC’s tool over the past decade is a computer model called MULTIFAN-CL. It integrates information from three main sources.
The first is length or frequency data, which is gained by counting and measuring a sample of the fish caught by commercial vessels. From this, it is possible to estimate the relative numbers of fish of different ages in different areas of the Pacific, and to understand recruitment and mortality in tuna populations.
The second is the relationship between the fishing effort (the number of days spent fishing) and the catch, captured using log sheets that commercial vessels are required to complete. As the number of fish in the sea is reduced, they become more sparsely distributed and an average fishing trip will produce fewer fish. Understanding this relationship helps researchers track changes in the size of the fish population.
The third source of information comes from tagging programs, in which tuna are caught, marked with small plastic numbered tags, and released. When tagged fish are re-caught, estimations can be made of fish populations.
The results of this modelling are provided to the WCPFC.
SPC also assesses tuna stocks using another model, SEAPODYM (Spatial Ecosystem and Population Dynamics Model). It uses data on climate, other environmental factors, and fish populations, among other factors. This model is important for understanding the potential impacts of climate change.
The SPC’s Oceanic Fisheries Programme Manager, Dr John Hampton, explains the use and benefits of the two stock-assessment models, and their basic differences (2.46 mins).
SPC conducts a region-wide tuna-tagging project. The data collected are fed into SEAPODYM modelling.
Tagging helps scientists get information about the growth, movements, natural mortality and fishing mortality of the tuna, which helps estimate the status of the stocks and the impacts of fishing.
SPC has a dedicated tuna-tagging portal that contains information about all the tagging programs, including details of what to do if you catch or find a tagged tuna.
Earlier reports on tuna stocks
The 2017 report conducted for the OFMP2 project outlines the status of the tuna species targeted by the industrial fishery. This has been updated by SPC’s latest assessments, outlined above.
The following critical research requirements have been identified to improve our knowledge of tuna stocks:
- Improve estimates of tuna growth, including regional differences.
- Continue tagging and analysis to support future assessments.
- Assess otoliths (inner-ear structure in fish) to work out fish age and growth.
- Continue to analyse pole-and-line catch rates, longline efficiency, longline models, and purse-seine indices.
- Improve estimates of natural tuna mortality and use parts of longline-caught fish to do so.
- Consider biological markers to improve estimates of east–west movement.
- Refine modelling approaches for maturity and sex of tuna.
Training on how to assess tuna stocks
The Oceanic Fisheries Management Project works with SPC to deliver annual training workshops on stock assessment. The workshops, which have been run since 2006, aim to increase regional fisheries officers’ ability to:
- understand and interpret the results from the regional oceanic fisheries’ stock assessments
- communicate this information to fishery managers within their countries
- increase their confidence to participate in scientific discussions of the WCPFC – in particular, during meetings of its Scientific Committee.
Workshop facilitator Steven Hare explains the content and format of the workshops (3.41 mins).
Assessing the impacts of climate change on fish stocks
Climate change has already altered the physical, chemical and biological characteristics of the ocean, and is likely to continue to do so. The changes influence the location and and behaviour of tuna, for example causing shifts in spawning conditions, and altering the suitability of habitat and the distribution of food. Where the different species of tuna live is influenced by temperature, oxygen in the water, prey and predators.
As well, catches – and therefore revenue – can fluctuate with phases of El Niño and La Niña.
Changes in the ocean environment mean that fishing grounds can move, fish may move deeper, the abundance of tuna may change, the proportion of tuna to bycatch may change, and shore facilities may be affected by rising sea levels or cyclones.
The Pacific Community, supported by OFMP2, researches the effects of climate change on tuna stocks, using a combination of research at sea and modelling. SPC researchers examine climate-change forecasts and assess the vulnerability of the region and its oceanic fisheries to such impacts. They:
- use models such as SEAPODYM to examine the impacts of climate change impacts on target tuna species, on several scales from sub-regional to national
- examine tuna diets to monitor how climate change affects food sources
- write reports on how climate change affects oceanic fisheries, and make recommendations.
Research on the ocean is expensive and is conducted in small, intense blocks of time. SPC’s marine biologist Valerie Allain, who provides important insights to OFMP2 on the possible impacts of climate change, describes the team needed for such a trip (2.19 min).
Valerie also talks about the data researchers need to collect on research trips on the open ocean (2.50 min).
Valerie talks about the highs and lows of life on board a research cruise vessel (2 min).
Earlier scientific findings were described in the baseline report for the OFMP2 project. Predictions that tuna would move east was confirmed in a report presented to the Scientific Committee of the WCPFC in 2018.
Several factors influence where tuna are found and how abundant they are; they also affect other marine life, including fish that tuna eat. Using data and improved models, the scientists predicted that, as ocean temperatures increase, the ocean becomes more acidic, and the amount of oxygen that is dissolved in seawater changes:
- Overall, concentrations of the most important tuna species will shift to the eastern Pacific Ocean.
- Skipjacktuna stocks will slightly increase until 2050, and decrease after 2060. They will move east and into higher latitudes, as feeding and spawning become more favourable there and less favourable in the warmer waters of the western equatorial warm pool of the western Pacific Ocean.
- Yellowfin tuna will also migrate east. Stocks are likely to drop slightly from 2050, and more markedly from 2080.
- The total weight of South Pacific albacoretuna (their biomass) may increase in the EEZs of Pacific Island countries and territories (PICTs), although this is uncertain.
- Bigeyetuna will also move east, but not as dramatically as skipjack and yellowfin. Water temperatures in the Western and Central Pacific will become too warm for spawning, and stock will be declining by the end of the century.
The research shows that, generally, tuna will become less abundant in the EEZs of Pacific Island states, as they move into the high seas.
The movement of tuna will affect island economies
The movement of tuna will cause reverberations around Pacific Island economies. So much so that Pacific region leaders meeting at the Forum Fisheries Committee Ministers’ Meeting in June 2019 said they considered climate change to be “the single greatest threat to the security of Pacific Island countries”.
Some states will be worse affected than others. It is believed that states that lie west of 170°E will see tuna move out of their EEZs. These include Federated States of Micronesia, Marshall Islands, Nauru, Palau, Papua New Guinea, and Solomon Islands.
States in the east – Cook Islands, French Polynesia, Kiribati, Niue, Samoa, Tonga, and Tuvalu – are likely to benefit from the shift in tuna location.
Fisheries managers can change fishing rules to help sustain tuna
But fisheries managers can use new knowledge about the effects of climate change on tuna and their environment by adapting fishing policies, rules and practices. This will help them continue to sustain stocks of tuna.
The small island developing states (SIDS) of the WCPO have been preparing for changes brought by a changing climate for some years.
The 2014 Palau Declaration “The Ocean: Life and Future” called for “strengthened regional efforts to fix baselines and maritime boundaries to ensure that the impact of climate change and sea level rise does not result in reduced jurisdiction”. Strong boundaries (such as EEZs) are vital for the ocean-based economies of SIDS, giving them:
- access to fisheries and other natural resources that secure food supplies
- continued access to culturally important social activities and economic activities
- continued revenue and livelihoods from tuna resources that exist in their waters.
The FAO has provided technical assistance to enable the SIDS members of FFA to develop a collective response to predicted changes in sea level due to climate change, as they are likely to affect maritime jurisdictional claims.
The Pacific Marine Climate Change Report Card 2018, produced by the UK’s Commonwealth Marine Economics Programme, summarises the impacts of climate change on coasts and seas in the Pacific island region, and how the islands can respond. Several more detailed scientific reviews have been published under the same programme.
FAO released the report Impacts of climate change on fisheries and aquaculture in 2018. It is an overview of the global implications of climate change for all kinds of fisheries and aquaculture – and for the millions of people who depend on these sectors for their livelihoods. The publication maps solutions that communities might use to adapt to climate change or lessen its impact. Chapter 14 deals with the WCPO. There is also a four-page summary of the report.
As part of its OFMP2 funding, FFA has produced a fact sheet on climate change and Pacific tuna fisheries.
Topics covered include:
- climate naturally affecting the distribution and abundance of tuna
- climate change under continued high greenhouse gas emissions causing changes to tuna habitats
- climate change reducing nutrients and food availability for tuna
- climate change affecting the four main species of tuna differently
- climate change affecting fishing catch and revenue, although there are options
- decline in coastal fisheries under climate change making tuna vital for food security
- research modelling addressing knowledge gaps.