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 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.
Modelling and assessing 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 variable processes. 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 then have to be compared with the population size that would produce the maximum yield in the future. SPC’s tool over the last decade is a computer model called MULTIFAN-CL. It integrates information from three main sources.
The first is length/frequency data 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 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 uses another model, SEAPODYM (Spatial Ecosystem and Population Dynamics Model), which assesses tuna stocks based on an assessment of the current state of the marine ecosystem and the likely effects of environmental changes due to human or natural activities. This model is important for understanding the potential impacts of climate change.
The SPC’s Oceanic Fisheries Programme Manager, Dr John Hampton, explains the benefits and use of the two stock-assessment models (2.46 mins).
Previous tuna stocks reports
The 2017 report conducted for the OFMP2 project outlines current status of tuna species targeted by the industrial fishery, but 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.
SPC conducts a region-wide tuna-tagging project.
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.
Tuna stock-assessment training workshops
The Oceanic Fisheries Management Project works with SPC to deliver annual stock-assessment training workshops. 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 will produce physical and biogeochemical changes in the ocean, influencing tuna through shifts in spawning conditions, the suitability of habitat and the distribution of food. The best habitats for tuna are influenced by temperature, oxygen, prey and predators.
This means that fishing grounds can “move”, fish may move deeper, or change in abundance, 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 OFMP, researches the effects of climate change on tuna stocks. They examine climate-change forecasts and assess the vulnerability of the region and its oceanic fisheries to such impacts. Catch, and therefore revenue, can fluctuate with El Niño and La Niña phases.
Pacific Community researchers:
- use models to examine climate change impacts on target tuna species on the scale of sub-regional to national (such as SEAPODYM, which integrates climate, fish populations, the environment and fisheries aspects to model)
- examine tuna diets to monitor how climate change affects food sources
- produce reports on how climate change impacts oceanic fisheries and make recommendations.
To find out more about the Pacific’s valuable tuna stocks, researchers need to go out on the ocean for intensive study. 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).
Researchers expect that this work can lead to managing fisheries more adaptively by better understanding the climate change impacts on fisheries.
As described in the baseline report for the OFMP2 project:
- Overall, there will be a shift in the concentrations of key tuna stocks to the east of the Pacific ocean, with potential impacts on both SIDS’ economies and the management of those stocks on the high seas.
- Skipjack tuna stocks will slightly increase until 2050 then decrease after 2060. Feeding and spawning areas will become more favourable in the eastern Pacific Ocean and extend to higher latitudes. The western equatorial warm pool will become less favourable for spawning. Tuna will clearly shift eastward.
- Albacore stocks will decline by about half by 2080 if the current fishing rate remains. This will likely reduce profitability, given the fishery is already under pressure.
- Bigeye stocks will benefit from an improvement in spawning and adult feeding habitats both at subtropical latitudes and the ETP; in the WCP the temperature will become too warm for spawning. There will be declining stocks by the end of the century.
- In addition, other research indicates that yellowfin stocks will move clearly eastward, with a decrease in western and central stocks and increase in eastern stocks, and that the impact of a more acidic ocean will likely be minor. Stocks will slightly decrease from 2050, then more markedly from 2080.
For Pacific SIDS, securing their maritime jurisdictions/boundaries is vital for their ocean-based economies, given the:
- access to fisheries and other natural resources that provide food security, revenue and livelihoods
- social and economic activities
- extent of their EEZs
- value of tuna resources that exist in those waters.
As well, the 2014 Palau Declaration “The Ocean: Life & 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”.
The FAO has also provided technical assistance to enable PacSIDS members of FFA to develop a collective response to changes in sea level due to climate change on maritime jurisdictional claims.
The Pacific Marine Climate Change Report Card 2018 provides a summary of climate change impacts on coasts and seas in the Pacific island region, and how Pacific islands can respond.
The Commonwealth Marine Economies (CME) Programme has also produced a series of supporting scientific review reports.
FAO released the report Impacts of climate change on fisheries and aquaculture in 2018. It is an overview of the implications of climate change for fisheries and aquaculture, and for the millions of people who depend on these sectors for their livelihoods. The publication maps out solutions for climate change adaptation and mitigation around the world.
For information on specifically the WCPO, see Chapter 14, “Climate change impacts, vulnerabilities and adaptations: Western and Central Pacific Ocean marine fisheries”. There is also a four-page summary of the report.
As part of the Oceanic Fisheries Management Project (OFMP2), 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.