Movement and breeding of tuna already altered by climate change

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.

Modelling and research at sea used to study tuna

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).

Current research confirms earlier studies

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.
  • Skipjack tuna 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 albacore tuna (their biomass) may increase in the EEZs of Pacific Island countries and territories (PICTs), although this is uncertain.
  • Bigeye tuna 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”.

In 2021, researchers calculated that, if the ocean continues to warm at current rates, by 2050 the tuna catch in the combined waters of the Pacific small island developing states (SIDS) will decline by an average of 20%. This will have serious consequences for the Pacific Islands peoples, who rely on tuna revenue not just for livelihoods but also to fund programs in other sectors such as health and education.

Fisheries managers can change fishing rules to help sustain tuna

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.

One option is to win agreement from fishing nations that Pacific SIDS maintain current benefits once tuna have moved into the high seas. This would happen through the Western and Central Pacific Fisheries Commission (WCPFC) annual meetings. WCPFC has paved the way for this to happen through the Resolution on Climate Change accepted at its 2019 meeting.

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.

Canning tuna. Photo: Francisco Blaha.