Climate change is drastically altering the ocean, with major consequences both for its ecosystems and for the services they provide us – from food and medicine to employment. A new study has predicted just how climate change will affect important fish populations, whilst identifying essential actions we can take to address the problem.
Marine ecosystems are inextricably linked to Earth’s climate. As the climate changes, so too does the ocean – with temperatures rising, waters acidifying and oxygen levels declining [1]. Each of these changes has a dramatic effect on marine life, from microscopic plankton through to the largest of fish. Under climate change, these species may move to new areas, reproduce at unusual times of year and experience devastating population losses. This grave issue is made all the worse by overfishing. More than 35% of the world’s fish stocks are overfished – including more than a quarter of stocks in the Northeast Atlantic Ocean [2], where industrial fishing has been taking place for over a century [3]. Together, overfishing and climate change pose a dire threat to fish stocks – and, thus, to the fishing communities which rely upon them.
To better understand the extent of this threat, a team of marine scientists simulated the impacts of climate change and overfishing in the Northeast Atlantic using a mathematical model. This model assessed a range of environmental conditions and other factors to predict changes in the ‘biomass’ – the total mass of all animals – across 739 fish and invertebrate populations. These populations – also called ‘stocks’ – are groups of animals of the same species which share certain characteristics, such as their location and the time of year when they reproduce. Many of the stocks in question are of great importance to fishing communities from the UK and Europe. The model analysed how stock biomass would change under different scenarios. These included differing levels of climate change – either severe or mitigated – and differing levels of fishing pressure – either overfishing, fishing at the maximum sustainable level or fishing under that level. Another factor considered by the model was the role of conservation efforts. Marine Protected Areas (MPAs) are one of the main tools for marine conservation and are used to limit fishing activity in certain regions, protecting the animals and ecosystems therein [4]. Simulations were run for three different conservation scenarios: a scenario where the total area of MPAs remains at its current level of around 5% of the Northeast Atlantic, a scenario where MPA area is expanded to 15% of the Northeast Atlantic and a scenario where MPAs cover 30% of the region – a key goal for global conservation efforts [5].
At first glance, the predictions made by the mathematical model seem bleak. Climate change is expected to cause severe declines in stock biomass: a sustainably-fished stock is projected to decline by 9.6% for every 1OC of warming. By 2100, without further action to combat climate change, fish stocks in the Northeast Atlantic could lose a third of their biomass. This would have major knock-on effects for fishing communities, with catches declining by as much as 25%. However, the study also offers us a glimmer of hope: there may be solutions which could offset these declines. Expanding MPAs to cover 30% of the region would likely lead to a 5.4% increase in stock biomass – rising to almost twice as much if the MPAs were established in ecologically-important habitats. Meanwhile, reducing fishing pressure could have even greater benefits. The management of fish stocks typically aims to achieve a balance between fishing and natural population growth, termed the Maximum Sustainable Yield (MSY). MSY is the quantity of fish which can be removed from the population by fishing without causing an overall decline in biomass. Unfortunately, as climate change alters marine ecosystems, even limiting fishing to MSY levels may not be enough to preserve stock biomass. The model predicts that reducing fishing to three-quarters of MSY levels could help – likely leading to a 29.2% increase in stock biomass. Combined with the potential 5.4% increase in biomass due to MPA expansion, this could largely offset the one-third decline in biomass which is predicted to result from climate change.
How to find Another Way
This study highlights two fundamental facts about climate change. The first is that climate change may have drastic – even devastating – impacts upon both ecosystems and human society. The second is that we – as a society – have the ability to make things better. As the study shows, we don’t just know that there are solutions, we know what those solutions are. It is on our governments and, indeed, all of us to make decisions which will lead to a brighter, more sustainable future. If this study’s predictions have alarmed you, you could try to make more sustainable choices when it comes to eating fish – for instance, try using the Marine Conservation Society’s ‘Good Fish Guide’ to identify the best options for reducing your impact! Together, we all can make a difference.
By Dan Bailey
References
Study Paper: Cheung WWL, Palacios-Abrantes J, Roberts SM (2024) ‘Projecting contributions of marine protected areas to rebuild fish stocks under climate change’, npj Ocean Sustainability, 3(11), https://doi.org/10.1038/s44183-024-00046-w
1: IPCC (2019) IPCC Special Report on the Ocean and Cryosphere in a Changing Climate, Intergovernmental Panel on Climate Change, Cambridge University Press, Cambridge, UK, https://doi.org/10.1017/9781009157964
2: FAO (2022) The State of World Fisheries and Aquaculture 2022, Food and Agriculture Organisation, Rome, Italy, https://doi.org/10.4060/cc0461en
3: Thurstan R, Brockington S, Roberts C (2010) ‘The effects of 118 years of industrial fishing on UK bottom trawl fisheries’, Nature Communications, 1(15), https://doi.org/10.1038/ncomms1013
4: Grorud-Colvert K, Sullivan-Stack J, Roberts C, Constant V, Costa BHE, Pike EP, Kingston N, Laffoley D, Sala E, Claudet J, Friedlander AM, Gill DA, Lester SE, Day JC, Gonçalves EJ, Ahmadia GN, Rand M, Villagomez A, Ban NC, Gurney GG, Spalding AK, Bennett NJ, Briggs J, Morgan LE, Moffitt R, Deguignet M, Pikitch EK, Darling ES, Jessen S, Hameed SO, Di Carlo G, Guidetti P, Harris JM, Torre J, Kizilkaya Z, Agardy T, Cury P, Shah NJ, Sack K, Cao L, Fernandez M, Lubchenco J (2021) ‘The MPA Guide: A framework to achieve global goals for the ocean’, Science, 373(6560):eabf0861, https://doi.org/10.1126/science.abf0861
5 – Kunming-Montreal Global Biodiversity Framework (2022), https://www.cbd.int/article/cop15-final-text-kunming-montreal-gbf-221222
