A new peer-reviewed study published in Frontiers in Marine Science, led by BCSS’s Norton Cossa and co-authored by Helder A. Machaieie, Anildo Nataniel, and BCSS’s Dercio Maoze under the supervision of Dr. Mario Lebrato, reveals how climate-driven ocean warming may significantly impact tropical tuna fisheries and the economies that depend on them across the Western Indian Ocean.
Using advanced modelling approaches, the research examines how environmental variability influences the commercial species skipjack tuna (Katsuwonus pelamis) distribution — and how these patterns may change under future climate scenarios. The findings highlight not only ecological implications, but also the potential impacts on regional fisheries, food security, and communities that depend on them.
Indicators of Ocean Health
Tropical tuna species are among the most commercially important and ecologically dominant pelagic species in the Indian Ocean. Previous research has already shown that climate variability is influencing their distribution globally, altering catch patterns over time. This can have major economic consequences on the fishing industry and its economy.
Yet, tens of thousands of tons of skipjack tuna are caught annually in the Western Indian Ocean region, according to the Indian Ocean Tuna Commission. As ocean conditions continue to shift, understanding how these highly mobile species respond has become increasingly important.
Beyond their economic value, tuna act as indicators of ocean health. Their distribution reflects underlying environmental conditions, including temperature, salinity, productivity gradients, and current systems — offering insight into how marine ecosystems function at scale.
Figure 1–2. Spatial and environmental drivers of skipjack tuna distribution in the Western Indian Ocean. Figure 1 shows the regional study area and the spatial distribution of skipjack tuna (Katsuwonus pelamis) catch biomass based on aggregated fisheries data. Figure 2 presents model outputs illustrating how environmental variables — including sea surface temperature (SST), chlorophyll concentration (CHL), net primary productivity (NPP), sea surface height (SSH), mixed layer depth (MLD), salinity (SSS), and pH — influence tuna distribution across space and time.
Why This Study Is Important
This research focuses on skipjack tuna (Katsuwonus pelamis) and examines how historical distribution and biomass catches relate to environmental variability across the northern Western Indian Ocean.
By linking long-term fisheries data with oceanographic variables, the study explores how the distribution and abundance of the species may shift under different climate scenarios driven by rising ocean temperature — providing insight into potential future changes in marine ecosystems.
What the Research Reveals
Projections of Katsuwonus pelamis distribution from 2005–2019 to 2100 under low and high emissions scenarios reveal contrasting outcomes. Under the low-emissions scenario, spatial patterns remain largely stable through 2050, with only minor, localized declines by 2100. In contrast, the high-emissions scenario suggests a progressive eastward expansion and increased abundance, particularly along the Somali coast and into equatorial regions, driven by stronger warming (~+3°C) that expands thermally suitable habitat. Overall, the results indicate gradual redistribution rather than abrupt change, with shifting catch intensity across the basin.
The findings reinforce a key principle in marine ecology: species distribution is not random.
Skipjack tuna biomass and distribution are closely linked to environmental drivers, including:
- Sea surface temperature
- Salinity
- Ocean productivity
- Mixed layer depth
- Sea surface height
- Chlorophyll-a concentration
These variables interact to create dynamic marine habitats that shift over time. As ocean conditions change, so too do the spatial patterns of tuna distribution — highlighting the need to understand marine ecosystems as fluid systems rather than fixed environments.
The study identifies several key trends:
- Suitable habitats for tropical tuna are projected to shift as ocean temperatures rise;
- Changes in productivity may alter where tuna can thrive;
- Impacts will vary regionally, with some areas experiencing declines and others increases;
- These shifts may reshape catch patterns and access to fisheries resources
Figure 3. Projected redistribution of skipjack tuna biomass under future climate scenarios in the Western Indian Ocean.
How the Data Were Collected
The study draws on long-term catch datasets alongside advanced analytical modelling to examine how tuna distribution responds to environmental variability across both space and time.
By integrating fisheries data with oceanographic variables, researchers were able to identify relationships between tuna presence and changing environmental conditions. These relationships were then used to model potential future scenarios under climate-driven change.
Why This Matters for Conservation and Management
For countries across the Western Indian Ocean, these findings carry significant ecological and economic implications.
As ocean conditions shift, tuna distributions are expected to change — not simply in abundance, but in location. This presents challenges for fisheries management, which has historically relied on relatively stable patterns of distribution.
Without an understanding of these dynamics, it becomes increasingly difficult to manage marine resources effectively or ensure long-term sustainability.
This research supports a shift toward ecosystem-based and adaptive management approaches, where decision-making reflects the dynamic nature of marine systems.
A large school of Katsuwonus pelamis joins seabirds in a surface feeding frenzyÂ
The System Behind the Science
Research of this scale depends on sustained observation and long-term data.
At the Bazaruto Center for Scientific Studies (BCSS), the Ocean Observatory plays a key role in monitoring marine ecosystems across the Western Indian Ocean. By generating continuous ecological data, it contributes to a growing understanding of how ocean systems are changing over time.
Looking Ahead
Authors conclude that anthropogenic ocean warming is likely to reshape the distribution of Katsuwonus pelamis unevenly across the Western Indian Ocean. Some regions may experience declines in catch potential, while others may see increases, driven by shifting environmental conditions and ocean productivity.
This highlights a critical insight: the future of fisheries is not only about how much fish there will be — but where those fish will be.
As climate change continues to alter ocean systems, understanding these patterns will be essential for sustaining both marine ecosystems and the communities that depend on them.
This work was funded and supported by University Eduardo Mondlane and is supported through BCSS’s Resort-to-Research (R2R) model, developed in partnership with Kisawa Sanctuary. By linking conservation, science, and sustainable funding, the model enables ongoing research in a region where long-term data is essential.
To explore the full study, access the publication via Frontiers in Marine Science: https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2026.1693205/full
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For questions about this article, please contact:Â
Ekaterina Kalashnikova, Bazaruto Archipelago – Ocean Observatory Bazaruto Center for Scientific Studies ekaterina.kalashnikova@bcssmz.org Â
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