Tuna are among the most sought-after fish in the world, both for their commercial value and their ecological role as top predators. But what makes some fish prey more appealing to tuna than others? And how will climate change affect the availability and distribution of these tasty snacks?
A new study by researchers from Canada and the United States has shed some light on these questions by creating a global database of more than 30 traits that characterize the prey species consumed by albacore tuna, a torpedo-shaped predator that migrates across the Pacific Ocean.
What do tuna like to eat?
The researchers analyzed the diets of albacore tuna from different regions and seasons and found that they have a diverse but selective appetite. They prefer prey that are high in fat and protein, such as anchovies, sardines, squid and mackerel. They also favor prey that are small, silvery, streamlined and fast-swimming, which make them easier to catch and digest.
The researchers also discovered that albacore tuna can adapt to different prey availability by switching their preferences depending on the location and time of year. For example, in the eastern Pacific, where prey are more abundant but less nutritious, tuna tend to eat more small fish and crustaceans. In the western Pacific, where prey are less abundant but more nutritious, tuna tend to eat more large fish and squid.
How will climate change affect tuna’s taste?
The researchers hope that their database will help them understand how climate change will affect the traits and distribution of tuna’s prey in the future. Climate change is expected to alter the ocean temperature, acidity, oxygen levels and currents, which will in turn affect the growth, survival and movement of marine organisms.
The researchers predict that some of the traits that make prey tasty to tuna, such as high fat and protein content, may become less common as the ocean warms and acidifies. This could reduce the quality and quantity of food available for tuna and affect their health and reproduction.
On the other hand, some of the traits that make prey easy to catch and digest, such as small size and silvery color, may become more common as the ocean loses oxygen and becomes more stratified. This could increase the efficiency and diversity of food available for tuna and enhance their growth and performance.
The researchers also expect that climate change will shift the distribution and abundance of tuna’s prey across different regions and seasons, creating new opportunities and challenges for tuna migration and feeding. For example, in some areas, prey may become more concentrated and accessible for tuna, while in other areas, prey may become more dispersed and scarce.
Implications for fisheries and conservation
The study has important implications for fisheries management and conservation of albacore tuna and other ocean predators. By understanding how climate change will affect the traits and availability of tuna’s prey, managers can better predict how tuna populations will respond and adapt to changing ocean conditions. This can help them set appropriate catch limits, allocate fishing quotas, design marine protected areas and monitor fish stocks.
The study also highlights the need for cross-border collaboration among scientists, managers and stakeholders to ensure the sustainable use and conservation of shared marine resources. Albacore tuna are regulated by a treaty between Canada and the United States, which requires both countries to cooperate on research, assessment and management of the fishery. The researchers hope that their database will facilitate this cooperation by providing a common framework and language to describe and compare tuna’s diets across different regions.
The study was published in the journal Global Ecology and Biogeography and is part of a larger project funded by the National Science Foundation (U.S.) to understand how climate change will affect ocean predators in the Pacific.
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