Tuna is one of the most commercially valuable and widely consumed fish in the world, highly appreciated for its taste. In Portugal, tuna is a crucial fishing resource. Although there are several species of tuna globally, only a few are commonly consumed. Unfortunately, according to the IUCN, the populations of these species are declining, primarily due to overfishing, illegal, and unregulated fishing practices.
One of the pressing challenges today is overfishing in the Indian Ocean, which is having a detrimental impact on yellowfin tuna populations, putting them at risk of collapse within a few years. This species is primarily caught using the purse-seine fishing method with fishing aggregation devices (FADs), which are designed to attract fish. However, several concerns are associated with this practice, including the capture of juvenile yellowfin tuna, increased bycatch (the capture of non-target species), and the contribution to ocean plastic pollution.
The depletion of tuna species can have important consequences, as tunas are top predatory species, which means they regulate the community structure of lower trophic levels (a process known as “top-down effects”). If other top predators in the ecosystem are also declining or absent, it could lead to the emergence or overpopulation of other species, potentially disrupting the balance of the ecosystem. Additionally, tunas, along with other large marine vertebrates, play a significant role in sequestering carbon dioxide, contributing to the blue carbon stock. These species affect carbon storage in various ways, indirectly by supplying nutrients and controlling populations of smaller species that impact coastal vegetation, and directly through their biomass, including when their carcasses sink to the ocean floor. Overfishing has the potential not only to alter carbon sequestration by reducing these species but also to contribute to blue carbon extraction by removing this biomass from the marine environment. Restoring or rehabilitating fish stocks, along with other marine vertebrates, could be a powerful Nature-Based Solution to climate change.
Given the critical role of tuna and other marine species, the question arises: "What can we do?"
Beyond moderating our overall consumption, it is essential to choose tuna responsibly by preferring sustainable fishing methods. Currently, the most sustainable method is pole-and-line fishing, where each fish is caught individually. This approach minimizes overfishing, reduces bycatch of non-target species like turtles or dolphins, and supports local communities. In Portugal, tuna caught using the pole-and-line method is available in supermarkets, offering consumers a responsible choice.
The impact of overfishing and unregulated fishing practices directly relates to SDG 14 – Life Below Water, which seeks to conserve and sustainably use the oceans, seas, and marine resources. The depletion of fish populations threatens not only marine biodiversity but also global food security and the livelihoods of communities dependent on the fishing industry. By supporting sustainable finishing methods, we can contribute to the preservation of marine ecosystems, protect the intricate balance of ocean life, and help combat climate change, taking a vital step toward achieving a more sustainable and resilient future for our oceans and all who rely on them.
Have a great and impactful week!
Patrícia Beltrão
Researcher at the Center for Responsible Business & Leadership