Human exploitation and climate change have ravaged many of the world’s precious biomes, but there are some that have managed to make promising recoveries in spite of ourselves. While finding Marine Protected Areas (MPAs) that have genuinely succeeded is rare, the Revillagigedo Archipelago in Mexican waters is a shining example. According to the Marine Conservation Institute, this archipelago, once depleted of sharks, rays and keystone fish like yellowfin tuna, is now experiencing a resurgence. These four islands – Isla San Benedicto, Isla Socorro, Isla Roca Partida, and Isla Clarión – demonstrate that with proper protection, balance between human activity and marine conservation can be achieved.

About 400 kilometres off Baja California Sur, Mexico, we ventured to the volcanic islands via liveaboard. These islands, part of a larger seamount formation, attract an incredible array of marine species, making them a biodiversity hotspot and a prime scuba diving destination. And our timing arriving at this far-away archipelago couldn’t have been better. After a 30-hour boat ride from the mainland, our first stop was San Benedicto, albeit not the primary focus of our voyage. The spectacular shark display– especially for a location that once saw no shark activity of this kind – was uplifting, proving the power of well-enforced MPAs right at the get go. At the underwater cleaning station that we explored close to 10 times, we encountered silkies, white tips, black tips, silver tips, Galapagos, and the occasional hammerhead shark swimming slowly all around us. With back-to-back dives, we found ourselves up-close with some of the planet’s oldest and most successful top predators.

Next, we ventured to Socorro, featuring oceanic mantas and pods of dolphins putting on show after show. Often referred to as the crown jewel of the archipelago, Socorro hosts the only naval base this far out to sea, established in 1957. However, this too wasn’t why we were here. We were headed to the second farthest point, our final stop, Roca Partida – a guano-covered island surrounded by strong, boiling currents. Our aim? To witness what I called the ‘great tuna festival of 2024’ – an ambitious quest to observe the resurgence of yellowfin tuna in this once-depleted area.

As we dropped down for our first dive at Roca Partida, we descended right into a massive school of tuna. Initially, we were graced by the smaller, younger fish moving slowly in perfect synchronised formations. Occasionally, one would flash its silver belly, glittering underwater and standing out among the thousands. We were enveloped by these small fish, unsure where the school started or ended, completely surrounded.

Then, the school changed. The fish moving past us were noticeably larger – much larger. The adults had arrived, each one the size of my entire body. It was clear where the name ‘yellowfin’ came from, as they had bright, small yellow fins on their anal fin, second dorsal fin, and finlets. These fish were a dark shimmering blue, transitioning to a silvery underside with about 20 vertical lines and a golden stripe along the sides. They moved effortlessly, barely using their fins for propulsion, while we struggled to match their pace.

Their streamlined, aerodynamic bodies were clearly designed for speed. They pulled us deeper, away from the light. Sharks weaved through the tuna, adding to the chaos and awe. It was an epic sight but also terrifying, as a single wrong move could mean losing sight of the surface altogether. The depth was already intimidating, and being dragged down further by the tuna was a harrowing thought. Not to mention, if one of these tuna struck us, we were going down, as they each weigh up to 440 pounds (200 kilogrammes). They are among the largest tuna species, reaching lengths of close to 8 feet (2 metres). Known for their high speed, endurance, and migratory patterns, they travel in large schools that include other tuna species, dolphins, and large marine animals, which is what we were witnessing in Roca Partida’s depths.

Seeing this was exhilarating, and that dive was just the first of many encounters with these massive tuna schools. However, these moments held more significance than just mind blowing dives. We later met with Dr. James Ketchum, a shark and manta ray scientist, who has studied this region for nearly 30 years – and he shared the history of tuna in these waters. Ketchum’s shark movement research was instrumental in designating 1,480,000 hectares as a marine protected area, extending 40 nautical miles around each island in 2017. But Ketchum wasn’t alone; numerous scientists contributed to the effort to highlight the impacts of leaving this archipelago unprotected.

Between 2006 and 2012, researchers tagged 52 yellowfin tuna in the Revillagigedo archipelago and tracked their movements. The study revealed that these tuna, aged between 1.7 to 8 years, predominantly stayed within the reserve. Their varied movement and diving patterns depended on their age and ocean conditions. This research established a crucial baseline, proving the significance of the marine environment in influencing yellowfin tuna behavior and highlighting their preference for the protected reserve. Despite this, the Mexican tuna industry opposed the creation of a no-take marine reserve around this UNESCO World Heritage site, claiming it would reduce local tuna harvests by 20%, which would lead to economic losses and higher tuna prices.

Conservationists and scientists, using data from Global Fishing Watch, successfully countered these claims by showing that nearly 75% of tuna caught by Mexican vessels originated from international waters, with less than 4% coming from areas near Revillagigedo. This evidence was pivotal in helping the Mexican government make an informed decision. In 2017, the archipelago was designated as a national park, becoming North America’s largest marine reserve. Fishing and other extractive activities are now banned in and around the islands, ensuring the protection of this unique and biodiverse ecosystem.

Yellowfin tuna, known scientifically as Thunnus albacares and locally in Mexico as ‘atún aleta amarilla’ or simply ‘atún’, is a key species in both commercial and artisanal fisheries. They are heavily fished worldwide, especially using purse seines and longlines in commercial fishing. In fact, they are the second most consumed species of tuna worldwide, only surpassed by skipjack tuna, according to Pew Charitable Trusts. Their catch significantly contributes to the global tuna market, with the Eastern Pacific, including Mexican waters, experiencing high fishing pressure. The annual global catch rates are around 1.5 million tons. However, commercial fishing methods are controversial due to depleted stocks, but also due to the by-catch of dolphins and other marine species. Sustainable efforts include catch quotas and area closures, although challenges persist in aquaculture and by-catch management. The highest quality yellowfin are sold for sashimi, while the majority are canned.

James shared that during his work tracking shark movement in the Revillagigedo Archipelago, tuna schools were nowhere to be found. When we reported our numerous encounters, he was shocked – but in the best kind of way. This indicated that the protected area was working, showcasing the success of the marine reserve. While the archipelago’s remoteness helps, it’s clear that with proper management, the benefits of a marine protected area (MPA) become evident over time.

In 2021, the Marine Conservation Institute awarded Parque Nacional Revillagigedo a Blue Park Award. Sarah Hameed, the Blue Parks Director and Senior Scientist, explained that Blue Parks aims to create a global refuge system protecting at least 30% of the ocean to revitalise ecosystems and conserve biodiversity. These awards recognise exemplary MPAs that meet science-based standards for conservation effectiveness. She emphasised that Revillagigedo stands out as one of the most successful protected areas globally, which was why she recommended we add this to the Edges of Earth expedition trail.

Sarah praised Revillagigedo for its stellar monitoring, inspection, and island surveillance efforts, supported by its strong collaborative efforts and partnerships. She noted that the high compliance with regulations has secured solid funding for the park, which significantly aids its conservation efforts. Unlike many MPAs worldwide that struggle with limited funding and resources, Revillagigedo has managed to thrive. However, she acknowledged that while the park is doing well, there is always room for improvement – and the same goes for the world’s tuna stocks.

When considering the global tuna industry, it’s vital to understand that there are seven primary commercial species, divided into 23 stocks for assessment and management, including albacore, bigeye, bluefin, skipjack, and yellowfin. Somewhat recent evaluations by The International Seafood Sustainability Foundation revealed informative statistics that opened our eyes to where tuna sits today. In 2020, the global tuna catch reached 4.9 million tonnes, with skipjack comprising 57%, yellowfin 30%, bigeye 8%, albacore 4%, and bluefin 1%. Of the 23 stocks, 61% are healthy, 13% are overfished, and 26% are at intermediate levels.

But what does this mean? Roughly 70% of the stocks are not experiencing overfishing, while 22% are. Most of the global catch comes from healthy stocks, thanks largely to robust skipjack populations (that we have seen firsthand as well!) However, some stocks, including one bluefin, one yellowfin, and one albacore, are overfished. Regional fishing quotas have been effective, leading to the recovery of several tuna species, as noted in the latest IUCN Red List of Threatened Species update. The Atlantic bluefin tuna has improved from Endangered to Least Concern, and the Southern bluefin tuna from Critically Endangered to Endangered. Albacore and yellowfin tunas have also shown recovery.

However, regional stocks still face challenges. The eastern population of Atlantic bluefin tuna has increased, while the western population has declined sharply. Yellowfin tuna continues to be overfished in the Indian Ocean, and the Pacific bluefin tuna remains critically low at less than 5% of its original biomass. These updates highlight the importance of enforcing sustainable fishing quotas and coordinated global management for long-term benefits to biodiversity and livelihoods.

So even though significant efforts have been made to revive these precious fish in Mexico – what is now easily my favourite dive destination on the planet – much work remains when considering the broader picture and long-term sustainability. However, we’ve proven it can be done. We now possess the knowledge, tools, resources, and case studies to guide us in the right direction. The next step is taking even more action, and applying these types of MPA methods elsewhere, providing the necessary funds and resources to ensure their success.

We were told by seasoned divers that our version of Revillagigedo Archipelago was far from its former glory – a narrative we hear often while on our expedition trail. Our baseline is certainly different. Yet, witnessing the resurgence and proof that protected areas can work provided a much-needed glimmer of hope. Sometimes, we need reminders that it’s possible to reverse the damage done within our lifetime. While these marine ecosystems might never fully return to their true splendour, we can certainly come closer. The ‘great tuna festival of 2024’ was indeed a celebration of what can be achieved through dedicated conservation efforts.