Cocos Island changed my life. In 2004, as an undergraduate student in marine biology I visited to contribute to a pilot study assessing the impact of diving activities on the island. I had the opportunity to do several dives and I saw hammerhead sharks on numerous occasions. I felt so much energy being surrounded by these beautiful creatures, but I also felt commitment towards them. I knew I had to do something to protect them. From that moment, when that first female retreated from our bubbles, I decided to dedicate myself to the conservation of the hammerhead shark.

The hammerhead shark, Sphyrna lewini, is a migratory species, threatened by human activities, including targeted fishing and as bycatch in fisheries. In 2008, the International Union for Conservation of Nature classified Sphyrna lewini as Endangered. As a result of this, I realised that we urgently needed to better understand the fisheries, which have a devastating impact on hammerheads, as well as the varying interactions and impacts they have with hammerhead sharks at different life stages.

If we want to protect a migratory species, it is necessary to integrate the conservation efforts into every phase of their life cycle. Adults hammerheads congregate in the cleaning stations around the oceanic islands of the Eastern Tropical Pacific, such as Cocos Island (Costa Rica), Malpelo (Colombia) and Galapagos (Ecuador). However, neonates and juveniles live in nursery areas located in coastal waters of estuaries, bays and mangroves, where nutrient rich waters provide food and protection from predators.

After that pilot study, I went back to the university, determined to study the conservation of hammerhead sharks. While writing my masters degree thesis I analysed the artisanal shark fisheries that were affecting the scalloped hammerhead shark in Costa Rica and visited several fishing communities. I discovered that the fishing of juvenile hammerhead sharks was taking place all along the coast, without any restriction.

This alarmed me greatly – you do not need to be an expert scientist to understand that if we do not protect juveniles today, we will not have any adults tomorrow. I started to work on the identification and protection of hammerhead nursery areas. In 2009, together with Andrés López, my life and work partner, I founded the NGO Misión Tiburón, dedicated to identifying critical areas for endangered shark species.

In Golfo Dulce we found a high abundance of juvenile hammerhead sharks. Golfo Dulce is considered to be a unique ecosystem, since it is one of just four tropical fjords in the world. Golfo Dulce has very special geomorphological features, which makes it one of the few low-circulation systems described for tropical areas of the world. Recently, it was declared as a Hope Spot by the International NGO Mission Blue, lead by the iconic Sylvia Earle.

Through our field research, we have concluded that Golfo Dulce is an important nursery ground for the hammerhead population of the Eastern Tropical Pacific. However, we also found that, while it is the most common shark in this gulf, the scalloped hammerhead shark is one of the most abundant species caught by long line fishing in this area.

When we started our project in Golfo Dulce almost 10 years ago, we did not expect to find such positive results in terms of the abundance of hammerhead sharks. That was a pleasant surprise. However, this joy was quickly extinguished when we observed the mountains of dead hammerhead sharks, captured by the bottom lines of artisanal fishermen.

On one specific occasion, we counted 72 hammerhead sharks, all between 70-90cm, all dead, caught by a line of 200 hooks. In my head I imagined one of the groups of hammerhead sharks that I observed on the Cocos Island, simply vanishing in the blue. I asked the fisherman what he planned to do with all the carcasses. “What am I going to do with these?” he said. “Nobody buys them. I will use them as bait.” I was horrified. A species classified as endangered used as bait. It was overwhelming.