Hammerhead Sharks Nearly Gone From Sea of Cortez

New Study Surveys Historical Sightings and Decline of Sharks, yet New Project Provides Hope

Scalloped hammerhead sharks have nearly disappeared completely from most of the Gulf of California (also known as the Sea of Cortez) a new scientific study finds. The study reported that Scalloped hammerhead sharks, once common, are now nearly absent, especially from seamounts where they once proliferated. The abundance of these sharks are estimated to have been reduced significantly at two major dive destinations off the coast of Baja California Sur in 40 years.1

As a part of her PhD dissertation, lead author, Dr. Kathryn Ayres, interviewed divers and photographers with historical knowledge of hammerhead sharks at two well known aggregation sites in the Sea of Cortez. Working with the Baja – based  Pelagios Kakunjá , Ayres surveyed observations from divers over the last 50 years and found that scalloped hammerhead sharks (Sphyrna lewini) were nearly absent at two seamounts where they were once most common. The study reports a 97% decline at the world famous El Bajo and a 100% decline at the Las Animas seamounts, both major dive and photographer destinations.2

Where Have All the Hammerheads Gone?

Aquarium of the World,” is how famed filmmaker and explorer Jaques Cousteau described the Sea of Cortez when his team filmed there in the 1960s. A myriad of colorful fish, healthy reefs and large schools of large sharks greeted the Cousteau dive team. The aquarium is turning into a desert. Once a major dive destination to see large schools of hammerhead and other sharks, the pinnacles and islands have been wiped out by industrial longliners by the turn of the century.

To learn more about the decline of hammerhead shark at the seamounts, the authors sent a questionnaire to dive guides, recreational divers, researchers and photographers. Fifty surveys were collected for El Bajo and 32 for Las Animas between 2017 and 2020.

In the survey, divers including famed conservation photographers Howard Hall and Marty Snyderman (as seen in the film Sharks of the Sea of Cortes’: A Lost Treasure), reported seeing an average of 150 sharks at El Bajo and 100 sharks at Las Animas, per dive in the 1970s. The same divers reported seeing only five sharks per dive at El Bajo and none at Las Animas in the 2010s.

Sea mounts are historical hotspots for large schools of hammerhead sharks. The study reports that between the late 1970s and 1980s, 225 hammerhead sharks were observed at El Bajo alone. Hammerhead sharks use seamounts as a refuge where prey fish aggregate, where cleaner fish assemble to remove parasites from the sharks and currents allow the sharks to glide and expend less energy while resting. 

This combination provides the perfect opportunity for divers to see and photograph these enigmatic but elusive sharks, yet this behavior also makes them easy targets by a directed fishery. Other factors adding to the sharks decline include a lack of fisheries management, changes in prey abundance, habitat loss and climate change. 

HOPE: Protecting 30% by 2030 Will Help Save the Hammerheads

When Dr. Sylvia Earle founded Mission Blue in 2010, she designated the Gulf of California as the very first Hope Spot. The Hope Spot recognizes the importance of wildlife in the Sea, including whale sharks, great hammerhead sharks, grey whales, green sea turtles, endemic mobula rays and other large fish found there. This unique Hope Spot is also home to over 800 species of fish, 2,000 species of invertebrates, in addition to marine mammals like sea lions, whales, and dolphins, as well as sea turtles and sharks. Yet Hope Spots do not add regulation or enforcement: that is up to the country or area to take it the next step into legal recognition.

The current President, Andrés Manuel López Obrador, has acted as a champion to protect Mexican lands and waters, providing increased hope for endangered sharks. Obrador has committed to protecting 30% of its marine territory by 2030 to comply with Target 3 of the Kunming–Montreal Global Biodiversity Framework, adopted during the 15th Conference of the Parties to the Convention on Biological Diversity. In 2023, the Secretariat of Environment and Natural Resources (Semarnat) announced 13 decrees of new Protected Natural Areas (ANP) in six states of the Mexican Republic, including the 2,076- hectare (5,129-acre) Nopoló National Park and 6,217-hectare (15,362-acre) Loreto II National Park in Baja California Sur. Overseen by the National Commission of Protected Natural Areas (CONANP), National Park status protects the flora and fauna on the islands and along the bays, but does not eliminate commercial fishing from marine waters. Connecting the National Parks to a north-south marine protected area will benefit species that migrate between them, the fish that live along the reefs and islands and benefit artisanal fisherman and support a base for ecotourism.

Worth More Alive Than Dead

Diving with sharks can be big business and bring long term benefits to areas that have been overfished, or without a market. The Revillagigedo Archipelago, a group of islands located in Mexican waters 240 Km west of Cabo San Lucas, is a world famous dive destination with large schools of hammerhead sharks, whale sharks and other species of marine megafauna. A World Heritage Site and marine protected area completely protected from fishing, over 1 million dollars per year are generated by dive tourists visiting the islands seeking schools of sharks and other large marine animals. On the tip of the Baja Peninsula located between Cabo San Lucas and La Paz, Cabo Pulmo is another successful MPA and popular shark diving destination. Established in 1995 as a marine protected area, the Park covers 27.5 square miles of the Cabo Pulmo reef. Once a fishing village, the MPA has become a dive tourism destination with recovered populations of bull sharks and reef sharks, a significant increase in fish inside the reserve and the healthiest most intact coral reef along the Baja Peninsula. A study published in 2020 estimated the value of dive tourism in Cabo Pulmo to be worth 8 million USD per year, shared among the families and community who formerly fished the area. In this same study, 23% of all divers visiting the Revillagigedos and Cabo Pulmo parks specifically identified they went their to see sharks.3

Another study in 2022 performed a comprehensive analysis of dive tourism in Mexico, evaluating 864 diving sites in Mexico. The authors found that dive tourism generates gross revenues ranging from USD 455 million to USD 725 million annually. These revenues are comparable to those generated by the artisanal and industrial Mexican fisheries together the study found. Of the total dive sites found, over half are located inside protected natural areas 443 (51.51%). 58 of the dive sites (6.74%) are within a No-Take zone, and 359 (41.74%) lack any protection.4

Hammerhead Iucn

Like other species of large shark, scalloped hammerhead sharks are more vulnerable to extinction than other fish. With late onset of reproductive maturity, these sharks produce few offspring, have long gestation periods and are slow growing, making them vulnerable to overfishing. According to the IUCN Red List of Threatened Species, scalloped hammerhead sharks are critically endangered globally. These sharks are threatened by fishing, particularly by commercial longlining which has nearly wiped the sharks out from the Gulf. These sharks are targeted for their large fins, which are used in shark fin soup, a luxury dish coveted among Asian cultures, especially China.

The economic opportunity for local fishermen turned tour operators is increasing, and shark tourism is a growing industry in Mexico. However the sharks and other migratory fish that visit marine protected areas do not enjoy protection when leaving areas outside the protected zone.

Research using acoustic and satellite tags by Pelagios Kakunja and others has demonstrated that seamounts and submerged ridges provide important habitat and serve as a migratory highway for scalloped hammerhead sharks. Eliminating commercial fishing along this corridor is an important step to allow these enangered sharks to recover. Protecting and connecting critical birthing and nursery habitat for scalloped hammerheads along this corridor are also essential component to support the recovery of this species.

The Loreto (Nopoló) Park and La Paz (Ballandras Bay) national parks include bays and islands that are located along the migratory swimway used by hammerhead sharks and other marine species including grey whales, green sea turtles and endemic mobula rays. Linking important feeding areas that are protected like Cabo Pulmo to other hot spots like El Bajo and Las Animas along the corridor to Loreto will provide an opportunity for the adults to survive, and for a dive tourism industry to flourish.

While fisheries are essential to sustain livelihoods of coastal communities, human-induced degradation is expected to produce revenue losses of up to USD 10 billion to fisheries worldwide by 2050.5

Shark Stewards has joined with Pelagios Kakunja to work with stakeholders and the Mexican government to develop a protected area that connects the shark aggregation sites to nursery areas and islands along the migratory pathway. Eliminating commercial fishing along this “Hammerhead Highway” will allow for the recovery of this charismatic predator while providing economic opportunity for local communities along the southeast Baja peninsula. Applying the successes realized in the marine protected areas will increase long term economic stability along the Baja peninsula, and allow the scalloped hammerhead to swim again.


  1. Kathryn A. Ayres, Frida Lara-Lizardi, Callum M. Roberts, Walter Pisco-Limones, Peter Klimley, Salvador J. Jorgensen, Felipe Galván-Magaña, Mauricio Hoyos-Padilla, James T. Ketchum,
    Local diver knowledge reveals decline in scalloped hammerhead sharks (Sphyrna lewini) at seamounts in the southwestern Gulf of California,
    Marine Policy, Volume 159, 2024, 105915, ISSN 0308-597X,

2. Hammerhead Sharks are Vanishing From Their Mountain Homes in the Gulf of California, Divers Say. Science Direct Dec 11, 2023

3. Pasos-Acuña, Carmen, Almendarez Hernández, Marcom Hoyos Padilla, Edgar Blazquez, Maria Carmen & Ketchum, James. (2020). Economic Valuation of Diving with Bull Sharks in Natural Conditions: A Recent Activity in Cabo Pulmo National Park, Gulf of California, Mexico. 10.1007/978-3-030-47264-1_25.

4. Ramiro Arcos-Aguilar, Fabio Favoretto, Joy A. Kumagai, Victoria Jiménez-Esquivel, Adán L. Martínez-Cruz, Octavio Aburto-Oropeza, Diving tourism in Mexico – Economic and conservation importance,
Marine Policy, Volume 126, 2021, 104410, ISSN 0308-597X, https://doi.org/10.1016/j.marpol.2021.104410.

5. V.W.Y. Lam, W.W.L. Cheung, G. Reygondeau, U. Rashid Sumaila, Projected change in global fisheries revenues under climate change, Sci. Rep. 6 (2016), 32607,