Diving the Sea of Cortez: Sea Lions, Mobulas and the Cabo Pulmo Comeback

The Sea of Cortez, also called the Gulf of California, is the 1,100 km arm of the Pacific between the Baja California peninsula and mainland Mexico. Deep basins, upwelling and strong tidal exchange make it exceptionally productive, and its islands and protected areas were inscribed as a UNESCO World Heritage Site in 2005. For divers the core of it is Baja California Sur: La Paz and the islands of Espiritu Santo and Cerralvo, Cabo Pulmo National Park at the tip of the peninsula, and the Loreto bay islands to the north.

This is not tropical diving. The gulf is bordered by desert, the topography is rock and boulder rather than coral wall, and the water swings from about 19C in late winter to 30C at the end of summer. What it lacks in hard coral it repays in animals: a resident California sea lion colony, seasonal aggregations of mobula rays that number in the thousands, juvenile whale sharks that come into La Paz Bay to feed, and at Cabo Pulmo a coral reef community and fish biomass that recovered dramatically after the area was closed to fishing in 1995.

Two ways to dive it

Most visitors dive from La Paz on day boats, running 45 to 90 minutes out to Espiritu Santo, Los Islotes and the wrecks in the bay. Cabo Pulmo is dived from the village itself, by panga, with a short run to the reef. A small liveaboard fleet also works the gulf, typically on five to eight night itineraries out of La Paz that reach the more distant seamounts and islands that day boats cannot, and some Pacific boats include the gulf on repositioning trips.

Access is straightforward. La Paz has its own airport, and Los Cabos International, a two to three hour drive south, has far more international flights. Both are served daily from the United States and from Mexico City, which makes the Sea of Cortez one of the easier places in the world to reach big-animal diving.

Jacques Cousteau called the gulf the aquarium of the world, and while that line has been worn thin by marketing, the density and variety of large animals in a small area still justify it.

• The Los Islotes sea lion colony: several hundred California sea lions on two rock islets north of Espiritu Santo, where juveniles interact with divers in 5 to 15 m of water. Closed to in-water visitors for pupping each summer.
• Mobula ray aggregations: Munk's devil rays gather in the thousands off the eastern cape between roughly May and July, forming some of the largest ray aggregations anywhere.
• Whale sharks in La Paz Bay: juveniles feed in the shallow bay from around October to April, in a strictly permitted, snorkel-only, guided operation.
• Cabo Pulmo: the only hard coral reef in the eastern Pacific of any size, and a no-take park where fish biomass recovered by an order of magnitude after protection. The jack tornadoes here are the signature sight.
• Wrecks close to town: the ferry Salvatierra and the scuttled Fang Ming sit in easy recreational depths in La Paz Bay and work as second dives.
• Whales at the surface: humpbacks from December to April, blue whales and fin whales in the same window, and orcas year-round, all seen from the boat rather than in the water.

Sites are spread across three clusters: the islands off La Paz, the exposed seamounts and Isla Cerralvo further out, and Cabo Pulmo at the southern tip of the peninsula. Wind decides the plan as often as anything else.

Los Islotes

Two rocky islets at the northern end of Espiritu Santo holding a breeding colony of several hundred California sea lions. The dive is shallow, 5 to 15 m over boulders and gullies, and the animals are the entire point: juveniles will circle, mouth fins and turn upside down in front of a mask. Adult bulls are territorial and guides keep divers clear of them. The colony closes to divers and snorkelers each summer during pupping.

El Bajo Seamount

A set of three pinnacles rising from deep water about 12 km northeast of Espiritu Santo, historically the most famous site in the gulf for its scalloped hammerhead schools. Those schools have thinned dramatically since the 1990s and are no longer a reliable sighting. What remains is a genuinely wild open-water seamount with big schools of jacks, wahoo, tuna, mobulas and the occasional whale shark. Exposed, current-swept and weather dependent.

La Reina, Isla Cerralvo

A lighthouse rock at the northern tip of Isla Cerralvo, also called Isla Jacques Cousteau, with a rocky slope dropping to 30 m. Known for large schools of jacks and snapper, morays, and mantas that visit seasonally. Current can be strong and the site is a longer run from La Paz, so it needs a settled day.

Salvatierra Wreck

A 90 m car ferry that sank in the San Lorenzo Channel in 1976 and now lies broken in about 18 m of sand. Easy, sheltered, full of life: green morays in every opening, schools of grunts and snapper, stingrays on the sand and nudibranchs on the plating. The standard second dive after Los Islotes.

Fang Ming Wreck

A Chinese vessel seized and deliberately scuttled near Espiritu Santo in 1999 as an artificial reef, sitting upright in roughly 18 to 25 m with cut openings for penetration. Soft coral and gorgonians have taken hold on the superstructure and the holds hold schooling fish. A better wreck dive than the Salvatierra for photographers.

Suwanee Reef

A rocky reef south of Espiritu Santo running from 8 m to about 25 m, made of boulders, ledges and sand channels. Reliable for reef fish density rather than big animals: king angelfish, Cortez angelfish, panamic green morays, guitarfish and marbled rays. A good choice when the exposed sites are blown out.

Cabo Pulmo: El Bajo and Los Morros

The heart of Cabo Pulmo National Park, a series of hard coral and rock ridges in 12 to 25 m. This is where the recovered fish biomass shows itself: dense schooling bigeye jacks that form a rotating tornado, large groupers, snapper walls, and bull sharks that have returned to the park. Diver numbers are capped and all diving is guided by local operators.

El Vencedor, Cabo Pulmo

A tuna boat that ran aground on the reef in 1981 and now sits in 12 m, broken but recognizable, at the edge of the park. Shallow, calm and heavily populated, with schooling grunts, groupers and often a resident green turtle. A good first or last dive of a Cabo Pulmo day.

The gulf holds around 900 fish species and roughly a third of the world's marine mammal species, a mix that comes from cold, nutrient-rich upwelling meeting subtropical water. Endemism is high: many of the reef fish here occur nowhere else.

Marine mammals

• California sea lions, resident year-round at Los Islotes and other haul-outs, with pups born in June and July.
• Humpback whales from December to April, blue and fin whales in the same window, all surface encounters from the boat.
• Orcas year-round in small numbers, and large pods of common and bottlenose dolphins.

Big animals and pelagics

• Whale sharks, juveniles feeding in La Paz Bay from roughly October to April, snorkel only under a permit system.
• Munk's devil rays, aggregating in vast numbers off the eastern cape from about May to July.
• Bull sharks in Cabo Pulmo, resident and increasingly frequently seen since protection.
• Schooling bigeye jacks forming tornadoes at Cabo Pulmo, plus yellowtail, wahoo, dogtooth-sized dogsnapper and tuna at the seamounts.
• Scalloped hammerheads at El Bajo, now scarce and no longer a dependable sighting.

Reef and macro

• Cortez and king angelfish, Moorish idols, panamic sergeant majors and endemic Cortez rainbow wrasse.
• Panamic green morays in numbers on the wrecks, plus jewel morays and zebra morays.
• Marbled and diamond stingrays, banded guitarfish and torpedo rays on the sand.
• Nudibranchs, Panamic cushion stars, chocolate chip stars and gorgonian-covered rock in the cooler months.

Water temperature has the widest range of any Mexican dive destination: about 19 to 21C from February to April, climbing through the spring to 27 to 30C from August to October, then falling back through the winter. A 5 mm full suit with a hood is the sensible year-round choice, 7 mm or a semi-dry in late winter, and 3 mm is enough in September. Thermoclines are common and can drop several degrees within a single dive.

Visibility follows the same cycle in reverse. Spring plankton blooms, the same productivity that feeds the whales and mobulas, can cut visibility to 5 to 10 m from March to May. From August to November the water clears to 20 to 30 m, which is the main reason those months are the peak season. Cabo Pulmo tends to be clearer than La Paz Bay.

Most sites are gentle. Los Islotes, the wrecks and the Cabo Pulmo reefs are suitable for Open Water divers, with depths under 25 m and manageable conditions. El Bajo and La Reina are exposed sites with real current and open-water entries that warrant Advanced Open Water and comfort in blue water. Wind is the limiting factor rather than depth: the coromuel wind blows from the southwest on summer nights, and northerlies from November to March can shut down the exposed sites for days at a time.

The gulf works all year but changes character completely between seasons. The trade-off is water clarity and warmth against which animals are present, and one hard constraint: the Los Islotes sea lion colony closes to in-water visitors for pupping each summer.

• August to November: the peak. Water 27 to 30C, visibility 20 to 30 m, all sites open including Los Islotes once the pupping closure lifts, and the best conditions for the exposed seamounts. September can bring a tropical storm or hurricane to the southern peninsula.
• October to April: whale shark season in La Paz Bay, a permitted snorkel activity independent of the scuba season, most reliable from November to March.
• December to March: cold and green, water 19 to 22C, but this is whale season at the surface and the quietest time on the boats. Northerly winds regularly cancel days.
• May to July: mobula ray aggregations off the eastern cape, warming water and lengthening days, but spring plankton keeps visibility low and Los Islotes closes to divers for pupping through most of this window.
• June to August: the pupping closure at Los Islotes, typically running from around the start of June to the end of August, with exact dates set each year by the park authority. Boats still visit for surface viewing but nobody gets in the water.

La Paz has its own airport, Manuel Marquez de Leon International (LAP), with domestic flights from Mexico City, Guadalajara, Tijuana and Monterrey and a small number of United States services. It is about 20 minutes from the La Paz marinas where the dive boats and liveaboards leave.

The larger and usually cheaper gateway is Los Cabos International (SJD), with direct flights from most major United States and Canadian cities and from Mexico City. From SJD it is roughly two to two and a half hours by shuttle or rental car to La Paz, and about one hour to Cabo Pulmo on a road that turns to dirt for the final stretch, so a high-clearance vehicle or an operator transfer is advisable. Loreto International (LTO) serves the northern bay islands and is used mainly for itineraries around Isla Coronado and Isla Danzante.

Day-boat diving leaves from the La Paz malecon marinas or Marina Costa Baja, with runs of 45 to 90 minutes to Espiritu Santo and Los Islotes. Liveaboards embark in La Paz on five to eight night itineraries. Cabo Pulmo diving is run entirely by operators in the village, with pangas launched from the beach.

Citizens of the United States, Canada, the United Kingdom, the European Union, Australia and many other countries enter Mexico visa-free for tourism, generally for up to 180 days.

Park fees: Espiritu Santo and Cabo Pulmo are both national parks under CONANP, and each charges a bracelet fee of roughly MXN 100 per person per day (around USD 5 to 6). Whale shark encounters in La Paz Bay carry a separate permit and guide fee. Operators usually add these on top of the dive price.

Rules: the whale shark activity is snorkel only, capped by permit, with a limited number of boats in the zone and no touching or flash photography. At Los Islotes divers keep clear of adult bulls, and the site closes entirely to in-water visitors during the summer pupping period. Cabo Pulmo is no-take, guided only, with capped diver numbers and no gloves.

Money: the Mexican peso is the currency; cards work in La Paz and Los Cabos but Cabo Pulmo village is largely cash and has limited power and connectivity. Carry pesos for park bracelets and crew tips.

Diving: nitrox is available in La Paz and on the liveaboards, less consistently in Cabo Pulmo. A 5 mm suit and hood should be your default. There is a hyperbaric chamber in La Paz; dive insurance covering evacuation is recommended, particularly for Cabo Pulmo, which is remote.

Practicalities: 127 V with type A and B sockets; Spanish is the language, with English spoken by most dive staff; Baja California Sur runs on UTC-7 year-round with no daylight saving.

• Check the Los Islotes closure dates before booking: the pupping closure typically covers June to August but the exact dates are set annually. If sea lions are your reason for coming, travel from September onwards.
• Overdress for the water: 5 mm with a hood is the right default even in warm months, because thermoclines and four dives a day beat most people down.
• Treat whale sharks as a separate excursion: the La Paz Bay encounter is a permitted snorkel activity, not a dive, and it is booked and paid for separately from your dive days.
• Give Cabo Pulmo its own nights: it is a long drive from La Paz on partly unpaved road, the village is small and cash-based, and the diving deserves more than a day trip.
• Build in a wind day: northerlies in winter and the coromuel in summer regularly cancel the exposed sites. A five-day trip with a spare day is far safer than three days back to back.
• Do not expect hammerheads: El Bajo was famous for them decades ago and the schools have not come back. Go for the seamount itself.
• Bring both lenses: wide for sea lions and jack tornadoes, macro for the wrecks and rocky reefs, which are far richer than the reputation suggests.