Diving Isla San Pedro Martir in Baja California’s Midriff Islands, Mexico

After two days diving Isla Angel de la Guarda, we made an overnight crossing to Isla San Pedro Martir, a spectacular and remote island in the middle of the Sea of Cortez. Isla San Pedro Martir is a critical habitat for sea birds, and indeed the island is covered in such thick bird guano that it was, long ago, a penal colony where ill-fated prisoners harvested guano as a fertilizer, often dying from hardship and exposure while carrying out their sentence.  Wikipedia has a succinct description of the island’s unique position in the ecosystem of the Sea of Cortez:

The island and its marine life are, since 2002, part of the San Pedro Martir Biosphere Reserve, and is regarded as a natural laboratory of adaptive evolution, similar to that of the Galápagos Islands. It is home to 292 species of fauna and flora (both land-based and aquatic), with 42 species protected by Mexican law, and 30 listed on the Red List of Threatened Species. San Pedro Martir is also unique in the area for its year-round quantity of birds. The island is the only island in the area with a perpetually swirling cloud of sea birds. This is because the water around the island, has some of the most successful marine productivity in the world, resulting in incredible densities of small-pelagic fish, such as anchovies and sardines, in comparison to other regions of the world. This attracts both seabirds and whales to its waters. Isla San Pedro is regarded as one of the most significant bird sanctuaries in the Sea of Cortes.

We dove near a small colony of sea lions, and a few came to see us, but for the most part they were standoffish. For me, the diving was highlighted by many species of gorgonians and, most especially, enormous expanses of dense “black coral” carpeting sheer walls that would drop out of sight into the depths below.  I spent most of my time seeking out the best patches of black coral. It is reasonably common to find black coral in the Sea of Cortez but I have never seen it in such profusion anywhere in the world, it was really striking.  I was also impressed with the forest of cardon cactus carpeting the top of the island. Cheers, and thanks for looking! See also part 1: Diving Isla Angel de la Guarda and part 3:Diving Islas San Lorenzo

California Sea Lion, San Pedro Martir Island, Sea of Cortez, Mexico, Zalophus californianus, Isla San Pedro Martir, Sonora

California Sea Lion, San Pedro Martir Island, Sea of Cortez, Mexico.
Image ID: 40375
Species: California sea lion, Zalophus californianus
Location: Isla San Pedro Martir, Sonora, Mexico

Gorgonians on Lush Rocky Reef, San Pedro Martir Island, Sea of Cortez. Gorgonians are colonial filter feeders, spreading their branches into the currents flowing over the reef in order to gather passing bits of food, Isla San Pedro Martir, Sonora, Mexico

Gorgonians on Lush Rocky Reef, San Pedro Martir Island, Sea of Cortez. Gorgonians are colonial filter feeders, spreading their branches into the currents flowing over the reef in order to gather passing bits of food.
Image ID: 40377
Location: Isla San Pedro Martir, Sonora, Mexico

Isla San Pedro Martir at sunset with extensive forest of Cardon Cactus seen on the summit ridge of the island, aerial photo, Sea of Cortez, Mexico. San Pedro Martir Island and its marine life are, since 2002, part of the San Pedro Martir Biosphere Reserve, and is regarded as a natural laboratory of adaptive evolution, similar to that of the Galapagos Islands. It is home to 292 species of fauna and flora (both land-based and aquatic), with 42 species protected by Mexican law, and 30 listed on the Red List of Threatened Species. San Pedro Martir is also unique in the area for its year-round quantity of birds. The island is the only island in the area with a perpetually swirling cloud of sea birds. This is because the water around the island, has some of the most successful marine productivity in the world

Isla San Pedro Martir at sunset with extensive forest of Cardon Cactus seen on the summit ridge of the island, aerial photo, Sea of Cortez, Mexico. San Pedro Martir Island and its marine life are, since 2002, part of the San Pedro Martir Biosphere Reserve, and is regarded as a natural laboratory of adaptive evolution, similar to that of the Galapagos Islands. It is home to 292 species of fauna and flora (both land-based and aquatic), with 42 species protected by Mexican law, and 30 listed on the Red List of Threatened Species. San Pedro Martir is also unique in the area for its year-round quantity of birds. The island is the only island in the area with a perpetually swirling cloud of sea birds. This is because the water around the island, has some of the most successful marine productivity in the world.
Image ID: 40397
Location: Isla San Pedro Martir, Sonora, Mexico

Gorgonians on Lush Rocky Reef, San Pedro Martir Island, Sea of Cortez. Gorgonians are colonial filter feeders, spreading their branches into the currents flowing over the reef in order to gather passing bits of food, Isla San Pedro Martir, Sonora, Mexico

Gorgonians on Lush Rocky Reef, San Pedro Martir Island, Sea of Cortez. Gorgonians are colonial filter feeders, spreading their branches into the currents flowing over the reef in order to gather passing bits of food.
Image ID: 40385
Location: Isla San Pedro Martir, Sonora, Mexico

Extensive Forest of Cardon Cactus on the Summit Ridge of San Pedro Martir Island, Sea of Cortez, Mexico. The island and its marine life are, since 2002, part of the San Pedro Martir Biosphere Reserve, and is regarded as a natural laboratory of adaptive evolution, similar to that of the Galapagos Islands. It is home to 292 species of fauna and flora (both land-based and aquatic), with 42 species protected by Mexican law, and 30 listed on the Red List of Threatened Species. San Pedro Martir is also unique in the area for its year-round quantity of birds. The island is the only island in the area with a perpetually swirling cloud of sea birds. This is because the water around the island, has some of the most successful marine productivity in the world, Isla San Pedro Martir, Sonora

Extensive Forest of Cardon Cactus on the Summit Ridge of San Pedro Martir Island, Sea of Cortez, Mexico. The island and its marine life are, since 2002, part of the San Pedro Martir Biosphere Reserve, and is regarded as a natural laboratory of adaptive evolution, similar to that of the Galapagos Islands. It is home to 292 species of fauna and flora (both land-based and aquatic), with 42 species protected by Mexican law, and 30 listed on the Red List of Threatened Species. San Pedro Martir is also unique in the area for its year-round quantity of birds. The island is the only island in the area with a perpetually swirling cloud of sea birds. This is because the water around the island, has some of the most successful marine productivity in the world.
Image ID: 40386
Location: Isla San Pedro Martir, Sonora, Mexico

Gorgonians on Lush Rocky Reef, San Pedro Martir Island, Sea of Cortez. Gorgonians are colonial filter feeders, spreading their branches into the currents flowing over the reef in order to gather passing bits of food, Isla San Pedro Martir, Sonora, Mexico

Gorgonians on Lush Rocky Reef, San Pedro Martir Island, Sea of Cortez. Gorgonians are colonial filter feeders, spreading their branches into the currents flowing over the reef in order to gather passing bits of food.
Image ID: 40387
Location: Isla San Pedro Martir, Sonora, Mexico

Two Divers in Huge Cavern, San Pedro Martir Island, Sea of Cortez, Isla San Pedro Martir, Sonora, Mexico

Two Divers in Huge Cavern, San Pedro Martir Island, Sea of Cortez.
Image ID: 40389
Location: Isla San Pedro Martir, Sonora, Mexico

Black Coral and Gorgonians on Rocky Reef, San Pedro Martir Island, Mexico, Isla San Pedro Martir, Sonora

Black Coral and Gorgonians on Rocky Reef, San Pedro Martir Island, Mexico.
Image ID: 40390
Location: Isla San Pedro Martir, Sonora, Mexico

Black Coral and Gorgonians on Rocky Reef, San Pedro Martir Island, Mexico, Isla San Pedro Martir, Sonora

Black Coral and Gorgonians on Rocky Reef, San Pedro Martir Island, Mexico.
Image ID: 40392
Location: Isla San Pedro Martir, Sonora, Mexico

Black Coral on Rocky Reef, Unidentified species, Midriff Islands, Sea of Cortez, Mexico, Isla San Pedro Martir, Sonora

Black Coral on Rocky Reef, Unidentified species, Midriff Islands, Sea of Cortez, Mexico.
Image ID: 40393
Location: Isla San Pedro Martir, Sonora, Mexico

Gorgonians on Lush Rocky Reef, San Pedro Martir Island, Sea of Cortez. Gorgonians are colonial filter feeders, spreading their branches into the currents flowing over the reef in order to gather passing bits of food, Isla San Pedro Martir, Sonora, Mexico

Gorgonians on Lush Rocky Reef, San Pedro Martir Island, Sea of Cortez. Gorgonians are colonial filter feeders, spreading their branches into the currents flowing over the reef in order to gather passing bits of food.
Image ID: 40394
Location: Isla San Pedro Martir, Sonora, Mexico

California Sea Lion, San Pedro Martir Island, Sea of Cortez, Mexico, Zalophus californianus, Isla San Pedro Martir, Sonora

California Sea Lion, San Pedro Martir Island, Sea of Cortez, Mexico.
Image ID: 40395
Species: California sea lion, Zalophus californianus
Location: Isla San Pedro Martir, Sonora, Mexico

Extensive Forest of Cardon Cactus on the Summit Ridge of San Pedro Martir Island, Sea of Cortez, Mexico. The island and its marine life are, since 2002, part of the San Pedro Martir Biosphere Reserve, and is regarded as a natural laboratory of adaptive evolution, similar to that of the Galapagos Islands. It is home to 292 species of fauna and flora (both land-based and aquatic), with 42 species protected by Mexican law, and 30 listed on the Red List of Threatened Species. San Pedro Martir is also unique in the area for its year-round quantity of birds. The island is the only island in the area with a perpetually swirling cloud of sea birds. This is because the water around the island, has some of the most successful marine productivity in the world, Isla San Pedro Martir, Sonora

Extensive Forest of Cardon Cactus on the Summit Ridge of San Pedro Martir Island, Sea of Cortez, Mexico. The island and its marine life are, since 2002, part of the San Pedro Martir Biosphere Reserve, and is regarded as a natural laboratory of adaptive evolution, similar to that of the Galapagos Islands. It is home to 292 species of fauna and flora (both land-based and aquatic), with 42 species protected by Mexican law, and 30 listed on the Red List of Threatened Species. San Pedro Martir is also unique in the area for its year-round quantity of birds. The island is the only island in the area with a perpetually swirling cloud of sea birds. This is because the water around the island, has some of the most successful marine productivity in the world.
Image ID: 40399
Location: Isla San Pedro Martir, Sonora, Mexico

Rugged Terrain of Isla San Pedro Martir, Sea of Cortez. Aerial photo. The large bird population deposits enormous quantities of guano on the island, resulting in the white appearance of the island contrasted with sparse vegetation. In the late 19th and early 20th century guano was heavily mined off the island and shipped as far as Europe for use as fertilizer. San Pedro Martir is seldom visited, having near vertical sides leaving only questionable fair weather anchorages in two locations. Landing access was possible near a small isthmus in the southeast of the island, but is now forbidden. In 2005, the island was classified along with 244 others as a World Heritage Site by UNESCO, and included in the Islands and Protected Areas of the Gulf of California

Rugged Terrain of Isla San Pedro Martir, Sea of Cortez. Aerial photo. The large bird population deposits enormous quantities of guano on the island, resulting in the white appearance of the island contrasted with sparse vegetation. In the late 19th and early 20th century guano was heavily mined off the island and shipped as far as Europe for use as fertilizer. San Pedro Martir is seldom visited, having near vertical sides leaving only questionable fair weather anchorages in two locations. Landing access was possible near a small isthmus in the southeast of the island, but is now forbidden. In 2005, the island was classified along with 244 others as a World Heritage Site by UNESCO, and included in the Islands and Protected Areas of the Gulf of California.
Image ID: 40401
Location: Isla San Pedro Martir, Sonora, Mexico

Black Coral on Rocky Reef, Unidentified species, isla San Pedro Martir, Midriff Islands, Sea of Cortez, Mexico, Isla San Pedro Martir, Sonora

Black Coral on Rocky Reef, Unidentified species, isla San Pedro Martir, Midriff Islands, Sea of Cortez, Mexico.
Image ID: 40411
Location: Isla San Pedro Martir, Sonora, Mexico

Gorgonians on Lush Rocky Reef, San Pedro Martir Island, Sea of Cortez. Gorgonians are colonial filter feeders, spreading their branches into the currents flowing over the reef in order to gather passing bits of food, Isla San Pedro Martir, Sonora, Mexico

Gorgonians on Lush Rocky Reef, San Pedro Martir Island, Sea of Cortez. Gorgonians are colonial filter feeders, spreading their branches into the currents flowing over the reef in order to gather passing bits of food.
Image ID: 40415
Location: Isla San Pedro Martir, Sonora, Mexico

Pink Sponges Encrusting Rocky Reef alongside various species of algae and gorgonians, San Pedro Martir Island, Sea of Cortez, Isla San Pedro Martir, Sonora, Mexico

Pink Sponges Encrusting Rocky Reef alongside various species of algae and gorgonians, San Pedro Martir Island, Sea of Cortez.
Image ID: 40417
Location: Isla San Pedro Martir, Sonora, Mexico

Offshore Islets of San Pedro Martir Island, Sea of Cortez. Small rocky islets around the larger Midriff Islands in the Sea of Cortez offer some of the best diving in the Sea of Cortez with a rich variety of invertebrate and fish life, Isla San Pedro Martir, Sonora, Mexico

Offshore Islets of San Pedro Martir Island, Sea of Cortez. Small rocky islets around the larger Midriff Islands in the Sea of Cortez offer some of the best diving in the Sea of Cortez with a rich variety of invertebrate and fish life.
Image ID: 40423
Location: Isla San Pedro Martir, Sonora, Mexico

Black Coral on Rocky Reef, Unidentified species, isla San Pedro Martir, Midriff Islands, Sea of Cortez, Mexico, Isla San Pedro Martir, Sonora

Black Coral on Rocky Reef, Unidentified species, isla San Pedro Martir, Midriff Islands, Sea of Cortez, Mexico.
Image ID: 40426
Location: Isla San Pedro Martir, Sonora, Mexico

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About Phil Colla

I am a natural history photographer. I enjoy making compelling images in the ocean, on land, and in the air. I have maintained the Natural History Photography blog since 2005 and my searchable Natural History Photography Library since 1997. Here are some tear sheets and behind the scenes views. Thanks for looking!

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