Marching by Moonlight, Cancun’s Blue Crab Migration

Every September, thousands of blue crabs (Cardisoma guanhumi) emerge from the mangroves surrounding the Nichupte Lagoon in Cancun for their annual moonlight migration to the sea where they lay their eggs. The migration coincides with the full moon and is taking place from September 28, 29 and 30 this year. It is repeated in October.

Blue crabs inhabit mangroves, coastal wetlands, jungle and scrub and dunes but spawn in the sea. They face a perilous journey to the water, not only are they tasty morsels for raccoons, coatimundis, frigate birds, herons and other predators, but they also have to negotiate manmade challenges such as busy roads, swimming pools and other barriers. Many never make it to the beach; they are run over by cars, trapped in mesh fences or drown in pools, cisterns and drains.

Biologists working in the Ecology Department at Cancun City Hall organize an annual campaign to protect the blue crab, which is now an endangered species in the area. Armed with buckets and helped by local volunteers they patrol two stretches of Kukulcan Boulevard in the Hotel Zone bordered by mangroves: Playa Linda and El Mirador II at Punta Nizuc, and Playa del Niño on the road from Puerto Juarez to Punta Sam, on the lookout for crabs approaching the road. When they see these crustaceans, they carefully scoop them up and place them in the bucket. They are then released in a safe place on the other side of the highway so that they can continue their journey. The patrols take place from 7 to 11 p.m. every night during the migrations in September and October.

Volunteers wear white and assemble at Playa Las Perlas and Punta Nizuc at 7 p.m. with buckets, leather gloves, torches and eco-friendly insect repellent. They patrol in pairs or small groups.
This incredible natural spectacle is repeated throughout the Mexican Caribbean and crabs can often be spotted crossing Highway 307 in the Riviera Maya on their way to the sea, a considerable distance!

The blue crab’s journey is just one of the natural migrations that take place during the year in the Mexican Caribbean. Lobsters and cow-nose rays migrate to their breeding grounds and from December to June sailfish pursue huge schools of sardines, anchovies, mackerel and jacks. Female sea turtles come ashore on area beaches in the summer to lay their eggs. And from mid-May to mid-September, abundant plankton and fish roe in the ocean between Holbox and Cabo Catoche and to the east of Contoy and Isla Mujeres attracts hundreds of manta rays and the world’s largest fish, the whale shark.

Photo by MSNBC