Thousands of jack fish swimming together at Cabo Pulmo National Park, Sea of Cortez, Baja California, Mexico

A day for our oceans

To celebrate World Oceans Day, we're swimming through a shoal of jack fish just off the coast of the Mexican state of Baja California, in Cabo Pulmo National Park. The coral reef in this marine park in the Sea of Cortez is estimated to be about 20,000 years old. Jacks are clearly plentiful, but divers and snorkellers in Cabo Pulmo can also come across many other species of fish and marine mammals, including sharks, whales, dolphins, tortoises and manta rays.

This year, World Oceans Day's theme is The Ocean: Life & Livelihoods, aimed at raising awareness of the nearly 3bn people worldwide who depend on oceans for their way of life. The residents of Cabo Pulmo know a little bit about this. To help revitalise their (previously unprotected and overfished) waters, the Mexican government turned Cabo Pulmo into a national park in 1995. But, more controversially, they also banned fishing, a big deal in an area where many residents lived off the food they caught by hand.

The preservation efforts paid off, though - researchers say the park experienced a 460% increase in the number of fish living in its waters between 1999 and 2009, turning Cabo Pulmo into one of the world's most robust marine reserves. Now, many residents who once relied on fishing have been able to move into jobs in ecotourism or other vocations supporting the park.