The villagers decided to start their own no-take zone , which in 1995 became an official marine park of Mexico . Today , these 7,000 hectares of land and sea are a UNESCO World Heritage Site . Fiercely protected by the locals , the 20 dive sites inside the park are limited by strict dive times and rotation of sites , which are allocated by lottery .
From the visitor ’ s perspective , the lottery system carries an element of uncertainty , because no-one can guarantee you will visit the best sites over a four-day visit . You are limited to two 50-minute long dives per day – by lunchtime there isn ’ t a boat on the water .
The sites themselves are usually flat or gently sloping sandy areas , with rocky ledges and gullies covered in purple gorgonians . There ’ s a nice smattering of reef fish and cleaning stations on the reef , but the real action takes place in the midwater zone .
On every dive , the water was thick with schooling fish , typically various species of trevally , tuna or grunts . In the grainy dark water , the silvery flanks of the burrito grunts shone like stars , but my favourites by far were the Panama porkfish , with their burnished gold bodies .
The Park is renowned for two things : an immense school of bigeye trevally , and a population of bull sharks . As the weather settled , it became easier to track the trevally , in a school so large it often stretches from the surface to the seabed at 17m . I had been told that the surest way of tracking the school is by smell – the sheer biomass of the fish is such that it emits a distinct odour at the surface .
Just part of the towering wall of trevally
A dolphin pauses below the school of trevally
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