Hundreds of whale sharks (Rhincodon typus), the largest living species of fish, have arrived for their annual summer congregation off the Mexican coast of Isla Mujeres.
The enormous fish converge in the coastal waters off Cancun from May to September.
Some 250 whale sharks have been seen so far this season, below the record-setting mark of two years ago, but still a positive sign for the species and the scientists who study them.
In 2009, the whale shark swarm comprised the largest grouping of whale sharks ever reported - up to 420 whale sharks were observed in a single aerial survey.
Isla Mujeres, in the Gulf of Mexico, is an area biologist Rafael de la Parra has identified as ideal for multiple marine species such as dolphins, stingrays, tuna fish and the whale shark, which feeds on plankton, algae, krill and sometimes small fish or squid.
Rafael de la Parra is the lead Marine Biologist for Project Domino, a conservation program implemented by the Mexican government. He thinks the sharks come to reproduce.
Biologists had thought increased sightings indicated that Isla Mujeres was a point along the sharks' migration route, but recent research indicates otherwise.
The whale shark is mainly gray in colour with a white underside. It is not dangerous to humans and can live between 60 to 150 years. Whale sharks have been recorded up to 14 metres (46 feet) in length and 15 tonnes in weight, but the average whale shark measures 7.62 metres (25 feet) in length.
Whale sharks are slow swimmers at around 4.8 kilometres per hour. Unlike many other sharks, they swim by moving their entire bodies from side to side.
To raise awareness of the need to preserve the area's marine ecosystem, the Ecotourism travel agency Ceviche Tours and the Isla Mujeres Department of Tourism organise an annual Whale Shark Festival held from July 15-17 in Isla Mujeres, Quintana Roo.
John Vater, owner of Ceviche Tours, which organises trips to see the whale sharks, says the creatures' greatest threat in the region is careless ship operators.
Tourists who attend the festival are able to swim with the whale sharks. The festival is sponsored by Amigos de Isla Contoy, a non-profit organisation that seeks to promote the conservation of Isla Contoy and areas in the Yucatan peninsula through the sustainable development of local communities.