Alcyone

Alcyone — Cocos Island, Costa Rica

Alcyone is the name given by Jacques Cousteau to the seamount southeast of Cocos Island that he documented in the 1980s — named after his research vessel, the successor to the Calypso. It is now one of the most celebrated dive sites at Cocos, and the site most strongly associated with the image that defines Cocos Island diving: a wall of schooling scalloped hammerheads at 30 meters.

The Site

Alcyone is a submerged pinnacle system, with the shallowest point at approximately 20 meters and the dive sites occupying 20–40 meters on the pinnacle's walls and saddles. The current is strong — this is the defining condition of all Cocos diving — and the thermocline is significant. Cold water from the deep frequently pushes up to 20 meters and drops visibility in the lower half of the dive zone. Most divers use 7mm wetsuits here.

The Hammerheads

Scalloped hammerheads school at Alcyone in numbers that depend heavily on current, season, and luck. On optimal days — most likely June through October — hundreds of hammerheads circle the pinnacle in a formation that occupies 25–35 meters of the water column. The school is a three-dimensional structure: viewed from outside, it looks like a slow-rotating cylinder of silver, the individual sharks visible only as shapes in the periphery. The preferred approach is to descend the pinnacle wall and position below the school's primary depth band, looking up — a silhouette of hammerheads against the surface light is among the most photographed images in diving.

The Rest of Cocos

Alcyone is one of seven or eight major dive sites at Cocos. Dirty Rock (Bajo Alcyone) is adjacent and produces similar hammerhead encounters. Manuelita is shallower (15–25m) with whitetip reef sharks resting in groups. Punta Maria and Isla Pájaro have different current patterns and different resident species. A full Cocos liveaboard itinerary visits all of them.

Practical Info

• Depth: 20–40m | Difficulty: Advanced — strong current, cold water, significant depth
• Access: Liveaboard only; 36-hour crossing from Puntarenas, Costa Rica
• Best season: June–October for peak hammerhead schooling; whale sharks year-round
• Marine life: Scalloped hammerheads, whale sharks, whitetip reef sharks, manta rays, Galápagos sharks, silky sharks