Bajo Manuelita, Cocos Island: seamount diving with pelagics

Bajo Manuelita is an extensive submerged pinnacle, or seamount, located in the waters surrounding Cocos Island. The site's topography features steep volcanic walls, basalt boulders, and numerous ledges that offer shelter and foraging grounds for a variety of marine life. This seamount rises from the depths to within 15 meters of the surface, creating a prominent landmark that influences currents and attracts pelagic species. Divers typically approach Bajo Manuelita as a drift dive, following the contours of its slopes and pinnacles, often starting with a descent into the open water directly above the seamount's apex.

The site presents two distinct faces to the diver, each offering a different experience. The exposed outer sections of Bajo Manuelita are where the stronger currents are felt, and it is here that you are most likely to encounter the larger oceanic species. These areas are characterized by open water and deeper profiles, creating an environment that attracts transient pelagics. In contrast, the more protected inner side of the seamount offers a calmer diving experience, with coral gardens and sandy patches that provide a different habitat and a chance to observe resident marine life in a less dynamic setting.

On the exposed outer slopes and along the deeper sections, particularly where the current is strongest, Bajo Manuelita is renowned for its pelagic encounters. Scalloped hammerhead sharks (Sphyrna lewini) are a primary draw, often seen in schooling aggregations, especially during specific seasons. Silky sharks (Carcharhinus falciformis) and Galapagos sharks (Carcharhinus galapagensis) also frequent these exposed areas, moving through the clear waters delivered by the oceanic currents. The anticipation builds during the descent, knowing that these large predators patrol the waters just beyond the seamount's edge.

The more sheltered, inner sections of Bajo Manuelita offer a different, but equally compelling, animal behaviour display. This side of the seamount is particularly known for dense aggregations of whitetip reef sharks (Triaenodon obesus). These sharks can often be observed resting in sandy patches or interacting around cleaning stations formed by specific rock formations. This protected environment allows for closer observation of their natural behaviours, providing a stark contrast to the fleeting encounters with pelagics on the exposed side of the seamount.

Beyond the sharks, the site hosts a diverse array of other marine life. Spotted eagle rays (Aetobatus narinari) and manta rays (Manta birostris) gracefully glide through the water column, often seen moving between the sheltered and exposed areas. Green sea turtles (Chelonia mydas) forage along the ledges, while marbled rays (Taeniura lymma) might be spotted on the sandy bottoms. The basalt formations themselves are home to moray eels (Muraenidae), lobsters (Nephropidae), and big soldierfish (Myripristis berndti), showcasing the site's rich biodiversity.

Visibility at Bajo Manuelita can range significantly, typically between 10 and 30 meters, influenced by thermoclines and plankton blooms that are common in these nutrient-rich waters. While excellent visibility offers wide-angle views of the seamount and its inhabitants, periods of reduced visibility often coincide with increased plankton, which can attract larger feeders like whale sharks (Rhincodon typus). The interaction of these natural elements shapes each dive, making every descent a unique experience.

The current is a defining feature of Bajo Manuelita, generally strong, especially on the channel and exposed outer sections. This strong flow, coupled with potential surge, is a key factor in attracting the large pelagic schools. However, conditions are variable; the more sheltered inside of the pinnacle can offer calmer periods, even while the outer faces are experiencing significant flow. This variability means divers need to be prepared for dynamic conditions and understand how to manage their position in the water column and around the seamount's topography.