Mammals (and other species) of the Golfo Dulce

Posted on August 28, 2018 at 10:20 AM


Whales and Dolphins

The waters surrounding the Osa Peninsula are recognized as the only locale in the world where humpback whales from the North Pacific and Southern Ocean geographically overlap and Golfo Dulce appears to serve as a calving ground and nursery. 

Humpback whales are an endangered species with international government-protected status. They are easy to see since they live at the ocean’s surface. They swim slowly and are known as the “acrobats of the sea” for their aerial frolicking. Humpbacks also are known for their “songs” – long, varied, and complex sequences of squeaks, grunts and other sounds. Only males have been recorded singing and they seem to produce the complex songs only in warm waters – thought by scientists, therefore, to be mating calls.

Golfo Dulce also is home to important resident and migratory communities of Bottlenose Dolphins, Spotted Dolphins, Spinner Dolphins, and the occasionally seen False Killer Whales. 

Sea Turtles

Four species of the family Cheloniidae are known to utilize Golfo Dulce: the Pacific green sea turtle, the olive ridley sea turtle, the hawksbill sea turtle and the near-extinct Pacific leatherback sea turtle. A large population of the Pacific green sea turtle may be found year round in the upper embayment including individuals originally tagged in the Galapagos.

Other interesting creatures of the Golfo Dulce

Whale sharks aggregate inside Golfo Dulce with historical sightings of more than twenty sharks at a time. The embayment also acts a nursery for scalloped hammerhead sharks, two species of needlefish—a key food source for the local Bottlenose dolphins—are known to spawn inside Golfo Dulce every month directly in front of Saladero Ecolodge.

Eight-two species of fish were described in just one Golfo Dulce estuary. There are other sharks and rays and an abundance of small species specific to the coral reefs.

The Yellow SeaSnake of the Golfo Dulce

We enjoyed having Brooke Bessesen stay at Saladero Ecolodge while completing her study of this endemic species.

Hydrophis platurus xanthos, or yellow sea snake, is separated from its conspecifics by a gap of about 22 kilometers—restricted to the inner basin of Golfo Dulce where the waters are warmer, often turbulent, and occasionally anoxic. This extremely rare subspecies is characterized by smaller body size, canary-colored skin and distinctive behaviors. Most remarkably, it feeds at night, assuming a peculiar sinusoidal ambush posture (Bessesen & Galbreath 2017).

Many thanks to for providing information about the marine ecosystems of the Golfo Dulce. This is a web site that organizes links to many references concerning scientific studies made regarding the Golfo Dulce.

Quote from the Homepage:

"Golfo Dulce is a Costa Rican treasure. As a marine bio-gem, it is one of Central America's preeminent riches. Critically endangered sea turtles rest, feed, mate and nest in the Gulf. A unique xanthic colony of pelagic sea snakes resides in the inner basin. Humpback whales from both northern and southern hemispheres enter the inlet to give birth and possibly provide sanctuary for young calves. Two resident species of dolphins breed and raise offspring in Golfo Dulce. Whale sharks aggregate there, scalloped hammerhead sharks are born and needlefish spawn. It is a vibrant bionetwork, essential to the welfare of the East Pacific ecology. 

Access to peer-reviewed data is vital for officials who must evaluate and determine conservation policies. Escalating pressure on the marine ecosystem has increased vulnerability of biodiversity in Golfo Dulce and overall wildlife populations seem to be in decline. Only through sound research and protective strategies may Golfo Dulce continue to be one of Costa Rica's most important and vibrant marine habitats."

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