Tour guides in Costa Rica’s Golfo Dulce say humpback whales have been more difficult to find this season, raising questions about whether warmer ocean water is changing their normal movements. Guides have said August usually brings regular whale sightings inside the gulf but this year, however, this year they have experienced days when dozens of tour boats searched the area but very few whales were seen.
On one recent morning, guides said that only one of approximately 30 to 40 boats reported seeing a whale. The observations do not prove that Costa Rica has fewer humpback whales this year but there has been no official population count showing a decline. The whales may simply be spending more time outside Golfo Dulce or moving between different parts of the southern Pacific coast.
Still, guides with years of experience say the change has been noticeable. Captains and guides, who has worked in the area for more than 12 years, said the whales previously remained inside the gulf for longer periods. This season, they appear to leave the protected waters more frequently and stay outside for longer.
The guides believe warmer ocean water could be influencing that behavior. They say they have personally noticed higher water temperatures while swimming and snorkeling. Some have also reported seeing coral with signs of partial or complete bleaching, which can occur when the ocean becomes unusually warm.
Golfo Dulce is one of Costa Rica’s most important whale-watching destinations and humpback whales from the Southern Hemisphere travel thousands of kilometers from waters near Antarctica to Costa Rica’s warm Pacific coast. The whales come north to mate, give birth and care for their calves before beginning the long journey back toward their feeding grounds. The southern whale season normally runs from July through October, with sightings often reaching their highest point during September.
Conditions inside Golfo Dulce are usually well suited for mothers and young calves. It’s warm, relatively calm water gives the animals a protected place during the first weeks of a calf’s life. Scientists have found evidence that water temperature and food availability can affect when humpback whales begin migrating.
A study published in 2025 followed 42 humpback whales traveling from breeding areas in Costa Rica, Panama and Ecuador toward feeding grounds near Antarctica. The researchers found that the whales used information from their surroundings, including water temperature and the amount of marine life in the water, to help decide when to leave.
Warmer water and El Niño conditions were connected with changes in the timing of their southward migration. The research suggests that humpbacks can adjust their movements when ocean conditions change. However, that study used tracking information collected between 2009 and 2016. It does not establish that warmer water is responsible for the sightings reported by Golfo Dulce guides in 2026.
Confirming such a connection would require current water-temperature measurements, whale counts and comparisons with previous seasons. For local tourism businesses, fewer sightings can create a difficult situation. Whale watching supports boat operators, guides, hotels, restaurants and other businesses across the Osa Peninsula and southern Puntarenas.
Guides sometimes remain at sea longer than usual while searching for whales because they know that visitors may have traveled a considerable distance for the experience. But sightings are never guaranteed, even during the busiest part of the season. Visitors can still encounter dolphins, sea turtles and other marine wildlife in Golfo Dulce. Tours in the area also commonly include snorkeling, mangrove visits and trips along the coast.
The guides’ reports offer an early warning worth examining, rather than proof of a permanent decline. Continued monitoring will be needed to determine whether this is an unusual season or part of a larger change in humpback whale migration.
