Are Golfo Dulce’s Whale Seasons Changing?

New research suggests that climate conditions may be changing when humpback whales arrive in Costa Rican waters.

Golfo Dulce is extraordinary for many reasons. One of the most remarkable is that humpback whales migrating from both the Northern and Southern Hemispheres use Costa Rica's Pacific waters.

For years, whale watching has generally been described in terms of two relatively predictable seasons.

New research suggests that reality may be becoming more complicated.

Scientists analysed humpback whale observations along Costa Rica's Pacific coast between 2001 and 2023, comparing whales associated with the endangered Central America population with animals migrating north from the Southeast Pacific.

Their findings indicate that environmental conditions thousands of kilometres away can influence when whales are observed in Costa Rican waters.

Periods of extreme warming, El Niño conditions and marine heatwaves were associated with changes in whale occurrence, particularly among the Central America population.

October and November could become especially interesting

One of the study's most intriguing findings concerns the period between the traditional seasons.

The researchers identified a possible October–November overlap window between whales arriving from the Northern Hemisphere and animals from the Southern Hemisphere.

Under unusually warm conditions, southern whales may remain longer while northern whales may arrive earlier.

That could make October and November particularly important months for future monitoring.

It also challenges a simple idea of fixed and predictable “whale seasons”.

What we still don't know

The findings need to be interpreted carefully.

The historical observations were not collected through a perfectly standardized long-term survey. Sampling depended partly on logistics and volunteer availability, and many periods were not surveyed.

The research therefore does not prove that Costa Rica's humpback whale population has declined.

What it does show is that whale occurrence and migration timing appear to be connected to changing environmental conditions.

That distinction matters.

Turning observations into better science

For #SaveGolfoDulce, the research points toward a practical next step.

Future monitoring should record not only where whales are seen, but also survey effort, group composition, environmental conditions, location, vessel activity and behaviour.

October and November deserve particular attention.

Over time, consistent observations from Golfo Dulce could help researchers understand whether migration patterns really are shifting and how whales respond to a changing Pacific Ocean.

The whales are telling us something.

We need to make sure we are collecting the data needed to understand it.

Source: Pelayo-González et al. (2026), “Hemisphere-Level Comparison of Climate-Driven Humpback Whale Breeding Migrations to the Eastern Pacific Off Costa Rica”, Ecology and Evolution.