When Are Humpback Whales Most Vulnerable to Vessel Strikes?

New drone research shows that collision risk depends not only on where whales and vessels meet. What a whale is doing at that moment can substantially affect its vulnerability.

Collisions with vessels are a serious threat to whales around the world.

Understanding that risk has traditionally focused on a relatively straightforward question: where do shipping routes and whale habitats overlap?

New research suggests that another question matters too:

What are the whales doing when vessels approach?

A peer-reviewed study published in Scientific Reports in August 2026 used drones to observe humpback and fin whales from above and analyse their movements, depth and behaviour.

The results provide a much more detailed picture of when whales may be particularly vulnerable to vessel strikes.

Whales spend much of their time close to the danger zone

Researchers conducted drone-based focal observations of humpback and fin whales in a Northeast Pacific feeding area.

They then calculated how much time the animals spent within the potential lethal depth zones of 11 different vessel classes, ranging from small recreational craft to large fuel carriers.

For humpback whales, the researchers estimated that they spent an average of 73.5% of their observed time at or above 17 metres depth, placing them within the potential lethal zone associated with large fuel carriers.

But depth was only part of the story.

The study found that vulnerability changed according to whale behaviour.

Resting and surface-travelling whales were particularly vulnerable.

Behaviour affected swimming speed, direction, visibility at the surface and the amount of time animals remained within depths where collisions could occur.

What does this mean for Golfo Dulce?

The study was conducted in Canadian waters, not Costa Rica.

Its numerical results therefore cannot simply be transferred to Golfo Dulce. Humpbacks using a northern feeding ground may behave differently from whales breeding, nursing calves or travelling through tropical waters.

But the research offers an important lesson for whale conservation here.

Golfo Dulce is not only whale habitat.

It is also used by fishing boats, whale-watching operators, recreational vessels, ferries and other marine traffic.

And among the humpbacks using these waters are mothers with young calves.

If we want to understand vessel risk properly, simply plotting whale sightings on a map is not enough.

We also need to know what the animals are doing.

Better observations can lead to better protection

Future whale monitoring in Golfo Dulce should therefore record more than species, number and location.

Useful observations should include:

• whale behaviour

• presence of mothers and calves

• direction and speed of travel

• time spent resting at the surface

• number and type of nearby vessels

• vessel distance and speed

• changes in whale behaviour when vessels approach

Drone research could eventually add another dimension by allowing scientists to observe behaviour that is difficult to assess from a boat.

Combined with vessel tracking and standardized field observations, this could help identify places and situations where whales face the greatest risk.

Conservation needs evidence

The new study does not demonstrate that vessel strikes are currently a major cause of humpback mortality in Golfo Dulce.

We should not make that claim without local evidence.

What the research does show is how much more precisely vessel risk can now be studied.

For #SaveGolfoDulce, that distinction is important.

Our objective should not simply be to say that boats and whales share the same waters.

We need to understand when that coexistence becomes dangerous, and use evidence to prevent avoidable harm before it occurs.

Scientific source

Baer, G., Keen, E., Jutras, L.S.J. et al. (2026). Drone-based assessment of humpback and fin whale vessel-strike vulnerability. Scientific Reports. Published 14 August 2026.