See a blow ? Go Slow: Whale–Vessel Collisions: Risks, Best Practices & Petition

Virginie Wyss
Aug 21, 2025
2 min read

Whale–vessel collisions cause tragedies at sea. What are the Hotspots? How to avoid ship strikes? What to do after a colision? Some of the tools that can be used (REPCET, Whale Alert) and a petition for mandatory speed limits.

Why this is a major issue ?

A magical encounter can turn tragic: violent impacts, fatal injuries for cetaceans, severe boat damage. Under-reporting hides the true scale.

I remembered that a couple of mine just arrived in the Azores with a sailing boat, and they heard a very strong noise... they had collisioned a sperm whale while crossing the Atlantic. The boat survived, but the whale was bleeding a lot and was never reported.

Another striking example comes from the world of offshore racing: during the 2016 Transat New York – Vendée (IMOCA Ocean Masters), even though a whale exclusion zone had been established, 8 out of 14 boats reported 15 collisions within 24 hours, some very likely involving cetaceans. Several skippers had to return to port or abandon the race.

This highlights that even modern racing yachts, increasingly fast and numerous, face significant risks of whale strikes.

High-risk areas & species

A study by Isabella C. Avila (2018) shows 72 marine mammal species are affected.

Mediterranean: 30% of global shipping, 8–40 whales killed annually.
Canary Islands: heavy coexistence of shipping and fauna.
Oman & Southern Ocean: rich biodiversity, increasing traffic.
California: ship strikes are the top cause of gray whale mortality.

Most affected species are blue whale, fin whale, gray whale, humpback & sperm whale.

Consequences

For whales: propeller scars, fatal injuries, undetected deaths.
For mariners: cracked hulls, costly damage, risk of sinking.
For ecosystems: loss of breeding individuals.

How to Prevent collisions ?

Sail by day (some whales rest at night on the surface).
Reduce speed < 10 knots in whale-dense areas.
Post a lookout, follow bird flocks.
Avoid sharp maneuvers, respect protected areas.

Tools available:

REPCET – reporting system (Mediterranean).
Whale Alert – app for North America.
See A Blow? Go Slow.
Sailors for the Sea – When Whales Meet Sails.
Sonic alarm research.
IWC – Ship Strikes.

What to do after a strike ?

Inspect hull, keel, water ingress.
Alert coast guard if whale is injured/surfacing.
Report to the IWC with GPS data.
Professional inspection recommended (video: post-strike check-up).

Petition: Mandatory speed limit in the Mediterranean

If you want to help reduce the ship strike, you can sign The petition, coordinated by OceanCare, that was officially handed to Spain’s VP Sara Aagesen on June 11, 2025 at UNOC3.

→ NGOs’ statement (PDF)→ Letter with 60 scientists & experts (PDF)

📧 To sign: send name + affiliation to Carlos Bravo (OceanCare) → cbravovilla@oceancare.org