Where Shipping Lanes Cross A Whale Habitat
Around 30,000 ships cross the Hellenic Trench every year, travelling between the western Mediterranean and the Adriatic towards the Aegean and the Black Sea, and vice versa. It’s one of the world’s busiest sea lanes. The challenge: these routes run directly through the core habitat of the eastern Mediterranean’s last sperm whales.
After deep dives, sperm whales spend 10 to 15 minutes resting at the surface, barely able to detect approaching vessels in time to dive again. Fast-moving ships cannot stop or steer clear quickly enough and risk to strike the whales. Collisions are frequently fatal; some animals survive but are badly wounded by ship propellers. The true number of victims is likely far higher than stranding records suggest: most whales killed at sea sink to the seafloor before they can be found.
Why speed matters
The survival chances of a whale in a collision depend primarily on the speed of the vessel. Numerous scientific studies show that the possibility of a collision to take place and having a lethal effect is very low when a vessel’s speed does not exceed 10 knots and that above this threshold, the risk of a fatal strike rises exponentially. Speed reduction also benefits the wider ocean environment: a 10 per cent reduction in speed across the world fleet could reduce shipping noise and would also reduce greenhouse gas emissions, a benefit for both whales and the climate.
However, voluntary speed reduction measures have a compliance rate of only 9 to 41 per cent, compared to over 80 per cent for mandatory measures. This is why OceanCare is calling for binding provisions and submit a corresponding proposal to the International Maritime Organisation (IMO).
The IMO has already recognised the effectiveness of speed reduction: in 2023 the IMO has passed a resolution which calls for voluntary speed limits of 10 to 13 knots to mitigate ship strikes involving sperm whales in the Northwestern Mediterranean Sea.
Areas, where re-routing of ships isn’t possible
The Hellenic Trench stretches from the Ionian Sea to the south of Crete and the Sea of Rhodes, a core habitat for sperm whales and a high-risk area for ship strikes. Across much of its length, a minor course adjustment of just a few nautical miles in an offshore direction can significantly reduce the risk of collision.
But there is one stretch where this is simply not possible: the area between the Strait of Kythira and Cape Tainaron at the southern tip of the Peloponnese. Ships travelling between the western Mediterranean and the Aegean or Black Sea must pass through this sensitive area regardless. With water depths exceeding 1,500 metres and high densities of both ship traffic and sperm whales, it is the most dangerous stretch along the entire trench and one where re-routing is simply not a feasible option.
SAvE Whales is being developed as a complementary early warning system. By detecting whales acoustically and alerting ships in real time about their presence, ships can slow down in time to mitigate risk of a fatal collision with a sperm whale.
