The Pelagos Sanctuary, between Provence, Liguria and Sardinia, is the main known summer feeding area of the fin whale in the Mediterranean. It is also one of the busiest shipping corridors in the world. The two overlap, and the result is a ship strike from time to time.
An overlap that nothing separates
Our reading of the distribution maps shows it clearly: in the Mediterranean, the presence of the fin whale is four times greater in July than in January. The animals gather in summer where upwelling concentrates the krill.
That same period concentrates passenger traffic towards Corsica and Sardinia, while freight runs all year round. The encounter is nothing like a statistical accident: it follows from a predictable overlap between a food resource, animals that follow it, and commercial routes that cross the same area.
Why a twenty-metre animal gets hit
The question comes up often, and the answer rests on three things.
The vessel arrives fast and from behind. A cargo ship at twenty knots covers more than six hundred metres a minute. A fin whale at the surface, busy breathing between two feeding dives, has very little time to react.
It hears the ship poorly. The noise of a large vessel is largely directed to the sides and astern; ahead of the bow there is a relatively quiet cone. The animal may therefore perceive diffuse traffic without locating the ship that is approaching. Our page on ocean noise covers this masking.
It does not flee the way one imagines. The documented avoidance responses are often late and limited in amplitude, in animals that have no natural predator at the surface and whose behaviour has not been shaped by this threat.
How a ship strike is established
The distinction is harder to make than it seems, and it governs every figure.
A carcass may carry propeller cuts without the vessel being the cause: a dead, floating animal is regularly struck after death. The necropsy must therefore establish that the injury preceded death, which is betrayed by signs of a vital reaction, haemorrhage in the tissues, coagulation, inflammatory response, all absent from a post mortem lesion.
Head-on strikes, for their part, often leave few external marks and a great deal of internal damage: vertebral or cranial fractures, massive haemorrhage. A superficial examination on a beach can miss them entirely.
This is why stranding networks able to carry out full necropsies are irreplaceable, and why the available statistics mostly describe the quality of local expertise. Our page on the causes of strandings sets out this approach.
What is known about the scale of the problem
This is where caution is needed. The real number of ship strikes is unknown, and probably much higher than the number recorded.
Documented cases come from three sources, all of them partial: stranded animals bearing marks of impact, carcasses carried into port on a ship’s bow, and voluntary reports from crews. An animal struck offshore that then sinks appears in none of these categories.
The same bias affects estimates of bycatch, where only a fraction of the animals that die are known to strand: our page on bycatch sets out this extrapolation mechanism.
What reduces the risk, and what would reduce it
| Reduce speed | the best established lever; the probability that a strike is fatal drops sharply below a certain speed threshold |
|---|---|
| Move the routes | shift the shipping lanes away from areas of high seasonal density |
| Detect in real time | acoustic or thermal systems carried on board, alerts shared between vessels |
| Map in fine detail | knowing where and when the animals gather, the condition for everything else |
The last line governs the others, and it is precisely what large-scale surveys such as the Mediterranean campaign of summer 2026 produce, along with networks of passive acoustic monitoring.
Speed, the only lever genuinely demonstrated
Of all the measures considered, speed reduction is the one whose effect is best established, and the reasoning is simple.
Two effects combine. First, the energy transmitted in an impact grows with the square of the speed: a vessel travelling at half the speed transmits about four times less energy. Second, a slower vessel gives both the animal and the bridge more time to react, and the distance needed for an avoidance manoeuvre falls.
Analyses carried out on other seaboards, in particular on the east coast of the United States for the right whale, show that the probability that a strike is fatal drops sharply below a certain speed threshold. It is on this basis that mandatory slow-down zones have been introduced there.
In the Mediterranean, the equivalent remains largely voluntary. Shipping companies undertake to slow down or to steer clear in certain sectors, but no general obligation governs speed within the sanctuary. The difference between an undertaking and a rule can be read in the rate of compliance.
What is still missing
Three gaps come up in every report.
The first is the absence of a reliable denominator: without a solid estimate of the number of animals present, there is no saying what fraction of the population is affected each year, and therefore whether the removal is sustainable. The Mediterranean campaign of summer 2026 is aimed precisely at filling this gap.
The second is under-reporting. A crew is under no general obligation to report an impact, and the event often goes unnoticed aboard a large vessel.
The third is the spatial resolution of the density maps. Shifting a shipping lane assumes knowing where the animals are to within a few nautical miles and a few weeks, which requires continuous monitoring rather than a summer snapshot. Our pages on marine protected areas and on cetacean demography place these requirements in context.
A sanctuary is not a barrier
The word is misleading. Pelagos is an area of cooperation between three states, with undertakings attached, and not a space in which navigation is restricted. Vessels move through it freely.
This is the general limit of protection by zoning when faced with mobile pressures, which our page on the international legal framework examines. A boundary protects effectively against what is fixed, an extraction or a development; it protects poorly against what passes through.
Sources: work by the Tethys Research Institute on collisions between large vessels and cetaceans in the Mediterranean; documents from ACCOBAMS and the International Whaling Commission on ship strike risk; distribution data from the 2024 DCSMM assessment.
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