Between Spain and Morocco, the Alborán Sea is the first basin that Atlantic water meets on entering the Mediterranean. It is narrow, deep, stirred by permanent gyres, and it concentrates a density of cetaceans with no equivalent in the western basin. From 18 May to 16 June 2026 the Spanish Institute of Oceanography carried out a dedicated survey there, whose first figures have just been released.
What the survey recorded
| Period | 18 May to 16 June 2026 |
|---|---|
| Area | between Nerja and Cabo de Gata, Andalusian coast |
| Total sightings | 561, cetaceans and marine turtles |
| Cetacean species | up to seven |
| Long-finned pilot whale | 70 encounters, the most frequently seen species |
| Cuvier’s beaked whale | 66 encounters |
The figure that deserves attention is the one for Cuvier’s beaked whale. Sixty-six encounters in one month, for a species usually described as rare and hard to see, is a remarkable density.
Why Cuvier’s beaked whale is so hard to observe
What a single encounter with a Cuvier’s beaked whale represents has to be understood in order to gauge what sixty-six are worth.
This species holds the diving records of the mammal kingdom, with durations exceeding two hours and depths of close to three thousand metres, as our page on diving records sets out. It therefore spends most of its time out of sight.
At the surface it is inconspicuous: no breaching, a low and barely visible blow, a modest dorsal fin set well back, and animals often alone or in small groups. An observer can pass a few hundred metres away and see nothing.
This is what makes dedicated surveys indispensable. Opportunistic observation from a ferry does not detect this species; it takes a slow vessel, trained observers, and a protocol designed for it.
What sets the Alborán Sea apart
Three features combine, and they account for the richness observed.
The topography. The seabed drops away sharply close to shore, and the basin is cut by canyons. The deep-diving species, Cuvier’s beaked whale and sperm whale, need accessible deep water, which most Mediterranean coasts do not offer.
The hydrology. Atlantic water, less saline and colder, enters through Gibraltar and forms two near-permanent gyres. These structures concentrate nutrients, and therefore plankton, and therefore prey.
Its position as a crossroads. The basin receives both Atlantic and Mediterranean species, which accounts for the diversity recorded. It is also where the Iberian killer whales live, following bluefin tuna in the neighbouring strait.
The other species of the basin
The long-finned pilot whale, with seventy encounters, is the most frequently seen species of the survey. Its Mediterranean situation deserves a mention, because it is a matter of concern for one particular reason.
It is a robust odontocete of five to six metres, highly social, living in stable family groups of several dozen individuals organised around related females. This cohesion, which is its strength, is also its weakness.
The Mediterranean population has suffered morbillivirus epizootics on several occasions, a virus related to that of measles, which have caused mass mortalities. A pathogen spreads all the faster when social contacts are frequent, and a tight-knit group becomes infected throughout.
These episodes have been aggravated by the burden of organochlorine contaminants, which weakens the immune response, a mechanism set out on our page on chemical pollution. The Mediterranean subpopulation is listed as Endangered, whereas the species is doing well globally.
Documenting its presence and its numbers in the Alborán Sea therefore has a value that goes beyond the inventory: it is the baseline against which a future epizootic will be assessed. Our page on cetacean demographics explains why this baseline is indispensable.
What these surveys are for
A one-month survey does not produce an abundance estimate on its own. It serves three more specific purposes.
Feeding the density maps, which govern every management measure, whether protected areas, traffic restrictions or the regulation of prospecting. We have described this mechanism in connection with the French distribution maps.
Documenting species sensitive to noise. Beaked whales are among the cetaceans most vulnerable to active sonar, and knowing their fine-scale distribution is the precondition for any avoidance measure, as our answer on military sonar explains.
Feeding the Mediterranean census. The survey is part of a wider whole, the large synoptic survey of the basin carried out in 2026, which aims to produce estimates comparable from one subregion to another.
Seven species in a very small space
The number of species recorded in one month is worth pausing over, because it is a result in itself.
The Mediterranean has a little under ten regular cetacean species. Seeing up to seven of them in a single sector, on a single four-week survey, means that the Alborán Sea concentrates almost all of them.
They include the two great divers, Cuvier’s beaked whale and sperm whale, which require accessible depths; the fin whale, the only regular mysticete of the basin; the long-finned pilot whale and Risso’s dolphin, cephalopod predators of the slope; and the surface delphinids, striped dolphin, common dolphin and common bottlenose dolphin.
This coexistence is possible only because the basin stacks several habitats within a small extent: coastal shelf, steep slope, canyons and deep water, all of it stirred by permanent gyres. Each species finds its depth and its prey there without competing with the others.
This is what makes the Alborán Sea a reference area for Mediterranean conservation, and what explains why it attracts so much research effort. Our pages on sighting hotspots and diets set out this sharing of resources.
The limits
A number of encounters is not a density, and still less a population size. It depends on survey effort, on the number of days at sea, on the weather and on the extent covered. Comparing 66 Cuvier’s beaked whale encounters with a figure obtained elsewhere, under a different protocol, would make no sense.
A one-month survey also gives a seasonal snapshot. Spring is a favourable period in this sector, and nothing guarantees that the distribution observed holds in winter.
Finally, these figures are the first elements released at the end of the survey. The analysed results, with their detection corrections, will come later and may give a different picture.
Why this work matters
The Mediterranean is a small, enclosed and intensively exploited sea, where field data remain uneven from one country to another. National surveys like this one are the raw material of any regional policy, and they cover species whose status is a matter of concern. Our pages on marine protected areas and sighting hotspots place the Alborán Sea within that whole.
Source: Spanish Institute of Oceanography, communication on the CETALBORAN0526 survey carried out from 18 May to 16 June 2026 between Nerja and Cabo de Gata.
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