While working in the Museum collections, I came across a small cardboard box containing few scattered bones. In that moment, I found kind of amusing that such a tiny box contained the remains of the largest living animal: the blue whale (Balaenoptera musculus Linnaeus, 1758). Whales have captured the imagination of seagoers and coastal inhabitants for millennia, assuming the forms of sea monsters or that of living islands. Churches were said to be built to commemorate the slaughter of enraged dragons, only to later find out that the beasts ‘bones, kept with much care, were in fact belonging to a cetacean. And even in modern times, with the amount of knowledge that we have, whales still are a sight to behold. Such a nicely curated introduction just to say that, as much as I would like to, I have never seen a live blue whale…

In my defense, coming from Italy my dream of seeing a “homemade” blue whale diving in front of my eyes is pretty much destined to remain unfulfilled. Even if we expand our focus at the entire Mediterranean Sea, the only resident baleen whale that can be spotted is the fin whale (Balaenoptera physalus Linnaes, 1758). More species were possibly present in the past, and from time to time other whales make an appearance before going back to where they came from. Still, no blue whales. Or maybe not.

In 2019, Bianucci and his team described a partial whale skeleton from Lake San Giuliano, near Matera (Basilicata, Italy). The bones date back to the Early Pleistocene (1.49 – 1.25 million years ago), and belonged to an animal that would have ranged between 23.4 and 26.1 meters in length. Furthermore, many characters described for the retrieved fossil share similarities with those found in a still-living species: the blue whale. As such, these remains were labelled as Balaenoptera cf. musculus (Fig.2), meaning that, while retaining some degree of uncertainty, this specific specimen could belong to a blue whale. These findings pushed back the dating for the appearance of gigantism in modern baleen whales to the Middle-Late Miocene. They also proved that blue whales, or something very similar, swam in the Mediterranean Sea in the, geologically speaking, very recent past. While intriguing, I have unfortunately yet to receive my own time machine. Change of plan.

Let`s go back to where everything started, when I stated that the Mediterranean Sea is now home to a single baleen whale species, the fin whale. Some individuals are resident, while others enter the Western Mediterranean from the North-Atlantic to feed during the winter period. And it is with these “visiting” whales that my quest could come to an end. In 2020 a juvenile whale was found stranded in Cala del Rio, near Naples (Campania, Italy). The whale, that from now on will be referred as ID531 (Fig. 3), was so secured, pictures were taken, and it was identified as a fin whale. What was not expected is that the analysis of part of the mitochondrial control region told a different story: ID531 bored the molecular signature of a different species, a blue whale. Rather than being a very odd blue whale, ID531 was suggested to be a hybrid, a theory that was later confirmed by further genetic analysis of the α-lactalbulmin nuclear gene. Previously overlooked traits, such as the size and position of the dorsal fin, where found to be in-between the two species or closer resembling those typical of blue whales.

Why ID531 came to be it`s still partly a mystery. Hybrids between blue and fin whales have been known from the late nineteenth century, when strange individuals were caught during commercial whaling activities. As blue whale`s populations are still recovering from the past hunting pressure, and finding a same-species partner could thus be difficult, females could be less selective in their mate choice. However, this would represent just a single piece of a much more complex puzzle. Blue whales and fin whales have overall similar sizes, an overlapping range and share in some cases the same feeding grounds where, despite behavioral barriers, interspecific hybridization could occur. New evidence are so needed to entangle this cetacean enigma.

And I still haven`t seen a live blue whale, yet.

References

Bianucci, G., Marx, F. G., Collareta, A., Di Stefano, A., Landini, W., Morigi, C., & Varola, A. (2019). Rise of the titans: Baleen whales became giants earlier than thought. Biology Letters, 15(5), 20190175. https://doi.org/10.1098/rsbl.2019.0175

Fioravanti, T., Maio, N., Latini, L., Splendiani, A., Guarino, F. M., Mezzasalma, M., Petraccioli, A., Cozzi, B., Mazzariol, S., Centelleghe, C., Sciancalepore, G., Pietroluongo, G., Podestà, M., & Caputo Barucchi, V. (2022). Nothing is as it seems: Genetic analyses on stranded fin whales unveil the presence of a fin-blue whale hybrid in the Mediterranean Sea (Balaenopteridae). The European Zoological Journal, 89(1), 590–600. https://doi.org/10.1080/24750263.2022.2063426