As Morski writes on the 20th of July, 2019, between the Dalmatian islands of Hvar, Brač and Šolta there has been an invasion of a certain unusual species of octopus. It is a blanket octopus (Tremoctopus violaceus), an otherwise very rarely seen species in the Adriatic sea.
Very similar occurrences such as this have been noted before, and it’s more than likely some of the hydrographic conditions in the sea were affected, which was conducive to the current ”invasion” of these animals in the Croatian Adriatic.
Just to get an idea of how rare this species actually is in the Adriatic, the last known appearance of the blanket octopus in such a small area took place back in 1936.
We know very little about the life of these creatures which are otherwise widespread but very “rare” in all of the world’s seas. Back in 2002, the first male was discovered and since then we have known that this is an animal with the largest difference in size between the two sexes. The males are only 2.4 centimeters long, while females can grow up to 2 metres in length.
An exploration of the feeding of large predatory fish in the Mediterranean in 2015 has shown that local predatory fish do eat the blanket octopus, and this tells us that this octopus might not actually be as rare in these parts as we think it is, but of course, we’re not fish, and fish know the world below the sea much better than we do or ever could.
If you see or manage to catch this type of blanket octopus, please make sure experts can officially record your findings, asks Podvodni.
Morski discussed this topic further with the editor of the Podvodni.hr portal, who is the author of numerous texts with marine themes, as well as an associate of the Institute of Oceanography and Fisheries in Split, Pero Ugarković.
”As far as the Adriatic is concerned, this is a sensational phenomenon that has appeared in such a small area, in such large numbers. Over ten of them have been caught, most of which were released back into the sea,” says Ugarković.
”Back in the 19th century, Kolombatović encountered several blanket octopus near Split when fishing and assumed that they’re often hunted, but since then there has actually been no data on this species except a few sporadic catches and several anecdotes about them. One similar phenomenon occurred in the northern Adriatic back in 1936 when several of them in the Adriatic were caught in a small area.
They’ve always been considered very rare in the whole of the Mediterranean, but they’d be seen from time to time. After a survey that was conducted three years ago, where they looked into what large predatory fish were eating, it was concluded that blanket octopus are still common in the sea. Tuna seem to eat a lot of them.
The problem is that we can’t see them. Some hydrographic conditions changed and that’s why there are suddenly a lot of them. An Italian who watched them be caught back in 1936 tried to connect it with the warming of the sea, with it reaching over 25°C, which would fit with this sudden emergence of them in the Croatian Adriatic.
We know little about this species, and when it comes to species we don’t know much about, we can’t even begin to estimate how threatened they are,” concluded Ugarković.
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