Did you know that there are sharks in the Baltic sea? None of the species living solely in fresh water (like river sharks or Freshwater stingrays), and fortunately not the Bullshark, but emigrants from North sea or Atlantic. Many have probably been dragged along by saltwater floods due to storms, or wander temporarily into the afterwards more saline waters. But one species made itself at home and lives even in areas far away from saltwater passages. The small-spotted catshark (Scyliorhinus canicula) or lesser-spotted dogfish is the most common European shark species and lives in the Mediterranean, the north-east Atlantic and the North sea, for some time incl. Skagerrak and Kattegat. But now it is even native in the German Baltic sea (to be precise off Poel island), as shown in this report.
The up to 3 ft 3 in -1 m- long Small-spotted dogfish is used commercially, too: for its meat (its liver is poisonous), its sandpaper-skin, oil or fishmeal. Now and then catsharks (named after their catlike eyes: horizontally oval eyes with elongated pupils and a nictitating membrane) have been caught in the Baltic sea, too. Afterwards they would be discarded (with high chances of survival) or go, as mentioned here, to aquariums (in which small-spotted catsharks are easy to keep and therefore a common species). Sometimes you are able to even touch them there. Together with my family I visited such an aquarium in Denmark and curiously touched sharks, rays and starfish under water – until I learnt this summer in Scotland, that you shouldn’t do that since it may damage the protective layer of slime above the skin. Why didn’t the other aquarium operators know that?
Like all catsharks the small-spotted catshark lays eggs called mermaid’s purses with curly tendrils at each end to cling themselves to underwater structures. Inside the egg case one embryo (seldom two) develops during 5 to 11 month, which can be studied easily (as done in laboratories). After hatching, the 4 in – 10 cm – long pups have to fend for themselves. On them it was observed for the first time, that they anchor their prey on the dermal denticles on their tail and tear bits off – they are really flexible.
This egg cases as well as pups have now been found in the Baltic sea, too – proof that they are not only temporary visitors. It is assumed that the reason is the climate change. How do they cope with the small level of salinity?