These fishermen are likely fishing for the European sea sturgeon (Acipenser sturio), a now-critically-endangered species whose other colloquial name is ironically the “common sturgeon”. They’re using a technique known as “longline fishing”, which is highly effective, but produces very high levels of bycatch - that is, fish or sea life that are unintended targets. Since most baits will attract multiple species to them, it’s very difficult to control for bycatch when using longlines, and many countries have strict regulations on them today.
Unterhaltungen aus der Naturgeschichte: Der Fische 1-2. Gotlieb Tobias Wilhelm, 1799.