sentences:  In the Mediterranean sea, the Portuguese dogfish is one of the most common deepwater sharks along with the blackmouth catshark ("Galeus melastomus") and the velvet belly lantern shark ("Etmopterus spinax"), and the only shark abundant below a depth of .By inhabiting deeper water, Portuguese dogfish in the Mediterranean may reduce competition with the other two species.The smaller size of Mediterranean sharks relative to those from the rest of the world may be due to limited food availability and/or the warmer, saltier environment.