Cetorhinus maximus by greg skomal.JPG
Elasmobranchs lack swim bladders, and maintain buoyancy with oil that they store in their livers. Some deep sea sharks are targeted by fisheries for this liver oil, including the school, gulper and basking sharks (pictured). All three of these species have been assessed by the IUCN as vulnerable due to overfishing.

From a practical point of view the life-history pattern of elasmobranchs makes this group of animals extremely susceptible to over fishing. It is no coincidence that the commercially exploited marine turtles and baleen whales, which have life-history patterns similar to the sharks, are also in trouble.

Elasmobranchii is a subclass of the Chondrichthyes or cartilaginous fish. It includes the modern sharks and the rays and skates.