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The central nervous system (CNS) consists of the brain and the spinal cord, immersed in the cerebrospinal fluid (CSF).
For centuries fishermen have conducted sustainable fisheries for sharks in coastal waters, and some still do. During recent decades an increase in effort and yield of shark catches, as well as an expansion of the areas fished has taken place. This leads to concern over the consequences for the populations of some shark species in several areas of the world's oceans.