Populations of five shark species in the Mediterranean Sea have declined by an average of 97 percent in the last 200 years, principally due to fishing, according to a new study to be published in the journal Conservation Biology. Researchers combed historical records and collected other data to piece together the long-term population trend of the blue shark, thresher shark, hammerhead, and two species of mackerel sharks. “There is a long history of fishing in the Mediterranean, especially coastal fishing,” said lead author Francesco Ferretti. “And until recently, these species were not valuable — they were caught as bycatch by boats chasing important species such as tuna — so they were declining without anyone noticing.” But strong demand for shark fins in some Asian nations has greatly increased the value of sharks as targets. Researchers are particularly worried about the ecosystem-wide effects of losing such large numbers of top predators.