Shark, ray populations have declined by 'alarming' 70 per cent since 1970s, study finds WedWednesday 27 Sharks swim in formation among schools of fish off Murray Island in the Torres Strait. ( Share Print text only Cancel Shark and ray populations have declined by around 70 per cent since the 1970s, according to research published today in Nature. Key points: Oceanic shark and ray populations have declined around 70 per cent since the 1970s, the study in Nature found Researchers attribute the decline to overfishing Scientists say more strict management measures are needed to bring populations back to viable levels A team of researchers from countries including the UK, Canada, and Australia looked at data from 18 shark and ray species, measuring their abundance as well as where they sat on the list of threatened species.