June 14, 2017 — Gray seals are booming. They’ve flocked to coastal Massachusetts, where hunters once killed the animals wholesale — a dead seal’s nose could fetch a $5 reward in the 1960s.
Twenty years ago, there were about 2,000 seals near Cape Cod and Nantucket. A new estimate, published Wednesday in the journal Bioscience, suggests there are now as many as 50,000.
‘‘We should be celebrating the recovery of gray seals as a conservation success,’’ said David Johnston, an author of the study and marine biologist at Duke University .
Where seals go, sharks often follow. Great white sightings in Cape Cod increased from 80 in 2014 to 147 in 2016. Johnston said the shark spike may be linked to the seals. ‘‘One of our tagged animals was killed by a white shark,’’ he said.
Maine and Massachusetts once placed bounties on seals because fishermen feared they would gobble up valuable fish such as cod. (There is little evidence that seals actually compete with fishermen, Johnston said.) The century-long bounty hunt claimed up to 135,000 animals.
The seals bounced back after 1972’s Marine Mammal Protection Act outlawed the killings. ‘‘I’m a firm believer if you just stop doing bad things to wildlife they will recover,’’ Johnston said. The seals’ recovery raised a question infrequently asked in conservation: What happens after success?
‘‘We haven’t done a great job of preparing people,’’ he said, ‘‘that they would be back again.’’
Part of that means quantifying the success. In 2011, a National Marine Fisheries Service aerial survey estimated 15,000 seals swam in southeastern Massachusetts waters.