A decomposing North Atlantic right whale found this week on Nashawena island northwest of Martha’s Vineyard is the 16th member of the endangered species to die this year, fisheries experts have confirmed.

The discovery came as the National Marine Fisheries Service released a new five-year review calling for more resources to address the critically declining population of marine mammals, now estimated at about 450.

The review found that right whale recovery efforts have not improved since the last five-year review was completed in 2012. Collisions with cargo ships, entanglement in commercial fishing gear and a variety of environmental stressors including noise pollution are among the key threats to whale survival.

“In many ways, progress toward right whale recovery has regressed,” the report said, citing numerous scientific studies. “The population has been declining since 2010 and has exhibited changes in habitat use. During this period, right whale calving rates have remained below average and body condition of the population has worsened.”

The discovery of the dead whale on Nashawena, one of the Elizabeth Islands, was announced Monday by the International Fund for Animal Welfare,which has been working with federal fisheries officials to address what it called the alarming number of right whale deaths in 2017.

A team of scientists was on the scene this week to take pictures and conduct tests on the carcass, but no cause of death has been identified.

“It’s very decomposed and we may never get an answer but we hope to get some more information with the testing,” said Jennifer Goebel, regional public affairs officer with the National Fisheries Science Center, part of NOAA, which is working alongside the animal welfare group.

The 16 North Atlantic right whales confirmed dead represent about three per cent of the remaining population of the species. Four of the 16 were found in U.S. waters, including one found in August in Edgartown Great Pond. That whale is believed to have died from entanglement in fishing gear.

The five-year review issued by the fisheries service recommends focusing additional resources on understanding the threats facing the species and determining the best ways to mitigate them.