March 25 (UPI) -- After decades of decline, many marine mammal populations have seen the numbers increase in recent years. Unfortunately, many others remain vulnerable to extinction.
According to a new survey, published Thursday in the journal Endangered Species Research, Earth's marine mammal species are at a crossroads.
Scientists analyzed dozens of studies and population surveys of Earth's 126 marine mammal species -- including whales, dolphins, seals, sea lions, manatees, dugongs, sea otters and polar bears.
Of the surveyed species, researchers found a quarter are a risk of extinction, classified as either vulnerable, endangered or critically endangered on the Red List of Threatened Species put out by the International Union for Conservation of Nature.
Of the most threatened species, the future of the vaquita porpoise is the most precarious. There are only a few dozen vaquita porpoises in the world, all of them in the Gulf of California.
The North Atlantic right whale is nearly as imperiled, with just a few hundred estimated to be still living in the ocean.
In a glimmer of hope, however, scientists observed a mini baby boom in 2019, spotting a few right whale calves swimming with their mothers off the coast of Massachusetts.
Other species are faring considerably better than the vaquita porpoise and right whale -- the northern elephant seal, humpback whale and Guadalupe fur seal have all responded positively to conservation efforts.
Scientists said they hope a close examination of successful conservation projects will offer insights that can aid the protection of other vulnerable marine mammals.
"Very few marine mammal species have been driven to extinction in modern times, but human activities are putting many of them under increasing pressure," lead study author Sarah Nelms said in a press release.
"Our paper examines a range of conservation measures -- including Marine Protected Areas, bycatch reduction methods and community engagement -- as well as highlighting some of the species that are in urgent need of focus," said Nelms, researcher with the Center for Ecology and Conservation at the University of Exeter.
The conservation status of more than 20 percent of the surveyed marine mammal species remains a mystery, researchers said.
And they simply don't have enough quality information to make a determination for these "data deficient" species.
"To continue conservation successes and reverse the downward trend in at-risk species, we need to understand the threats they face and the conservation measures that could help," said study co-author Brendan Godley.
"Technology such as drone and satellite imaging, electronic tags and molecular techniques are among the tools that will help us do this. Additionally, sharing best practice will empower us -- and this is why we are so proud to be part of such a large and international group for this project," said Godley, professor and head of the Exeter Marine research group.