The ocean's mammals are at a crucial crossroads, with some at risk of extinction and others showing signs of recovery, a new review by an international team of marine researchers has found.
The research team, led by the University of Exeter and including scientists from Griffith University and more than 30 other institutions in 13 countries, reviewed the status of the 126 marine mammal species finding that accidental capture by fisheries (bycatch), climate change and pollution are the key drivers of decline.
"Marine mammals such as whales, dolphins, seals, sea lions, manatees, dugongs, sea otters and a host of others, play essential ecological roles in aquatic ecosystems," said Associate Professor Susan Bengtson Nash from the Centre for Planetary Health and Food Security.
"They are key to community structure and function and can be indicators of ecosystem health.
"To continue the successful recovery of some marine mammal species and reverse the downward trajectories of others at-risk, we evaluated the threats they face and the conservation mechanisms available to address them, including Marine Protected Areas (MPAs), bycatch reduction methods and community engagement."
A quarter of these species are now at risk of extinction being classified as vulnerable, endangered or critically endangered on the IUCN Red List, with the near-extinct vaquita porpoise and the critically endangered North Atlantic right whale among those in greatest danger.
"We have reached a critical point in terms of marine mammal conservation," said lead author Dr Sarah Nelms, of the Centre for Ecology and Conservation, University of Exeter.
"Very few marine mammal species have been driven to extinction in modern times, but human activities are putting many of them under increasing pressure."
The researchers say 21% of marine mammal species are listed as "data deficient" in the IUCN Red List - meaning not enough is known to assess their conservation status.
This lack of knowledge makes it difficult to identify which species are in need of protection and what actions should be taken to save them.
"Chemical pollution and the associated toxic effects is one area that remains particularly poorly understood," Associate Professor Bengtson Nash said.
"The diversity and amount of chemicals present in the natural environment cause both planetary health and direct toxicological impacts to marine mammals.
"The presence of chemicals can alter food webs and prey availability for marine mammals, and can directly affect the animal's health by various mechanisms including suppression of the immune system or interference with normal endocrine (hormonal) function."
In addition to building an understanding of the threats ocean mammals face, this research helps reverse the downward trend in at-risk species by identifying knowledge gaps in marine mammal research and highlighting research and conservation priorities in urgent need of focus.
