What do you do when a 45 ton animal keeps stealing your catch? This is the problem facing many fishermen in Alaska, as sperm whales continue swiping the fish off their lines faster than the men can haul them in. A current study has suggested that recently rebounded populations of once endangered species, such as various whales, are creating an urgent new challenge of how to manage them.

“Most people support the idea of saving endangered species,” says Joe Roman, lead author of the study published in Trends in Ecology and Evolution. “But when native species return, it can be a struggle for communities. After generations away, these forgotten species can suddenly be seen as newcomers—or even pests.”

The researchers, from the University of Vermont, mainly looked at the population data for marine mammals, and found that of the 87 species of whales, dolphins and porpoises (cetaceans) investigated, 22 are recovering. This might sound encouraging, but they also note that 45 of the species couldn’t be evaluated as there isn't sufficient data available on their numbers.

But they do highlight some pretty major conservation success stories. Great whales, for example, have benefitted massively from the (almost) worldwide ban on hunting. The number of Australian humpback whales crashed to around 1,600 individuals in the 1960s, but after whaling was outlawed their numbers rocketed up to more than 40,000.

And it’s not just the whales that are doing well. The northern elephant seal was reduced to only a few dozen creatures as people prized them for their oil and museums for their collections, but now there are an incredible 200,000 of the animals bobbing in the ocean off the western coast of America, and it’s a similar story for the sea otter.

The return of the brown bear to much of Europe is giving many policy makers a headache in how to deal with their rising numbers. Credit: Erik Mandre/shutterstock

But with such great success, often comes conflict. “The takeaways here are that conservation clearly can work, which is important to celebrate given the trend of declining global biodiversity,” said Roman. “But wildlife managers need to do a better job of planning for the return of these species to avoid future conflicts.”

The epitome of this conflict is the return of wolves and bears to the forests of Europe. Hailed as a major triumph by biologists, and despite the animals being native to the area, farmers of the region are a little less enthusiastic about the predators roaming the countryside. How this is going to resolve itself is anyone's guess, but as their numbers keep climbing it looks like Europe’s forests will continue to echo with the howl of the wolf for a while longer at least.   

The researchers lay out four recommendations in order to help policy makers try and avoid such situations in the future. These include planning ahead, delisting species that no longer require protection so that efforts can be focused on those that need more help, reassessing how to deal with ‘problem’ animals and sharing successes with the public to try and get them involved and invested.

As for the sperm whales in Alaska, the fishermen have enlisted the help of scientists to try and evade the pesky cetaceans. By tagging the main offenders, known locally as the “bad boys,” the fishermen hope to simply avoid the leviathan thieves and thus the conflict that comes with their swelling numbers.