Whales in the North Atlantic are shrinking in size, researchers have found, with entanglements in fishing gear blamed for the steady decline in the length of the animals over recent generations.
On average, a right whale born today is expected to reach a total length about a meter shorter than one born 40 years ago, according to the new study. This is an average decline in length of about 7% during this period.
North Atlantic right whales are now typically less bulky, as well as shorter, than they once were, with some individuals experiencing extreme diminishment from previous norms. “There are some outliers that are around 3 meters shorter, which was really striking to see,” said Joshua Stewart, a marine researcher at the National Oceanic and Atmospheric Administration (Noaa).
“I saw pictures of 10-year-old whales that are the size of two-year-old whales, which was shocking. These are really short, stunted whales,” Stewart added.
Stewart, along with colleagues from Noaa, the New England Aquarium, Oregon State University and Woods Hole Oceanographic Institution, used a wealth of aerial images taken of whales from crewed aircraft and remote drones over the past 20 years to assess the lengths of the right whales.
The researchers were able to closely track the growth of individual whales by identifying them from distinctive patterns on their heads. North Atlantic right whales are some of the most closely studied whales in the world, with only about 400 of the cetaceans left in the wild.
published in Current Biology, suggests that the whales are suffering long-term intergenerational damage from being snared in fishing nets and lines set to catch other species. The fishing gear saps the strength of the whales, preventing them from using their energy to pile on weight and length. The whales are also at risk of being hit by ships in busy North Atlantic shipping routes.
“If you are dragging around fishing gear you have less energy for growth, it’s a pretty clear mechanism,” said Stewart, “If I strapped a sandbag on to you and asked you to walk around a lot, you’d get skinny pretty quickly. For whales, this also means they may also produce smaller calves that have lower survival probabilities. We are seeing a long-term decline in their size.”
The species gets its name as it was the “right whale” to target for whalers due to their slow speeds and penchant for casually feeding upon plankton at the ocean surface. The whale hunts may have now ended but the whales are suffering from other manmade threats in the Atlantic, such as ship strikes and entanglements, while the heating-up of the ocean is making their prey harder to find.
the International Union for the Conservation of Nature announced the species was just one step from extinction, shifting its classification from “endangered” to “critically endangered”. According to the IUCN, of the 30 deaths or serious injuries to North Atlantic right whales recorded between 2012 and 2016, 26 were caused by fishing gear entanglement.
The fishing industry has raised concerns over the cost of upgrading gear to avoid right whale entanglements but scientists say immediate action is required to avoid the species being completely wiped out.
“Implementing proven solutions such as reduced vessel speeds, lower breaking strength ropes and ropeless fishing gear more broadly throughout their range are critical and urgent steps needed to stave off the extinction of this species,” said Amy Knowlton, a co-author of the new study and a scientist at the New England Aquarium in Boston.