Not the right size

For centuries the worldwide population of North Atlantic right whales has been shrinking. Now, scientists say the whale itself is getting smaller.

In a report published June 3 in Current Biology, researchers with the National Oceanic and Atmospheric Administration and other research institutions said the subspecies of right whale is now on average three feet shorter than they were two decades ago. The shrinking makes right whales more susceptible to injury from fishing lines and has scientists worried about the survival of the once-plentiful species. North Atlantic right whales now rank as one of the world’s most endangered species.

“This isn’t about ‘short’ right whales, it’s about a physical manifestation of a physiological problem, it’s the chest pain before the heart attack,” said Whale and Dolphin Conservation North America director Regina Asmutis-Silvia. Though she was not part of the study, Asmutis-Silvia warned that unless greater conservation efforts are taken, the North Atlantic right whale could be on a collision course with extinction.

Commercial whaling devastated the global population of right whales during the 18th and 19th centuries. According to study co-author and New England Aquarium senior scientist Amy Knowlton, today there are only 356 known right whales left in the North Atlantic. A 1930s international ban on taking the animals helped slow the decline, but poaching and entanglements with commercial fishing equipment have kept the whale’s numbers down.

Scientists collected data by taking pictures of right whales from a drone over Cape Cod Bay from 2016 to 2019 and comparing them to similar images collected from 2000 to 2002. By using identifying features on the whales’ backs, the team could typically individually identify the animals to check their age. In all, the team photographed 129 separate whales representing more than a quarter of the worldwide population of North Atlantic right whales.

According to the researchers, the measurements indicate the current average North Atlantic right whale measures 43 feet long, down from an average of 46 feet from the 2000-2002 sample. The scientists attribute the shortening of the species to injuries to juveniles that get caught in modern fishing lines.

Those entanglements pose a growing threat to the species, according to the study’s authors. Whales that get tangled in nets and lines in their youth and survive fail to grow to full size. And those same smaller whales are more susceptible to injury or death from entanglements than adults. Researchers also noted that whales with stunted growth tend to reproduce less than unaffected whales. “Over 83 percent now of the species has been entangled at least once in their lifetime, some as many as eight times,” Knowlton said. “If it doesn’t kill them, it’s certainly going to affect their ability to reproduce.”