Why are right whales in the North Atlantic smaller now than they were 40 years ago?

Right whales in the North Atlantic appear to be shrinking: they are around a meter shorter today than they were in the 1980s. And some whales are up to three meters shorter than their forefathers. To put this in context, some 10-year-old whales are only developing to the size of a one- or two-year-old whale from 40 years ago.

A recent study that looked over decades of data came to this conclusion. It's just another setback for an endangered species that are already struggling to live. Despite attempts by both the Canadian and American governments, the whales, which presently number less than 400, die each year after becoming entangled in fishing gear or being hit by ships.

"I was surprised," said Joshua Stewart, a research associate at the National Oceanographic and Atmospheric Administration and the study's main author on the publication, which was published in the peer-reviewed journal Current Biology. Field biologists would photograph what they assumed was a one-year-old calf based on its size, only to discover later that the whale was actually five to ten years old. This sparked Stewart's interest in the subject.

Stewart gathered as much data on whale size as he could with the support of other academics and biologists dating back to the early 1980s. "Data was acquired before I was born," he stated from Mexico, where he is currently employed. The researchers compared decades-old aerial pictures from planes to more contemporary aerial images from drones for the study. Field scientists' detailed notes and measurements from the 1980s were also vital to their work.

The big difference became apparent after the study was concluded. Whales are being entangled in fishing nets."We discovered that whales with long-term entanglements, which can last months or years, had stunted growth compared to whales who aren't entangled," Stewart said. At some time during their lives, most North Atlantic right whales become entangled in fishing nets and traps. "Over 85% of the population has entanglement injuries, either scars or attached gear, so it's a really chronic concern for this group," said Amy Knowlton, a senior scientist at the Anderson Cabot Center for Ocean Life in Cambridge, Massachusetts.

After years of documenting whale entanglements, Knowlton donated the entanglement data for the study. A whale's body is severely damaged by getting caught in nets and lines, and it frequently dies as a result. According to Stewart, other whale species that are frequently trapped are likely to be shrinking as well. However, because North Atlantic right whales have been on the verge of extinction for so long, they're one of the only animals with such a comprehensive data set that researchers can use to prove it.

It's not just the mature whales caught in fishing gear who are shrinking. According to the research, whale calves with entangled mothers are more likely to be stunted. This is due to the fact that moms who are caught in gear are simultaneously trying to make milk and nourish their children. Trying to stay alive consumes energy that could otherwise be used to produce milk.

According to Knowlton, using weaker fishing ropes would give whales a better opportunity of escaping. Better yet, eliminating ropes entirely and replacing them with ropeless traps would prevent whales from being ensnared in the first place. Both scientists believe that if the whales are given an opportunity to recuperate, the species will return to its former size.

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