Why North Atlantic right whales are smaller now than they were 40 years ago
Decades of data shows today's average whale is a metre shorter than it was in the 1980s
North Atlantic right whales seem to be shrinking: They are an average of a metre shorter today than whales of the same species were in the 1980s.
And some whales are as much as three metres smaller than their predecessors.
To put that into perspective, some of today's 10-year-old whales are only growing the size of a one- or two-year-old whale from 40 years ago.
That's the finding of a recent study looking at several decades of data. It's another blow to the endangered species, which has struggled to survive. The whales, which currently number less than 400, are dying after being trapped in fishing gear or hit by ships each year, despite efforts by both Canadian and American government interventions.
"I was pretty shocked," said Joshua Stewart, a research associate with the National Oceanographic and Atmospheric Administration and the study's lead author on the paper, which appears in Current Biology, a peer-reviewed journal.
Stewart started looking into the topic when field biologists would photograph what they thought was a one-year-old calf based on its size, only to realize later the whale was actually five to 10 years old.
WATCH | Why the right whale population is declining:
With the help of various other researchers and biologists, Stewart amassed as much data as he could on the size of the whales dating back to the early 80s.
"The data was being collected before I was even born," he said from Mexico, where he's currently working.
For the study, the researchers compared decades-old aerial shots from planes to more recent shots from drones. Detailed field biologists' notes and measurements dating back to the 80's also proved crucial to their work.
When the research was completed, the size difference became clear.
The likely culprit? Whales are getting caught in fishing gear.
"The big thing that we found were that whales that have these extended entanglements that last for months or years are stunted compared to whales that aren't entangled," said Stewart.
Most North Atlantic right whales become trapped in fishing nets and traps at some point in their lives.
"Over 85 per cent of the population has entanglement injuries, either scars or attached gear, so it's a pretty chronic problem for this population," said Amy Knowlton, co-author of the paper and a senior scientist with the Anderson Cabot Center for Ocean Life based in Cambridge, Mass.
Knowlton contributed the entanglement data for the study after spending years documenting whale entanglements.
The toll being caught in nets and lines is extremely damaging to a whale's body and often leads to its death.
"You could sort of imagine like if we were to strap a sandbag to you and you had to drag that around for a few months or a year," said Stewart. "You're going to have a lot less energy to devote to other things, especially if you're still growing. You might end up stunted just because you're burning so much energy dragging that sandbag around."
Stewart says there's a good chance other whale species that are often ensnared are experiencing a similar decrease in size. But as North Atlantic right whales have been on the brink of extinction for so long, they're one of the few species with such a detailed data set dating back decades that researchers can use to prove it.
It's not just the mature whales caught in gear that are getting smaller.
Whale calves whose mothers are entangled are also more likely to be stunted according to the study.
That's because mothers caught in gear are also trying to produce milk and feed their young. Spending energy on trying to survive takes away from energy that would otherwise be spent producing milk.
"For a female with severe injuries there would also be the energy she's needing to heal from those injuries and that's diverting energy away from nursing her calf so that she can try and heal and survive," said Knowlton.
Using weaker ropes for fishing would give whales a better chance at freeing themselves according to Knowlton. Better yet getting rid of ropes altogether, using ropeless traps, would prevent whales from getting caught in the first place.
Both scientists believe that if the whales given the chance to recover the species would eventually return to its normal size.
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