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

North Atlantic right whales seem to be shrinking: They are an average of a metre shorter today than whales of thesame species were in the 1980s.

And some whales are as much as threemetressmaller 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'sthe findingof a recent study looking at several decades of data. It's another blow to the endangered species, which hasstruggled to survive. The whales, which currently number less than 400,aredying 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 theNational Oceanographicand Atmospheric Administration and the study's lead author on the paper, which appearsin Current Biology, a peer-reviewed journal.

Stewart started lookinginto 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 wasactuallyfive to 10 years old.

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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 compareddecades-oldaerialshots from planes to more recent shots from drones. Detailed field biologists' notes and measurements dating back to the 80'salso proved crucial to their work.

When the research wascompleted,the size difference became clear.

The likely culprit? Whales are getting caught in fishing gear.

"Thebig thingthat we foundwere that whales thathave these extended entanglementsthat last for monthsor yearsarestuntedcompared 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 centof 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 Centerfor 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 linesis extremely damaging to a whale's body and often leads to its death.

"You could sort of imaginelike 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 upstuntedjust becauseyou're burning so much energy dragging that sandbag around."

Stewart saysthere'sa good chance other whale species that are oftenensnaredare experiencing a similar decrease in size. But as North Atlantic right whales have been on the brink of extinction for solong, they'reone of the few species with such a detailed data setdating back decades that researchers can use to prove it.

It'snot just the mature whales caught in gear that are getting smaller.

Whale calves whose mothers are entangled are also more likely to bestuntedaccording to the study.

That'sbecausemothers caught in gear are also trying to produce milk and feed their young. Spending energy on trying to survive takes away from energy that wouldotherwise be spent producing milk.

"For a female with severe injuries there would also be the energy she's needing to heal from those injuriesand 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, usingropelesstraps, 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 toitsnormal size.