Endangered Whales’ Baby Bust Is Linked to Fishing Gear Entanglement

Researchers think injuries North Atlantic right whales suffer from fishing lines could be responsible for a 40 percent drop in their birthrate.
Researchers conducting photo identification of North Atlantic right whales. (Photo: Getty Images)
Sep 6, 2016· 2 MIN READ
David Kirby has been a professional journalist for 25 years. His third book, Death at Seaworld, was published in 2012.

Is the endangered North Atlantic right whale on the road to recovery or isn’t it?

A new paper suggests that deaths from fishing gear entanglement and a 40 percent drop in the birthrate over the past five years have contributed to the population’s sluggish growth and increased its “vulnerability to extinction.”

Even more ominously, the entanglements and low birthrate may be related.

That gloomy assessment follows a more upbeat statement from the National Oceanic and Atmospheric Administration in January that said, “We’re making significant progress in reversing the population decline of the species, and are seeing signs of recovery.”

But the whales “are not yet a conservation success story,” researchers wrote in a paper published in the recent issue of Frontiers in Marine Science.

“Right whales need immediate and significant management intervention to reduce mortalities and injuries from fishing gear,” the paper’s authors wrote, “and managers need a better understanding about the causes of reduced calving rates before this species can be considered on the road to recovery.”

The whales were listed as endangered in 1973 under the U.S. Endangered Species Act. They were near extinction in 1935, when hunting them was banned, and they rebounded to about 295 animals by 1992.

By 2010, there were an estimated 500 whales, a growth rate of about 2.8 percent a year—encouraging but far below the estimated rate of 6 to 7 percent among right whale populations in other regions.

One likely reason: fishing gear.

“Despite a nearly 20-year U.S. federal effort to reduce accidental kills of whales in fishing gear, sub-lethal and lethal entanglement rates have increased,” the authors wrote.

Entanglement rates have been fairly steady in recent years, with 15.5 percent of the animals on average showing new scars each year. But the rate of serious entanglements is increasing, and so is the total percentage of right whales killed.

Between 1970 and 2009, forty-four percent of diagnosed right whale deaths were caused by ship strikes, while 35 percent were from entanglements.

RELATED: An Unlikely Alliance Forms to Save Whales From Deadly Entanglements

In 2008, new vessel speed restrictions were placed in areas whales frequent, and ship-strike deaths dropped dramatically, to just 15 percent between 2010 and 2015. Entanglement deaths spiked to 85 percent, even though total annual mortality from human activity, about 4.3 deaths, remained unchanged.

“That may be an underestimate,” said Scott Kraus, the paper’s lead author and vice president of the Anderson Cabot Center for Ocean Life at the New England Aquarium. “We don’t see bodies that often on the beach. They die offshore and disappear.”

When right whales go missing, they are not counted as dead for six years, making recent mortality rates impossible to calculate, Kraus said.

There are at least two possible reasons why severe and potentially lethal entanglements are becoming more common.

Record warm temperatures in the Gulf of Maine may have changed migration patterns of prey fish, causing the whales to travel more to find food.

“The more you travel, the more you increase the risk of entanglement,” Kraus said. “There are also probably more encounters with offshore gear, which tends to be heavier and uses more heavy ropes, so the injury rate is going up.”

The ropes have also become stronger. In the 1990s, manufacturers introduced “poly-steel” rope that is much harder to break. “By the early 2000s, we started seeing more severe entanglements and more mortality,” Kraus said.

The New England Aquarium is working to develop ropes that break away when they entangle whales.

Then there’s the birthrate, which has fallen by about 40 percent since 2010, Kraus and his colleagues estimate. No one is sure why, but again, fishing gear might be involved.

“Imagine a whale with rope around its tail for a few weeks or months with cuts six centimeters deep,” he said. “Now it has to recover and devote metabolic resources to do so, and it may have been unable to travel and feed and isn’t putting on enough fat. That actually interferes with reproduction in females.”

Dispersed prey and reproductive diseases are other possible explanations, he said.

Kraus said NOAA has not taken into account the low birthrate data, which he hopes will be published this year.

“NOAA has ignored it because it’s not in the peer-reviewed literature, so we decided to publish it so it would be out there,” he said.

NOAA Fisheries said in a statement that the agency shared the researchers’ concerns: “We look forward to working with them and others to better understand right whale status and the factors that may be holding back recovery.”