Recovery of whales in danger hindered by humans long after the hunt

When a North Atlantic Right Whale, an endangered woman, spends months, or even years, unraveling discarded fishing nets, there is not much energy left to mate and nurse.

According to a study released Wednesday, the recovery of majestic marine mammals has been seriously hampered by the management of such debris, ship collisions and other forms of human encroachment.

The northern whale population, which once had tens of thousands of individuals – rising to around 450 today – has been slowly increasing since 1990, but has again begun to decline towards 2010.

If the Canadian and American waters they had crossed during this quarter century had been immaculate and free from human trafficking, "the number of species would be almost double what it is now, and their current situation would not be so bad, "according to scientists reported by Peter Corkeron of NOAA Northeastern Fisheries Science Center in Massachusetts.

Specifically, there would be twice as many female whales: "The overall slope of the recovery trajectory depends on female mortality," they added.

Between 1970 and 2009, 80% of the 122 known North Atlantic right whale deaths were caused by objects or activities of human origin.

The species has not been hunted for more than half a century.

Sister species

But beyond the number of whales killed, there was the question of whether the population of the species could have been reduced more subtly by people.

To find out, Corkeron compared birth rates to the southern right whale, a sister species in the southern hemisphere – estimated at around 15,000 – that is doing much better and is much less exposed to harmful human emissions.

The data collected over the last three decades have made it possible to count the number of new calves born in different subpopulations of the two poles.

Northern and southern whales have long been considered as a single species until genetic analysis shows the opposite.

As it was suspected, the three groups of whales in the south – off the coast of eastern South America, southern Africa and southwestern Australia – produced twice as many offspring. faster than their northern relative.

The study found that the poor health of females and their pups was further evidence of the negative impact on the North Atlantic environment.

"Ghost nets"

"Female baleen whales that give up breeding because of poor body condition are well established," said the authors.

What caused the lacerations, the reduction in body weight and the apparent reluctance to mate?

The most likely culprits are the "ghost nets", tentacles of fishing gear often made of synthetic fibers as strong as durable, concluded the study.

It is known that more than 80% of all right whales in the North Atlantic have been entangled at least once in an abandoned net, and more than half have gone twice or more.

"The entanglements can last from several months to several years and recovery can take a similar time," wrote the authors. Royal Society Open Science.

For southern whales, the problem is non-existent.

Formerly numbered in the hundreds of thousands, right whales that moved slowly – migrating along the coast – were both easy prey and preferred prey of whalers until the twentieth century.

The species can reach 20 meters (65 feet) and weigh 100 tons, more than a commercial jet at full load.

They are also docile and full of the fat from which whale oil was made.

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More information:
The recovery of the North Atlantic right whale, Eubalaena glacialis, has been hampered by human-caused mortality, Royal Society Open Science, rsos.royalsocietypublishing.or … /10.1098/rsos.180892