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Atlantic right whale with part of a fishing net: "Changes in body size can be an indicator of the collapse of an entire population"
Photo:
Florida Fish and Wildlife Conservation Commission / AP
According to the lexicon, the Atlantic right whale can in special cases be up to 18 meters tall.
According to a new study, the entry should be revised in the near future.
As researchers led by Joshua Stewart from the US climate agency Noaa have now found out, the animals have shrunk significantly in recent years.
The right whale species from the North Atlantic is about one meter shorter today than it was 40 years ago, and on average they are now more than 13 meters long.
The marine mammals are also becoming less massive.
This corresponds to an average loss of length of around seven percent in this relatively short period of time, the scientists report in the journal Current Biology.
Some animals that were measured for the study were even three meters shorter, but these are outliers, it is said.
For more than 20 years, the researchers measured almost 130 whales, some several times.
For this purpose, the team used recordings from drones but also photos taken from airplanes.
Animals of all ages were measured - from one year to almost 40 years.
A computer program then compared old and new recordings of animals of similar age.
Scientists can differentiate between the individual whales based on typical patterns on their bodies, which is why the northern right whales are considered to be one of the best-studied whale species, although only a few hundred animals remain and the population has continued to decline since 2010.
From the point of view of the researchers, there is a clear reason for the physical decline of the northern right whales (Eubalaena glacialis) swimming near the coast, which were already badly decimated by whaling in historical times: The whales are repeatedly caught in fishing nets that are in so-called ghost nets, or they are injured by collisions with ships.
A good dozen of the whales photographed even had nets hanging around their bodies.
More than 80 percent of the whales get tangled
How much the animals are affected by the nets and are under stress becomes clear when one looks at the periods of time during which they tried to get rid of the braided ropes. Some struggled with it for a good two months, others for almost a year. As a result, the animals lack the resources they would normally need to gain weight and length. In addition, there is also a lack of energy that has to be used for reproduction. Therefore, the researchers fear that they have not only observed a short-term effect, but that it is a long-term effect that is reflected in reproduction. "Changes in body size can be an indicator of the collapse of an entire population," the study says.
Over 80 percent of whales get tangled in nets at least once in their lifetime.
In addition, the range of the animals has shifted in recent years.
In ancient times they even lived in the western part of the Mediterranean, later in the eastern Atlantic.
But now the animals go hunting for plankton mainly off the east coast of the USA and Mexico.
"We know that climate change has affected some of their main prey sources, so the tangled whales are likely to be exposed to a triple exposure," said Boris Worm, a marine biologist at Dalhousie University, who was not involved in the study, of the Associated Press.
According to the researchers, very simple measures could help the animals, for example if ropes with a lower breaking strength were used for nets or if fishing boats reduced their speed.
Such regulations are urgently needed to ensure the survival of the whales.
It would be even better if the nets didn't get into the oceans in the first place.
Because it is possible that the northern right whales are not alone affected.
Other species are likely to disappear as well.
We only know about the problems of whales because the animals, which swim at a speed of around eight kilometers per hour, can be used as a study object with relatively little effort.
joe