Human activity has “broken” one of the fundamental laws of nature

In 1972, scientists discovered that ocean life followed an unchanging mathematical rule: the smaller an organism, the more abundant it is in the ocean. the krill for example is a billion times smaller than the tuna, but it is a billion times more abundant. And this rule is incredibly precise: Analyzing water samples taken from the Atlantic and the Pacific, Ray Sheldon, a oceanologist of Bedford Institute of Oceanography in Canada, found that for every size slice of plankton, you get exactly the same biomass. In a liter of water for example, you will have mass a third of plankton between 1 and 10 micrometers in diameter, a third of plankton between 10 and 100 micrometers and a third between 100 micrometers and 1 millimeter. The concentration is variable depending on the depth (there is less than biomass in deep water), but the proportions remain unchanged.

A valid rule from bacteria to whales

It turns out that this rule is repeated for all marine animals, from the simplest bacteria to whales. In 2019, a Russian researcher even discovered that it applied to organisms present in the soil. Many hypotheses have been put forward to explain this phenomenon, such as the metabolism, the speed consumption of food and reproduction or death rate, all correlated with the size of living organisms.

This natural harmony is however in the process of being upset, warns Eric Galbraith, professor at McGill University in Montreal (Canada) today. Co-author of a study published in November in Advances Sciences, the scientist argues that this rule is no longer respected for very large animals. ” Human impacts appear to have dramatically truncated the top third of the spectrum », He explains. Researchers have estimated for the first time the size distribution of the biomass of 12 major groups of marine organisms at around 33,000 points in the global ocean. They then reconstructed this same data with what it was before the start of the peach industrial in 1850. And the observation is clear: if the famous distribution rule remains valid for the great majority of cases, it seems to have broken in large fish and mammals. ” The biomass of fish over 10 grams and marine mammals has been reduced by around 2 gigatons since 1850, a 60% reduction, and the largest size classes appear to have experienced a nearly 90% reduction in biomass since 1800 », Decrypts the researcher. And the culprit is all found: the overfishing and the whaling.

Man, a predator unlike any other

” Humans are now the main predator of theecosystem marine, after extracting most of the predatory fish and mammals that previously occupied the upper beaches of the spectrum of size. This begs the question: are humans playing the same role today that the predators we have eliminated previously played? Are we now acting as a functionally equivalent predator? The answer is clearly no », Says Eric Galbraith. It suffices, moreover, to compare the biomass human to that of the large fish and mammals that humans have eliminated only to find that it remains ridiculously small.

The BOFFFF, the first victims of overfishing

The problem is that fishing primarily targets the most valuable and easy-to-find sea creatures, which scientists call BOFFFF (Big, old, fat, fecund, female, fish – either big, old, fat, of fertile age, female and fish). This preference completely destabilizes the natural balance, since it prevents cash to reproduce properly. In general, we also observe that large animals are more affected by human activities than small ones, in particular because they are more sensitive to changes in the ecosystem. It is no coincidence that the mammoths and the megafauna prehistoric have now disappeared.

The good news is that while humans are wiping out species at an accelerated rate, they also have the power to protect them. In his last report on the red list of threatened species, the International Union for the Conservation of Nature (IUCN) noted that four of the seven most fished tuna species are in the process of recovery, thanks to the establishment of quotas. The bison population is starting to increase again in Europe and around ten species of birds have been lifted from the critically endangered category. An effort that remains, however, a drop in the ocean.

Large marine animals victims of the sixth mass extinction

Article by Marie-Celine Ray published on 09/15/2016

Human activities are at the origin of the sixth mass extinction of species on Earth and, in the oceans, large animals (sharks, whales, tuna …) are paying the heaviest price. An unprecedented situation that could have long-term consequences.

In a new study to appear in Science, Jonathan Payne (Stanford University) and his colleagues analyzed the link between the risk of extinction and the characteristics of marine animals, whether they are mollusks or from vertebrates. They compared the last 500 years to the previous 445 million years.

The authors found an unprecedented phenomenon: today, large organisms are more likely to disappear than smaller ones. Thus, when the mass of the animal increases by a factor of 10, the risk of extinction climbs by a factor of 13, which the scientist summarizes by: “The bigger you are, the more likely you are to become extinct. “ The sixth mass extinction would therefore particularly affect large marine animals such as the great White shark, the blue whale, or the Red tuna.

The overfishing is clearly questioned because humans tend to prefer large animals for their consumption. This extinction big ones Marine animals could have significant consequences for ocean ecosystems. This is why the researcher calls for collective responsibility: “There is little we can do to quickly reverse the trends of ocean warming or theocean acidification, which are the two real threats that need to be addressed. But we can change the treaties about how we hunt and fish. The populations of Pisces also have the potential to recover much faster than the weather or the chemistry oceans. We can turn this around relatively quickly with appropriate management decisions nationally and internationally. “