Whales eat about three times more than previously estimated. This is the conclusion reached by a team of scientists led by Matthew Savoca from Stanford University. An adult blue whale devours about 16 tons of krill per day, a North Atlantic right whale about five tons of small zooplankton daily and a bowhead whale about six tons. This is reported by Savoca and colleagues in the journal »Nature«.
The huge appetite of marine mammals has consequences for the ecosystem in which they live: Because they fertilize the native surface through their faeces, they create the conditions in which they find sufficient food. In particular, the lack of availability of iron limits the productivity of marine ecosystems. The whales, on the other hand, are eliminated the absorbed iron on the water surface and thus prevent it from sinking into the deep sea. In this way you recycled the nutrient.
Until now, researchers had estimated the food requirements of baleen whales using indirect methods, such as analyses of stomach contents. Savoca and his team have now equipped a total of 321 whales with measuring devices between 2010 and 2019. The transmitters gave them information not only about the whereabouts of the animals, but also about their swimming and feeding movements, cameras provided images of the environment. Again and again, the whale researchers moved out in small boats to visit the places where their tagged animals had just eaten. There they then determined how much krill and microorganisms were present in one cubic meter of water. From the combination of all data, the scientists finally calculated how many tons of food the whales actually ingest.
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Thanks to their results, previous estimates of the impact of marine mammals on the environment are outdated. In 2008, it was calculated that the whales living along the North American Pacific coast consume around two million tons of fish, krill, zooplankton and squid per year. In the light of the new data, a different value is calculated: According to this, each of the three populations of blue, fin and humpback whales alone needs two million tons per year.
The results also allow far -reaching conclusions to be drawn about the conditions in the oceans before the emergence of industrial whaling in the 20th century. Based on the historically transmitted inventory data for whales in the South Pole Army, it can be converted that mink, humpback, blue and fin whales eat around 430 million tons of krill there each year. This corresponds approximately double the total amount of krill, which are currently occurring there. The scientists attribute this immense krilling of back then to the role of whales as nutrient recyclers, which at the time die ten times as much iron into the water as today: around 12,000 tons. When they were shot down, her prey, the krill, also lacked the livelihood.
The ecosystem in the sea functions as extremely important carbon sinks: dying plankton and other small creatures drop into the deep sea, where the carbon that they have absorbed on the water surface when growing is included. The more productive the ecosystem, the more carbon is withdrawn from the atmosphere. If the whale populations recover, they could increase the productivity of their waters by around eleven percent and bind an additional 215 million tons of carbon, the scientists calculate.
