It has been a long-standing irony in the animal world. The largest animals to ever live on Earth, which are the size of Boeing 737s, sustain themselves by eating small fry like zooplankton or krill. Scientists have discovered that the giant mammals eat tiny creatures by the thousands, filtering huge amounts of seawater and gulping them down.
A new study published in Nature today has shown that the world's baleens consume three times as much krill, small fish, and animal plankton per year than previously thought. On a single feeding day, some marine mammals can eat up to a third their huge body weight. Whales produce more poop than they eat, which is a crucial fertilizer in the marine food chain. The study shows that today's declining populations and their correspondingly low poop production might be the key to why some of the world's marine ecosystems are only a shadow or a fraction of their former glory.
Because underwater feeding is difficult to observe, researchers had difficulty estimating how much a whale of 30 to 100 feet ate. Based on computer models of whale metabolisms and stomach examinations, previous estimates indicated that whales could eat as much as 5% of their body weight per day. The new study tracked hundreds of baleen whales and found that they can consume between 5 to 30% of their body weight per day.
For example, a North Pacific blue whale consumes 16 tons of shrimp-like crustaceans and krill on a single feeding day during the foraging period. That's roughly the same weight as a bus. North Atlantic right whales consume 5 and 6 tons, respectively, of small zooplankton.
You might believe that whales would make it more difficult to live in the oceans, as they eat small sea creatures in large numbers. Scientists believe that the reverse may be true. Scientists believe that the greater the amount of krill whales consume, the more species are found in certain parts of the oceans. This is because whales eat more krill, and their poop releases nutrients such as iron into the ocean water, fertilizing the growth of phytoplankton which, in turn, serves as a primary food source for the marine food web. How can you make phytoplankton grow better? They are just plants so fertilize them," co-author Matthew S. Savoca of Stanford University, an ecologist at Hopkins Marine Station. How do you fertilize plants in open ocean? This is exactly what whales do.
Savoca, along with colleagues including Nicholas Pyenson (curator of fossil marine mammals at Smithsonian’s National Museum of Natural History), measured the feeding habits of 321 individual baleens from seven species between 2010-2019. Information on three important aspects of feeding was merged using technology, creativity, and hard work. Based on the size of the whale's mouth, and the amount of food available in each swarm, scientists determined how often it ate and how much.
Savoca compares the high-resolution tags to "whale iphones", and suction cups to animals. These devices had GPS to track location and accelerometers to measure feeding movements such as distinctive lunges. The tags allowed the team to track where and when whales were eating, which was confirmed by video cameras attached to the devices.
Also, drones were flown over 105 whales by the team. They measured the whale's size, as well as its mouth size. This data was used to determine how much ocean water each whale could filter and what food it could eat.
The third piece of information was vital--a measure of how much food is actually in each mouthful. Scientists fed whales from small boats equipped with fisheries audio devices. These sent out pulses and used them to calculate the density of prey swarms. Savoca says that echolocation is similar to how toothed and sperm whales find food.
"So, we know from the tag how often the whale eats per hour or daily, we can estimate the size of the whale’s mouth using the overhead drone images and we also have an approximate density of the krill-swarm the whale is eating on these sonar type technologies."
Researchers found that the blue, fin and humpback whaling populations between British Columbia and Mexico consume an estimated six millions metric tons of food annually.
Joe Roman, a University of Vermont conservation biologist who was not part of the research, said that "the results of this study suggest the influence of whales upon marine ecosystems might have been greater than we thought." This study provides a better understanding of what was happening at the population and ecosystem levels.
Whalers killed three million whales in the 20th century. This was a devastating impact on the ocean ecosystem that scientists still don't fully understand. According to new research, the whales in the Southern Ocean ate an estimated 430 million tons of Antarctic Krill per year before the whaling era. This is a lot of poop. All of the krill in the Southern Ocean now only make up about half that amount.
It's now a degraded ecosystem due to the large areas of old whale feeding grounds in the open ocean. It's almost like a semi-arid, tropical land environment that was once a rainforest," said Victor Smetacek (a German plankton ecologist at the Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research), who wasn't involved in the research.
There are far fewer whales today, which means that their huge appetites have likely been greatly reduced in ocean ecosystems. Whaling records indicate that approximately one million krill-destroying whales were killed off in the Southern Ocean. Today, however, the number of Southern Ocean krill is much lower than it was in the pre-whaling period. It was described as a color change in the surface waters due to its abundance. Scientists believe that iron-rich whale poop could explain the 'krill paradox.
Victor Smetacek explains that "Krill" is a huge iron reservoir. "The whales tapped it, and every year, let's just say one-fourth, it goes into phytoplankton. The krill then pick it up [by eating phytoplankton] again and the whales eat it." In this unique relationship, blue whales and the krill complement each other. This is why the krill population has plummeted since the whales were killed. Victor says they need each other."
Industrialized whaling used steam power, harpoon guns, radio, aircraft spotter, onboard processing, and other advanced technologies to be frighteningly efficient. In the 50- to 60 year span of the 20th century one blue whale was killed. This is a staggering figure.
While countries like Norway, Japan, and Iceland continue to whale today, other nations subscribe to the International Whaling Commission ban to help recover global populations. Humans are trying to protect whales against other causes of death, such as entanglement in fishing gear or shipping collisions.
Savoca points out that although we don't know all the effects of bringing back whales, and we also haven't identified all of the consequences of losing them. However, this study provides another piece of evidence that shows that regions like the Southern Ocean, only a few hundred year ago, were richer than we are today.
He says, "We can rebuild that system and whales play a key role in that." There is a lot of evidence to show that more whales will result in more productivity, more fish and more krill. However, whether we see this for hundreds of years into the future depends on what choices we make over the next few decades.