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Why Are Blue Whales So Gigantic? A Summary

· whales,ocean,summary,science

This is a summary of the Why Are Blue Whales So Gigantic? article from Scientific American.

The sheer size of whales leaves even modern scientists in awe. Why are whales the largest animals to have ever lived? Only since the end of the last century have we known enough to explain why.

Whales' size has been linked to their diet and their evolution happening concurrently with a generalized increase in food-rich water upwelling. The first to evolve, baleen whales consume plankton by filter-feeding. Rorquals, a subsequent evolution, feed on krill and large schools of small fish and do so by lunge feeding. The mechanics of this different type of prey favors bigger mouths. The sudden increase in ocean upwelling gave larger whales plenty of small prey to eat during their evolution, favoring their growth.

What about the blue whale? Why is this type of rorqual twice as massive as the next biggest sea mammal? Evolutionary ecology will be useful to answer this question, since species must be studied within the context of their environment.


When rorquals first developed lunge feeding, competition with other sea predators was fierce. Specialization allowed the rorqual to target schooling fish and plankton, among all swarming prey.


Blue whales are the most specialized of rorquals, eating only krill for the most part. Krill abunding only in specific places at specific times, blue whales had to develop extreme long-range mobility and large energy reserves to travel between pockets of food. Large, hydrodynamic bodies allowed them to do exactly that. The downside was a loss of maneuverability. The blue whales's larger mouth, which comes with their larger body, is their asset for catching krill fast enough, since its evolution made it less maneuverable than other whales.


Ecological specialization has its downsides: fragility. Paradoxically enough, the solution to this is even more specialization.


Blue whales lost maneuverability for long-distance efficiency. This is an obstacle to chasing alternative prey, because their evolution left them less adapted to its chasing than other species of rorquals are, confining them to krill. Largeness allows a larger mouth, but also requires more food, and large pockets of food are more rare, which requires more travel, which requires a bigger body with bigger energy reserves, which requires even more krill. As the species evolve, blue whales become more fragile.


So it is this cycle of specialization that made the blue whale the biggest animal to ever live.


In light of its past specialization, what does the blue whale's future look like?


Commercial whaling decimated the population to 0.1 percent of its original size. Blue whales face increasing obstacles such as phytoplankton and krill decline caused by human activity. Being specialists, not generalists, blue whales cannot easily adapt to other prey, even when their food of choice becomes scarce.


Ultimately, what will happen to the blue whale depends on us.

Photo credit: Hari Nandakumar

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