How Big Are The Largest Marine Animals?

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Lisa Winter

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573 How Big Are The Largest Marine Animals?
Matthew Maxwell and Pablo Alvarez Vinagre at StudioAM

Comparing the size of large marine animals to everyday objects, such as a school bus, is meant to make it easier to imagine the size of these massive creatures. Unfortunately, this has led to exaggerations and misconceptions about the animal’s true size. In an effort to reign in reality, a team of researchers has analyzed the legitimate sizes of 25 large marine animals. Craig McClain of the National Evolutionary Synthesis Center in North Carolina is lead author on the paper, which was published in the journal PeerJ.

"Several years ago I noticed that people kept staying that giant squids reached 60 feet in length, which is amazingly long," McClain said in a press release. "When I started actually looking at the data, I found that that estimate was actually quite unrealistic.”


Much of the confusion about the length of giant squids stemmed from analysis of specimens that had washed onto beaches during the 1800s. The problem was that by the time the squids got to the beach, they had already begun to decompose. This caused the muscle fibers to break down and stretch out, making them seem much longer than their living counterparts actually are. Unfortunately, living specimens are so rarely seen that it was difficult to reconcile those findings with reality. McClain’s team found that the true length of a giant squid is right around 12 meters (39.4 feet). 



A human is included in each column for size comparison. Click to view the image larger. Image credit: Matthew Maxwell and Pablo Alvarez Vinagre at StudioAM

The researchers obtained their data from a variety of sources, including scientific literature, speaking with experts, and analyzing specimens in museums and private collections. McClain enlisted the help of students at Duke University, who reached out to other scientists, engaged others in social media, and pored over data sets.


All of the data was tracked using a website developed by the team, which was also used to connect with other scientists and the public. This database revealed that even though certain species may be capable of growing to extreme lengths, not all of them do. Just as humans can grow to a variety of heights—with outliers on either end—the same is true for marine fauna. 

McClain’s team also explored how these species came to grow to such a tremendous size. After all, it takes a considerable amount of food to sustain such a large creature, and tough times could make it more difficult to obtain enough food. Some of the species have adapted interesting ways of getting around this. While giant clams gain extra energy through symbiotic relationships with algae and photosynthetic bacteria, whales have enough fat stored up to allow them to travel greater distances in search of food.

"Metabolism is a function of size because it indicates how much oxygen and carbon an animal consumes," McClain explained. "Knowing whether a whale shark is 10 tons, 15 tons, or 20 tons lets us know how many light bulbs worth of energy it uses every day.”

While this paper does a fantastic job of analyzing what science knows about the true sizes of these large marine animals, there is still room for continued improvement. Gaps in the scientific literature and lack of cooperation among some institutions to provide access to data have hindered the team. Additionally, changing ecosystems due to climate change, pollution, and overfishing have reduced the maximum size for some of these species; a trend that is likely to continue. 


Even so, the team hopes to continue adding to their findings in order to correct understandings of the size of these animals.

"Precise, accurate, and quantified measurements matter at both a philosophical and pragmatic level," McClain concluded. "Saying something is approximately 'this big,' while holding your arms out won't cut it, nor will inflating how large some of these animals are.”


  • tag
  • misconceptions,

  • size,

  • marine animals,

  • giant squids