January 13, 2015

How large are the ocean’s biggest whales, squids and turtles?

How long are the tentacles of the largest jellyfish and how big are the ocean’s famed whales?

It turns out it’s difficult to get exact measurements of many of the world’s largest marine megafauna, for the reasons one might expect: many of these animals are few in number, tricky to find and logistically hard to measure or weigh. We know surprisingly little about the maximum sizes these species can reach, though popular culture might say otherwise.

Now, a team of undergraduate students and scientists, including a researcher from the University of Washington, has analyzed the body sizes for 25 marine species, including whales, sharks, leatherback turtles, squids and even giant clams. The project gets at both the challenges of arriving at exact measurements and our human bias toward larger animals.

“Several years ago I noticed that people kept saying that giant squids reached 60 feet in length, which is amazingly long,” said Craig McClain, assistant director of the National Evolutionary Synthesis Center in Durham, North Carolina, and editor of the blog Deep Sea News. “When I started actually looking at the data, I found that that estimate was actually quite unrealistic.”

McClain, lead author on a paper published this week in the journal PeerJ, recruited graduate and undergraduate students from around the country to join the project and choose marine species to study ranging from well-known behemoths like the great white shark, giant octopus and walrus to more obscure creatures such as the giant tube worm and the colossal squid. They created a blog, The Story of Size, for students to share updates and impressions on their findings.

The goal was to get accurate size measurements for the largest known marine species in each taxon and use that information to build equations to help researchers estimate total length and weight of other species. Understanding how large an animal can get and the variation within a species is important for knowing how to conserve these animals and their habitat, researchers said.

“This is the first time anyone has tried to compile anything like this and will set to rest a whole lot of myths about the size of the largest specimens of all kinds of animals,” said co-author Trevor Branch, a UW assistant professor of aquatic and fishery sciences and @TrevorABranch on Twitter. “It’s a massive piece of work, compiling the data.”

Branch got involved when he found the students’ tweets about their project, then commented on their blue whale blog posts. He pointed them toward a helpful database, and helped analyze the data and interpret the results for the whale species.

The paper’s authors contacted marine centers and other scientists, and scoured the available literature and data to find measurements for the species studied in this paper. They said it wasn’t always easy to get data from their sources, and the team hopes its work will help shift the attitude toward open access in a more favorable direction.

Despite challenges, McClain is pleased with his team’s results, which he thinks will slowly replace the erroneous measurements found in academic papers, fishery databases and textbooks.

“Precise, accurate, and quantified measurements matter at both a philosophical and pragmatic level,” McClain said. “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.”

This research was funded by the National Science Foundation and the National Evolutionary Synthesis Center.

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This post was adapted from a National Evolutionary Synthesis Center news release.