Why Whales Echolocate: Size Matters When Sensing in the Ocean

Why do whales use echolocation when bacteria do not? Now, scientists have announced that body size determines available sensing modes.

Size is key when it comes to characterizing biological processes in marine environments, such as metabolic rates, feeding and mating strategies of animals. Surviving in a watery world, though, means that organisms need to have a way to collect information from their surroundings through various senses. These senses can be smell, touch, vision, hearing and echolocation among others.

In nature, the smallest organisms, like bacteria, depend heavily on chemical signals. Larger animals, like copepods, sense flows through their sense of touch. Larger organisms, such as fish and crustaceans, rely on sight. Even large animals, such as whales, rely on echolocation.

"When confronted with the diversity of marine life it seems plausible to ask: Why don't bacteria have eyes? Or why do fish not echolocate?" said Erik A. Martens, one of the researchers, in a news release. "We wanted to see if we could find and understand a pattern on the grounds of physiology and physics, which are the two basic constraints on the workings of any organism."

In this latest study, the researchers analyzed the underwater physics of various sensory organs, including smelling, touch, vision, hearing, and echolocation. They determined the limits of body size where the sense can and cannot function.

So what did they find? Size matters a lot when it comes to how animals sense their environment in the ocean.

"It all comes down to physics and physiology," said Navish Wadhwa, co-author of the new study, in a news release. "Although many of our theoretical models are only rough estimates, they work surprisingly well in capturing the reality of nature. That knowledge may help towards developing better ecological models of the marine environment."

The findings are published in the journal Proceedings of the Royal Society B: Biological Sciences.

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