Nurse Sharks With Remarkably Slow Metabolism Are a Sluggish Success

Rather than exerting a lot of energy like their great white relatives, nurse sharks kick back and relax under rocks. As it turns out, nurse sharks actually have the lowest metabolic rate measured in any shark, according to a recent study from the Mote Marine Laboratory in Florida. An apparent lack of enthusiasm should not be short-changed, though. Researchers say this lackadaisical behavior has helped the species survive for 1,000 years.  

"If we know about a shark's metabolism -- their basic energy needs -- then we can start to estimate their energy use in the wild to better understand their impact on the ecosystem," Dr. Nick Whitney, manager of the Behavioral Ecology and Physiology Program at Mote, explained in a news release. "Sharks are often the top predators in the food web, consuming a lot of calories from animals on lower levels. As such, they often have a larger impact on the balance of the ecosystem than other species. To better understand the ecosystems that we want to preserve, we need to better understand sharks."

While some large sharks, such as the mako shark, are high-powered swimmers that chase swift prey and eat plenty to replenish their energy, nurse sharks favor slow or unwary prey that they can suck out of small crevices -- such as lobsters, conchs or resting reef fish.

Furthermore, nurse sharks can pump water across their gills while lying on the bottom, which allows for low-energy loitering instead of constant swimming - a rather uncommon trait among sharks.

Throughout the course of their study, which lasted from September 2014 to May 2015, researchers monitored nurse sharks in a tank with a sealed plastic lid, thus ensuring the amount of oxygen would decrease in a measurable way as the nurse sharks breathed.

To assess their metabolic rate, researchers measured how much oxygen the nurse sharks consumed at rest, compared to when they were swimming at a specific distance and speed.

"Overall, nurse sharks have a very low metabolic rate; they don't move much, and when they do move, it's a lot of work," Whitney added. "With this low metabolism, they probably don't need to consume a lot of calories in order to maintain themselves. So their impact on the ecosystem could be less than you'd expect from other large predators. If they had a higher metabolic rate, like a mako shark, you'd expect their impact to be greater."

Their findings were recently published in the Journal of Experimental Marine Biology and Ecology.

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