Walking Sharks Defy Reproductive Expectations

New research from James Cook University (JCU) has revealed that epaulette sharks — often called “walking sharks” — can reproduce and lay eggs without any measurable increase in energy use, challenging long-held assumptions about animal biology.

The study, published in Biology Open, was led by JCU’s shark physiology research team under Professor Jodie Rummer and focused on the metabolic costs of reproduction in epaulette sharks.

“Reproduction is the ultimate investment … you are literally building new life from scratch,” Prof Rummer said.

“We expected that when sharks make this complex egg, their energy use would shoot up. But there was no uptick in energy use, it was completely flat.”

While reproduction is typically considered a high-energy process, this is the first time researchers have directly measured the metabolic cost of egg laying in sharks. The findings suggest epaulette sharks have evolved a unique physiological efficiency.

“These sharks appear to have adapted their physiology to be able to optimise their energy use,” Prof Rummer said.

“This work challenges the narrative that when things go wrong — such as warming oceans — that reproduction will be the first thing to go.”

Epaulette sharks usually produce two eggs every three weeks, with peak laying occurring between September and December. The research team monitored five female sharks before, during and after egg encapsulation in temperature-controlled tanks at JCU’s Marine and Aquaculture Research Facility in Townsville.

Lead author and recent JCU PhD graduate Dr Carolyn Wheeler said oxygen uptake, blood chemistry and hormone levels remained stable throughout the process.

“Under environmental stress many species will choose between survival and reproduction, but the epaulette shark might be able to continue to produce eggs,” Dr Wheeler said.

“That’s encouraging, because healthy sharks equal healthy reefs.”

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