Researchers at James Cook University have found that epaulette sharks, also known as walking sharks, lay eggs without any measurable rise in energy use, defying expectations for reproductive costs. The study tracked metabolism, blood, and hormones throughout the sharks' reproductive cycle, revealing remarkable stability. This efficiency could indicate resilience in changing ocean conditions.
Epaulette sharks have surprised scientists by reproducing with no detectable increase in metabolic demands, according to a new study from James Cook University in Australia. Led by Professor Jodie Rummer, the research team examined the physiological costs of egg-laying in these small, bottom-dwelling sharks, which are nicknamed walking sharks for their ability to move across shallow reef flats using their pectoral fins.
The findings, published in Biology Open in 2025, mark the first direct measurement of metabolic costs during shark reproduction. "Reproduction is the ultimate investment … you are literally building new life from scratch," Prof Rummer explained. Yet, contrary to assumptions that egg production would spike energy needs, the sharks maintained flat oxygen uptake rates—a key indicator of metabolism—throughout the process.
Five female epaulette sharks (Hemiscyllium ocellatum) were monitored in temperature-controlled tanks at JCU's Marine and Aquaculture Research Facility in Townsville. These sharks typically lay two eggs every three weeks, with peak activity from September to December. The team measured oxygen consumption, blood chemistry, and hormone levels before, during, and after egg case formation. Lead author Dr. Carolyn Wheeler, a recent JCU PhD graduate, noted, "Everything was remarkably stable, so this research challenges our fundamental assumptions about chondrichthyan fishes (sharks, rays, skates and chimaeras)."
Prof Rummer highlighted the implications for environmental stress: "These sharks appear to have adapted their physiology to be able to optimize their energy use." Under pressures like warming oceans, many species trade off survival for reproduction, but epaulette sharks may persist in egg production. Dr. Wheeler added, "Under environmental stress many species will choose between survival and reproduction, but the epaulette shark might be able to continue to produce eggs, even under such stressors. That's encouraging, because healthy sharks equal healthy reefs."
This resilience suggests epaulette sharks have evolved efficient systems not previously observed in oviparous species, potentially buffering reef ecosystems against climate change.