Walking sharks break the rules of reproduction

Scientists at James Cook University have found that epaulette sharks reproduce and lay eggs without any measurable increase in energy use. The research tracked metabolic rates, blood chemistry, and hormone levels through the full reproductive cycle and found all measures remained stable. Researchers had expected egg production to raise energy demands significantly. The study was led by Professor Jodie Rummer and published in Biology Open. It monitored five female sharks before, during, and after egg case formation. The animals were kept in temperature controlled tanks at the Marine and Aquaculture Research Facility Unit in Townsville. Oxygen uptake rates served as the proxy for metabolic rate. Lead author Dr. Carolyn Wheeler reported that blood and hormone levels stayed remarkably stable. The results challenge assumptions about the high energy cost of reproduction in chondrichthyan fishes. Epaulette sharks typically produce two eggs every three weeks, mostly between September and December. Professor Rummer said the sharks appear to have adapted their physiology to optimize energy use during this process. The findings indicate these sharks may sustain reproduction even under environmental stress.