The team studied two shark species with contrasting movement patterns: nurse sharks, which are relatively less mobile and tend to remain in the same areas for long periods; and blacktip sharks, which are highly mobile and regularly move across broad coastal regions.<\/p>\n
The results showed a clear species-specific response. Nurse sharks exposed to higher levels of artificial light at night had significantly lower melatonin concentrations than nurse sharks sampled in darker environments. In contrast, melatonin levels in blacktip sharks did not differ between brightly lit and darker areas.<\/p>\n
\u201cThese findings suggest that exposure to artificial light at night can suppress melatonin levels in wild sharks, but vulnerability depends on behavior,\u201d said Abigail Tinari, the lead author of the study who conducted the research for her master\u2019s thesis at the Rosenstiel School. \u201cSpecies that are highly resident in light-polluted areas appear more susceptible than species that regularly move between illuminated and darker habitats.\u201d<\/p>\n
Melatonin plays an important role in regulating daily biological rhythms and is linked to overall health and physiological functioning across many animals. Disruptions to this hormone have been associated with sleep and metabolic disturbances in humans and terrestrial wildlife, but its role in sharks has remained largely unexplored.<\/p>\n
\u201cThe first sharks started roaming the Earth’s waters more than 400 million years ago. That this study suggests sharks might respond like humans emphasizes the fundamental importance of this process, because it is highly conserved over evolutionary time,\u201d said Danielle McDonald<\/a>, a co-author of the study and a professor in the Department of Marine Biology and Ecology<\/a> and Director of the Glassell Family Center for Marine Biomedicine<\/a> at the Rosenstiel School. \u00a0<\/p>\n \u201cIt also reinforces concerns doctors have about LED lighting, screens, and urban light pollution as contributors to illness and chronic disease,\u201d McDonald said. \u201cFurthermore, researchers might now look to other aspects of shark melatonin physiology to explore if there are differences in their melatonin receptors that may inform new therapies or targets for drug development for melatonin-related disorders.”<\/p>\n The study represents the first assessment of blood melatonin levels ever reported in sharks, establishing baseline values for both nurse and blacktip sharks. These baseline data provide a critical foundation for future monitoring and for comparing how different shark species respond to increasing coastal development.<\/p>\n Researchers conducted the study over roughly one year, capturing sharks at night using short-duration research drumlines designed to minimize stress. Blood samples were collected immediately and analyzed for melatonin levels. The team also measured environmental variables such as light intensity, water depth, and temperature, allowing them to directly link urban light exposure with physiological changes. Nighttime sampling was conducted using low-impact red lighting to avoid interfering with sharks\u2019 natural light perception.<\/p>\n \u201cSharks play a key role in maintaining balanced marine ecosystems, and physiological changes in top predators could have cascading effects throughout the food web,\u201d added Neil Hammerschlag, the senior author of the study who contributed to the research while at the Rosenstiel School. \u00a0\u201cOur findings highlight light pollution as a meaningful environmental stressor that warrants consideration alongside more widely recognized threats such as habitat loss and chemical pollution.\u201d <\/p>\n
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