Urban Light Pollution Disrupts Shark Night Hormones

First-ever measurements of melatonin in wild sharks show artificial light from coastal cities can disrupt nighttime hormone levels.

Feb. 4, 2026 at 2:31am

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A new study published in Science of the Total Environment found that sharks living in brightly lit coastal waters near large urban areas had altered melatonin levels at night compared to sharks living in darker, less developed environments. The findings reveal that artificial light at night, an often-overlooked form of pollution, can influence marine predators and may have broader implications for ocean ecosystems.

Why it matters

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. The study suggests that exposure to artificial light at night can suppress melatonin levels in wild sharks, which could have cascading effects throughout the marine food web.

The details

Researchers at the University of Miami Rosenstiel School conducted nighttime fieldwork off Miami, Florida and compared sharks sampled in urban waters with individuals from nearby, darker coastal areas. They 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. The results showed that nurse sharks exposed to higher levels of artificial light at night had significantly lower melatonin concentrations than nurse sharks sampled in darker environments, while melatonin levels in blacktip sharks did not differ between brightly lit and darker areas.

  • The study was published on January 20, 2026 in the journal Science of the Total Environment.
  • The researchers conducted the study over roughly one year, capturing sharks at night using short-duration research drumlines.

The players

Abigail M. Tinari

The lead author of the study who conducted the research for her master's thesis at the Rosenstiel School.

M. Danielle McDonald

A co-author of the study and a professor in the Department of Marine Biology and Ecology and Director of the Glassell Family Center for Marine Biomedicine at the Rosenstiel School.

Neil Hammerschlag

The senior author of the study who contributed to the research while at the Rosenstiel School.

University of Miami Rosenstiel School of Marine, Atmospheric and Earth Science

The institution where the research was conducted.

Shark Research and Conservation Program

The program at the University of Miami Rosenstiel School that conducted the research.

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What they’re saying

“These findings suggest that exposure to artificial light at night can suppress melatonin levels in wild sharks, but vulnerability depends on behavior. Species that are highly resident in light-polluted areas appear more susceptible than species that regularly move between illuminated and darker habitats.”

— Abigail Tinari, Lead author of the study (Science of the Total Environment)

“The first sharks started roaming the Earth's oceans 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.”

— Danielle McDonald, Co-author of the study and professor at the Rosenstiel School (Science of the Total Environment)

“Sharks play a key role in maintaining balanced marine ecosystems, and physiological changes in top predators could have cascading effects throughout the food web. Our findings highlight light pollution as a meaningful environmental stressor that warrants consideration alongside more widely recognized threats such as habitat loss and chemical pollution.”

— Neil Hammerschlag, Senior author of the study (Science of the Total Environment)

What’s next

Researchers plan to continue monitoring shark melatonin levels in urban and non-urban environments to better understand the long-term impacts of light pollution on shark health and behavior.

The takeaway

This study provides the first evidence that artificial light at night can disrupt the natural hormone cycles of sharks, a finding that could have significant implications for the health and balance of marine ecosystems. As coastal development continues to expand, understanding and mitigating the effects of light pollution on top predators like sharks will be crucial for preserving the delicate balance of ocean life.