Sharks may be closer to the city than you think, new study finds
The world’s coastlines are rapidly urbanizing, but how this increased human presence might affect ocean-dwelling species isn’t entirely clear. In a new study led by scientists from the University of Miami’s (UM) Rosenstiel School of Marine and Atmospheric Science, researchers tracked the movements of three shark species, the bull, nurse and great hammerhead shark, in relation to the city of Miami. . Given the chemical, light and sound pollution emanating from the coastal metropolis, researchers expected sharks to avoid areas close to the city, but that’s not what they found.
Some animals, such as pigeons and raccoons, thrive in cities. Known as “urban exploiters,” these species often become dependent on human waste for food. Other animals, known as “urban adaptors,” may show some use of urban areas, but still rely largely on natural areas. On the other hand, some species, such as land predators like wolves, are very sensitive to human disturbance. These ‘city avoiders’ avoid big cities.
“Few studies have examined ocean predator movements in relation to urbanization, but since other studies have shown that land predators are urban avoiders, we expected sharks to be too,” said Neil Hammerschlag, director of UM Shark Research and Conservation Program and lead author of the study. “We were surprised to find that the sharks we tracked spent so much time near the lights and sounds of the busy city, often close to shore, regardless of the time of day.” The researchers concluded that the behavior of the sharks being monitored resembled that of “urban adapters”. The study speculates that sharks may be attracted to shore by land-based activities, such as discarding fish carcasses.
The relatively high use of urban areas by the tracked sharks may affect both sharks and humans. “Spending so much time close to shore, sharks are at risk of being exposed to toxic pollutants and fishing, which can affect their health and survival,” Hammerschlag says. While shark bites in humans are rare, the study also points to areas close to shore that could be avoided by human water users to reduce the chance of a negative shark encounter, promoting human-shark coexistence.
The study, titled “Urban Sharks: Residency patterns of marine top predators in relation to a coast metropolis” was published June 16, 2022 in the journal Marine Ecology Progress Series†
The authors of the study are: Neil Hammerschlag, Mitchell Rider of the UM Rosenstiel School and Robbie Roemer of Ocearch; Austin J. Gallagher from Beneath the Waves; and Lee Gutowsky of Trent University.
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N Hammerschlag et al, Urban sharks: residence patterns of marine apex predators in relation to a coastal metropolis, Marine Ecology Progress Series (2022). DOI: 10.3354/meps14086
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