How does the rapid urbanization that is taking place on the coasts of the world affect aquatic animals? This is one of the questions that a team of scientists led by researchers from the Rosenstiel School of Marine and Atmospheric Sciences at the University of Miami (UM) has tried to answer. To do this, the researchers followed the movements of three shark species: 13 specimens of the bull shark ( Carcharhinus leucas ), 15 of the nurse shark ( Ginglymostoma cirratum ) and 14 of the great hammerhead shark ( Sphyrna mokarran ) with respect to the city of Miami. Scientists thought, at first, that the animals would avoid approaching the city given the chemical, light and noise pollution that emanates from the city. What happened was just the opposite.
There are animals that thrive in cities. These species are called urban exploitative species and often feed on human waste. Examples of them are raccoons and pigeons. Urban adapter species are those that, although they use urbanized areas, continue to depend mostly on natural areas. Finally, there are the urban avoidant species, which are those that are very sensitive to human disturbances such as terrestrial predators and therefore avoid cities. It would be the case of the wolves.
“Few studies have investigated the movements of oceanic predators in relation to urbanization, but as other studies have shown that land-based predators avoid cities, we expected that sharks would as well,” said Neil Hammerschlag, director of the Research and Development Program. UM Shark Conservancy and lead author of the study. “We were surprised to find that the sharks we tracked spent so much time close to the lights and sounds of the busy city, often close to shore , regardless of the time of day.” The researchers concluded that the behaviors of the tracked sharks resembled those of urban adapters. The study hypothesizes that sharks could be attracted to the coast as a result of discarding (returning live or dead fish to the sea that are commercially uninteresting in capturing) that is done in fishing.
The relatively high use of urban areas by tracked sharks may have consequences for both sharks and humans. “By spending so much time close to shore, sharks are at risk of exposure to toxic pollutants and fishing , which could affect their health and survival,” says Hammerschlag. Although it is rare for a shark to bite a human, the study points out the areas near the coast that bathers should avoid to reduce the probability of having a scare, thus promoting peaceful coexistence between people and sharks.
The study, titled Urban sharks: residence patterns of marine top predators in relation to a coastal metropolis , was published June 16 in the journal Marine Ecology Progress Series .
Referencia: Hammerschlag N, Gutowsky LFG, Rider MJ, Roemer R, Gallagher AJ (2022) Urban sharks: residency patterns of marine top predators in relation to a coastal metropolis. Mar Ecol Prog Ser 691:1-17. https://doi.org/10.3354/meps14086
