Palm Beach County, United States – Each winter, thousands of blacktip sharks migrate to the shallow, clear waters off South Florida, but recent research highlights a growing challenge: murky conditions caused by beach nourishment projects.

In northern Palm Beach County, annual beach nourishment adds sand to widen beaches, protect shorelines, and provide habitat. However, repeated projects create prolonged turbidity, or cloudy water, which can persist longer in areas with silts and clays.

Florida Atlantic University researchers tracked turbidity events and shark behavior along both nourished and natural beaches during the 2020 and 2021 seasons. They combined low-flying aerial surveys capturing over 10,000 images with underwater cameras to monitor shark presence and fish diversity.

The study found thousands of blacktip sharks closely hug the coastline within about 50 meters of shore, where prey is concentrated. Sustained turbidity could interfere with hunting and increase accidental encounters with humans.

“What’s striking is how closely the distribution of blacktip sharks overlaps with areas impacted by turbidity events,” said Stephen Kajiura, Ph.D., co-author. “Because these sharks rely on clear water to visually hunt, sustained reductions in visibility can change where they go, how successfully they feed, and how they interact with their environment. It also has implications for people, since these sharks are present in large numbers right where we swim.”

Researchers documented 24 sediment plumes over two years, some stretching nearly 15 kilometers alongshore and over 250 meters offshore. These plumes coincide with peak shark activity, highlighting the ecological tradeoffs of coastal engineering projects.

“Beach nourishment is a critical tool for combating erosion, but in some cases it may come with tradeoffs that we’re only beginning to fully quantify,” said Tiffany Roberts Briggs, Ph.D., co-author.

The study calls for improved monitoring and refined sediment management to balance coastal protection with marine ecosystem health.

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