Florida Beach Nourishment May Threaten Local Shark Populations ... And Us

While beach nourishment can serve coastal communities by creating a barrage against erosion and storm damage, they can also cause sand to shift, pile up, and appear in unintended places. Further, a new study published in the Journal of Coastal Research puts forth that they may be impacting the feeding activities of coastal sharks—namely, blacktips.

The study, led by Florida Atlantic University (FAU) researchers and titled “Effect of Beach Nourishment–Driven Turbidity on Water Quality and Blacktip Shark Aggregations,” notes that, based on 10,000 aerial photos of the Palm Beach area taken during and after beach nourishment, the waters tend to get pretty churned up, expectedly.

“Beach nourishment is a critical tool for combating erosion and protecting infrastructure, 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, chair and associate professor of geosciences in FAU’s Charles E. Schmidt College of Science.

Not discounting dredging the benefits of dredging altogether, Briggs adds, “These projects involve dredging and placing large volumes of sediment onto the beach, and what we observed was turbidity in the adjacent nearshore on a scale that exceeded what’s typically described in the literature—with plumes stretching for kilometers and persisting across the exact time and space where marine species are most active. That tells us we need to take a closer look at how the entire process of beach nourishment may be influencing marine habitat.”

At the center of the study’s concerns? Blacktip sharks. The murky waters left behind become the stuff of nightmares not just for surf-bathing folk in sharky waters, but perhaps the sharks themselves.

The blacktip shark (Carcharhinus limbatus) is a smaller, coastal species of shark that tends to travel and hunt in large numbers along the shoreline. When their hunting grounds become turbid (murky), their success rates can plummet.

So, too, can their discernment, which could mean a big uh oh for anybody and everybody with flesh and blood in the water.

Again, blacktips tend on the smaller side to feast on smaller fishes, so the dangers of them setting their maws on humans are (relatively) limited. That said, it’s far from unheard of, and while not one of the “big three” (great white sharks, tiger sharks, bull sharks) known to bite humans for one reason or another, blacktips do fall within the top-ten list. Fomenting more doom is the statistic that the beaches of Palm Beach County consistently tally some of the highest numbers of reported shark attacks annually. (It currently ranks third in the United States per the Florida Museum of Natural History).

Of course, that all has to be taken with a grain of salt and a sidecar of Twainian humor: “There are,” after all “three kinds of lies: lies, damned lies, and statistics.”

Keeping your head about you (and not in a shark’s gullet) is a game of luck, to be sure, but it often relies on a bit of sensibility, too. Avoiding the surf when sharks are particularly present and turbidity is high goes a long way.

Regarding the blacktips’ part in all this, they tend to be most active along Palm Beach between February and March, per FAU. When they do mistake—or resort to—humans for foodstuffs, it tends to be among moments of frenzied feasting, when their discernment can become compromised—and who can fault them for that?

The blacktip is, after all, the real casualty at hand. Blacktips migrate to the area to feed during the winter months, precisely when the replenishment projects take place in the off season.

The aerial photography, captured between 2020 and 2021, showed plumes stretching for nearly 10 miles and extending more than 800 feet offshore. “That tells us we need to take a closer look at how the entire process of beach nourishment may be influencing marine habitat,” posits Briggs.

The tampering with the blacktips’ feeding grounds leaves Briggs and the study’s other authors concerned about the potentially greater ecological impacts along the US’ East Coast at large, which may also affect not just feeding but aggregation and migration of a keystone species.

In the meantime, mind your fingers and toes in murky surf as ever and always.