Miami, Mar 3 (IANS): Thousands of migrating blacktip sharks are gathering off the South Florida coast, as they do every year, but scientists have warned that their numbers were shrinking.

Aerial photos of the sharks offshore published on Friday were enough to make beachgoers think twice, reports Efe news.

Experts at the Florida Atlantic University (FAU) have cautioned people planning to enter the water that the sharks are likely to come within 60 ft of the shoreline.

The images show the cean filled with black dots in certain areas, although photos from previous years taken in the same place show larger shark populations.

According to FAU professor Stephen Kajiura, who has studied these migrations for years, it used to be possible to spot more than 15,000 blacktip sharks in one area but that figure has now dropped.

Kajiura's team has manually counted some 100,000 blacktips.

Blacktip sharks along the US East Coast migrate south during winter toward warmer waters, extending from North Carolina to South Florida.