NECN reports that east-facing beaches in Chatham, Massachusetts have been closed to swimming due to shark sightings and “increased activity.” A large number of grey seals (Halichoerus grypus) are currently in the waters of the beaches affected by the closures. The grey seal is a natural prey item for great white sharks (Carcharodon carcharias), which migrate to the waters of Cape Cod in the summer months.

The beach closures were announced just before the Labor Day holiday weekend, which is one of last big beach weekends of the summer for vacationers in the area.