Water Quality Issues

Scientists from the Northwest Atlantic Seal Research Consortium are using data collected by the Massachusetts Department of Public Health (MDPH) to investigate whether seals may impact beach water quality along Outer Cape Cod.

A growing population of gray seals has been cited as the reason for beach closures due to poor water quality on the outer Cape.  But is there evidence to support these water quality statements?

The study focused on beaches around three seal “haul-outs” on the lower Cape where large numbers of gray seals leave the water at low tide to avoid predators, regulate their body temperature, and socialize. Sites in the area include High Head on the outer Cape in the National Seashore/Truro area; Jeremy Point on the Cape Cod Bay side of Wellfleet; and North Island in Chatham. (NMFS/USFWS Permit No. 932-1905-00/MA-009526)

Lower Cape Water Quality

Researchers examined ten years of water quality data collected by the Massachusetts Department of Public Health, focusing on 89 sites at public beaches in six towns surrounding the large, seal haul-out areas on Cape Cod. Bathing beach water quality is highly variable from year to year, but overall, the study found no change in the trend of water quality exceedances for Lower Cape Cod region. (Courtesy Rebecca Gast, Woods Hole Oceanographic Institution)

Water Quality Near Seal Haul-Outs

Researchers divided the beaches in the lower Cape region into those within 5 miles of seal haul-outs, and those more than 5 miles from seal haul-outs. This distance was thought to be a reasonable distance for the dispersion and inactivation of fecal indicator bacteria (FIB) on a daily tidal schedule. Analysis found that the beaches near the haul-outs actually showed a decreasing trend in yearly FIB exceedance events over the last decade, while the beaches away from seal haul-outs showed an increasing trend. (Courtesy Rebecca Gast, Woods Hole Oceanographic Institution)

Last updated: September 20, 2018