Rainy weather pushing jellyfish south in Chesapeake Bay

One byproduct of the rainy weather over the past month is that jellyfish, the bothersome stinging creatures found in the middle Chesapeake Bay this time of year, are being pushed southward and upriver in bay tributaries.

In recent years, we have seen the opposite -- jellyfish making their way up into the Baltimore harbor as summer drought has increased salinity in the bay. The creatures known as Chrysaora quinquecirrha can only survive in water measuring 10-16 practical salinity units, said Raleigh Hood, a professor with the University of Maryland Center for Environmental Science.


Those levels are pushing farther south than usual. Nearly 8 inches of rain fell in June, the wettest for that month since record-setting June 1972. More rain was expected Wednesday.

A jellyfish forecasting model run by the National Oceanic and Atmospheric Administration's Chesapeake Bay office predicts high probabilities of sea nettles between the Bay Bridge and the Patuxent River, particularly in some of the Eastern Shore tributaries along that span.


But Hood said it's likely the model isn't taking into account the recent rainfall, instead showing a more typical jellyfish distribution.

The probability of running into a jellyfish in waters around Annapolis was 14 percent, and just 0.7 percent at the southern end of the Patapsco River, according to the Chesapeake Bay Interpretive Buoy System.

Farther south at Goose's Reef, in the middle of the bay between Calvert and Dorchester counties, the likelihood is about 48 percent, and it's 65 percent at the mouth of the Potomac at Point Lookout.

Around one of the center's labs at Horn Point, near Cambridge, researchers have noticed a drop-off in jellyfish as salinity levels have dropped below the requisite 10 units, Hood said.