The Maryland Department of the Environment investigated a “Crab Jubilee” and fish kill reports on July 8th in St. Jerome’s Creek on the lower western shore of Maryland’s Chesapeake Bay. A “Jubilee” has been the regional term used when crabs leave the water and tends to occur when unsuitable habitat conditions (i.e., extremely low dissolved oxygen) are present. The conditions measured in the headwaters of St. Jerome Creek’s North and South Branch showed severely stressful to lethal dissolved oxygen conditions well below 1 mg O₂/L (approximately 0.5 mg/l) from the surface to bottom in the North Branch. Live crabs were observed clinging to pilings and walking along the shore at this location.

A similar “jubilee” had been observed on the South Branch of St. Jerome’s Creek the morning of the investigation but a thin layer of oxygenated water within 6 inches of the surface (8.0 mg O₂/L) at the time of the investigation could have provided refuge for the crabs to return to the water since none were observed later in the day in this area. However, approximately 30,000 fish were observed dead along the shoreline of the South Branch consisting of species frequenting headwater habitats during the summer: mummichogs, silversides, striped killifish, young-of-the-year menhaden, juvenile white perch and atlantic croaker.

Water color was noticeably green in the North and South Branch of the St. Jerome’s Creek. Algal samples from the North Branch were dominated by a non-toxic euglenoid form of plankton known as Eutreptiell marina. However, overall plankton numbers were low and suggested an algal bloom die-off may have fueled the low dissolved oxygen conditions.

Near the mouth of St. Jerome’s Creek, water quality conditions were good during the day with low numbers of Eutreptiella (53-424 cells/ml) and moderate concentrations of the possibly toxic dinoflagellate Karlodinium micrum (7,000-17,000 cells/ml). A return visit to the mouth of the creek late in the day, however, showed red-colored waters. A water sample indicated bloom conditions of K. micrum was present at 67,000-107,000 cells/ml. Fish in the area near shore were observed swimming with normal behavior at that time.

Several of the patchy but strong algal blooms throughout the bay area have died off over that last two weeks causing fish kills, primarily along the Calvert and Saint Mary’s County shorelines. These kills often are confined to in headwater environments, but a few have happened in the mainstem of the bay resulting in the few thousand fish many recreational boaters and residents observe floating back and forth in the bay between Southern Maryland and the adjacent Eastern Shore.