Boat Propeller Scarring of Seagrass Beds in Lower Chesapeake Bay, USA: Patterns, Causes, Recovery, and Management

Abstract

Seagrass beds are subject to numerous anthropogenic influences, including nutrient pollution, shoreline development and modification, and overfishing. Direct human impacts on seagrass though, such as through contact with boat propellers and fishing gear, remains relatively uninvestigated. Here, we use 26 years of aerial imagery and 3 years of ground surveys to explore the degree, distribution, and recovery of scarring in seagrass beds as the result of boat propellers in lower Chesapeake Bay, USA, specifically from commercial haul seine fishing activity. We find that propeller scarring is extensive, particularly on the western shore of the Bay, where pressure from haul seining is more intense. In two areas with the most intense scarring, Browns Bay and Poquoson Flats, annual total length of scars averaged 5575 and 3206 m, respectively. Despite the considerable presence of observable scarring, an individual scar generally persisted for only 2.7 years on average, implying quick recovery, aided by the diverse reproductive habits of the two seagrasses in this region, Zostera marina and Ruppia maritima. Moreover, regulations adopted by the regulary agency responsible for protecting marine habitats in Chesapeake Bay, the Virginia Marine Resources Commission, concerning the timing of haul seining in response to these findings reduced the frequency of new scars 43% at Browns Bay and 90% at Poquoson Flats since 2003. These results demonstrate that swift and decisive management action, in cooperation with relevant science, can lead to effective conservation of underwater grasses.