Effects of Harvest on Bottom Habitat and Recruitment of Oysters in the Chesapeake Bay, Maryland

The eastern oyster (Crassostrea virginica) has been commercially important in the Chesapeake Bay, Maryland because the 1820s with a dockside value of $21.4 million during 2021–2022. Oysters are also ecosystem engineers that create habitat for themselves and other organisms in addition to providing other ecosystem services. Dredging and other harvest practices have been shown to reduce the height of oyster reefs, but the effect of harvest on their habitat remains uncertain including the effects of alternative fishing gears. The objective of this study was to estimate the effect of harvest, particularly dredging, on recruitment and the amount of oyster shell bottom habitat (i.e., cultch) for oysters in the Chesapeake Bay, Maryland using analyses of two sets of complimentary harvest and survey data. Before-after-control-impact ANOVAs were conducted using data collected from areas opened to power dredging and reference sites during 2010–2015. Additionally, Maryland Department of Natural Resources fall dredge survey (FDS) data and harvester reports during 2010–2019 were used to estimate effects of the amount of harvest and the gear type on bottom habitat and recruitment. The estimated effects for change in cultch and change in spat catch per unit effort in areas opened to power dredging were negative but had substantial uncertainty. A negative effect of dredging was estimated on the change in cultch from the FDS, and the loss of shell habitat was greater than the removals from harvest alone. Harvest did not appear to improve conditions for recruitment. The sign and magnitude of the effects of dredging were consistent across the analyses, which suggests that dredging likely causes loss of shell volume beyond the removal of harvested oysters on oyster reefs in Maryland.