Anchors Out! Illegally moored boats damage ecologically significant eelgrass beds in San Francisco Bay.

Authors: Julia Kelly*, University of Colorado, Daniel Orr, Audubon California, John Takekawa, Suisun Resource Conservation District
Topics: Coastal and Marine, Human-Environment Geography, Environment
Keywords: effects of human activity, seagrass, anchor scour, aquatic vegetation, ecosystem conservation, San Francisco Bay
Session Type: Lightning Paper
Presentation File: No File Uploaded


Eelgrass (Zostera marina) is considered a foundational marine habitat due to the vast array of marine invertebrates, fish, birds, and mammals that eelgrass beds support both directly and indirectly. Protecting eelgrass is a priority, yet few studies have documented the extent of loss and how human activities contribute to eelgrass loss. In California, San Francisco Bay comprises >50% of the state’s eelgrass acreage, and the estuary represents a stronghold for eelgrass on the Pacific coast. One of the largest eelgrass beds in San Francisco Bay, found in Richardson Bay, has experienced a severe reduction in extent due to the presence of illegally-moored vessels known locally as “anchor-outs.” The anchor-out issue has been disputed over for decades and is made difficult by a lack of scientific evidence about the extent to which the boats damage the eelgrass beds. Using aerial imagery and GIS analyses, we determined the amount of direct damage to eelgrass caused by anchor-outs. Our findings show that boats damage up to 41% of the eelgrass bed, and each boat may cause up to 0.3 ha of damage. These results can be used to encourage stakeholders and state agencies to make informed decisions about the anchor-out issue. Furthermore, our efficient analytical approach could be implemented in other coastal regions seeking to mitigate boat damage to seagrass.

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