Investigating the impacts of commercial anchorages on benthic ecosystems

The expanding shipping industry has led to escalating use of commercial anchorages, with ships spending more time at anchorage and spreading to previously little used areas. Coastal communities have expressed concerns about anchorage stressors including visual pollution, noise, light, contaminant discharges, and seabed impacts. A recent Pathways of Effects conceptual model identified a range of possible effects of anchoring on physical habitats and marine biota but documented only a few scientific studies globally, with the focus on shallow recreational boat anchoring. Anchorages are often situated in soft sediment areas; understudied ecosystems with high diversity which play an important role in ecosystem function, and support commercial and ecologically significant species. Here we describe research to document the impacts of commercial shipping anchorages on marine benthic ecosystems of the Salish Sea and north coast of Pacific Canada. We undertook mapping of presumed anchoring-related marks observed in multibeam imagery and analysed data on anchorage activities, including age of anchorage, the intensity of use and the duration of anchoring events. We used the results to inform an initial Remotely Operated Vehicle (ROV) survey to examine visual evidence of the physical impacts of anchoring with field survey sites stratified across a range of seabed types and anchorages. The research investigates the mechanism behind seabed disturbance from anchorages in heavily trafficked areas, quantifies the extent of impact, and provides a baseline for change detection in these areas. Following this research, we aim to provide recommendations on considerations for siting and usage of anchorages for a more sustainable use of the seabed.