Vessel Noise Exposures of Harbor Seals Tagged in the Elbe Estuary

Harbor seals are top marine predators in the North Sea and neighboring estuaries, including the Elbe. The Elbe estuary is a major shipping corridor, with ~7000 vessels, including cargo ships, tankers, and cruise liners, arriving and departing Germany’s Hamburg Port annually—Europe’s third largest port. To investigate the potential impacts of shipping noise on marine wildlife, eight harbor seals were captured in the Elbe and equipped with sound and movement tags (DTAGs) to measure fine-scale movements and vessel noise exposure. From over 1200 hours of underwater recordings, 574 ship passages were identified with received sound<br/>pressure levels &gt;97 dB re 1 μPa in the 2 kHz decidecade band and signal-to-noise ratios &gt;6 dB above ambient. Four seals remained in the estuary throughout the deployment, while others transited into the Wadden Sea and/or North Sea. Daily<br/>vessel exposure rates varied among individuals, depending on habitat use rather than tagging location, with estuarine seals experiencing up to 55 high-amplitude vessel passes per day—an order of magnitude higher than rates recorded on seals from the Wadden Sea. As harbor seals are known to respond to vessel noise, further analyses will evaluate behavioral and energetic consequences of vessel exposures in the Elbe estuary.<br/>