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Wavebreaking News – Spring 2004

Welcome to Wavebreaking News………brought to you by NOAA’s National Ocean Service.

Measuring Air Gap Aids Navigation

A new navigation tool that measures clearance between the water surface and bridges, also known as air gap, is now available. The first sensors to measure air gap were placed recently on the center spans of two bridges over the Chesapeake and Delaware Canal. The sensors take readings every six minutes to account for changes in water level, volume of traffic crossing the bridges, and air temperature, all of which cause bridge clearance to fluctuate. As ships become taller, some are passing under bridges with just inches to spare. This new capability is available through NOAA’s Physical Oceanographic Real-time System, which provides quality-controlled oceanographic and weather data at U.S. seaports to aid navigation.

Unravelling Dolphin Entanglement Deaths

Scientists are using computers to identify commercial fisheries that may be responsible for dolphins’ deaths from entanglement in fishing gear. Generally, most fishermen in any fishery use ropes with similar diameter and braiding patterns. Impressions and wounds left by the ropes on dolphins’ skin can help identify the fishery that caused entanglement. NOAA scientists superimpose photographs of impressions from dolphin carcasses with computer-generated rope images to match dolphin entanglements with fisheries. This technique promises to be an important way to investigate suspected fishery-related marine mammal deaths.

Asian Oyster Under Scrutiny for Cheseapeake Bay

State and federal agencies, including NOAA, will study a proposal to introduce a non-native oyster from Asia to the Chesapeake Bay. This study will investigate the effects that this species may have on the bay’s ecosystem and its oyster industry. Some concerns of introducing the Asian oyster are its ability to successfully reproduce in the bay’s environment, exposing native species to new diseases, and competition with the native Eastern oyster. The decline of the Eastern oyster, which is attributed to over-harvesting, poor water quality, and disease spurred the proposal by the states of Maryland and Virginia to introduce the Asian oyster. Large-scale efforts to restore the native oyster are still in the early stages, and are showing mixed results.

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For More Information

Tide Predictions Accessible from Cell Phones

Center for Operational Oceanographic Products and Services

NOAA Magazine


Contact: Mike Szabados, Center for Operational Oceanographic Products and Services,

Measuring Air Gap Aids Navigation

Air Gap Data

Center for Operational Oceanographic Products and Services

Contact: David Macfarland, Center for Operational Oceanographic Products and Services,

Unravelling Dolphin Entanglement Deaths

Sources of Mortality in Commercial Fisheries Predicted with GIS

Contact: Wayne McFee, National Center for Coastal Ocean Science,

Asian Oyster Under Scrutiny for Cheseapeake Bay

Oyster Restoration Presentation (pdf, 890 kb)

NOAA Chesapeake Bay Office

Maryland Sea Grant

Virginia Institute of Marine Science

U.S. Army Corps of Engineers

Contact: Jamie King, NOAA Chesapeake Bay Office,

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