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Ocean Monitoring Update

On-going ocean monitoring in Oregon’s Marine Reserves is unlocking secrets about temperatures and oxygen levels known to impact groundfish and invertebrate activities, create stresses on ecosystems and even alter sport anglers’ catches. Some of the data go back two decades at what is now the Cape Perpetua Marine Reserve near Yachats and are buoyed by oceanography monitoring in recent years at the state’s four other marine reserves.

The phenomenon is called hypoxia, and data collected in the reserves is showing an apparent trend in size and length of these episodes, and that they differ throughout the Oregon Coast.

“In some places we’ve never looked until recently, we’re starting to see our first glimpses of it,” said Dr. Lindsay Aylesworth, the Marine Reserves Program Leader. The program’s main oceanography monitoring began this month with the placement of special moorings in the Cape Falcon Marine Reserve as well as in a nearby comparison area off Cape Meares. The moorings, which were deployed by the Garibaldi-based F/V Lady Lee hired by the program, contain sensors that track ocean temperature and oxygen levels through early fall, when they will be removed.

Collectively, early data show a relationship between oxygen levels, wind direction and water temperatures. North winds, desired for good ocean nutrient conditions, routinely coincide with decreases in sea surface temperature and periods of low oxygen levels, which can plunge to hypoxic levels. These zones disperse with the return of south winds that bring warmer water and higher oxygen levels to the surface. The size of these low-oxygen zones come and go and vary across state waters, but they have grown and persisted for longer durations of time in recent years.

Low oxygen levels, particularly when they plunge to levels of hypoxia, are known to place stress on fish, invertebrates, and underwater ecosystems. Along the coast, the south has seen the fewest episodes of hypoxia, when compared to central and north coast conditions. During days of high levels of dissolved oxygen, catch rates during the marine reserves’ hook-and-line surveys show better catches of groundfish, data show. Days with low oxygen levels correspond to relatively poor catch rates among survey volunteers.

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