Tag Archives: Aquatic ecology

Low-oxygen scenario following unusual course this year in Hood Canal

Death came early to Hood Canal this year, demonstrating just how odd and unpredictable ocean conditions can be.

Fish kills caused by low-oxygen conditions in southern Hood Canal usually occur in late September or October. That’s when low-oxygen waters near the seabed are pushed upward by an intrusion of heavier water coming in from the Pacific Ocean and creeping along the bottom. Winds out of the south can quickly blow away the surface waters, leaving the fish with no escape.

That’s basically what happened over the past month, as conditions developed about a month earlier than normal. South winds led to reports of fish dying and deep-water animals coming to the surface to get enough oxygen, with the worst conditions occurring on Friday. Check out the video on this page by Seth Book, a biologist with the Skokomish Tribe, who found deep-water ratfish swimming near the surface.

The story of this year’s strange conditions actually begins about a year ago and involves a 1,000-mile-long “blob” of unusually warm ocean water off the West Coast. State Climatologist Nick Bond, who coined the term “blob,” explains its formation in an article in Geophysical Research Letters with a summarized description by Hannah Hickey in UW Today.

The warm, low-density coastal waters related to the blob came into Hood Canal on schedule last fall, but they were not dense enough to flush out the low-oxygen waters, according to University of Washington oceanographer Jan Newton.

Hood Canal entered 2015 with the least-dense waters at depth over the past 10 years. They remained in a hypoxic state, meaning that levels were below 2.5 parts per million. Sea creatures unable to swim away can be unduly stressed and unable to function normally at that level. Conditions worsened into the summer, when the hypoxic layer at Hoodsport grew to about 300 feet thick.

By then, the annual intrusion of deep seawater with somewhat elevated oxygen levels was on its way into Hood Canal, spurred on by upwelling off the coast. This year’s waters are more normal in density, though their arrival is at least a month early. By August 9, the hypoxic layer at Hoodsport was reduced from 300 to 60 feet, pushed upward by the denser water.

It’s always interesting to see this dynamic play out. The layer of extreme low-oxygen water becomes sandwiched between the higher-oxygen water pushing in from the ocean and the surface water, which ordinarily stays oxygenated by winds and incoming streams. Without south winds, the middle low-oxygen layer eventually comes up and mixes into the surface layer.

If south winds come on strong, however, the surface layer is blown to the north, causing the low oxygen water to rise to the surface. Fish, shrimp and other creatures swim upward toward the surface, trying to stay ahead of the rising low-oxygen layer. When the low-oyygen layer reaches the surface, fish may struggle to breathe in the uppermost mixing layer. Unfortunately, the fish have no way of knowing that safer conditions lie down below — beneath the low-oxygen layer and within waters arriving from the ocean.

Jan Newton reported that the low oxygen levels in southern Hood Canal earlier this year were the most extreme measured over the past 10 years. So far, however, the fish kills don’t seem as bad as those in 2003, 2006 and 2010, she said.

The graph below shows how the deep layer coming in from the ocean at 279 feet deep contains more oxygen than the middle layer at 66 feet deep. The surface layer, which normally contains the most oxygen, dipped to extremes several times near the beginning of August and again on Friday, Aug. 28. These data, recorded from a buoy near Hoodsport, are considered unverified.

Graph

A vision for a holistic ecosystem, humans included

Hood Canal Coordinating Council is undertaking an effort to bring average residents into the discussion about how to preserve the Hood Canal ecosystem.

While Hood Canal is becoming known for its low-oxygen problem and occasional fish kills, it’s good to remember that the canal remains famous for its shrimp, oysters and crabs. Furthermore, history tells us that the canal once abounded in sealife, including all kinds of salmon and bottomfish.

Can the canal ever come close to its heyday? I don’t know, but plenty of people would like to give it a try. (By the way, if you want to argue that the problems are caused entirely by over-fishing, we’ll need to discuss individual species — including those that aren’t harvested at all.)

The underlying premise of the Hood Canal Integrated Watershed Management Plan is that people can find ways to benefit from a healthy ecosystem, that natural processes — including the survival of plants and animals — can continue without wrecking the lifestyles of humans. Check out my story in the Kitsap Sun Oct. 26 for an overview of this project.

The vision for this approach is articulated in a document called “Development of Ecological and Socioeconomic Targets” (PDF 60 kb). The vision section begins with a short, positive statement:

Humans benefit from and coexist sustainably with a healthy Hood Canal.

The document goes on to elaborate on the vision within various goals, consistent with goals of the Puget Sound Partnership:
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Report notes oxygen troubles in Northwest waters

Low-oxygen problems in Hood Canal and along the Washington-Oregon Coast are highlighted as “case studies” in a new federal report regarding the growing number of “dead zones” across the United States. See “Scientific Assessment of Hypoxia in U.S. Coastal Waters” (PDF 2.7 mb).

Incidents of hypoxia have increased 30-fold since 1960, according to the report. The new federal review describes the causes of hypoxia, discusses past and ongoing research efforts and lays out policy recommendations to deal with the problem. Eight troubled waterways are reviewed as “case studies.”

In a news release (PDF 116 kb) accompanying the report, Jane Lubchenco, administrator of the National Oceanic and Atmospheric Administration, offered these comments regarding hypoxia and the seasonal low-oxygen area off the coast of Washington and Oregon:

“The report shows good progress on research into the causes of hypoxia and the specific management requirements to restore systems such as the Gulf of Mexico and Chesapeake Bay, but we still have a long way to go to reduce this environmental threat. The discovery of a new seasonal hypoxic zone off the coast of Oregon and Washington that may be linked to a changing climate emphasizes the complexity of this issue.”

That West Coast dead zone is now ranked the second largest in the United States and the third largest in the world. Federal officials say there may be serious consequences to the ecological health of the region.

Lisa Jackson, administrator of the Environmental Protection Agency, said the EPA is proud to have played a role in the research leading up to the report:

“These growing dead zones endanger fragile ecosystems and potentially jeopardize billions of dollars in economic activity. This science can be the foundation for measures that will preserve our waters and reverse the trend, including innovative, watershed-based solutions to this challenge.”

Mike Lee, a reporter with the San Diego Union-Bulletin, interviewed Tony Koslow, who studies low-oxygen areas at the Scripps Institution of Oceanography.

“This is a large phenomenon not due to nutrient outflows” from land, Lee quoted Koslow as saying. “The big question is, ‘Is this due to climate change?’ ”

As the oxygen-rich surface layers warm up, they mix less with colder layers down deep where oxygen levels are low, Koslow said. Global climate models predict that the oxygen levels in deep oceans will decline 20 to 40 percent the next century.

“There are substantial ecosystem concerns,” Koslow said. “A number of species that live in the deep ocean are very sensitive to changes in oxygen levels. These species — although they are not of commercial interest — are prey to squid, fish, marine mammals and seabirds, so changes in oxygen will have repercussions throughout the food web.”

The report suggests these policy actions:

  • Develop and implement cost-effective and scientifically
    sound nutrient reduction strategies to achieve healthy water
    quality in rivers, lakes and coastal waters.
  • Improve ecosystem models to assess how hypoxia
    affects commercially important fish populations in order to
    refine management strategies to protect coastal economies.
  • Improve scientific understanding for emerging sites such
    as the Oregon and Washington shelf, where hypoxia may be
    driven primarily by events linked to climate change. This
    knowledge will help managers mitigate impacts on natural
    resources and coastal economies.
  • Expand stream and river monitoring to document extent
    and sources of nutrients and progress in achieving management
    goals. This can lead to more strategic and effective targeting of
    nutrient reduction actions.
  • More systematically monitor oxygen levels in coastal
    waters using new technologies and observing systems. This is
    critical for forecast model development, fisheries management,
    and determining nutrient reduction success.