Growing Hypoxic Zones Reduce Habitat for Billfish and Tuna

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  1. Matthew
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    Growing Hypoxic Zones Reduce Habitat for Billfish and Tuna

    ScienceDaily (Dec. 23, 2010) — Billfish and tuna, important commercial and recreational fish species, may be more vulnerable to fishing pressure because of shrinking habitat, according to a new study published by scientists from NOAA, The Billfish Foundation, and University of Miami Rosenstiel School of Marine and Atmospheric Science.
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    An expanding zone of low oxygen, known as a hypoxic zone, in the Atlantic Ocean is encroaching upon these species' preferred oxygen-abundant habitat, forcing them into shallower waters where they are more likely to be caught.

    During the study, published recently in the journal Fisheries Oceanography, scientists tagged 79 sailfish and blue marlin with satellite tracking devices in the western North Atlantic, off south Florida and the Caribbean; and eastern tropical Atlantic, off the coast of West Africa. The pop off archival satellite tags monitored horizontal and vertical movement patterns. Researchers confirmed that billfish prefer oxygen rich waters closer to the surface and will actively avoid waters low in oxygen.

    While these hypoxic zones occur naturally in many areas of the world's tropical and equatorial oceans, scientists are concerned because these zones are expanding and occurring closer to the sea surface, and are expected to continue to grow as sea temperatures rise.

    "The hypoxic zone off West Africa, which covers virtually all the equatorial waters in the Atlantic Ocean, is roughly the size of the continental United States, and it's growing," said Dr. Eric D. Prince, NOAA's Fisheries Service research fishery biologist. "With the current cycle of climate change and accelerated global warming, we expect the size of this zone to increase, further reducing the available habitat for these fish."

    Less available habitat can lead to more fish being caught since the fish are concentrated near the surface. Higher catch rates from these areas may give the false appearance of more abundant fish stocks. The shrinking availability of habitat and resulting increases to catch rates are important factors for scientists to consider when doing population assessments.

    Researchers forecast that climate change and its associated rise in ocean temperatures will further increase the expansion of hypoxic zones in the world's oceans. As water temperature increases, the amount of oxygen dissolved in water decreases, further squeezing billfish into dwindling available habitat and exposing them to even higher levels of explo\\


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    Acidification Is ?Fundamentally Altering? Oceans (Fourth in a series) | Coastal and Estuarine Research Federation (CERF)

    in CERF 2009 September 2009
    Author: John Bragg, South Slough National Estuarine Research Reserve, John.Bragg@state.or.us
    *Note to readers: With CERF’s biennial conference in Portland, Oregon, only a few weeks away, we examine how increased ocean acidification and the development of hypoxic waters along the West Coast are affecting the region’s shellfish, and the implications of ocean acidification for coastal waters, in a fourth and final article about Pacific Northwest estuaries. The third article, “Adapting to Climate Change,” discussed management options for addressing climate change in the Pacific Northwest, with a special focus on wind energy production along the Columbia River (CERF June 2009). The second article, “Diversity of Pacific Northwest Estuaries,” highlighted some of the habitats found in estuaries from Humboldt Bay, California north to coastal Washington, Puget Sound and the Fraser River (CERF February 2009). The first article, “Pacific Northwest Estuaries Were Born of Fire and Ice,” discussed the physical and geological setting of northwest estuaries (CERF October 2008).
    The series of articles is coordinated by John Bragg, coastal training coordinator for the South Slough National Estuarine Research Reserve in Charleston, Oregon.

    In 2005 oyster growers in Willapa Bay, Washington, took it in stride when their oysters failed to reproduce, but as successive brood also failed in 2006, 2007 and 2008, the oystermen went looking for an answer. Even as they watched, the wave of deaths spread to Oregon, where in Netarts, a tiny seafront town, the epidemic struck a shellfish hatchery that supplies oyster-growers up and down the West Coast. Nearly four-fifths of the hatchery’s brood died. University and industry scientists scrambled into the field to search for answers. What was causing such catastrophic losses?
     

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