Growing hypoxic zones reduce habitat for billfish and tuna

Dec 22, 2010
This Atlantic sailfish was tagged by NOAA scientists off Senegal as part of a study on how oxygen depleted zones in the eastern Atlantic Ocean affect fish habitat. Credit: NOAA

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.

An expanding zone of low oxygen, known as a hypoxic zone, in the Atlantic Ocean is encroaching upon these species' preferred oxygen-abundant , 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 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."

Samples of surface skin slime are taken from the Atlantic sailfish to determine gender. Credit: NOAA

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 . 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 exploitation.

Explore further: Earth's resource budget for 2014 already spent, NGO says

More information: Fisheries Oceanography article:
onlinelibrary.wiley.com/doi/10… 419.2010.00556.x/pdf

add to favorites email to friend print save as pdf

Related Stories

Hypoxic event ends off Oregon coast

Oct 30, 2006

U.S. scientists say the longest, largest and most devastating hypoxic event ever observed in marine waters off the Oregon Coast has finally ended.

Gulf of Mexico dead zone to be studied by marine scientists

Oct 24, 2007

University of Texas at Austin marine scientists have been awarded $781,000 by the National Oceanic and Atmospheric Association (NOAA) to better understand how nutrient pollution from the Mississippi River affects the large ...

Aquatic 'dead zones' contributing to climate change

Mar 11, 2010

The increased frequency and intensity of oxygen-deprived "dead zones" along the world's coasts can negatively impact environmental conditions in far more than just local waters. In the March 12 edition of the journal Science, Univer ...

Low oxygen in coastal waters impairs fish reproduction

Aug 29, 2007

Low oxygen levels in coastal waters interfere with fish reproduction by disrupting the fishes’ hormones, a marine scientist from The University of Texas at Austin Marine Science Institute has found.

Recommended for you

Earth's resource budget for 2014 already spent, NGO says

14 hours ago

In under eight months, humanity has used up its yearly quota of replenishable Earth resources, according to a report published Tuesday by an environmental thinktank that monitors mankind's impact on the planet.

User comments : 0