October 23, 2021

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Dropping Oxygen Levels In The Ocean Are Pushing Fishes To Shallow Waters



Dropping oxygen concentrations in oceans is leading to dozens of fish species migrating to shallow waters.

In a new paper published in the journal Global Change Biology, researchers from the University of Carolina and UC Santa Barbara have published their findings of a study conducted over the last 15 years.

Erin Meyer-Gutbrod, the lead of the author of the study and a professor at the University of South Carolina, says that they found declining levels of oxygen across various depths they surveyed. The researchers took measurements and conducted surveys of the ocean in depths of 50 meters to 350 meters. They found many species of fish moving into shallower areas where the concentration of oxygen is relatively higher.

The decreasing levels of oxygen in the ocean waters could be due to several reasons, such as ecological changes, changes in seasons, and even due to storms. But, according to the paper, the most significant reason could be that warmer ocean water holds less dissolved oxygen.

The fish are moving to shallow waters because oxygen dissolves easily in shallow waters due to atmospheric mixing. But, due to rising temperatures, the differences in the density between cold and warm surface waters have increased. This had led to a clear divide between warm and cold water, keeping oxygen from dissolving into deeper waters.

Between 1995 and 2009, the researchers conducted surveys of fish at various depths between Santa Cruz and Anacapa islands in Southern California, to determine the impact of declining oxygen levels on fish distribution.

They identified around 60 types of fish that were observed in most of these surveys through the years and found that four species had migrated to deeper waters, while 19 species had moved to shallower depths. Along with the levels of oxygen, the researchers also measured salinity and temperature, both of which remained relatively constant throughout the years.

Despite the study being confined to a small area, the researchers say it allowed them to eliminate confounding factors involved in surveying large geographic areas. They noted that as a consequence of this trend, many of these fish species could be driven out of their ideal habitat and may struggle to adapt to new ones. That could result in stress being put on the fishing industry.

Cover Image: Shutterstock



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