Declining oxygen levels in the ocean push fish into shallow water
Declining oxygen concentrations in the oceans are causing dozens of fish species to migrate into shallow waters.
In a new article published in the journal Biology of global change, researchers at the University of Carolina and UC Santa Barbara have published the results of a study conducted over the past 15 years.
Erin Meyer-Gutbrod, lead author of the study and professor at the University of South Carolina, says they found declining oxygen levels at various depths that they studied. The researchers took measurements and conducted surveys of the ocean at depths of 50 to 350 meters. They found many species of fish moving to shallower areas where the oxygen concentration is relatively higher.
The decrease in oxygen levels in ocean waters could be due to several reasons, such as ecological changes, seasonal changes and even storms. But, according to the document, the most important reason could be that the warmer water in the oceans contains less dissolved oxygen.
Fish move to shallow water because oxygen easily dissolves in shallow water due to atmospheric mixing. But, due to rising temperatures, the density differences between cold and warm surface water have increased. This had led to a clear separation between hot and cold water, preventing oxygen from dissolving in deeper water.
Between 1995 and 2009, researchers conducted surveys of fish at different depths between the Santa Cruz and Anacapa Islands in Southern California, to determine the impact of declining oxygen levels on the distribution of fish.
They identified around 60 types of fish that were seen in most of these surveys over the years and found that four species had migrated to deeper waters, while 19 species had moved to shallower depths. In addition to oxygen levels, the researchers also measured salinity and temperature, both of which have remained relatively constant over the years.
Although the study was limited to a small area, the researchers say it allowed them to eliminate the confounders involved in investigating large geographic areas. They noted that due to this trend, many of these fish species could be driven out of their ideal habitat and may struggle to adapt to new ones. This could put pressure on the fishing industry.
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