{"id":4367,"date":"2024-09-23T08:51:30","date_gmt":"2024-09-23T12:51:30","guid":{"rendered":"https:\/\/ncseagrant.ncsu.edu\/hooklinescience\/?p=4367"},"modified":"2024-09-23T11:56:56","modified_gmt":"2024-09-23T15:56:56","slug":"are-low-oxygen-waters-affecting-fish-calls","status":"publish","type":"post","link":"https:\/\/ncseagrant.ncsu.edu\/hooklinescience\/are-low-oxygen-waters-affecting-fish-calls\/","title":{"rendered":"Are low-oxygen waters affecting fish calls?"},"content":{"rendered":"\n\n\n\n\n

Silence reveals clues about estuarine water quality. <\/em><\/strong><\/p>\n\n\n\n

Research Need<\/strong> <\/p>\n\n\n\n

Nutrient pollution can degrade water quality and lead to hypoxia \u2014 when oxygen levels drop too low to support aquatic life. Prolonged periods of hypoxia negatively impact fish growth and reproduction, often with severe consequences for both recreational and commercial fisheries. Estuaries in North Carolina regularly experience hypoxia during the summer months, which can lead to fish kills and alter where fish and crabs live and gather. <\/p>\n\n\n\n

Many marine organisms become stressed when oxygen levels fall below 5 milligrams of oxygen per liter of water, and lethal effects occur at levels under 2 milligrams per liter. For fish, this lethal limit is like breathing on Mount Everest without supplemental oxygen, making survival extremely challenging. <\/p>\n\n\n\n

To address this, state managers have implemented plans to reduce hypoxic events through nutrient pollution control and water quality monitoring. North Carolina has defined hypoxia as oxygen levels below 4 milligrams per liter. <\/p>\n\n\n\n

But how exactly do low oxygen conditions affect fish reproduction and movement? Will fish return to an area after oxygen levels are restored to normal? <\/p>\n\n\n\n

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Lead researcher Joseph Luczkovich with the hydrophone recording system that he and his team used.<\/figcaption><\/figure>\n\n\n\n

What did they study?<\/strong><\/p>\n\n\n\n

A research team developed an underwater buoy system that simultaneously recorded fish sounds and water quality data to test whether low oxygen levels reduce fish reproductive calls. Researchers deployed this system at two high-salinity sites near Beaufort, North Carolina, where hypoxia was absent, and at one low-salinity site in Pamlico Sound, NC, which experienced periodic hypoxia. The team selected these sites based on the well-documented presence of drum fishes, like red drum and weakfish. <\/p>\n\n\n\n

Additionally, the team placed passive acoustic recorders near established water quality monitoring stations to compare fish sounds with dissolved oxygen levels. This second approach also tested whether passive acoustic monitoring could effectively track changes in fish calls related to water quality across the estuary. <\/p>\n\n\n\n

Listen to the sound of red drum calls at normal oxygen levels:<\/em><\/p>\n\n\n\n

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