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Extreme Weather Events Forcing Fish to Change Location

09 November 2016

US - Researchers from the University of Maryland Center for Environmental Science have investigated the impact that severe storms have on fish populations as it forces them to make sudden and unexpected trips away from their preferred habitat, to more hospitable waters.

"These events happen naturally, but having them occur more frequently may have a bigger impact on the fish," said the study's lead author Helen Bailey.

"If you get more frequent storms during the year, it is possible you could interrupt their breeding and feeding in ways that impact their population."

Ms Bailey and Dave Secor tracked 22 striped bass in the Hudson River Estuary (which hosts one of the largest populations of this species) and New York Harbor during the Tropical Storms Irene and Lee in 2011. Occurring about a week apart, the significant weather events caused heavy rainfall, major flooding, and sudden influxes of fresh, cold water into the waterways.

The year before, during normal conditions, researchers had tagged the fish that lived there with small electronic transmitters that regularly pinged their every move. After the storms, they were able to compare the data to examine how their behavior was impacted by the extreme storm events.

"There are very few studies on this because it so hard to sample during these storm events. You can't predict when they will happen and these can be hazardous conditions to work in," said Bailey. "Telemetry data gave us the opportunity to do it."

The researchers discovered that when the storms hit, most of the fish rapidly left the Hudson River and New York Harbor, moving south along the coast. A few remained in the harbor and were able to avoid being displaced. Others did a few exploratory trips later back to the harbor to check on conditions over the next few months and eventually returned up the river.

"It's not unusual for fish to be leaving this area at this time of year," said Bailey. "What was very unusual was that so many of them did it, they went so far south, and they did it so quickly."

There were several changes to the behavior that the researchers didn't expect. Most concerning, depending on when the storm events occurred, some of the striped bass that evacuated the areas did not immediately return, adopting new migration behaviors.

"The responses of fish species to extreme weather events will need to be considered when planning management strategies to ensure efforts are appropriately targeted to maintain key population segments and critical evacuation routes," said Dave Secor, the study's co-author at the University of Maryland Center for Environmental Science's Chesapeake Biological Laboratory.

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