Surviving the cold:
Fellow studies northern speckled trout

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When winter temperatures plummet, some speckled trout go belly-up. Researchers call these events cold stuns. Temperatures drop to near-freezing for days at a time, and fish die from hypothermia. After an especially severe cold stun in 2014, recreational fishermen requested the speckled trout fishery be closed for a season to allow the fish populations to recover.

Cold stuns—and colder winter temperatures in general—are a particular challenge for speckled trout in Virginia, nearing the northernmost limit of their range.

“From a scientific standpoint, speckled trout in Virginia is a good case study to study natural populations and natural selection in action,” says Jingwei Song, a Virginia Sea Grant Graduate Research Fellow and graduate student at the Virginia Institute of Marine Science (VIMS).

To see how Virginia’s speckled trout have adapted to colder water, Song is studying the fishes’ metabolic response to changes in temperature and the genetics that lay the foundation for cold tolerance. Previous research found genetic differences between speckled trout along the U.S. East Coast. Song’s work will determine whether some of these differences are related to adaptions in the northern population that make them more resilient to the colder winter.

“This could actually have applications for how these fish are going to respond to climate change,” says Jan McDowell, a research assistant professor at VIMS and Song’s research advisor.

Song’s project has three different layers of analysis: scanning the speckled trout genome to identify genes that might be related to their adaption, gene expression, and the physiological characteristics that might contribute to cold tolerance.

Song has already identified a couple dozen genetic markers that are strong candidates capable of explaining a large portion of the differences between northern and southern populations. Next, he’ll determine the function of these genes and compare which genes are turned on and off after the fish are exposed to extreme temperatures.

Cold stuns can kill anywhere from a quarter to half of the speckled trout population when fish venture into shallow waters looking for food. The shallow waters get cold much more quickly, causing hypothermia in the fish, leaving them unable to breathe.

“They’re seeking out this warm bit of water in the winter that will warm up during the day,” says Patrick McGrath, a marine scientist at VIMS who helped Song with data collection.“The problem is when we get an extreme cold event that lasts, for approximately a week, and water temperatures consistently stay below 5 °C. A good percentage of them die.”

Cold stuns—and colder winter temperatures in general—are a particular challenge for speckled trout in Virginia, nearing the northernmost limit of their range.

While smaller fish move to deeper waters and avoid cold stuns, McGrath says the larger speckled trout that often go into the shallow water are “essentially very stubborn fish. They think they can outlast the cold, and most years they do. Some years they don't.”

In addition to the genetic side of speckled trout adaptation, Song studies the physiological characteristics that contribute to cold tolerance. He uses a respirometry chamber to measure oxygen consumption rate of northern and southern fish at different temperatures. This gives Song insight into the fishes’ metabolism in colder or warmer waters.

Managers and recreational anglers alike want the speckled trout fishery to thrive, and knowing how northern speckled trout populations have adapted to colder winters will help managers make decisions about the fishery, according to Sheldon Arey, an avid speckled trout fisherman and member of the Virginia Marine Resources Commission’s Recreational Fishing Advisory Board.

“Certainly, in today’s world of colder colds and hotter hots experienced in global warming, this is a finding that is very useful to our future,” Arey says.

Contributed video from Jingwei Song

Video by Aileen Devlin and Lisa Sadler | Virginia Sea Grant

Written by Madeleine Jepsen | Virginia Sea Grant

TAKEAWAYS

  • Northern speckled trout populations in Virginia and North Carolina have not been studied as well as southern speckled trout populations.
  • Jingwei Song, a graduate research fellow, is investigating the genetic differences of northern speckled trout populations and whether these fish are more tolerant of cold temperatures.
  • Song’s work will help anglers and fishery managers understand how speckled trout adapt to their environment, and how the populations might respond to climate change.

  • Cold stuns can kill anywhere from a quarter to half of the speckled trout population when fish venture into shallow waters looking for food. The shallow waters get cold much more quickly, causing hypothermia in the fish, leaving them unable to breathe.
     
    “Certainly, in today’s world of colder colds and hotter hots experienced in global warming, this is a finding that is very useful to our future,” Arey says.

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