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The invasive blue catfish is already spreading in the Chesapeake Bay and eating a lot in the process. A new study by the Virginia Institute of Marine Science (VIMS) shows that the blue cat population can extend even further thanks to the warming water along the Atlantic coast.
Dr. Vaskar Nepal and Mary Fabrizio of VIMS build on an earlier study that showed that blue catfish tolerate salinity peaks better than most freshwater fish, potentially expanding their range downstream into the main Chesapeake tribe and into new tributaries, or even here as Delaware Bay.
Blue catfish was introduced as recreational fishing destinations in the tidal freshwater stretches of the James, York, and Rappahannock Rivers in the 1970s and 1980s. Now they are in 12 major rivers. from the bottom up in the bay. They feed on almost everything on their way – vegetation, mollusks, and fish – and often outperform native species like white catfish. As an omnivore, this can also pose a threat to yellow perch, shadows, crabs, and striped bass. Hence, their continued proliferation is of concern to fisheries managers.
In the study, published in a recent issue of PLOS ONE, Drs. Nepal and Fabrizio long-term manipulated salinity and temperature to see how they affected catfish health and behavior. Since Chesapeake Bay is (generally) warmer and salty in summer, but colder and fresher in winter and spring, their approach is more natural.
Dr. Vaskar Nepal tests the temperature and salinity tolerance of blue catfish. Photo: Mary Fabrizio / VIMS.
“By manipulating both factors, we were able to close an important knowledge gap and more precisely simulate real-world conditions in which salinity and temperature can and must vary over a number of time scales.” says Nepal. Their heat and salt content can also vary over shorter periods of time during periods of rain, drought, heat waves or cold spells.
The researchers monitored 160 young blue catfish spread across eight tanks with varying levels of salt and temperature, similar to those found in many of the bay’s tributaries. They examined the catfish in their tanks for three months.
Nepal and Fabrizio’s findings show that the warmer water temperature has a positive impact on blue catfish biology under salinity conditions that are common in estuary waters. The blue cats grew faster, were healthier, and ate more in 72-degree water than in 54-degree water. The fish appeared to thrive in warmer, fresher water, as scientists predict with climate change in the Chesapeake.
However, when the water got too salty, the catfish ate much slower and was less healthy overall. They were essentially bathed in water that was saltier than their own internal tissues.
“Many brackish habitats along the US east coast may be vulnerable to invasion by blue catfish,” says Nepal, “especially in the face of rising temperatures due to global warming.” Based on the results, Nepal advises: “State and regional administrative authorities should pay particular attention to the habitats in these saline levels, especially in areas that are home to native species that are protected.”
Is there a silver lining? As sea level rise continues to bring salty water into rivers and streams, the intrusion of salinity may prevent the blue cats from moving from tributary to tributary rather than staying upstream.
-Meg Walburn Viviano