Invasive fish kill might be due to colder temperature

We don’t like them, but that doesn’t mean we don’t want to know why they died.

The appearance of dead armored suckermouth catfish, (plecostomus, or “pleco” for short) along the San Marcos River downstream of its confluence with the Blanco were quickly followed over the weekend by groups of vultures intent on taking advantage of the free feast.

An invasive species, plecos are controlled in the river within the city limits by Nick Menchaca, whose company, Atlas Environmental has a contract with the city for their removal.

When they showed up downstream, it was first thought someone was removing them there. But residents including Hugh Fairly, who found 17 on his property on Cottonseed Rapids, disagreed. “These fish had not been speared,” he said.

The prevailing wisdom seems to be that colder water killed the tropical fish. While the spring-fed San Marcos River is a constant 72 degrees year-round in San Marcos, farther downstream the water fluctuates in temperature. The water also “gets cooler in winter with rains,” which were plentiful in the fall, Dianne Wassenich of the San Marcos River Foundation said.

Further, it’s thought that the fall rains and fuller river ushered the invasives downstream, since there hadn’t been a similar occurrence last winter or in years before.

Whatever the reason, Wassenich is among those not sorry to see the massive kill. “Hope this knocks them back, they are very de-stabilizing for the banks since they burrow into the banks,” she said.