Fort Worth — As daytime temperatures remain above 100 degrees, Texas Parks and Wildlife Department Inland Fisheries biologist received a call Tuesday, August 30 regarding a large number of dead fish near the Silver Lake Marina – in a cove near the dam at Lake Grapevine. Water is a very interesting medium: as the temperature increases, the solubility of gases (specifically oxygen) decreases. With this in mind, fish are more likely to die of low oxygen stress when water temperatures are elevated because less dissolved oxygen is held in warm water and the fish’s metabolic requirements for oxygen are increased as temperature increases.
Dissolved oxygen levels were just 1.2 parts per million (ppm) Tuesday morning. Oxygen levels below 3 ppm can cause fish to become stressed and die. “The fish kill affected several species including gizzard and threadfin shad, bluegill, white bass, freshwater drum, largemouth bass, smallmouth bass, and white crappie,” said TPWD fisheries biologist Tom Hungerford. “By far the most abundant fish were the shad species,” Hungerford added.
TPWD staff conducted counts along transects to estimate the total number of fish impacted. “Based on our transects we estimated the total number of fish lost at 124,360 with 98.8% being threadfin shad,” said TPWD Kills and Spills biologist Melissa Dudley. “Less than 1% of fish observed were game fish,” she added. Additionally, a water sample was also collected and analyzed to rule out harmful algal blooms. The extreme temperatures and severe drought have impacted the amount and quality of water throughout Texas.