“This summer, as they have every summer since 1985, NOAA scientists headed out to the Gulf of Mexico to monitor fish populations and to find and measure the Dead Zone. Summer can be a tough time for many species in the Gulf of Mexico, when the combination of nutrient-rich river runoff and warm temperatures can rob coastal bottom waters of oxygen. Where that happens, shrimp, fish, and other creatures can be forced to flee to fresher waters, leaving a so-called dead zone behind. This week NOAA announced the official size of the dead zone. But because low oxygen levels impact valuable species of shrimp and fish, NOAA Fisheries scientists also conduct a separate study that covers a wider area and looks at how oxygen levels affect the distribution of marine animals. The annual summer groundfish survey runs from the Texas-Mexico border around to the Florida Keys. Scientists stop at nearly 300 randomly selected points along the way to sample the bottom with a trawl net—that’s the only way to know what species are down there—and to measure environmental variables including dissolved oxygen.”