Scientists measure inlet's effect on marine life
An HRI survey of a recently reopened waterway that connects the Texas mainland to the Gulf of Mexico found juvenile red drum, a key indicator species, at nearly every predicted impact site. The findings give researchers optimism that the reconnected inlet is positively influencing the densities of juvenile fish, shrimp and crabs (nekton) in Mesquite Bay near Rockport, Texas.
Cedar Bayou, which runs through Matagorda Island and connects the Texas mainland with the Gulf of Mexico, was intentionally closed in 1979 to prevent contaminants from the Ixtoc oil spill in the Bay of Campeche from reaching the Texas mainland. The reopening of Cedar Bayou was deemed so environmentally crucial to the State of Texas that, in April 2014, the U.S. Army Corps of Engineers issued a permit to permanently open the bayou's mouth, a task that was completed in late September using funds secured by Aransas County and the Coastal Conservation Association.
Due to immense interest from within the scientific and fishing communities concerning how fish and crustacean assemblages and densities in the Mesquite Bay complex may change due to the reopening of Cedar Bayou, HRI's Center for Sportfish Science and Conservation has been charged with monitoring Cedar Bayou. Currently, researchers are taking rigorous and repetitive measurements at fixed control and impact locations throughout Mesquite Bay and comparing them to measurements taken prior to reopening Cedar Bayou. These surveys will continue until late 2015.
"In the two years of data collection before the reopening, no juvenile red drum were found at the impact sites near Cedar Bayou," said Quentin Hall, an HRI Master of Science student whose research focuses on the effects of reopening Cedar Bayou on nekton species. "This finding is very encouraging and we look forward to getting a better picture of how reopening Cedar Bayou will influence juvenile nekton densities over the next year."
Recent research has documented how inlets such as Cedar Bayou play an important role as migratory routes for spawning fish as well as access to estuarine nursery habitat. For example, a study conducted on the Packery Channel showed that reopening the inlet approximately 38 miles southwest of Cedar Bayou resulted in increased densities of economically important species in the surrounding area.
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"Adult red drum spawn offshore and the resulting young rely on tidal inlets such as Cedar Bayou to migrate into seagrass beds located in bay systems," said Dr. Greg Stunz, Director of the Center for Sportfish Science and Conservation. "We suspect that with Cedar Bayou closed, these juveniles could not make their way into Mesquite Bay. Numerous other species rely on tidal inlets for this reason as well, including southern flounder and blue crab."
Access to nursery habitats has both ecological and economic implications because as much as 75 percent of commercially or recreationally important species in the Gulf of Mexico are estuarine dependent. Post-opening densities of larval/juvenile fish suggest that Cedar Bayou provides important and increasingly rare access to nursery habitat populations and indicates that reopening barrier island inlets increases access to estuarine nursery habitats.
Direct beneficiaries of this increased productivity of the new inlet will most certainly be recreational fishermen and also commercial crab and shrimp fleets throughout the Gulf of Mexico. Economic recovery is especially critical following manmade and natural disasters such as the Deepwater Horizon oil spill and Hurricane Katrina.
The refuges bordering Cedar Bayou are also the wintering grounds of endangered whooping cranes that rely on Cedar Bayou's blue crab population for 41 percent of their winter diet. Given that times of lower blue crab abundance may be linked to increased winter mortality for whooping cranes and that the reopening of inlets has been shown to increase blue crab recruitment densities, the reopening of Cedar Bayou will likely play a decisive role in increasing this good food source and subsequent whooping cranes survival during the winter months.
BY STEVE PASCHAL/HRI NEWS EDITOR