Earlier this year, Texas Parks and Wildlife Department coastal fisheries biologists began a two-year study of Arroyo Colorado, a tidal stream connected to lower Laguna Madre. Biologists received a grant to measure the quality of aquatic life in this ecologically important area.
This effort is part of a larger coast-wide assessment of tidal streams that has been under way for the better part of a decade.
“Specifically, we are working in conjunction with the existing Arroyo Colorado Watershed Partnership, as they update their watershed plan, with the goal of ultimately improving water quality for the Arroyo Colorado and Lower Laguna Madre,” said Janet Nelson, TPWD coastal biologist.
Tidal streams are components of estuaries, a better-known term for areas where freshwater from rivers and saltwater from bays converge. Because they provide a special kind of habitat, tidal streams are vital nursery grounds for many types of fish and shellfish.
“Tidal streams are complex ecosystems,” Nelson said. “We need to know more about threats to them that could undermine biodiversity in general and our sport and commercial fisheries in particular. We have been studying tidal streams in Texas for over ten years, and we now have a better understanding of what drives changes in these systems.”
Nelson said tidal stream salinity varies seasonally with rainfall, and this drives changes in fish populations. During times of abundant rainfall, freshwater fish such as gar, carp, and blue catfish are very abundant in the tidal stream, whereas during a drought many marine species, such as red fish, spotted sea trout, and pinfish can be found in these same areas. Other factors that affect habitat and water quality include hydrology (water movement), freshwater inflow, subsidence, land use and wastewater discharges.
Biologists will sample organisms (like fish, crabs, and shrimp) and water quality in the Arroyo Colorado during the spring, summer and fall. Habitat in the Arroyo and on its banks will be recorded at the beginning of this study. The land use for the surrounding area will also be analyzed. When the fieldwork is completed in November 2015, TPWD biologists will analyze the data and report on the ecological health of the Arroyo Colorado.