Biologists Launch Study of Two Texas Tidal Streams

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AUSTIN, Texas — In March, Texas Parks and Wildlife Department biologists began a two-year study of two tidal streams on the middle coast, sampling fish, bottom-dwelling organisms, and water quality to measure the quality of aquatic life inhabiting these ecologically important areas.

Tidal streams are areas where saltwater from bays mix with freshwater coming down from rivers. They are components of estuaries, a better-known term for areas where freshwater and saltwater converge. Because tidal streams provide a special kind of habitat, they are vital nursery grounds for many types of fish and shellfish, including economically important species like shrimp and game fish.

"Tidal streams are complex ecosystems," said Janet Nelson, a TPWD coastal biologist. "We need to know more about threats to them that could undermine biodiversity in general and our sport and commercial fisheries in particular. There hasn’t been enough study of tidal streams to completely understand what drives changes in these systems."

Nelson said tidal stream salinity varies seasonally with rainfall, and this drives changes in fish populations. Other factors that affect habitat and water quality include hydrology (water movement), freshwater inflow, subsidence, land use in the watershed and wastewater discharges.

The Texas Commission on Environmental Quality has contracted with TPWD to study two tidal streams, the tidal portions of Aransas and Mission rivers connected to Aransas Bay. Field sampling began in late March and will continue until November 2009. Sampling will occur every six weeks during the spring, summer and fall seasons. Water and sediment (bottom) samples will be collected for laboratory analysis. Other parameters that will be measured include dissolved oxygen, pH, temperature salinity, and stream flow.

Fish, shrimp, crabs and other swimming organisms will be collected, identified and measured. Sediment from the bottom of the streams will be collected to see what types of organisms live there. A detailed field study will be done of habitat within the stream and on the banks. Also, a GIS land cover analysis will be done to see how the land surrounding the stream is being used.

When the fieldwork is completed, the final report to is due to TCEQ in 2010. This gives TPWD scientists about one year to analyze and interpret all the data and write a report on the ecological health of each stream.