Crane numbers rise in years when salinity in their feeding areas is low because the blue crabs they eat need low salinity. Good freshwater inflow keeps salinity at healthy levels.

A Big Challenge
People have known for a long time that the fresh water flowing into Aransas National Wildlife Refuge is critical for Whooping Cranes and other species that live in the estuary. Ten years ago (before some Journey North participants were born!) there was a report in the San Antonio Light newspaper (Nov 16, 1992) about the water needs of Whooping Cranes and how their needs sometimes conflict with human uses of water. The article stated that whoopers, just like San Antonians, depend on water from the Edwards Aquifer. This aquifer is a source of spring water that feeds the Guadalupe and San Antonio Rivers. Of course, rainwater and runoff also provide fresh water for the rivers; but during dry spells, aquifer springs may contribute than 80 percent of the fresh water entering the bay. When people remove this aquifer water for individuals, farmers, ranchers, and manufacturers, the estuary ecosystem can be damaged.

Drought Difficulties
Gary Powell, director of the bays and estuaries program for the Texas Water Development Board, said "The bay needs between 1 and 2 million acre-feet of water per year to maintain a productive life." (An acre-foot is the amount of water needed to cover an acre of land 1 foot deep, or 325,851 gallons.) "If it drops below1 million acre-feet, the quality of bay water would drop, which could hurt marine life along the coast. San Antonio Bay receives an average of about 2.3 million acre-feet of water each year."

During some droughts, the annual freshwater in-flow into the bay may be only 275,000 acre-feet. Comal Springs in New Braunfels, which normally spews 206,928 acre-feet of water a year, went dry in 1956, during a severe drought.

Water Shortages Threaten Cranes
During years when not enough fresh water flows from the rivers into the estuary, Whooping Crane winter deaths increase. "We found when salinity in the marshes reach 23 parts per 1,000 (and sea water is 35 parts per 1,000), the whooping cranes have to fly to fresh water to drink at least twice a day. And we find there's more crane mortality when the salinity is at 23 parts or higher," said Tom Stehn, Whooping Crane coordinator at the Aransas National Wildlife Refuge. Also, cranes reproduce more poorly once they reach their breeding grounds in years when salinity is high, because they are lacking the basic nourishment their bodies normally get from blue crabs.

Wildlife Needs Fresh Water
It's not only Whooping Cranes that depend on the fresh water inflows to the estuary. Other endangered or threatened species that live in the bay include

• brown pelican
• reddish egret
• piping plover
• Texas diamondback terrapin
• Kemp's Ridley sea turtle, the most endangered of all the sea turtles.
   

As scientists determine exactly how much fresh water is needed to maintain the ecosystem and the species that live in San Antonio Bay and Guadalupe River estuary, regulations could affect how much water people are allowed to pump. The human population of Texas is expected to double in the next 50 years (2002 projection). Do you think it's possible for humans to meet our own needs AND those of Whooping Cranes?