JEFFERSON CITY — For the past two and a half years they tracked her every move. Now, they are coming to find her.
She’s out there somewhere in the Missouri River currents, carrying clues as to why her kind is in danger. A transmitter, previously placed in her belly, chirps like a cricket every 10 seconds; her name is the same as the unique audio code that the transmitter emits — 1094.
Pallid sturgeon are used to being hunted. In the 19th century, humans almost wiped out this ancient species to satisfy cravings for caviar. In the late 20th century, the construction of dams on the upper Missouri River altered their natural habitats.
Lately, humans come for other reasons. Studying the reproductive patterns of pallid sturgeon is key to understanding what caused the species to be classified as endangered in 1990 and what might be disrupting their behavior enough to threaten their existence. Now the scientists at the U.S. Geological Survey’s Columbia Environmental Research Center track pallid sturgeon.
Aaron DeLonay, an ecologist for the River Studies Branch of the center, sets out on a chilly morning in October to capture 1094 for a specific purpose: to see if she will spawn this April. If so, her fertility will make her special.
Despite intensive efforts by federal and state agencies to capture females with eggs, less than a dozen of the female pallid sturgeon captured each year have eggs and are ready and able to reproduce.
And so DeLonay's crew searches the 9-mile stretch of the river downstream from the Capitol that she’s inhabited since July. They come armed with an underwater microphone and receivers to track her signature chirp. But even 9 miles of river is an ocean when you are using a hydrophone with a range of 300 to 800 meters.
There is no rush of activity on this morning. The hydrophone’s receiver lets out nothing but a scratchy hiss, the sound of the river.
Pallid sturgeon 1094 isn’t found.
Studying spawning fish holds answers to population declines
Seeing if a fish is ready to spawn is a guessing game. Female pallid sturgeon take 11 to 12 years to reach reproductive maturity, and they only spawn every two to five years.
The true age of 1094 is a mystery. Like a tree trunk, the age of a pallid sturgeon is best understood by slicing a piece of its fin and counting the rings that form every year. But the center rarely does this to endangered fish, and 1094’s fin remains intact.
Her 37-inch, 7-pound body and the fact that she has yet to spawn for the first time indicate that she's around 9 to 12 years old, DeLonay said.
The U.S. Fish and Wildlife Service first netted 1094 near the mouth of the Osage River in 2008. She was thought to be a good candidate to be a parent in an artificial propagation program in a state fish hatchery, but she wasn’t old enough to spawn. She’s been captured by the Columbia Environmental Research Center three times since, but she has yet to reach sexual maturity.
She is familiar with the scramble that follows her captures: a net, a quick struggle aboard a 21-foot aluminum boat, a series of tests and a rush to get all of it done quickly.
It seems like a dreaded doctor’s check-up: ultrasounds, blood samples, a small surgical incision, a replacement data tag and a new transmitter with fresh batteries. A fading scar marks her smooth, white belly where the transmitter and data tag were inserted in April 2008 before she was released from the hatchery.
The data tag records her life on a microchip: the depths she’s encountered, the water temperatures she’s endured, the routes she’s taken. When she is captured, tag information is transferred to a computer database.
This information helps scientists such as DeLonay learn about the environment 1094 lives in as well as factors that disrupt it. And learning about the effect of the environment on reproduction helps scientists understand why the pallid population is in trouble.
Pallid sturgeon affected by habitat changes, contaminants
Pallid sturgeons don’t just lie at the bottom of the river — they "fly" in the eyes of DeLonay.
Big pectoral fins help them glide and float through currents. Unlike their shorter-lived shovelnose cousins, they can live to be 60 to 80 years old.
Because they are constantly exposed to river conditions and because of their long lives, pallid sturgeon are particularly sensitive to the three main things that threaten sturgeon populations: habitat changes, dam construction and contaminants.
River flow is key to survival; sturgeons require access to free-flowing rivers and are sensitive to factors that disrupt it, such as dam construction. Changes to the river channel, such as mining for sand or gravel and bank stabilization to prevent erosion, also affect sturgeon habitats by changing water depths and currents.
In 2000, the U.S. Fish and Wildlife Service and the Army Corps of Engineers, which manages Missouri River flow, began several programs to protect sturgeon. These programs have included the construction of shallow-water habitats for pallid sturgeon, experimental flows from dams to encourage sturgeon to spawn, the transfer of sturgeon to hatcheries to produce more baby sturgeon, as well as more research into the behavior and health of the species.
Although many agencies have joined together to help this species, the sturgeon populations still struggle to reproduce.
And as more information is discovered about water contaminants, a new problem is on the horizon. The Columbia Environmental Research Center believes hormonal compounds like those found in women’s birth control pills may cause shovelnose sturgeon to develop both male and female sex organs. And though intersex has only been found in a few pallid sturgeon, the fact that the condition is occurring with regularity in the closely related shovelnose sturgeon is concerning to scientists like DeLonay.
The center will continue to track 1094
They find 1094 a month later about 4 miles above the mouth of the Osage River and only a half-mile downstream from where DeLonay and his crew searched for her in October.
Perhaps she had been hiding behind a dike or sandbar that October day. Perhaps the debris from a recent storm had cluttered the currents and she changed locations to avoid it. Perhaps she had moved with the changing water levels.
But when they finally capture her, she isn't ready to spawn.
She is a little heavier, a little more mature, but she is not ready to travel hundreds of miles upstream this spring to gather with other spawning sturgeon and release her eggs. A male pallid sturgeon will not follow behind her closely to release sperm into the water to fertilize her eggs. Her eggs will not stick to gravel and rocks in fast currents, waiting to hatch.
One day, when 1094 is ready to spawn she may embark on such a journey. She'll join a small group of spawning pallid sturgeon that scientists currently track between St. Louis and the Gavins Point Dam on the Nebraska-South Dakota line.
But until then, the Columbia Environmental Research Center will continue to patrol the waters she calls home, checking in on that signature chirp.