Missing from the Pearl River for 50 years, state and federal biologists working to save Pearl Darter

Matt Wagner, a fish and wildlife biologist at the United States Fish and Wildlife Service, says the reason why populations declined so drastically in the Pearl system remains unclear. 

“The main reason that the species was listed [as threatened] was its loss of range in the Pearl River drainage, going from being in the drainage to completely extirpated from the drainage since 1973,” said Wagner, who is also lead biologist on the restoration project. 

“There was a biologist out of Tulane who did annual samples at several sites throughout the whole Pearl River drainage, including the Strong River. And all of a sudden, in the early seventies, they just stopped showing up in the samples – it was very abrupt. For a fish to stop showing up in a river over two or three years is kind of crazy.”

‘We don’t know what it was’

The question of what happened to the Pearl darter is made more complicated by the fact that, while missing from the Pearl River system, the insect-eating fish have been found in abundance throughout the Pascagoula River system over the same period. 

Found only in those two river basins, they’re known to live as far north as the source of the Strong River near Morton and as far south as Walkiah Bluff, along the Pearl. But according to Wagner, extensive sampling and environmental DNA tests haven’t produced any evidence of their presence.

One reason could be the manner in which each river has been developed for various uses, including large industrial and navigation projects. 

“There's a bunch of different projects that have happened on the Pearl, generally navigation projects, that have destabilized the sediment within the drainage and caused some erosional waves to move through the system,” said Wagner. 

“We don't know if it was potentially agriculture or chicken farming where they just dumped their waste from chicken farms right into the Strong River, the big trib [sic] to the Pearl. We just don't have the monitoring — something knocked them out of the Strong River and the Pearl River, and we don't know what it was.”

River changes and a chain reaction

For its part, the Pearl River of today has been shaped by a number of navigational projects, such as the West Pearl Navigation Canal, dams and even more channelization projects. There’s also the 32,000-acre Ross Barnett Reservoir northeast of Jackson, an upstream drinking water development. 

Both types of projects carry with them profound effects on the river’s hydrology, both in riverbank erosion causing increased sediment flow and a change in coastal freshwater availability where the Pearl runs into the Mississippi Sound. 

For a species like the Pearl darter, whose populations rely heavily on clean substrates, those effects can be especially pernicious. 

Nickpoints often form where newly-dug channels create sharp changes in a river’s slope, leading to erosion at that point, which can often turn into a wave that slowly makes its way further up the river, weakening and ultimately eroding river banks into the water and increasing sediment in the water.

The Pascagoula River system, however, is the largest unmodified river system in the Southeast, and possibly even the lower-48 states and southern Canada. 

Wagner says similar sampling has placed Pearl darter in the main stem as well as major tributaries Chickasawhay and Leaf Rivers, and even in smaller water bodies like Black and Okatoma Creeks, where water is allowed to flow freely and pollutants are limited. 

“We have no big dams on the Pascagoula. There's some small dams on some of the tributaries, but the main stem, Chickasawhay and Leaf don't have any dams on them. There's been very little modification in the ways of channels or dredging, so it's a natural system without disturbance, which leads to stability,” said Wagner. 

Still, the question of what caused the Pearl darter’s demise throughout the larger Pearl River system remains a mystery. With no flood, drought or chemical spill on record from 1973 – and an average lifespan of 2 to 3 years – Wagner says it could have been one event on the Strong River that caused a chain reaction downstream and into the Pearl. 

“They're not known from the Pearl River above the Strong River. So basically, anything that would have happened in the Strong would have wiped them out — the entire Strong and then in the Pearl below. But we're not sure what caused it exactly.”

But the Strong River, meandering 95-miles down south-central Mississippi before it feeds into the Pearl River near Georgetown, has experienced little in the way of navigation projects, making it an ideal place to begin the process of the Pearl darter’s recovery.

Recovery

That process began in earnest in 2018, only a year after the Pearl darter’s listing as a threatened species, at the Private John Allen National Fish Hatchery in Tupelo. 

While federal hatcheries are typically a place to breed aquarium and game species such as striped bass or sturgeon, the Pearl darter is the first listed species the federal hatchery has raised and eventually stocked. Everything else has been a game species or something that's not listed but still has conservation needs, such as alligator gar or the Yoknapatawpha darter along the Yocona river. 

The goal is to raise enough of the species at the hatchery in order to later reintroduce it to its habitat in hopes the larvae will float downstream and eventually reproduce in the wild. 

While Wagner says he would have preferred July 31’s stocking had been 300 Pearl darter instead of 39, he expects surveys and subsequent stocking will take place beginning next year and continue for the next 5 to 10. 

“So then the recovery plan for the Pearl darter was just published earlier this year, and the main recovery action to delist Pearl darter from the Endangered Species Act and establish it in the Pearl River drainage,” said Wagner. “And by reestablish we mean we’re not putting them in every single year, but to stock them to a point where they're reproducing and self-sustaining as a population.”