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Research underscores toll of human-engineered Missouri River on pallid sturgeon

Research underscores toll of human-engineered Missouri River on pallid sturgeon

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A new study of an endangered fish along the lower Missouri River paints a sobering picture of its future.

Pallid sturgeon are dying off at a much younger age than previously thought and are spawning a fraction of normal, according to the report this summer in Scientific Reports/Nature.

The study also confirms how inhospitable the reengineered lower Missouri River is to the pallid sturgeon’s health compared to the more naturally flowing portions of the upper river.

“This really affects how many fish we think are out there, and the number of times these fish would become reproductively ready,” said Kirk Steffensen, a fisheries biologist with Nebraska Game and Parks Commission who was one of the authors of the report.

For now, Steffensen said, it’s clear that maintaining the population will require stocking the river.

Protecting the fish from extinction is a politically, economically and emotionally charged issue given the competing interests along the river, notably farming and barge traffic.

Some farmers say protecting the pallid sturgeon will result in them losing land, while barge operators say the river needs to kept artificially narrower so that it will run deep enough to carry their loads.

Southwest Iowa farmer Leo Ettleman said he’s not convinced that solutions proposed by scientists will work.

“It’s a tough call,” he said. “It’s almost like it’s too late to go back.”

Ettleman’s ability to farm his bottomland has been hindered by high water and floods. Recurring flooding, he said, has destroyed the ecosystem along the river.

“There are no pheasants or quail or rabbits along the river anymore because of this reoccurring flooding,” he said. “It’s tough to see any balance right now, I can tell you that.”

But scientists say the best way to address the lower river’s tendency to flood is to return some of the width that was eliminated to make it suitable for barges. More designated room for the river will reduce the frequency and height of flooding, they say, which will give farmers more certainty and produce an environment healthier for the pallid sturgeon.

“If we improve the river in terms of flooding, it would help the pallid sturgeon and farmers,” said Gerald Mestl, a fisheries biologist and the retired Missouri River program manager for the Nebraska Game and Parks Commission. “We think we’re on the same side.”

Mestl estimated that the river has been forced into about half the space it used to occupy. If the channel’s capacity was doubled by purchasing land from willing sellers, he said, flooding would be reduced by 90%.

And while the pallid sturgeon is the species protected by law, any improvements that help that fish will help the entire river ecosystem, Steffensen said.

As difficult as species conservation is, Steffensen said it’s worth trying.

“Pallid sturgeon serve as a good indicator species of the health of the river,” he said. “They were around for millions of years, and they were able to survive. Now all of a sudden, they’re an imperiled species.”

Since 2019’s catastrophic flooding, government officials have been meeting with various interests along the lower river to chart a path forward. How species protection will rank compared to other human interests remains to be seen. For now, though, federal funding of habitat restoration has largely been suspended.

Complicating the viability of the species is the already recognized near impossibility of pallid sturgeon embryos spawned in the wild surviving into adulthood.

Through DNA analysis, fish biologists know that the majority of adults they find in the river were raised in a hatchery before being released into the river as fingerlings. Only about 8% of all pallid sturgeon captured in the lower Missouri River were spawned there, Steffensen said.

(Of the 4,487 pallid sturgeon captured along the lower Missouri River from 2003 to 2015, only 358 were spawned there.)

For the purposes of this study, the upper river is the area near the confluence of the Missouri and Yellowstone Rivers, below Fort Peck Dam in northeast Montana. The lower Missouri River is that portion downstream of Gavins Point Dam to the river’s confluence with the Mississippi River (from north of Sioux City, Iowa, to St. Louis, Missouri).

The new research compared the health, fertility and life cycles of pallid sturgeon on the reconstructed lower Missouri River to the more naturally flowing upper Missouri River. (The upper Missouri, above the dams, doesn’t carry commercial barges so a narrowing and deepening of the river isn’t required.)

Compared to the upper Missouri, the study found that in the lower Missouri River:

  • Pallid sturgeon live about one-third as long, 19.8 years compared to 56.4 years. (Before the river was altered, pallid sturgeons were believed to live as long as 100 years.)
  • Females weighed one-seventh as much.
  • Females’ reproductive cycles have accelerated, with females reaching sexual maturity about age 10 compared to age 17.
  • Reproduction has been less successful, despite the females’ earlier sexual maturity. Females have spawned about one-fourth to one-half as often and laid about one-tenth as many eggs.

The research was led by the University of Nebraska-Lincoln School of Natural Resources, assisted by the Nebraska Game and Parks Commission.

Mark Pegg, a UNL fisheries ecologist, and then-UNL post-graduate students Martin Hamel and Jonathan Spurgeon were the other authors. Pegg said he was prepared to see some difference in the numbers but was surprised by how much their health varied.

“I didn’t expect it to be that dramatic,” he said.

Steffensen said scientists thought pallid sturgeon lived to about 40 years in the lower Missouri. A lifespan half that long means that females have fewer years to reproduce. (That’s a problem because pallid sturgeon lay eggs only every couple of years.)

20201019_new_pallidsturgeon​_map

The lineage of the pallid sturgeon dates back some 70 million years, but as this study underscores, nothing in its past has equipped it to adapt to the changes humans have brought to the Missouri River.

During the last century, humans effectively straitjacketed the lower Missouri River by narrowing, deepening and shortening it so that it could serve as a watery highway for commercial boating. And except for the more naturally free flowing stretches, the upper river now is home to six massive dams — the largest reservoir system in North America.

The entire stretch of river from Sioux City to St. Louis has been channelized, with armoring added on the outside of bends of the river and in-stream barriers constructed on the insides of bends. If not for these restrictions, the river would follow multiple, shallower paths that braid together and split apart. (Levees were an add-on, built to reduce flooding.)

Largely gone in the lower Missouri are shallow pools and nutrient-rich side channels of varying depths. It was in these nurseries where larval pallid sturgeon took refuge and found the food needed to mature into fingerlings. And it’s also this type of habitat, which is more common on the upper river, that best nourishes adult pallid sturgeons.

The ecological value of a more naturally flowing river also has been borne out by annual fluctuations in the health of the pallid sturgeon that mirror river conditions on the lower Missouri.

During years of high water, when the river escapes its man-made confines and wanders through adjacent low-lying areas, the fish thrive, gaining weight, Steffensen said. During years in which the river remains within its constructed route, the fish are much thinner, he said.

During those high water years, pallid sturgeon can weigh a third more. Researchers know this because they pull pallid sturgeon from the river to assess their health.

Steffensen said high water years probably produce healthier fish because the river climbs out of its banks and creates pools and slower flowing areas on the floodplain, which is nutrient-rich with insects, minnows and other organisms.

And while pallid sturgeon are healthier, live longer and spawn more often on the upper Missouri River, that stretch of the river poses its own problem to the species’ survival. The reservoirs created by the dams apparently are fatal to pallid sturgeon embryos, Steffensen said.

That’s because the embryos float downstream for about two weeks as they mature, and over that period of time, scientists believe they float into reservoirs, sink to the bottom and die.

That means strategies to preserve the fish differ on the upper and lower river, Steffensen said. On the upper river, the focus is on finding a way to create sufficient distance for the embryos to drift. The solution to this is building bypass channels. On the lower river there’s plenty of drift distance, but not enough nursery habitat off to the side of the river. The extent to which future nursery habitat receives federal funding remains to be seen.Eagles along the Missouri River

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Nancy Gaarder helps cover public safety and weather events as an editor on The World-Herald's breaking news desk. Follow her on Twitter @gaarder. Email: nancy.gaarder@owh.com

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