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Channel Engineering Helps Protect Endangered Least Tern and Pallid Sturgeon
by Paul Hartfield
Photo Credit: USFWSe
The most prominent geographical feature in Mississippi is the mighty river that is its namesake. The Mississippi River has the largest drainage basin in North America. The river and its tributaries flow from Canada to the Gulf of Mexico, capturing water from the Appalachian Mountains to the East and the Rocky Mountains to the West. Although it is one of the most engineered river systems on Earth, many reaches, including the 954-mile portion downstream of the Ohio River confluence, remain highly functional ecosystems supporting unparalleled fish and wildlife resources.
Photo Credit: Bruce Reid, Lower Mississippi River Conservation Committee
Extremely low or high water discharges from the middle of the Mississippi River at Vicksburg, Mississippi, create havoc. Extremely high water discharges cause flooding, and extremely low water discharges hamper navigation and commerce. However, it is this natural – sometimes extreme – discharge that builds wildlife habitat and drives the Mississippi River ecosystem.
Among the animals that inhabit the Lower Mississippi River are two endangered species, the interior least tern (Sterna antillarum) and pallid sturgeon (Scaphirhynchus albus). These two species have more in common than their present status under the Endangered Species Act. Both are species of extremes—found at the northern and southern extremes of the continental U.S., from Montana to near the Gulf of Mexico, under climatic conditions ranging from arid to semi-tropical, and in small rivers, such as the Yellowstone River, to the largest, Lower Mississippi River. The habitats of both species are formed, maintained, and dependent upon high flow events, specifically periodic floods.
Both the interior least tern and pallid sturgeon were protected under the ESA primarily because of the construction of dams in the major tributaries of the Mississippi River, including the Missouri, Platte, Red, Arkansas, and Ohio Rivers. During the last century, large multi-purpose dams were constructed to capture high seasonal rainfall or snowmelt for flood storage and hydroelectric generation. Stored water is released gradually to reduce flooding and provide water for irrigation, human consumption, electricity, and navigation during dry seasons and droughts. Regardless of the purpose of the dams, they all function to reduce extreme flow events, creating relatively stable conditions for human activities but diminishing or eliminating habitats for wildlife.
Photo Credit: U.S. Army Corps of Engineers
During the 1980s, the Corps' Mississippi Valley Division began developing, testing, and incorporating engineering techniques and designs – such as grooves in bank paving to increase aquatic insect productivity and notches in dikes for maintain flows to backwaters – to reduce the negative effects of channel engineering to habitat quantity, quality, and ecosystem productivity. By 2001, the Mississippi Valley Division was prepared to work with the Service and other partners to focus these new tools on the habitat needs of species, such as the interior least tern and pallid sturgeon, and to begin mitigating the ecosystem effects of almost 100 years of channel engineering. Because these techniques are designed into routine channel construction and maintenance actions, they can be implemented with little to no extra cost to the program. The Corps has also worked with partners over the last decade to cost-share the restoration of nearly 40 miles of high value secondary channels benefitting hundreds of acres of channel habitats.
The interior least tern and pallid sturgeon are both benefitting from these efforts. Numbers of nesting terns on the Lower Mississippi River have nearly doubled, from an average of fewer than 6,000 birds per year during the 1990s to over 10,000 birds per year. Sturgeon spawning and other habitats are being protected and restored. Documented site records have increased from fewer than a dozen sturgeon in the Lower Mississippi River to more than 1,000. Other animals are also benefitting, including the endangered fat pocketbook mussel (Potamilus capax), which has expanded its range into the Lower Mississippi River by colonizing several of the restored secondary channels.
The Service, the Corps, and state partners have demonstrated the potential and value of using channel engineering as primary conservation tools to protect and recover endangered species and their habitats.
Paul Hartfield, a biologist in the Service's Mississippi Ecological Services Field Office in Jackson, Mississippi, can be reached at firstname.lastname@example.org or 601 965-4900.
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