Written by MNWR Aquatic Biologist Dominic Bachman and Peter Pearsall/Photos by MNWR
A new carp removal project at Malheur Refuge will employ an electronic fish barrier (e-barrier), installed near the mouth of the Blitzen River, to assist the management of invasive common carp that are negatively affecting water quality in Malheur Lake and the Blitzen River.
During low-water years, which occur approximately every six out of 10 years, this barrier will be used to stop carp from 1) spawning in the river, which is their only viable location on dry years; and 2) using the river as a refugia when the lake water quality, depth, ice make it uninhabitable to carp. Refuge staff and partners—including High Desert Partnership, Oregon Department of Fish and Wildlife, and Friends of the Malheur National Wildlife Refuge—will use the electronic barrier to easily capture and remove large amounts of carp from the watershed.
Conservation work has had a major focus on the Blitzen watershed and the overall health of Malheur Lake. Wetlands within the Harney Basin are considered to be a high-priority habitat for migratory and resident bird populations within the Pacific Flyway, as identified in the Intermountain West Joint Venture as “wetland landscapes and spring migratory priority areas” (Intermountain West Joint Venture Implementation Plan, 2013).
Malheur Lake conditions have changed since the introduction of common carp. As described by Deubbert (1969), “After carp were introduced into the Silvies River watershed in the early 1920’s, these fish often became sufficiently numerous in the lake to be detrimental to submerged aquatic vegetation. By 1955 carp activity had created such turbidity that desirable submerged aquatics were nearly eliminated. In 1955 the carp population was controlled with rotenone, a fish toxicant. It was estimated that 1.5 million carp averaging 20 to 25 inches in length were killed. The beneficial effect was demonstrated the next year when sago pondweed showed immediate response to improved growing conditions and covered 15,000 acres”. Carp populations have ebbed and flowed and many recent attempts to manage them have been challenging. (Malheur National Wildlife Refuge Comprehensive Conservation Implementation Plan Update 2021).
Malheur and Harney Lakes experienced extreme flooding in the mid 1980s. When flood levels subsided, the emergent vegetation that characterized the marsh conditions of Malheur Lake failed to recolonize the lakebed and the complex topography of the lakebed was smoothed to an even surface by ice and wind (Malheur National Wildlife Refuge Comprehensive Conservation Plan 2013). Historic flows into Malheur Lake have also changed dramatically. Malheur Lake now is dependent on flows from the Blitzen River and gets little contribution from the Silvies River. Silver Creek rarely flows to Harney Lake. Reduced inputs among many other factors make managing wetland vegetation and carp reduction a difficult task. Recent data has shown a significant amount of the lake’s turbidity is coming from Blitzen water. It is likely that carp, which heavily utilize the Blitzen in low water years, are having a negative effect on that stream’s health and increasing turbidity.
When Malheur Lake had abundant submergent vegetation, it supported up to 150,000 breeding waterfowl and many other avian species. The current condition is turbid water with little emergent vegetation and very little submergent vegetation. Recognition of this condition, and growing understanding of the processes that are keeping Malheur Lake in this perpetual degraded condition, has refocused restoration strategies in the 2021 Malheur National Wildlife Refuge CCP Implementation update.
Restoring and sustaining wetland conditions and clear water habitat to the extent possible is the primary goal for Malheur Lake. Managing the carp population, reintroduction of emergent vegetation, and managing substrate conditions to restore marsh conditions are objectives to move towards a clear-water lake system.
In fall of 2022, during a very low-water year, Refuge staff and partners removed a total of 43 tons of carp by hand from the area of the Blitzen River below Sodhouse dam. This was considered an extremely low carp population, and it is estimated that on some years at least three times that many carp would be found in this stretch of river, causing damage to the bottom and banks, increasing turbidity, and significantly affecting water quality and food availability for native fish and wildlife. The e-barrier would exclude the carp from this area and force them into a shallow area near the mouth of the lake where they would be easy to remove and face excessive predation.
“Taking what has been learned over the last decade, we have focused on taking targeted action to reduce the carp population through harvest and exclusion from the Blitzen River,” said Dominic Bachman, MNWR Aquatic Biologist. “We have partnered with Carp Solutions to design an e-barrier that will not allow carp moving into the river for spring spawning or for refugia during hot weather, heavy ice, or drought conditions.”
Bachman added, “Radio telemetry and carp surveillance has shown that during low water conditions, carp can only spawn in the Blitzen River wetlands, and much of that area can be blocked with this barrier. The barrier has been designed to stop large carp. This design also allows smaller native fish through the barrier. Much of the use of this system can be automated by using new pit tag technology that alerts staff when multiple fish are at the barrier. This system is designed to corral and remove carp from the river with very little effort or manpower.”
The project began in November 2023 and is expected to wrap up by December 2025.
