QUESTIONS AND ANSWERS
REGARDING THE 12-MONTH FINDING FOR
SICKLEFIN CHUB AND STURGEON CHUB
What is a 12-month finding?
Publication in the Federal Register of a 12-month finding makes public the Serviceís decision on a petition to list a species as threatened or endangered under the Federal Endangered Species Act. That finding is based on a detailed assessment of the available information on the species, as detailed in the speciesí status review. One of three possible conclusions can be reached as part of the finding: that listing is warranted, not warranted, or warranted but presently precluded by other higher-priority listing activities involving other species. In the case of the sicklefin and sturgeon chubs, the Service found that they were not likely to become a threatened or endangered species within the foreseeable future. Therefore, listing of the sicklefin chub and the sturgeon chub as a threatened or endangered species under the ESA is not warranted at this time.
What are the sicklefin and sturgeon chub?
The sicklefin and sturgeon chub are members of the Cyprinidae, or minnow, family. They are native to the Missouri River basin and the Mississippi River downstream from the confluence with the Missouri River. Both species are highly adapted for conditions found in large free-flowing rivers with relatively high levels of turbidity.
What do they look like?
The sicklefin chub is usually yellowish or tan colored on the back and silvery-white on the belly with a snout protruding slightly beyond the mouth. A single pair of maxillary barbels is located at the corners of the mouth. Average adult length ranges from 1.4 to 4.0 inches with the average adult weight ranging from 0.02 to 0.2 ounce. The sicklefin is a relatively short-lived species with a small percentage of the population reaching age 4. The sicklefin chub can be most readily distinguished by its elongated pectoral fins and a sickle-shaped dorsal fin.
The sturgeon chub is tan to pale green on the back and cream to white on the belly. A few black speckles occasionally are present on the sides and back. It has a long, fleshy snout with a single pair of maxillary barbels located at the corners of the mouth. Average adult length ranges from 1.5 to 3.8 inches and average adult weight ranges from 0.01 to 0.3 ounces. The sturgeon chub is relatively short-lived species with a maximum life-span of about 4 years. Sturgeon chub can be identified by the unique longitudinally-arranged ridges or keels on most scales.
What is their historic range?
Sicklefin Chub: The sicklefin chub was historically found in the Lower Yellowstone River, Missouri River, and Mississippi River downstream from the confluence with the Missouri River.
Sturgeon Chub: Sturgeon chub have been collected at or near the same locations where sicklefin chub populations have been documented in the Yellowstone, Missouri, and Mississippi Rivers. They also ascend further upstream in the Yellowstone and Missouri Rivers than the sicklefin chub and have been historically collected in 30 of the larger tributaries to the Yellowstone and Missouri Rivers.
Who petitioned the Fish and Wildlife Service to list the sicklefin chub and sturgeon chub as endangered?
The Service received a petition from the Environmental Defense Fund, American Rivers, Mni Sose Intertribal Water Rights Coalition, National Audubon Society, and the Nebraska Audubon Council.
Why did the petitioners think the sicklefin and sturgeon chubs were endangered?
The petitioners cite impacts associated with the construction and continuing operation of the Missouri River main stem dams and channelization as the principal threats affecting these species and their habitats.
What is the difference between a "threatened" or an "endangered" designation?
"Endangered" means a species is in danger of extinction throughout all or a significant portion of its range. "Threatened" means a species is likely to be come endangered within the foreseeable future.
What did the Service find regarding the status of the sicklefin and sturgeon chubs?
The Service reviewed the best available data from fisheries investigations conducted throughout the range of these species and found that sicklefin and sturgeon chub are more common and more widely distributed than previously believed.
Sicklefin Chub: Self-sustaining populations of sicklefin chub occur in three locations within the Missouri River basin: above the headwaters of Fort Peck Reservoir in Montana; in the Yellowstone-Missouri River confluence area of Montana and North Dakota; and in the Missouri River from St. Joseph, Missouri to the confluence with the Mississippi River. Data collected by the Missouri Department of Conservation since 1997 indicate that a viable population of sicklefin chub are present in the Middle Mississippi River and in the Wolf Island area of the Lower Mississippi River. The Service estimates sicklefin chub populations currently occupy approximately 54 percent of its historic range in the Missouri River basin.
Sturgeon Chub: Viable populations of sturgeon chub are found at or near the same locations where sicklefin chub populations have been documented. In addition, sturgeon chub populations are currently present in 11 of the 30 tributaries to the Yellowstone and Missouri Rivers where they were historically collected. Sturgeon chub populations currently occupy about 1,155 miles or about 55 percent of its former range in the Missouri River.
Historic Records: Historic records for the sicklefin chub and sturgeon chub provide an incomplete picture of the range of these fish and their populations prior to construction of dams and other water development activities. Historically, studies designed to document fish populations primarily focused on sport fish, with limited attention given to native minnows. Since the Service was petitioned to list the chubs as endangered, a number of field studies have been conducted to sample chub populations. Data available from recent field investigations provide a more complete record of the locations where sicklefin and sturgeon chub occur.
How did the Service obtain its information regarding the sicklefin and sturgeon chubs?
The Service received information concerning the status of the sicklefin and sturgeon chub populations from state game and fish departments, universities, and other organizations and individuals. In addition, the Service also evaluated information from peer-reviewed journal articles, agency reports, and interviews and written correspondence with fisheries biologists familiar with these species.
How have population sampling methods changed since the earlier status reports?
The effectiveness of sampling techniques has dramatically improved. Traditionally, chub populations were sampled using seines to collect fish in shallow water. Beginning in 1994, studies were initiated using modified benthic trawls to sample fish populations in deep water habitats where seines are ineffective. Studies conducted in Montana, North Dakota, and Missouri using benthic trawls indicate that sicklefin and sturgeon chub comprise a significant portion of the fish population in certain segments of the Yellowstone and Missouri Rivers. Also recent studies conducted by the Missouri Department of Conservation document viable populations of both sicklefin and sturgeon chub in the Middle Mississippi River and in the Wolf Island area of the Lower Mississippi River.
Seine collection employs a fishing net that hangs vertically in the water by means of weights at the lower edge and floats at the top.
Benthic trawl collection employs a large tapered and flattened or conical fishing net towed along the lake or river bottom.
What is the difference between the sicklefin and sturgeon chubs and the pallid sturgeon - all natives of the Missouri and Mississippi Rivers? Why are the chubs sustaining their populations while the pallid sturgeon borders on the brink of extinction?
While the chubs and the pallid sturgeon evolved in the same, large, free-flowing big river systems characterized by swift, highly variable flows, braided channels, and high turbidity, there are fundamental differences.
Life and reproduction cycles:
The chubs are short-lived minnows with a short reproductive cycle. Sicklefin and sturgeon chub are successfully reproducing and maintaining populations in widely dispersed areas. Pallid sturgeon are long-lived with individuals reaching 50 years of age. However, males do not reach sexual maturity for 7-9 years, with up to 3-year intervals between spawning. Females are not expected to reach sexual maturity for 7-15 years, with up to 10-year intervals between spawning.
Spawning home range:
Probably the most significant difference between the two species of chubs and the pallid sturgeon are their respective home range needs for successful spawning. The home range of the pallid sturgeon can extend over hundreds of miles. Pallid sturgeon migrate upstream to spawning areas and the subsequent larvae drift considerable distances downstream after hatching. For the pallid sturgeon larvae to survive they must find suitable downstream habitat. The home range needs for sicklefin and sturgeon chub to successfully reproduce is suspected to be considerably smaller and more localized. As a result, dams and reservoirs on the Yellowstone and Missouri Rivers that have resulted in the fragmentation of turbid, riverine habitat have had a greater impact on pallid sturgeon populations.
Pallid sturgeon populations are in danger of becoming extinct and this species is facing several roadblocks to recovery. In the Yellowstone and Missouri Rivers in North Dakota and Montana, pallid sturgeon are at or near the end of their reproductive cycles and there is no evidence that successful spawning is occurring. In the Lower Missouri and Mississippi Rivers limited reproduction has been recently documented by the collection of larval pallid sturgeon. However, information concerning the survival of larval pallid sturgeon is lacking. Hybridization rates between shovelnose and pallid sturgeon also appear to be increasing in this portion of the pallid sturgeonís range. Pallid sturgeon propagated in hatchery facilities have been stocked in several reaches of the Missouri River as an attempt to keep this species from edging close to extinction.
The sicklefin chub, sturgeon chub, and pallid sturgeon prefer silty rivers with a diversity of depths and velocities forming braided channels, sand bars, sand flats, and gravel bars. All three have been affected by changes in the Missouri River and are extirpated from the 800 miles of the Missouri River that has been impounded and converted to reservoir habitat by the six main stem dams. The difference is the chubs have managed to effectively reproduce where habitat conditions allow. The pallid sturgeon, however, has been unable to adapt as well as the chubs to the present conditions of the Missouri River. Researchers have found no evidence that pallid sturgeon are successfully reproducing in the Upper Missouri River. Throughout the remainder of the pallid sturgeonís range evidence of successful reproduction and recruitment is rare.
The Service released a Biological Opinion concerning the operation of the Missouri River system in November 2000. Does the course of action detailed in the Biological Opinion influence the not warranted decision for sicklefin and sturgeon chub?
The updated status review for sicklefin and sturgeon chub evaluates the available scientific information concerning chub populations and the threats they face throughout their range. Fisheries research studies conducted since 1994 indicate that sicklefin and sturgeon chub are more common and more widely distributed than previously believed. Given the type, scope , and level of threats that exist today, the Service concluded that listing is not warranted at this time. That conclusion was not based on the course of action detailed in the Missouri River Biological Opinion.
The updated status review addresses the conservation measures described in the Biological Opinion. The primary conservation measures identified for the Missouri River include flow enhancement, flow modification, and habitat rehabilitation and creation in key sections of the river. The Service believes that implementing the conservation measures, through an adaptive management approach, will have a significant beneficial effect on native fish populations, including sicklefin and sturgeon chub.
Will the below normal snow pack in the upper reaches of the Missouri River basin and the below normal runoff that is anticipated this spring (2001) impact sicklefin and sturgeon chub populations?
Sicklefin and sturgeon chubs have evolved with both prolonged drought and extended periods of high water conditions. The Service does not believe the anticipated low water conditions in the Missouri River will have a long-term affect on chub populations.
FWS Sicklefin Chub Information
Other FWS Sturgeon Chub Information
Fish of the FWS Mountain-Prairie Region
Mountain-Prairie Region Web Site
National FWS Web Site