Rivers of the southern Great Plains are some of the most dynamic and harsh river environments in the world. Stream temperatures may reach up to 104 degrees Fahrenheit during heat of the summer, while river flows range from overtopping their banks, to long dry sections of river where only small isolated pools exist. This environment may not sound like an oasis for aquatic life, but many organisms, including the peppered chub (Macrhybopsis tetranema), are well-equipped to handle these types of conditions.
Although the peppered chub is specialized to persist under this harsh environment, changes to large prairie rivers since the early 1980s have led to its decline. The peppered chub was once widespread and common in the western portion of the Arkansas River Basin in Kansas, New Mexico, Oklahoma and Texas, and has at least one historical detection in Colorado. This species has subsequently disappeared from 94% of its historical range and is currently restricted to a portion of the South Canadian River, between Ute Dam in far eastern New Mexico, downstream to Lake Meredith in the Texas panhandle, which is roughly 170 river miles.
The peppered chub was petitioned for federal listing under the Endangered Species Act in 2007, based on reductions of its range, as well as numbers. This was due primarily to habitat destruction and modification through channelization, construction of impoundments, stream dewatering, diversion of surface water, groundwater pumping and water quality degradation. On December 1, 2020, the U.S. Fish and Wildlife Service published a proposed rule to list the peppered chub as endangered, with designated critical habitat (85 FR 77108). A final rule is forthcoming.
Partnerships that focus on supporting natural flow regimes that maintain river connectivity and habitat complexity are essential to the conservation and recovery of the species. For more detail on why water conservation and natural flow regimes are important for the peppered chub, refer to the habitat and reproduction sections of the species profile.
Peppered chubs are generalists that feed aggressively to fuel rapid growth, as documented by Bottrell and others in 1964. Peppered chubs have evolved for feeding in highly turbid streams. Peppered chubs have barbels, large olfactory lamellae and taste buds that cover their bodies, including their eyes. These adaptations help them find prey in turbid waters where sight feeding is difficult. They feed primarily on larval insects, small crustaceans, immature aquatic insects and plant material. At about 10 days old, they begin to forage among sediments on the river bottom. Large quantities of sand are taken into the mouth, sorted for any food it may contain and then ejected from the mouth and gill openings. They also sometimes rise to the top and hit the surface to dislodge food held by surface tension.
The peppered chub is a small minnow with a fusiform body shape, which means that it is tapering at both ends, which rapidly tapers to a conical head. Mouth position is inferior and horizontal, with two distinct pairs of barbels present. Taste buds are present over most of the body. Adults attain a maximum length of 3 inches. Although somewhat variable, there are eight fin rays typically present in the dorsal, anal and pelvic fin. Anal and dorsal fins are slightly falcate, meaning that they are curved or hooked. Peppered chub have rounded pelvic fins and pectoral fins that are long, falcate and just reach the bases of the pelvic fins in adult males. Adult females have shorter and pointed pectoral fins, usually not reaching the pelvic fin bases. This species also has two to 10 pectoral rays that are greatly thickened in large nuptial males, and bear rows of small, conical, antrorse, meaning that they point forward, tubercles. Basal parts of rays bear one to two rows of tubercles. Females are without tubercles.
Pigment is nearly confined to the dorsal half of the body, with dark spots scattered across this area. The lateral stripe is poorly defined and centered one scale row above lateral line. Small pale areas are often present at the posterior and anterior base of the dorsal fin. The head has pigment over the brain; a preorbital bar is present, but often indistinct. Dorsal fin rays are weakly pigmented and darker at the bases. Pigmentation is lacking on pectoral, pelvic and anal fins. The caudal fin has a white ventral border. The rays are poorly pigmented, and coloration is darker at the base of each caudal lobe.
Peppered chubs are believed to live two to three years in the wild.
Peppered chubs are a member of a reproductive guild, known as pelagic broadcast spawners, that broadcast spawns semibuoyant eggs, which means that the eggs are kept suspended and hatch in flowing water. This reproductive strategy appears to be an adaptation to highly variable environments where stream flows are unpredictable and suspended sediments and shifting sand can cover eggs that are laid in nests or crevices, as noted by T.H. Bonner in 2000. Without stream flow, eggs sink to the bottom where they may be covered with silt and die, as documented by S.P. Platania and C.S. Altenbach in 1998. Once saturated with water after spawning, semibuoyant eggs remain suspended in the water column as long as current is present. For peppered chub, fertilized eggs develop as they drift in the current and hatch 25 to 28 hours after fertilization as documented by C.E. Bottrell and others in 1964, p. 398 and later confirmed by H.W. Robison and T.M. Buchanan in 1988. In 1964, C.E. Bottrell and others found that captive raised peppered chub eggs hatched, on average, 25.5 hours after fertilization. They also noted that on the third day, the young fish begin to swim with purposeful movements and feed.
A natural flow regime that supports wide, shallow braided rivers, with characteristic channel complexity, as well as a connection to the floodplain, is essential for attenuating downstream movement of eggs and larvae. As T.A. Worthington and others documented in 2014, this allows for a shorter distance to develop and seek refuge, as compared to a single-threaded and narrower channel that has higher velocities. Without moderate to high flow events and maintenance of historical base flows, vegetation begins to encroach within the banks and results in a narrower river over time, as documented by N.L. Poff and others in 1997 and later confirmed by C.S. Mammoliti in 2002. As the river becomes more entrenched and narrows, habitat complexity that is typical of a wide and shallow Great Plains river is lost, and the river’s connection to its historical floodplain is diminished. An adequate combination of river length, as well as a natural flow regime and sufficient degree of channel complexity and floodplain connection, should allow the species to repopulate upstream areas that would otherwise not occur if eggs and larva are transported downstream over greater distances, noted R.K. Dudley and S.P. Platania in 1999, as well as T.H. Bond and others in 2000 and later by T.A. Worthington and others in 2014.
Although they show some preference for cobble substrate during the spring, and gravel substrate during the summer, the peppered chub occurs in shallow, relatively wide and braided channels where current flows over sand. Peppered chubs are more adapted for headwater streams than other closely related chub species. Research indicates a preference for turbid, or cloudy, water partly because peppered chub are able to outcompete other fishes that are less adapted to foraging in those situations. Turbid water also gives this species an advantage in avoiding predators.
A natural body of running water.
Land on which the natural dominant plant forms are grasses and forbs.
Areas where ground water meets the surface.
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