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 (Dean Hendrickson) |
General information: (E. Phil Pister) |
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The Rio Grande sucker is a member of the Catostomidae, a primary fish family. Eddy (1969) characterized the sucker family as . . . "softrayed fishes that possess a toothless and sucker-like protractile mouth with thick lips. The last pharyngeal arch bears a row of numerous comb-like teeth which distinguishes the suckers from the minnows. The head is naked and the body is covered with smooth cycloid scales."
Adult Rio Grande sucker are usually four to six inches long. This dorsal side is dull brown with scattered black blotches. During the breeding season, males develop broad, black and bright red lateral stripes that contrast with a white ventrum. Breeding males are tuberculate on the caudal and anal fins. The dorsal fin of Rio Grande sucker is short with eight to ten rays. There is a complete lateral line with more than 77 to 90 scales crowded anteriorly. The axillary process of the pelvic fin is undeveloped. The lower lip has well-developed anterolateral notches, a shallow median notch, two to three rows of papillae in the midline and a well developed cartilaginous ridge.
The Rio Grande sucker is endemic to the Rio Grande drainage, but the Rio Grande sucker ancestor was derived from the Colorado River basin (Smith 1966). In contrast to the Rio Grande sucker and Rio Grande chub (Gila pandora), and probably Rio Grande cutthroat trout, (Oncorhynchus clarki virginalis), the other fourteen native fishes of the Rio Grande basin have Mississippi - Missouri basin origins. The former genus Pantosteus (mountain sucker) was reduced to a subgenus of Catostomus (Smith 1966; Smith and Koehn 1971). This was based largely on the ideas that the two species, C. plebeius and C. columbianus are intermediate between Catostomus and Pantosteus species and that these two genera frequently hybridize and even backcross when sympatric (Hubbs et al. 1943; Hubbs and Hubbs 1947; Smith and Koehn 1971; Miller 1976).
The first written record of Rio Grande sucker, called "matalote" (meaning catostomid [sucker-like] fishes according to Salvadore Contreas-Balderas, pers. comm.) was by Father Morfi on the 1779 Comanche expedition (Thomas 1969). In 1874, Cope and Yarrow (1875) found the Rio Grande sucker "very abundant in the tributaries of the Rio Grande as far as we explored it, i.e., from Fort Garland, Colorado, to Santa Fe, New Mexico." The reference of Rio Grande sucker at Fort Garland might correspond to collections made from Trinchera Creek. In Colorado, Jordan (1891) collected Rio Grande sucker from the Rio Grande at Del Norte and at Alamosa and from the Rio Conejos at McIntyre's Ranch and described them as "...very abundant everywhere, especially in the deeper places and eddies . . ." Evermann and Kendall (1894) listed previous studies for the Rio Grande drainage including point locations in Colorado for the Rio Grande sucker. Jordan and Evermann (1902) agreed with the reportedly high relative abundance of the Rio Grande sucker in the Rio Grande, Colorado. Ellis (1914) seined 309 Rio Grande suckers on 27 July 1912 in the Rio Grande at Alamosa, Colorado and described the sucker as " . . . quite abundant throughout its range . . ." (San Luis Valley, Colorado south into Chihuahua, Mexico). Rostlund (1952) gave a distribution map of the mountain suckers for North America including three dot locations on the Rio Grande, Colorado for C. plebeius. Fish examined in Smith's (1966) extensive study of the subgenus Pantosteus included museum collections from the Rio Grande drainage in Conejos, Alamosa and Rio Grande counties. Minckley (1980) presented a distribution map showing four point locations in Colorado on the mainstem Rio Grande, which are apparently based on old records. Lee et al. (1980) described distribution in the southwestern United States and Mexico
Between 1982 and 1985 the DOW, in cooperation with Colorado State University (CSU), conducted an intensive, fish sampling program in the San Luis Valley. Survey crews collected approximately 250 samples of fish from locations in the Rio Grande, Conejos and Closed basin drainages. The results and implications of that inventory as it pertained to Rio Grande sucker (and Rio Grande chub) were described by Zuckerman and Langlois (1990). Other results from those field surveys are stored in the permanent lake and stream survey files kept at the Division of Wildlife office in Montrose, Colorado. Thus, the main body of the inventory work to discover populations of Rio Grande sucker has been completed. Possible leads for locating additional populations include the Rio Chama based on New Mexico distribution (David Propst pers. comm.) and the Silver Lakes region of the upper Alamosa River drainage (Jim Keeton pers. comm.).
In addition, examples of the fishes sampled from the San Luis Valley were prepared for permanent storage and reference as a museum collection. This collection was transferred to the U.S. Fish and Wildlife (USFWS) at their museum facility in Fort Collins, Colorado. It is currently housed at the University of New Mexico.
Zuckerman collected Rio Grande sucker from only two isolated locations during the mid 1980s: Hot Creek on the Hot Creek State Wildlife Area and the Conejos River at McIntyre Springs. At that time about less than 100 Rio Grande sucker were found in Hot Creek and three specimens at McIntyre Springs. Suckers from West Indian Creek showed some Rio Grande characteristics such as small scales, papillose lips, anterolateral notches, and a broad lateral red stripe. No phenotypic Rio Grande sucker were collected from the Trinchera Creek drainage.
In November 1993, the Colorado Wildlife Commission passed a regulation that designated Rio Grande sucker as an endangered fish in Colorado. The protection afforded Rio Grande sucker under this regulation is: "Any endangered fish taken by any means shall be returned unharmed to the water immediately." (Chapter 10, Article II, #1002). This regulation was based in part on the rarity of the species in the state. Rio Grande sucker are not listed as federally threatened or endangered by the USFWS.
This year, Swift (1994) revisited the these two sites to collect data about the species richness, the Rio Grande sucker population structure, and habitat associations. Five stations surveyed on Hot Creek revealed that the fish community contained a population of approximately 1400 Rio Grande sucker. Despite intensive work at McIntyre Springs (which included one of the men from Zuckerman crew some ten years before) no Rio Grande sucker were found. It appeared that this population was extirpated and only the Hot Creek population remains.
In New Mexico, Rio Grande sucker are more widespread (Hatch 1985; Hubbs and Echelle 1972; Platania 1991). In March 1994, a survey crew consisting of personnel from DOW, CSU, and New Mexico Game and Fish visited the Rio Brazos, Rio Jemez and Rio Mimbres drainages. Electrofishing revealed that Rio Grande sucker were extremely abundant (hundreds found in less than thirty minutes) in the Rio Mimbres. There was a moderate population in the Rio Jemez, and the species was scarce in the headwaters of the Rio Brazos. Subsequent conversations between Swift and Steve Platania at the University of New Mexico reinforced that several other waters in northern New Mexico also support populations of Rio Grande sucker.
Swift (1994) described habitat associations of Rio Grande sucker in Hot Creek. The fish tended to be observed in areas with clean gravels although some embeddedness was tolerated. They were also associated with clear pools in stream bends that had been former beaver ponds. They were not associated with turbid silt-laden areas. Instream woody debris and large amounts of aquatic vegetation were also correlated with Rio Grande sucker presence.
In Rio Mimbres, Rio Brazos and Rio Jemez in New Mexico, Rio Grande sucker existed in habitats that shared common features yet had striking differences. Common characters were: substrate composition included fifteen to 55 percent gravel; low embeddedness; some angular rubble in the substrate that was capable in accumulating woody debris and periphyton; instream vegetation such as watercress and filamentous algae; and, riparian vegetation of cottonwoods, willows and grasses providing some overhead cover. At the same time, on the Rio Brazos, the gradient was much steeper (more than 1%), the elevation was 1600 to 2300 feet higher, and the bank stability much poorer than either the Rio Mimbres or Rio Jemez. The Rio Mimbres was suffering from both overgrazing and dewatering which caused poor width depth ratio, yet had an abundant population of Rio Grande sucker.
The Rio Grande sucker is more omnivorous than other subgenus Pantosteus suckers. They feed largely upon filamentous algae and other organisms that they scrape off rocks with the aid of their specialized jaws equipped with a well-developed cartilaginous ridge (Koster 1957). Ellis (1914) reported ". . . the stomachs and intestines of twenty specimens" . . . "were packed with slime, algae and mud." Specimens taken by Smith in the Rio Mimbres, New Mexico contained small fingernail clams in the intestine. Larger individuals (6.5 in) do most of their feeding in fast, rocky riffles, but they also forage in rocky pools. Hendrickson et al. (1981) found Rio Grande sucker in pools during the day, moving into riffle areas at night and in early morning. No one has studied the diet and feeding of Rio Grande sucker in Colorado.
Rio Grande sucker are normally a spring spawner. Tuberculate, ripe males and gravid females were collected on 29 May 1985 from Hot Creek. Breeding coloration was observed for many Rio Grande sucker in March 1983 and April 1984 when water temperatures ranged from 51 to 60 oF. During November from 1982 through 1984, and on November 28, 1984 spawning coloration was observed in Hot Creek, the maximum air temperature was -14 oF. In the San Luis Valley this should be called winter rather than fall spawning, since air temperatures are often below 0 oF in November. These observations are consistent with reports of spring and fall spawning in some areas of New Mexico (Koster 1957; Propst and Bestgen, pers. comm.) and Smith's (1966) report of spawning individuals taken in February and March in the southern part of their range (i.e., Mexico).
Spawning occurs over gravel patches (Koster 1957), as is common for stream- dwelling catostomids. Rio Grande sucker males mature at a length of 2.5 to 3.2 in and 2.8 to 3.5 in for females (Smith 1966). Probable spawners from Rio Trujillo, Zacatecas, Mexico contained ova 0.06 in diameter (Smith 1966). Ova approximately 0.06 in diameter have been observed in specimens taken in September in the Rio Grande drainage while elsewhere in the same drainage specimens with ova 0.02 in diameter have been recovered the same month (Smith 1966). Early development has been described by Butler (1960). Larvae approximately 0.08 in standard length have been collected in February in the Nazas and Lake Guzman drainages and in May and July in the Rio Grande drainage (Smith 1966).
Additional studies of the life history and ecology of the Rio Grande sucker will prove important for understanding the reason for its decline to endangered status. One idea that may be worth exploring is that interaction with nonnative fishes in degraded habitats has lowered population viability.
Both Zuckerman and Langlois (1990) and Swift (1994) observed that Rio Grande sucker populations they examined contained hybrids with introduced white sucker (Catostomus commersoni). In the field, hybridization was suggested by specimens that have typical white sucker characteristics (large scales, body sizes greater than twelve in). They also shared some typical Rio Grande sucker characteristics (large papillose lips, cartilaginous ridge, anterolateral notches on lips and red lateral breeding stripe). Other individuals showed intermediacy in some characteristics such as the median cleft of the lower lip, lateral line scale count, a weakly developed cartilaginous ridge, weakly developed anterolateral notches sometimes only on one side of the mouth, dorsal ray counts and gill raker counts. Using principal component analysis, Zuckerman and Langlois (1990) showed that when used together, counts of dorsal fin rays and lateral line scales would differentiate Rio Grande sucker - white sucker hybrids from pure Rio Grande sucker. Fishes collected from Hot Creek showed intermediate characters. So, it appeared that introgression of Rio Grande sucker with white sucker was occurring.
The introduced white sucker has replaced the endemic Rio Grande sucker in Colorado very rapidly (approximately forty years) except in Hot Creek and, until recently, in McIntyre Springs. Cope and Yarrow (1875) observed that the Rio Grande sucker never coexisted with other species of suckers. Mike Hatch (pers. comm.) found that as white sucker were introduced into waters containing Rio Grande suckers in New Mexico, a long-term decline in native sucker populations was observed. However, Rio Grande sucker are sympatric with white sucker in the Rio Brazos in New Mexico. Swift (1994) observed Rio Grande sucker males in breeding coloration using the same pools as white sucker in June. We may be witnessing such a slow, long term decline in the Hot Creek population as well as that which has apparently extirpated the McIntyre Springs population.
In some waters, northern pike may have led to the extirpation of Rio Grande sucker by preying on them. Zuckerman in the mid 1980s found that wherever northern pike were present, both Rio Grande sucker and Rio Grande chub were missing. This seemed especially true in the lower portions of the Trinchera Creek drainage.
Additionally, many Rio Grande sucker collected by Zuckerman were in poor condition. Many Rio Grande sucker were emaciated and heavily infested with 'blackspot disease' [metacercaria of various trematodes (Post 1983)] more often than sympatric white sucker. In contrast, white sucker from Hot Creek appeared robust in body shape.
It is currently known only in general terms what role perturbations of habitat played in the decline of Rio Grande sucker. A variety habitat modifications in the Rio Grande basin from the late 1800s through the 1920s preceded the decline of Rio Grande sucker. These physical and chemical habitat problems can be observed today although range management practices have generally improved. Reiman and McIntyre (1993) suggested that subtle, long term degradation of fish habitats can eventually lead to loss of population viability. The general response of the fish community in some waters may have been a shift toward species tolerant of degraded habitat. Thus, white sucker may have a competitive advantage when introduced into a degraded habitat. It is possible that this phenomenon has affected Rio Grande sucker in Colorado. In New Mexico, Hatch (pers. comm.) suggested that degradation of stream banks, loss of concealment cover, reduced flows, and poor water quality may limit Rio Grande sucker populations. The DOW, CSU and USFS have begun intensive studies of the fish community and habitat associations of Rio Grande sucker in Hot Creek. One product of this work will be additional insight into the role of habitat problems in the decline of Rio Grande sucker.
During the mid-1970s there was significant use of rotenone in the San Luis Valley by the DOW and others to eradicate nonnative fishes to improve sport fishing. These activities occurred at the same time as a decline in Rio Grande sucker populations. It is possible that some rotenone projects had an effect on sucker, particularly where the chemicals unintentionally escaped downstream. In other cases, Rio Grande sucker were not affected because the species was absent from the lakes and streams treated.
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|
(Dean Hendrickson) |
General information: (E. Phil Pister) |
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This page last modified: 09 December 2003