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<br />The more conspicuous changes and the probable reason for them are as
<br />follows: The shovelnose sturgeon, the goldeye and the sturgeon chub have
<br />apparently disappeared from the North Platte River where they formerly occurred.
<br />The cause for the elimination of these species may be the effects of pollution from
<br />a variety of sources in the lower North Platte River in the past 50 years. This
<br />condition has been remedied to a great extent in recent years. Several other species,
<br />including the plains minnow, the suckermouth minnow, the hornyhead chub, and
<br />the common shiner have apparently been greatly reduced in numbers in this same
<br />drainage. Three of these species, the hornyhead chub, the suckermouth minnow
<br />and the common shiner are species which prefer clear, cold streams with a
<br />permanent gravel bottom, and their earlier occupancy of this drainage was not
<br />primarily in the North Platte River proper, but in the.small clear creeks tributary to
<br />the North Platte in Natrona, Converse, Platte, and Goshen counties at elevations
<br />mostly below 6,000 feet. Various agricultural uses have caused siltation and
<br />increased the intermittency of these streams, and this is the probable reason for the
<br />decrease in numbers of these species. In the case of the plains minnow and
<br />conceivably also the gold eye and sturgeon chub, which were formerly common in
<br />the North Platte proper and which are tolerant of the very silty streams of the
<br />Missouri River system, it is quite possible that it is the reduction in the turbidity of
<br />the North Platte proper in recent years as a result of the construction of reservoirs,
<br />and a consequent increase of species such as the white sucker and creek chub which
<br />are intolerant of high turbidity, that has brought about the disappearance of these
<br />species from the North Platte. The plains minnow is still common in the silty rivers
<br />and creel<s in the northeastern counties of Wyoming and seems in no real danger of
<br />extinction in that area.
<br />
<br />
<br />Ie species have
<br />ortant changes
<br />
<br />as a full species
<br />:orm of Cottus
<br />
<br />Expansion of Ranges:
<br />
<br />Two species have apparently expanded their ranges as a result of their
<br />tolerance to the conditions that have reduced the numbers of the species mentioned
<br />above. These are the green sunfish and the plains killifish. The green sunfish is
<br />tolerant of intermittency in streams and thrives in streams and ponds with an
<br />abund&nce of such hardy species as the fathead minnow and the white sucker; it has
<br />spread widely throughout the northeastern counties of the state. Part of this spread
<br />is probably attributable to illegal transplants of this species to farm pond reservoirs
<br />and various stock-watering impoundments such as are common on the high plains,
<br />by persons desiring to establish some species of game fish in these habitats. The
<br />plains killifish is tolerant of silting, high alkalinity, and high salt content. Once
<br />established in habitats which are almost intolerable for most freshwater fish, this
<br />species increases rapidly. Examples are the establishment of this species in Twin
<br />Buttes Lake in the Laramie Basin where the salt content is about 35,000 ppm, and
<br />its present abundance in the sandy, intermittent streams in the Casper area.
<br />
<br />The creek chub, lake chub, fathead minnow and the white and longnose
<br />suckers have been established in the Little Snake and Green River drainages and are
<br />on the increase there. The Utah chub and the redside shiner have also been
<br />established in the Green River drainage. In Yellowstone Park, the longnose sucker
<br />and the lake chub have been established in Yellowstone Lake where they are not
<br />native, and, from the Snake River drainage, the redside shiner has also been
<br />established in Yellowstone Lake. These transplantations have almost certainly
<br />resulted from the release of live bait minnows.
<br />
<br />..,
<br />
<br />
<br />ies on the basis
<br />le state.
<br />
<br />been relegated
<br />
<br />.
<br />~I
<br />
<br />f,.~
<br />
<br />leen included in
<br />and Blair, et aI,
<br />estate.
<br />ds the range of
<br />57 p. 143-144),
<br />s in the western
<br />
<br />153
<br />
<br />
<br />
<br />oming:
<br />
<br />in recent years
<br />Ition of stream
<br />transplanting of
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