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NATURAL HISTORY

VIRGIN RIVER SPINEDACE } Lepidomeda mollispinis mollispinis
FAMILY: Cyprinidae

DESCRIPTION: The Virgin River spinedace is a medium-sized, silvery minnow with scattered black blotches and a brassy sheen. Reddish-orange coloration develops at the base of the paired and anal fins during the breeding season. The spinedace averages 2 to 4 inches in length and reaches a maximum length of 6 inches. Its body is flat-sided and broad, and the top line curves smoothly. The species’ name is based on a weak fusion of the first two dorsal rays, which creates a spine at the leading edge of the dorsal fin. During the breeding season, females become more robust and plump while males remain streamlined.

HABITAT: Virgin River spinedace prefer cool, clean tributaries and inflow areas of larger streams. They are most abundant in runs or pools with cover such as boulders, logs, overhanging vegetation or undercut banks, though they tend to avoid heavily shaded areas. Larvae are associated with backwaters or slowly moving water along stream margins, particularly in areas with filamentous algae. Spinedace habitat is harmed by diminished flow, which increases water temperature.
 
RANGE: The spinedace is endemic to the Virgin River and its tributaries in northwestern Arizona, southeastern Nevada and southwestern Utah. The Virgin River originates in south-central Utah and flows in a southwesterly direction for approximately 200 miles from Utah to northwestern Arizona and southeastern Nevada before emptying into Lake Mead.

MIGRATION: Spinedace do not migrate.

BREEDING: Spinedace spawn from April through June, when photoperiod is greater than 13 hours per day and water temperature ranges from 55 degrees Fahrenheit to 63 degrees Fahrenheit. Peak spawning is closely correlated with peak spring flows, and laboratory results indicate that flowing water is required to stimulate spawning behavior.

LIFE CYCLE: Under natural conditions spinedace live for approximately three years. The vast majority of the population in any given year is comprised of one-year-olds.

FEEDING: Spinedace feed on a variety of insects, including the larvae of beetles and flies and adult mayflies and caddisflies. Spinedace eat primarily insects, but shift diets seasonally depending on food availability, consuming organic debris and filamentous algae when insect availability is decreased.

THREATS: The primary threat to spinedace is flow depletion due to excessive water withdrawals from the Virgin River and its tributaries. Spinedace are also threatened by nonnative fishes and crayfishes and by habitat degradation from cattle grazing, pollution, development, recreation, drought, flooding and global climate change.

POPULATION TREND: The spinedace was once common but has undergone a drastic decrease from historical abundance. Remaining populations are isolated and fluctuate based on flow conditions resulting from water withdrawals.

 

Photo by Ken Collins, USFWS