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NATURAL HISTORY

RIO GRANDE CUTTHROAT TROUT } Oncorhynchus clarki virginalis
FAMILY: Salmonidae

DESCRIPTION: The Rio Grande cutthroat trout has a bright, reddish-orange slash of color beneath its lower jaw that extends over its gill covers. There is a bluish tinge in the lining of the mouth and on the membrane under the upper jaw, and the subspecies is distinguished by relatively large, round, black spots speckling its body. Toward the tail, these spots come together to form club shapes. There are few spots on the forward half of the body. Adults in small streams can grow to be 10 inches long; in larger rivers, they average 14 to 15 inches in length.

HABITAT: Rio Grande cutthroat trout live in clean, cold mountain streams and rivers with a moderate gradient. They require low summer water temperatures and clean gravel for spawning beds.

RANGE: Historically, these fish were widely distributed in streams within the Rio Grande, Pecos, and Canadian river drainages in Colorado and New Mexico. Today they are restricted to some 690 stream miles in southern Colorado and northern New Mexico.

MIGRATION: These trout are nonmigratory.

BREEDING: Rio Grande c utthroat spawn in the spring during snowmelt, which depending on latitude and elevation occurs anywhere between April and July. Some populations and individual females spawn every other year; egg production varies between 200 and 4,000. The fish mature sexually at four years of age.

LIFE CYCLE: Rio Grande cutthroat trout generally live five to eight years.

FEEDING: Cutthroat trout feed on midge larvae, mayflies, and other aquatic and terrestrial invertebrates. Smaller fish will sometimes eat zooplankton, and larger fish will sometimes feed on smaller fish.

THREATS: Habitat loss and fragmentation is the primary threat to the survival of the Rio Grande cutthroat trout. Of the various human activities that lead to this destruction, livestock grazing is the most potent and pervasive. Other threats include water diversions, logging, road construction, genetic isolation, disease, and competition and hybridization with nonnative trout species.

POPULATION TREND: T he widely distributed historic populations of this species have been reduced in number over the past two centuries, having been lost from more than 90 percent of their former range. Only five fragile populations are currently secure from any threats. The rest of today’s surviving Rio Grande cutthroat trout could die out due to their genetic isolation.

Photo courtesy of USFWS