Distribution and notes on the biology of Zuni bluehead sucker, Catostomus discobolus yarrowi, in New Mexico

Zuni bluehead sucker, Catostomus discobolus yarrowi, is endemic to the Litt le Colorado River drainage of west-central New Mexico and east-central Ariz ona. The extent of its historical distribution is uncertain, but included s everal tributaries of the Little Colorado River upstream of Grand Falls, Ar izona; origin of the taxon is ambiguous and contributes to poor definition of its former distribution. Fish eradication efforts in the 1960s eliminate d the subspecies from portions of the Zuni River drainage in New Mexico. Su rveys in New Mexico during 1990 through 1993 found it in about 15 km of Rio Nutria headwaters. Zuni bluehead sucker persists where habitat degradation (channel incision and sedimentation) is limited and nonnative fishes (part icularly Lepomis cyanellus) are rare or absent. Seasonally dry channels and low waterfalls limited movement among headwaters. We found the sucker most commonly in low-velocity (<10 cm/sec), moderately deep (0.3 to 0.5 m) pool s and pool-runs with seasonally dense perilithic and periphytic algae. Life history studies (1994 and 1995) documented reproduction in spring (April t hrough early June) when water temperature was 6 to 13<degrees>C. Based on l ength-frequency data, some individuals matured by age 1 and most were matur e by age 2. Females typically produced 400 to 600 ova annually; spawning ma y be bimodal, with most occurring early in the season. Individuals may atta in 50 to 60 mm SL in their first year (age 0), thereafter growth is about 3 0 to 40 mm per year. Few suckers were >150 mm SL and most individuals were less than or equal to age 3; few survived to age 4. Survival of Zuni bluehe ad sucker without intensification and expansion of current conservation eff orts is doubtful.