SPAWNING ECOLOGY OF FLANNELMOUTH SUCKER, CATOSTOMUS-LATTIPINNIS (CATOSTOMIDAE), IN 2 SMALL TRIBUTARIES OF THE LOWER COLORADO RIVER

We report the first published accounts of spawning behavior and spawni ng site selection of the flannelmouth sucker in two small tributaries of the lower Colorado River in the Grand Canyon, Arizona. Spawning was observed on 20 March 1992 and from 28 March to 10 April 1993 in the P aria River, and from 16 to19 March 1993 in Bright Angel Creek. Flannel mouth suckers exhibited promiscuous spawning behavior-individual femal es were typically paired with two or more males for a given event and sometimes changed partners between events. Multiple egg deposits by di fferent females sometimes occurred at one spawning site. Flannelmouth sucker selected substrates from 16 to 32 mm diameter in both streams. Spawning occurred at depths of 10 to 25 cm in the Paria River and 19 t o 41 cm in Bright Angel Creek. Mean column water velocities at spawnin g locations ranged from 0.15 to 1.0 m sec(-1) in the Paria River and f rom 0.23 to 0.89 m sec(-1) in Bright Angel Creek. Water temperatures r ecorded during spawning ranged from 9 to 18 degrees C in the Paria Riv er and 13 to 15 degrees C in Bright Angel Creek. Spawning flannelmouth sucker ascended 9.8 km upstream in the Paria River and 1.25 km in Bri ght Angel Creek. Spawning females (410-580 mm) were significantly larg er than spawning males (385-530 mm) in the Paria River. The mean size of spawning fish in the Paria River was significantly smaller than the entire stock, averaged throughout the study period (350-620 mm). Howe ver, fish spawning in 1992-1993 averaged 53 mm larger than fish spawni ng in the same reach of the Paria River in 1981, indicating a shift in the size structure of this stock.