Otoliths Reveal Spawning Ecology and Early Life History of Sympatric Catostomids

Differences in spawning ecology and early life history may influence the recruitment success of three sympatric catostomids in the Colorado River basin: the Bluehead Sucker Catostomus discobolus, Flannelmouth Sucker C. latipinnis, and federally endangered Razorback Sucker Xyrauchen texanus. In the San Juan River, all three species annually produce larvae, but only Bluehead and Flannelmouth suckers regularly recruit to the juvenile phase and older. Otolith microstructure analysis can determine age, growth rates, and spawning periodicity and may elucidate possible reasons for differences in recruitment among species. Larval suckers were collected from low-velocity habitats in the San Juan River in 2011; fish were measured, and ontogenetic phase and fish age were determined from otolith increment counts. Otolith age was used to determine hatch dates and spawning periodicity, calculate daily growth rates, and develop three candidate growth functions relating fish age and body length. Relative to Bluehead and Flannelmouth suckers, Razorback Suckers had a shorter spawning period, lower growth rate, and a higher proportion of the least developed ontogenetic phase. The small size of Razorback Suckers relative to other suckers may result in higher predation and lower prey acquisition, thus restricting their transition to more developed phases and limiting recruitment to the juvenile phase. Model ranking based on Akaike's information criterion (corrected for small sample size) was nearly identical for all growth functions. The early life history information we provide may guide flow releases in this regulated system to provide suitable backwater habitat and warmer water temperatures compatible with reproduction, growth, and survival of native catostomids, including the endangered Razorback Sucker. However, due to the limited temporal and geographic extent of samples used in this study, data presented herein are not inclusive of all conditions under which suckers may be present in the San Juan River.