| DISTRIBUTION, HATCHING PERIOD, AND DISPERSAL OF LARVAL RAZORBACK SUCKER IN THE SAN JUAN RIVER, NM, CO, UT: ELEVEN YEARS OF RESEARCH (1999-2009) |
| BRANDENBURG W. H., Farrington, M. A., Platania, S. P. American Southwest Ichthyological Researchers, 800 Encino Place NE, Albuquerque, New Mexico 87102-2606. howard_brandenburg@asirllc.com, michael_farrington@asirllc.com, steven_platania@asirllc.com |
| As part of the San Juan River Recovery Implementation Program, larval fish surveys have been conducted on the San Juan River since 1999 to detect spawning of stocked razorback sucker, Xyrauchen texanus. The study area, encompassing the San Juan River from Cudei, New Mexico, to Clay Hills Crossing, Utah (228 km), comprises five distinct geomorphic reaches ranging from a low gradient, braided, meandering segment (upstream) to a canyon bound, highly channelized reach (downstream). Fish were sampled monthly from April through June (1999-2001) and April through September (2002-2009). Nursery habitats of larval fish (low velocity areas) were sampled in the study area using fine-mesh seines (0.8 mm mesh). A total of 2,289 larval and early- juvenile razorback sucker were collected from 1999-2009 with reproduction of razorback sucker documented in each of the 11 years. Catch rate of larval razorback sucker differed among years, as did the range of ontogenetic stages documented in a given year. Age-0 razorback sucker were collected from mid-April to early August, with the highest catch rates occurring in May. Larval razorback sucker were distributed throughout the study area but the highest catch rate was in the lower-most reach indicating a downstream displacement of propagules. Distribution of protolarval razorback sucker suggested multiple spawning sites. Hatching dates of razorback sucker larvae were back-calculated and plotted against mean daily discharge and water temperature. Back-calculated hatching periods of razorback sucker often began 1-2 weeks prior to spring run-off and concluded during the ascending spring discharge. While much information has been acquired about the early life history of razorback sucker, the collection of larvae of this species is infrequent compared to that of the other two native San Juan River catostomids. Otoliths are now being examined in an effort to determine (more precisely) hatching and spawning dates of San Juan River razorback sucker larvae and correlate their reproduction with abiotic factors. |
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