Annual Report Technical Report

Rio Grande Silvery Minnow Reproductive Monitoring During 2024

URL: https://webapps.usgs.gov/mrgescp/documents/2024-RGSM-Reproductive-Monitoring-Final.pdf

Date: 2024/10/30

Author(s): Dudley R.K., Platania S.P., White G.C.

Publication: Contract 140R4021C0007: Requisition 0040656539, Submitted to U.S. Bureau of Reclamation Albuquerque Area Office, 555 Broadway NE, Suite 100, Albuquerque, NM 87102

Abstract:

The primary objective of the Rio Grande Silvery Minnow (RGSM) Reproductive Monitoring Program is to characterize the timing, duration, frequency, and magnitude of spawning for RGSM in the Angostura, Isleta, and San Acacia reaches of the Middle Rio Grande. Additional objectives included characterizing reach-specific spawning patterns over time; examining the relationships between flow, temperature, and spawning; and assessing linkages between egg passage rates and seasonal flows across years. In 2024 (i.e., 22 April to 10 June), we collected drifting eggs from three fish species. All eggs (n = 4,586) were immediately identified in the field as Common Carp (n = 19), RGSM (n = 4,566), or Flathead Chub (n = 1). We caught the most RGSM eggs at San Marcial (n = 4,138), followed by Albuquerque (n = 344), and Sevilleta (n = 84). Based on the total sampling effort across all sites (ca. 600 h), we collected about 7.61 eggs/h for this species in 2024.

Reproductive monitoring of Rio Grande Silvery Minnow was reinitiated at the Albuquerque and Sevilleta sites in 2017, which allowed for comparisons of estimated egg-passage rates (E(x); eggs per second) across reaches. These passage rates, which accounted for differences in mean daily discharge, were similar at Albuquerque, Sevilleta, and San Marcial in 2024 (2.76·10^-1, 1.41·10^-1, and 1.74·10⁰, respectively). We roughly estimated that about 1.19·10⁶ eggs, 6.08·10⁵ eggs, and 7.52·10⁶ eggs were transported downstream of Albuquerque, Sevilleta, and San Marcial, respectively, during 2024.

Long-term spawning patterns and trends were based on all available data across sites and years (2003–2024). Logistic regression modeling of daily egg presence-absence data revealed strong associations with the percentage change in mean daily discharge (i.e., independent of flow magnitude) just prior to egg collection. The probability of collecting eggs (i.e., daily egg-occurrence probability) was highest when river flows increased substantially across consecutive days. The occurrence probability during a 100% increase in flow was 0.79, whereas the occurrence probability was 0.96 during a 200% increase in flow. In contrast to the robust discharge relationship, daily egg presence-absence data revealed a weak and nonsignificant association with mean daily water temperature.

Annual egg-passage rates, which were estimated using data from all sites (2003–2024), revealed notable differences across years. Passage rates were lowest in 2004 (1.66·10^-3) and highest in 2011 (2.32·10¹). There was a steady increase in passage rates from 2019 to 2021, followed by a decline in 2022. Passage rates increased again from 2022 (6.89·10^-2) to 2024 (3.12·10^-1). Changes in egg-occurrence probabilities and egg-passage rates, using data from all sites, were moderately predicted by differences in seasonal river flows across years (2003–2024). Overall, we found that egg occurrence probabilities were higher during years with low and truncated spring flows, whereas egg passage rates were lower during years with high and prolonged spring flows.