Spawning periodicity and growth of larval Colorado Pikeminnow and Razorback Sucker in the San Juan River, in response to abiotic and temporal variables

Authors: Stephani Barkalow, Martinique Chavez, Steven Platania

Year: 2019

Abstract

Colorado Pikeminnow, Ptychocheilus lucius, and Razorback Sucker, Xyrauchen texanus, federally endangered species, spawn annually in the San Juan River, yet a recruitment bottleneck persists between larval and juvenile life phases. The larval ontogenetic phase, though temporally short, is a period of high natural mortality and vulnerability to predation and starvation. Match/mismatch of spawning activities with larval abiotic requirements influence recruitment and survival. Age and growth of larval Colorado Pikeminnows (n = 514) and Razorback Suckers (n = 522) collected in the San Juan River from 2009 through 2017 were determined from otoliths. Daily ages of larval fish were used to calculate spawning dates and growth. Annual differences in adult spawning periodicity and larval fish growth were analyzed using ANOVA. Multiple linear regression was used to examine the relationship between abiotic variables (growing degree days (GDD), river mile, day length, and multiple parameterizations of discharge (Q) and temperature) on spawning dates and growth; multicollinearity was assessed for each model using variance inflation factors (VIF) and any variable with VIF>5 was removed. Colorado Pikeminnow growth and spawn dates were both significantly different across years (P < 0.0001). Length (SL) was predicted by age, mean July Q, river mile, water temperature on collection date, and GDD (R2= 0.72). Spawning periodicity was predicted by GDD, 7-day change in water temperature, 7-day change in discharge, and day length (R2 = 0.90). Adult Razorback Sucker spawn dates and larval fish growth were both significantly different across years (P < 0.0001). Length (SL) was predicted by age, mean April Q, river mile, and temperature (R2 = 0.76). Spawning periodicity was predicted by GDD, discharge, 7-day change in discharge, and day length (R2 = 0.99). Variation in Colorado Pikeminnow spawning periodicity was most impacted day length (53% of variation), whereas Razorback Sucker spawning periodicity was most impacted by GDD (76% of variation). Knowledge of spawning periodicity and growth, as well as the factors influencing them increases understanding of the needs of larval endangered Colorado Pikeminnow and Razorback Sucker and can help improve timing of management activities to benefit the species.