Using Fyke-Net Capture Data to Assess Daily Trends in Abundance of Spawning Rio Grande Silvery Minnow

Abstract

Assessments of the assumptions underlying catch-per-unit-effort (CPUE) data are necessary to determine whether catch data provide a reliable relative abundance metric. Rio Grande silvery minnow Hybognathus amarus were collected with fyke nets from seasonally flooded habitats of the Rio Grande in New Mexico to determine habitat use by the species during spring runoff in May and June of 2008 and 2009. The CPUE was calculated as fish/h to assess relative abundance among sites and sampling dates due to differences between the durations of the samples in 2008 and 2009. The assumption that the number of fish captured with fyke nets is proportional to effort was assessed by using a multiple-regression model. Catch per unit effort was also compared over the course of a day to determine whether diel differences in catch rate exist. Catch of Rio Grande silvery minnow increased with fyke-net soak time during 2008 and 2009; however, the proportion of the variability explained by the model was greater for 2009 than for 2008. The CPUE did not differ among 24-h collections at high density (mean = 8.24 fish/h) or low density (mean = 0.12 fish/h) sites. These results indicate that fyke-net catches of Rio Grande silvery minnow are proportional to soak time, and calculation of CPUE as fish/h may be used to compare the relative abundance of the species among and between fyke-net samples collected from seasonally flooded habitats. © 2012 American Fisheries Society.