Estimating Wild Celery Winter Bud Density and Energetic Carrying Capacity for Waterfowl in Pools 4, 8, and 13, of the Upper Mississippi River

Abstract

The Upper Mississippi River provides important staging areas during migration for waterfowl including canvasbacks (Aythya valisineria). Wild celery (Vallisneria americana) is a species of submersed aquatic vegetation that produces energy rich winter buds within the substrate that is a preferred forage for canvasbacks during migration. Since 1998, the Upper Mississippi River Restoration Program, Long Term Resource Monitoring (LTRM) element has monitored aquatic vegetation by conducting rake samples where aboveground biomass of aquatic vegetation species are given a value from 1-5, based on species relative abundance on a rake. Because the rake does not sample underground structures, there remain questions on how data collected by the LTRM translates to waterfowl habitat quality and bioenergetics. Our goal was to examine if a relationship exists between LTRM rake scores and wild celery winter bud density from substrate core samples in Pools 4, 8, and 13, of the Upper Mississippi River, USA. Rake samples were collected in summer 2018 and 2019 in Pools 4, 8 and 13, and substrate cores were collected at the same locations as rake sample sites before the annual waterfowl migration in autumn 2018 and 2019, and spring 2019 and 2020. Rake score and river pool were the only predictors in the best fit statistical model estimating the probability of wild celery winter bud presence at a site. For an average rake score of 1, there is a 60% (95% CI: 36-79) chance the site has a wild celery winter bud in Pool 4, 90% in Pool 8 (95% CI: 82-95), and 88% in Pool 13 (95% CI: 74-96). The probability rises to 99% at average rake scores >2.1 in Pool 4, and 1.7 in Pools 8 and 13. Rake score, pool, management status, season, and an interaction between season and management status were in the best fit statistical model predicting winter bud density (P < 0.05, R2 = 0.357). Results indicate LTRM rake scores and other variables can be used to predict the presence of wild celery winter buds and predict winter bud density. This is encouraging to managers as it presents a possible alternative to labor intensive and costly traditional quadrat or core sampling used to quantify underground plant structures.