Ecology and Habitat Use of Age-0 Paddlefish in the Unimpounded Middle Mississippi River
Quinton E. Phelps, Sara J. Tripp, James E. Garvey, David P. Herzog, David E. Ostendorf, Joseph W. Ridings, Jason W. Crites, and Robert A. Hrabik
Abstract.—How paddlefish Polyodon spathula early-life history dynamics affect recruitment is relatively unknown. We quantified factors affecting age-0 paddlefish abundance, hatch time, growth, and survival in an unimpounded reach of the Mississippi River during 2000–2008. We trawled several habitats, collecting 2,074 age-0 paddlefish from 10 to 170 mm total length. Paddlefish hatch timing varied across years (30–60 d), generally commencing in the middle of April and ending in June when a threshold water temperature was reached and river stage variability increased. Correspondingly, an analysis of covariance revealed a strong interaction between year and habitat for catch per unit effort in the small (10–50 mm) (P = 0.025) and medium (51–100 mm) (P = 0.040) size-classes, indicating that habitat preferences were likely influenced by year. However, no relations between these variables in the large size-class (>100 mm) existed (P = 0.88). Age-0 paddlefish growth rates differed among years (i.e., 1.87–3.31 mm/d) and were positively related to water temperature (r = 0.64; P = 0.083). Mortality rates varied by year (range = –0.26 to –0.57) and were positively correlated with the number of days water temperature was below 28°C during April 15 through July 15 (r = 0.67, P = 0.070). Water temperature and river stage variability may regulate early-life dynamics of paddlefish. Early-life history dynamics are likely interrelated with habitat conditions present in the river. The highest catch rates of young paddlefish were on the main channel side and side channel of islands, suggesting that these habitats are important to paddlefish. Within these habitats, paddlefish frequently occupied moderate velocities (i.e., 0.4–0.6 m/s), moderate depths (i.e., 3–5 m), and sand substrate.