Optimizing underwater camera sampling to assess overwintering backwater fish habitat on the Upper Mississippi River

Abstract

Gear limitations imposed by ice conditions in temperate regions have created a significant knowledge gap regarding the winter habitat use of the backwater fish assemblage. We developed and optimized an underwater camera method for under – ice sampling in four freshwater backwaters on the Upper Mississippi River. We found that site depth (Σwi = 1.0), water clarity (Σwi = 0.99), snow depth (Σwi = 0.89), and ice depth (Σwi = 0.86) were the main factors influencing camera viewing distance. Rarefaction analysis showed 21 sampling sites per backwater and 15 – minute recordings sufficiently captured species richness and relative abundance. Using this optimized underwater camera method, we evaluated the effect of environmental factors on fish assemblage metrics (i.e., species richness and combined MaxN) and species – specific data for Bluegill, Largemouth Bass, and Yellow Perch. Random forest models ranked water temperature (°C) and dissolved oxygen (mg/L) as the primary factors influencing the fish assemblage metrics and the centrarchid presence and relative abundance. Yellow Perch presence and relative abundance were driven by site depth (m) and conductivity (μS), respectively. The results of this study can be used by managers to guide restoration strategies incorporating environmental factors that promote quality overwintering habitat for backwater fishes.