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Investigating phenology of larval fishes in St. Louis River estuary shallow water habitats
Peterson, Greg, J. Hoffman, A. Trebitz, C. Hatzenbuhler, H. Ramage, J. Barge, M. Pearson, W. Bartsch, AND J. Launspach. Investigating phenology of larval fishes in St. Louis River estuary shallow water habitats. St. Louis River Summit, Superior, WI, March 14 - 15, 2017.
Larval fish monitoring is conducted for many purposes including early detection of non-native species. To optimize surveys, we need to understand temporal and spatial patterns related to the development and dispersion of larval fishes, as well as the environmental factors that influence them. This research will inform survey designs and could improve non-native fish early detection.
As part of the development of an early detection monitoring strategy for non-native fishes, larval fish surveys have been conducted since 2012 in the St. Louis River estuary. Survey data demonstrates there is considerable variability in fish abundance and species assemblages across different habitats and at multiple temporal scales. To optimize early detection monitoring we need to understand temporal and spatial patterns of larval fishes related to their development and dispersion, as well as the environmental factors that influence them. In 2016 we designed an experiment to assess the phenological variability in larval fish abundance and assemblages amongst shallow water habitats. Specifically, we sought to contrast different thermal environments and turbidity levels, as well as assess the importance of vegetation in these habitats. To evaluate phenological differences we sampled larval fish bi-weekly at nine locations from mid-May to mid-July. Sampling locations were split between upper estuary and lower estuary to contrast river versus seiche influenced habitats. To assess differences in thermal environments, temperature was monitored every 15 minutes at each sampling location throughout the study, beginning in early April. Our design also included sampling at both vegetated (or pre-vegetated) and non-vegetated stations within each sampling location throughout the study to assess the importance of this habitat variable. Hydroacoustic surveys (Biosonics) were conducted in alternate weeks between larval fish sampling events, to quantify the progressive development of vegetation. Temperature data show that shallow upper estuary habitats warm faster than similar habitats in the lower estuary. Higher variability in warming rates was observed amongst lower estuary habitats. These and other habitat patterns will be compared to larval fish abundance and assemblage data to assess temporal and spatial relationships that could improve non-native fish early detection.