Do rearing salmonids predictably occupy physical microhabitat?

Abstract

Microhabitat suitability models are commonly used to estimate salmonid habitat abundance and quality with unknown accuracy or reliability. When tested, the metrics used to evaluate these models are often limited by the methods used to develop them. More generalized bioverification strategies that transcend methodology are therefore needed in ecohydraulics. This study further developed and applied such a generalized bioverification framework to four approximately 1-m-resolution rearing salmonid microhabitat suitability models. Water depth and velocity habitat suitability criteria (HSC) functions were developed for two size classes of rearing Oncorhynchus tshawytscha and O. mykiss using snorkel survey data collected over three years at seven sites along the lower Yuba River in California, USA. An expert-based cover HSC function was modified from previous studies. HSC functions were applied to previously validated, approximately 1-m-resolution two-dimensional hydrodynamic models and cover maps of the river. Mann-Whitney U tests confirmed that suitability values were significantly higher at utilized locations compared to randomly-generated, non-utilized locations for all four models. Bootstrapped forage ratios demonstrated that microhabitat suitability models accurately predicted both preferred and avoided habitat beyond the 95% confidence level. This generalized bioverification framework is recommended for evaluating and comparing the accuracy and reliability of ecohydraulic models used in habitat management worldwide.

Automated analysis of lateral river connectivity and fish stranding risks. Part 2: Juvenile Chinook salmon stranding at a river rehabilitation site

“…Moniz et al (2019) developed and bioverified observation‐based LYR habitat suitability criteria functions for two size classes of rearing Chinook salmon and steelhead. This study used their juvenile Chinook salmon functions to calculate combined (geometric mean) depth and velocity habitat suitability indices in River Architect.…”

“…This study used their juvenile Chinook salmon functions to calculate combined (geometric mean) depth and velocity habitat suitability indices in River Architect. Though it is important (Moniz et al, 2019), cover was not accounted for in this analysis mindfully to isolate the influence of altered morphology on stranding risks. Little vegetative or streamwood cover exists in the recontoured terrain to make cover a factor differentiating project stages.…”

Chinook salmon rearing habitat–discharge relationships change as a result of morphodynamic processes

“…Habitat suitability criteria (HSC) functions for depth, velocity, and cover type were developed and bioverified for Chinook salmon fry by Moniz, Pasternack, Massa, Stearman, and Bratovich (2020). HSC functions were applied to 2014 depth, velocity, and cover rasters, resulting in a set of univariate depth, velocity, and cover habitat suitability rasters at a range of discharges between 14.16 and 42.48 m 3 /s.…”

“…Despite its widespread use, the WUA index has been highly criticized for lacking statistical certainty (Williams, 1996), interpretability (Mather, Bason, Purdy, & Silver, and biological meaning (Railsback, 2016). Unlike those indices, however, bioverified models such as the one used in this study provide biologically meaningful and spatially explicit interpretable areas of preferred microhabitat with known statistical certainty (Moniz et al, 2020). Furthermore, as demonstrated in this study, these areas of preferred microhabitat can be spatially compared over time to determine exactly where and how much habitat is lost, sustained and/or gained, and then compare those changes to changes in physical habitat conditions.…”

“…Delineating preferred microhabitatTo evaluate and explain changes in Chinook salmon fry rearing habitat availability in the LYR, this study applied the HSC functions developed and bioverified byMoniz et al (2020) to a subset of the 2006/2008 depth, velocity, and cover rasters summarized above. Using the preference threshold observed by Moniz et al (2020) for Chinook salmon fry in the LYR, cells in the 2006/2008 and 2014 habitat suitability rasters with suitability values ≥0.5 were classified as preferred microhabitat and converted into polygon features to be further analyzed in this study.…”