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.

Keywords:

• Microhabitat suitability model
• aquatic habitat
• salmonid habitat
• rearing habitat
• two-dimensional hydrodynamic model

Acknowledgements

The authors would like to thank Casey Campos, Ryan Greathouse, Derek Givens, Leslie Alber, Kyle Thompson, Byron Mache, Matthew Weber, Chelsea Hopkins and Paulo Silva for their assistance in collecting and processing data used in this study as well as Geoff Rabone, Sebastian Schwindt, Sean Luis and several anonymous reviewers for their feedback on previous drafts of this manuscript.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

Primary support for this study was provided by the Yuba Water Agency [award number 201016094] and as in-kind aid from the Yuba Accord River Management Team. This project was also supported by the USDA National Institute of Food and Agriculture, Hatch [project number CA-D-LAW-7034-H] and scholarships from the Fly Fishers of Davis, California Fly Fishers Unlimited and Diablo Valley Fly Fishing Club.