Habitat connectivity as a metric for aquatic microhabitat quality: application to Chinook salmon spawning habitat

Abstract

AbstractQuality of fish habitat at the scale of a single fish, at the metre resolution, which we defined here as microhabitat, has been primarily evaluated on short reaches, and their results have been extended through long river segments with methods that do not account for connectivity, a measure of the spatial distribution of habitat patches. However, recent investigations of quality of aquatic habitat at the stream segment scale, at hundredth of metre resolution macrohabitat, indicate that the spatial distribution of aquatic habitat quality and size is an important factor at the network scale. Here, we hypothesize that aquatic habitat connectivity, quality and patch size are also important at the microhabitat scale. We test this hypothesis by modelling Chinook salmon (Oncorhynchus tshawytscha) spawning habitat in a 6‐km long reach of Bear Valley Creek (Idaho, USA) with microhabitat resolution of 1‐m square. We use two‐dimensional hydraulic numerical modelling coupled with suitability curves to predict the spatial distribution of spawning habitat quality. We quantify connectivity for each habitat patch with the ratio between the area of neighbouring patches and their squared hydrographic distances. Results from a logistic regression analysis comparing predicted with observed spawning locations indicate that habitat quality and patch size are important factors and connectivity among patches may have a secondary effect. Therefore, spatial distribution of aquatic habitat and size of habitat patches are important aspects of its quality, suggesting that composite metrics such as weighted usable area may not be sufficient in defining the condition of the river environment. Copyright © 2015 John Wiley & Sons, Ltd.