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

Abstract

Quality 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.

Effects of habitat quality and ambient hyporheic flows on salmon spawning site selection

“…Our results showed that habitat quality, characterized by surface water depth and velocity, is the primary predictor of site selection for salmonid spawning. This is in agreement with previous results on the importance of surface hydraulics and conditions that are used to quantify habitat quality [ Bjornn and Reiser , ; Bovee , ; Carnie et al ., ; Kondolf , ; Waddle , ].…”

“…We did not include substrate size in our analysis because median gravel size of 35 mm, suitable for spawning, is ubiquitous throughout the study reach [ McKean and Tonina , ]. We quantified the habitat quality from spatially distributed numerically predicted depths and velocities and univariate spawning habitat preference curves adopted from previous studies [ Bjornn and Reiser , ; Carnie et al ., ; Groves and Chandler , ; Hampton , ; Raleigh et al ., ; Smith , ; Tonina et al ., ].…”

Does variable channel morphology lead to dynamic salmon habitat?

“…Previous research highlights the connection between channel morphology and topography and larger-scale sediment supply dynamics, such as those imposed by channel-hillslope coupling (Hoffman and Gabet, 2007;Hassan et al, 2019). Due to a limited number of long-term datasets, habitat modeling studies typically focus on short timescales or on spatial aspects of habitat (Harrison et al, 2011;Cienciala and Hassan, 2013;Hafs et al, 2014;Carnie et al, 2016), or examine conditions over longer timescales but assume static morphology (Fabris et al, 2017). Several flume-based and dam removal studies have noted that variations in sediment supply lead to changes in channel bed topography, such as bar building and erosion (Lisle et al, 1993;Dietrich et al, 2005;Venditti et al, 2012;Major et al, 2017) and pool filling (Hoffman and Gabet, 2007;Major et al, 2017).…”

Upscaling site‐scale ecohydraulic models to inform salmonid population‐level life cycle modeling and restoration actions – Lessons from the Columbia River Basin

“…With a few exceptions across limited spatial extents (McKean et al , ; Fonstad and Marcus, ; Carnie et al , ), none of these technologies can yet deliver the promise of a habitat census across the diversity of riverscapes occupied by salmonids (Bangen et al , ). While hybrid approaches combining multiple techniques have emerged as the most realistic way to obtain complete coverage of a portion of a riverscape (Legleiter, ; Javernick et al , ; Williams et al , ), for now, the notion of a physical habitat census is something we can only achieve across limited portions (albeit still impressive at 10–50 km) of rivers (Pasternack, ; Grams et al , ; Wyrick and Pasternack, ; Benjankar et al , ).…”