Does resolution of flow field observation influence apparent habitat use and energy expenditure in juvenile coho salmon?

Abstract

This study investigated how the resolution of observation influences interpretation of how fish, juvenile Coho Salmon (Oncorhynchus kisutch), exploit the hydraulic environment in streams. Our objectives were to evaluate how spatial resolution of the flow field observation influenced: (1) the velocities considered to be representative of habitat units; (2) patterns of use of the hydraulic environment by fish; and (3) estimates of energy expenditure. We addressed these objectives using observations within a 1:1 scale physical model of a full-channel log jam in an outdoor experimental stream. Velocities were measured with Acoustic Doppler Velocimetry at a 10 cm grid spacing, whereas fish locations and tailbeat frequencies were documented over time using underwater videogrammetry. Results highlighted that resolution of observation did impact perceived habitat use and energy expenditure, as did the location of measurement within habitat units and the use of averaging to summarize velocities within a habitat unit. In this experiment, the range of velocities and energy expenditure estimates increased with coarsening resolution (grid spacing from 10 to 100 cm), reducing the likelihood of measuring the velocities locally experienced by fish. In addition, the coarser resolutions contributed to fish appearing to select velocities that were higher than what was measured at finer resolutions. These findings indicate the need for careful attention to and communication of resolution of observation in investigating the hydraulic environment and in determining the habitat needs and bioenergetics of aquatic biota. Key Points:Coarsening the resolution of observation impacts perceived habitat selection and energy expenditure Coarse resolutions created biases toward lower selectivity by fish and for higher velocities Coarse observations may lead to overestimating energy expenditure and suitability of high velocities

Mapping river bathymetries: Evaluating topobathymetric LiDAR survey

“…Thus, EAARL‐B surveys can be used to detect and study habitats formed by large bedforms including pools, riffles, runs, bends, and gentle‐sloping banks. However, it cannot be used to study micro‐habitats formed by single features whose sizes are smaller or similar to the EAARL‐B horizontal resolution (meter scale) and vertical elevation uncertainty (0.11 m within the streambed and 0.23 m on the banks), such as large cobbles or logs (Crowder and Diplas, ; Tullos et al, ).…”

Hydraulic complexity at a large river confluence in the Amazon basin

“…M 2 is similar to M 1 but scaled by kinetic energy of the flow at the point of lower velocity, so it is indicative of the average rate of change in kinetic energy per unit mass and unit length between two points (1/m). The impact of hydraulic complexity on fish energy expenditure will likely be a function of fish length and swim velocity and the resolution of the sampling; Tullos, Walter, and Dunham () demonstrated that estimates of fish habitat characteristics depend on sampling grid size, and grid lengths of 0.1 m generated lower estimates of velocity and energy expenditure than grid lengths of 1 m. Both metrics can be adapted to quantify vertical, lateral, or longitudinal velocity gradients, depending on which gradient best describes a specific habitat. However, in subsequent papers by Crowder and Diplas ( and ), the authors suggested that the optimal hydraulic complexity metric may vary from situation to situation and more than one metric may be needed to appropriately quantify the complexity and hydraulic habitat features of interest.…”

Exploitation of Velocity Gradients by Sympatric Stream Salmonids: Basic Insights and Implications for Instream Flow Management

“…This is well supported by numerous examples showing that focal holding velocities are often lower than velocities in adjacent areas where prey are captured (Bachman ; Hayes and Jowett ; Tullos et al. ). However, few prior studies have explicitly tested for differences in the magnitude of velocity gradient exploitation between sympatric salmonid species.…”

“…This bias is not well documented (however, see the following: Beecher ; Tullos et al. ; Mocq et al. ) but is a concern for applications where credible predictions are needed to optimize productive capacity or to inform trade‐offs between fish habitat requirements and human water use.…”