Riverscape nesting dynamics of Neosho Smallmouth Bass: To cluster or not to cluster?

Aim

Hierarchical stream habitat conditions influence patterns of fish abundance and population dynamics. The spawning period is important for stream fishes but coincides with unpredictable environmental conditions and stressors. Thus, identifying habitats that confer suitable spawning is crucial to managing vulnerable fish populations, including narrow-range endemics. Here, we evaluate reach- and catchment-scale habitat features related to Neosho Smallmouth Bass (Micropterus dolomieu velox) nest presence, abundance and aggregations (clusters) and quantify nest microhabitat.

Location

Ozark Highlands ecoregion, USA.

Methods

We conducted snorkel and habitat surveys from 2016 to 2018 to quantify nest abundance, describe nest cluster characteristics and quantify nest microhabitat. We used field-collected and geospatial variables and developed generalized mixed models to evaluate the influence of multi-scale habitat features on nest cluster presence and nest abundance.

Results

Nest clusters, scarcely known for other Smallmouth Bass populations, contained 25% of all documented nests. Presence of nests was more likely in warmer stream reaches with wide, shallow channels and more pool habitat. Nest cluster presence was more likely with greater nest densities and earlier in the spawning season. The abundance of Smallmouth Bass nests was related to several reach-scale habitat conditions, with greater nest counts in warmer reaches and reaches with deeper pool habitat. Regardless of cluster behaviour, nesting Smallmouth Bass used similar microhabitats, including a range of depths (0.26–1.85 m), low velocities (