Assessing Habitat Availability in a Hydrodynamic Reservoir System

Abstract

Habitats may become unavailable to fish in reservoirs at different water elevations. Coves are particularly vulnerable to habitat loss, as these peripheral zones may become isolated from the main reservoir. Quantifying habitat loss at different water elevation reductions and estimating the cost of replacing specific types of habitat or maintaining a target percentage of total habitat cover can help fisheries managers to plan for habitat restoration projects in reservoirs. We used side-scan sonar to estimate areas of rock, tree, and brush habitat in one cove within Harlan County Reservoir, Nebraska, and used quotes for materials, placement, and personnel from recent habitat restoration projects to estimate replacement and maintenance costs. Materials included riprap rock, cedar trees, and those needed to construct Georgia cubes. Overall, rock, brush, and trees covered a total of 2% of the cove at conservation pool. Rock habitat covered 10 times more area than brush and 100 times more area than trees. All habitats became unavailable when water elevation decreased by 3.5-4.0 m. The cost to replace each habitat type increased as water elevation decreased, and the total cost to replace all habitat at 3.5 m of elevation loss was US$390,000. The cost to maintain the original area of habitat available in the cove (2% of the total cove area) increased for each type of habitat but only until water elevation decreased by 2.5 m. At this point, the total cost to maintain similar habitat coverage was $219,000. Climatic variability may lead to greater oscillations of water elevations in reservoirs, making the vertical distribution of available habitat even more relevant to management planning. The findings of this study serve as an example for how managers can identify the vertical distribution of available habitats and estimate costs for habitat restorations.

Resetting the Clock: How a Reconnection Event Reshaped Cove Fish Assemblages in a Nebraska Reservoir

“…All study coves are generally small (<25 ha at conservation pool), with intermittent streams that provide inflow after precipitation events or seasonal irrigation runoff. Habitat within coves includes limited coarse woody debris and submergent and emergent vegetation (Schriener et al., in press [this special section]), and water quality measurements were largely similar among coves (Table 1).…”

Old Reservoirs, Old and New Challenges: Introduction to the 2021 Reservoir Symposium

“…In reservoirs that fluctuate in water elevation, water-level management can further reduce or increase the accessibility and amount of habitat available to fish and other aquatic organisms. Lateral disconnection of reservoir coves resulted in decreased fish species richness in a Nebraska reservoir (Ruoss et al 2022, this special section), and the cost to replace such habitat can be substantial (Schriener et al 2022, this special section). Reservoir drawdowns also reduced habitat volume available to coldwater fish in an Idaho reservoir as a result of temperature-oxygen squeeze (McLaren et al 2023, this special section).…”

“…2022, this special section), and the cost to replace such habitat can be substantial (Schriener et al. 2022, this special section). Reservoir drawdowns also reduced habitat volume available to coldwater fish in an Idaho reservoir as a result of temperature‐oxygen squeeze (McLaren et al.…”