Forebay use and entrainment rates of resident adult fish in a large hydropower reservoir

Abstract

Fish entrainment occurs when individuals are displaced from reservoirs to downstream waters by way of water diversion through turbines or other water release structures. While much effort has been put into quantifying and reducing entrainment of downstream migrating salmonids, considerably less research has focused on fish that are residents in reservoirs and in many cases are the top piscivores in these systems. We used 2 yr of acoustic telemetry data on adult bull trout Salvelinus confluentus and burbot Lota lota tagged in Kinbasket Reservoir (British Columbia, Canada) to investigate entrainment vulnerability by measuring forebay use and entrainment rates. Our results revealed that (1) adult bull trout and burbot made little use of the forebay; (2) bull trout used the forebay more and had higher rates of entrainment than burbot; and (3) both forebay use and entrainment varied among seasons. Bull trout used the forebay more intensively and were mostly entrained in the fall and winter. Limited forebay use and entrainment data for burbot suggest that they are more vulnerable to entrainment in the fall. These findings should be generally applicable for adult bull trout and burbot in reservoirs that maximize operations in the fall and winter, and could help managers and industry to make informed decisions on how to mitigate and compensate for entrainment.

Behavioral attributes of turbine entrainment risk for adult resident fish revealed by acoustic telemetry and state-space modeling

“…Our findings revealed marked seasonal changes in adult bull trout behavior in the forebay of Kinbasket Reservoir, which helps to explain the increased entrainment rates in the fall and winter observed previously [23]. Specifically, we observed increased residence time (see also [23]) and proximity to intakes in the fall and particularly in the winter, as well as slow, undirected movement in the forebay when body temperatures were low (mostly in the winter).…”

“…We did not detect bull trout approaching or moving into the intakes in this study, though adult bull trout entrainment is known to occur through Mica Dam in the fall and winter [23]. The closest distance we detected bull trout from an intake was 23 m-a distance where water velocities are <0.2 m/s during turbine operations [49].…”

“…Specifically, we observed increased residence time (see also [23]) and proximity to intakes in the fall and particularly in the winter, as well as slow, undirected movement in the forebay when body temperatures were low (mostly in the winter). Although turbine operations are maximized during the fall and winter at Mica Dam [26], we did not find any evidence that operational discharge directly influenced adult bull trout behavior in the forebay.…”

“…As a result of climate change, overfishing and habitat loss, as well as fragmentation and degradation, a number of bull trout populations have been listed as threatened in the United States and designated as of special concern or threatened in three of five biogeographic populations in Canada [19,20]. Reservoir populations of bull trout are further impacted by entrainment losses of adults, which occur mostly in the fall and winter and at annual rates ranging from 3.5% to 11.3% [21][22][23]. Seasonality in entrainment risk is most likely associated with temporal changes in physical (for example, turbine operations, water temperature) and biological (for example, prey distribution) factors affecting behavior and forebay use [11,23].…”

“…Reservoir populations of bull trout are further impacted by entrainment losses of adults, which occur mostly in the fall and winter and at annual rates ranging from 3.5% to 11.3% [21][22][23]. Seasonality in entrainment risk is most likely associated with temporal changes in physical (for example, turbine operations, water temperature) and biological (for example, prey distribution) factors affecting behavior and forebay use [11,23].…”