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The freshwater opossum shrimp Mysis diluviana can undergo extensive diel vertical migration (DVM) to feed in shallow, prey rich strata at night. Bright moonlight limits their night-time migration presumably due to predator avoidance. Using a linked, foraging-bioenergetics model, we evaluated the cost of avoiding predators by simulating the effects of prey density, water temperature, and light intensity on daily feeding and growth of M. diluviana in Lake Pend Oreille, Idaho, USA. We found that when mysid distribution was not limited by moonlight intensity, simulated food consumption (10.3 J day−1) increased 1.6-fold compared to estimated consumption (6.1 J day−1) based on their observed, vertical distribution. Moreover, simulated growth of mysids (0.61 mg day−1) increased 74% compared to that estimated from observed distribution patterns (0.35 mg day−1), when they were located in deeper, darker strata. Given recent insights into partial DVM by M. diluviana, we note that proximate factors associated with predator avoidance in pelagic (light availability) and benthic (hunger level, body size and reproductive status) habitats may convey complimentary benefits to M. diluviana fitness by reducing predation mortality and increasing metabolic efficiency. [ABSTRACT FROM AUTHOR]

Methods for improving spawning habitat for lakeshore spawning kokanee, Oncorhynchus nerka (Walbaum), were explored by quantifying incubation success of embryos exposed to three substrate treatments in Lake Pend Oreille, Idaho, USA. Substrate treatments included no modification that used existing gravels in the lake (EXISTING), a cleaned substrate treatment where existing gravels were sifted in the water column to remove silt (CLEANED) and the addition of new, silt-free gravel (ADDED). Incubation success was evaluated using Whitlock–Vibert incubation boxes buried within each substrate treatment that contained recently fertilised embryos. Upon retrieval, live and dead sac fry and eyed eggs were enumerated to determine incubation success (sac fry and eyed eggs × 100/number of fertilised embryos). Incubation success varied significantly among locations and redd treatments. In general, incubation success among ADDED redds (0.0–13.0%) was significantly lower than that for EXISTING (1.4–61.0%) and CLEANED (0.4–62.5%) redds. Adding new gravel to spawning areas changed the morphometry of the gravel-water interface and probably exposed embryos to disturbance from wave action and reduced embryo survival. Moreover, efforts to improve spawning habitat for lakeshore spawning kokanee should consider water depth and location (e.g. protected shorelines) as important variables. Adding clean gravel to existing spawning areas may provide little benefit if water depth or lake-bottom morphometry are altered. [ABSTRACT FROM AUTHOR]

We evaluated the behavior and use of overwintering habitat of adult largemouth bass Micropterus salmoides in the Pend Oreille River, Idaho, using radiotelemetry after increases in winter water levels. Largemouth bass tagged in late summer remained in backwaters until the initiation of the fall drawdown, when they moved to deeper shoreline areas. As water temperatures declined further, all but 1 of the 19 largemouth bass tagged throughout a 44.2-km-long section of river migrated to one of two overwintering areas. Once there, largemouth bass either showed no movement or migrated freely between the two overwintering areas. The overwintering areas were adjacent to the river, had an abundance of aquatic macrophytes, were more than 1 m deep, and had zero water velocity. Higher winter lake levels of 0.6 m did not attract wintering largemouth bass to backwaters. We hypothesized that habitat in overwintering areas was preferred because water temperatures there were several degrees warmer than in shallow backwaters. [ABSTRACT FROM AUTHOR]

Presents information on a study that combined zooplankton abundance and size estimates to describe community dynamics at Lake Pend Oreille, Idaho. Comparison between the zooplankton community along vertical and horizontal gradients; Methodologies of the study; Results of the study.