Geology topics

Jon A. Firehammer

Publications and source records attributed to Jon A. Firehammer.

3 recordsLinked to original sources

USGS2025

Food habits of nonnative Smallmouth Bass in Coeur d’Alene Lake, Idaho

Smallmouth Bass ( Micropterus dolomieu ) has been widely introduced beyond its native distribution where interactions with other organisms are largely unknown. We examined the food habits of Smallmouth Bass in Coeur d'Alene Lake, Idaho. Smallmouth Bass were sampled monthly from March 2012 to May 2013 using short duration (1–2 hr sets) gill netting and electrofishing. In total, food habits were evaluated from 904 Smallmouth Bass varying in total length from 39 to 492 mm using gastric lavage. Diet composition varied by season and age. Smallmouth Bass less than 100 mm had diets dominated by invertebrates, particularly Ephemeroptera, Odonata, and Diptera. Fishes were increasingly important in the diet of Smallmouth Bass longer than 100 mm. Interestingly, crayfish (Decapoda) were virtually absent in Smallmouth Bass stomachs; only eight Smallmouth Bass had crayfish in their diet. Native vertebrates were also rare in Smallmouth Bass diets. Rather, kokanee ( Oncorhynchus nerka ), a nonnative species, was generally the most commonly consumed fish prey item (present in 5–15% of Smallmouth Bass across seasons). Kokanee contributed the highest percentage of total energy (approximately 45% of all energy) of any prey item. Results of this study suggest that native fishes of conservation concern are a minor component of Smallmouth Bass diets and that kokanee is important in meeting the energy demands of nonnative Smallmouth Bass. Further research on the distribution and abundance of crayfish in the system and on the population-level effects of Smallmouth Bass predation on kokanee would be insightful and help guide management actions in Coeur d'Alene Lake and similar systems in western North America.

Idaho↗

USGS2015

Trophic ecology of northern pike and their effect on conservation of westslope cutthroat trout.

Westslope Cutthroat Trout Oncorhynchus clarkii lewisi in Coeur d’Alene Lake, Idaho, have declined in recent years; predation by Northern Pike Esox lucius , a nonnative sport fish, is thought to be a causative mechanism. The goal of this study was to describe the seasonal food habits of Northern Pike and determine their influence on Westslope Cutthroat Trout in Coeur d’Alene Lake by using a bioenergetics modeling approach. Fish were sampled monthly from March 2012 to May 2013 using pulsed-DC electrofishing and experimental gillnetting in four bays. Northern Pike catch rates from electrofishing were generally low but increased slightly each season and were highest in the southern portion of the lake; catch rates from gillnetting were approximately 50% higher during the two spring sampling periods compared with the summer and fall. Seasonal growth and food habits of 695 Northern Pike (TL = 16.2–108.0 cm; weight = 24–9,628 g) were analyzed. Diets primarily consisted of kokanee O. nerka , Westslope Cutthroat Trout, and Yellow Perch Perca flavescens . Results of a bioenergetics model estimated that Westslope Cutthroat Trout represented approximately 2–30% of the biomass consumed by age-1–4 Northern Pike. Total Westslope Cutthroat Trout biomass consumed by Northern Pike (2008–2011 year-classes) across all seasons sampled was estimated to be 1,231 kg (95% CI = 723–2,396 kg), and the total number consumed was 5,641 (95% CI = 3,311–10,979). The highest occurrence of Westslope Cutthroat Trout in Northern Pike diets was observed during spring. Thus, reducing Northern Pike predation on Westslope Cutthroat Trout would be one tool worth considering for conserving Westslope Cutthroat Trout populations in Coeur d’Alene Lake.

Idaho↗

USGS2015

Population structure and dynamics of northern pike and smallmouth bass in Coeur d’Alene Lake, Idaho.

Numerous species have been introduced to Coeur d'Alene Lake, Idaho over the last century, but minimal research has been completed to understand their population dynamics. The objective of this study was to describe the population demographics and dynamics of northern pike ( Esox lucius ) and smallmouth bass ( Micropterus dolomieu ), two important nonnative sport fishes in the system to provide information that will assist with guiding management decisions. The oldest northern pike was age 7 and the oldest smallmouth bass was age 11. Populations of both species exhibited very stable recruitment with a recruitment coefficient of determination of 0.99 for northern pike and 0.98 for smallmouth bass. Total annual mortality was estimated as 66% for northern pike and 42% for smallmouth bass. Growth of northern pike in Coeur d'Alene Lake was comparable to the 50–75th percentiles of growth exhibited by lentic northern pike populations across North America. Northern pike in Coeur d'Alene Lake were most similar to populations in the north-central and northeast United States with fast growth rates and short life spans. In contrast, smallmouth bass grew slowly and generally fell within the 5th percentile of lentic smallmouth bass populations in North America. Smallmouth bass in Coeur d'Alene Lake were similar to other populations in northern regions of the United States displaying slow growth rates with high longevity. Results of this study provide important insight on nonnative northern pike and smallmouth bass population dynamics.

Idaho↗