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This Article is brought to you for free and open access by the Natural Resources, School of at DigitalCommons@University of Nebraska -Lincoln. It has been accepted for inclusion in Papers in Natural Resources by an authorized administrator of DigitalCommons@University of Nebraska -Lincoln.Breeggemann, Jason J.; Kaemingk, Mark A.; DeBates, Timothy J.; Paukert, Craig P.; Krause, Jacob R.; Letvin, Alexander P.; Stevens, Tanner M.; Willis, David W.; and Chipps, Steven R., "Potential Direct and Indirect Effects of Climate Change on a Shallow Natural Lake Fish Assemblage" (2016 ). Bioenergetics models were used to simulate the effects of climate change on growth and food consumption using predicted 2040 and 2060 temperatures in a shallow Nebraska Sandhill lake, USA. The patterns and magnitude of daily and cumulative consumption during the growing season (April-October) were generally similar between the two predators. However, growth of northern pike was always reduced (À3 to À45% change) compared to largemouth bass that experienced subtle changes (4 to À6% change) in weight by the end of the growing season. Assuming similar population size structure and numbers of predators in 2040-2060, future consumption of bluegill and yellow perch by northern pike and largemouth bass will likely increase (range: 3-24%), necessitating greater prey biomass to meet future energy demands. The timing of increased predator consumption will likely shift towards spring and fall (compared to summer), when prey species may not be available in the quantities required. Our findings suggest that increased water temperatures may affect species at the edge of their native range (i.e. northern pike) and a potential mismatch between predator and prey could exist.

Northern pike (Esox lucius) was first documented in West Long Lake, Nebraska, in 1998 when two pike <380 mm were collected. In 2002, a Peterson mark-recapture population estimate on northern pike revealed density and standing stock (i.e., biomass) estimates of 35.8 fish/ha (95% CI= + 8.8) and 22.0 kg/ha (95% CI= + 5.41, respectively. Consequently, West Long Lake was sampled in 2002 to compare relative abundance, size structure, and growth of bluegill (Lepomis macrochims), largemouth bass (Microptems salmoides), and yellow perch (Percaflavescens) prior to and after the establishment of a high-density northern pike population. Bluegill, largemouth bass, and yellow perch relative abundances were significantly lower in 2002 than 1998. Similarly, size structures of all three species were significantly different between years. Size structure declined for both bluegill and yellow perch, and increased for largemouth bass. Growth was significantly higher for bluegill, largemouth bass, and yellow perch in 2002 than 1998. While the fish community changes were expected with the establishment of northern pike, they occurred in a relatively short time period (i.e., four years).

Removal of piscivores may affect population size structure, abundance and growth rates of the remaining fish community. A total of 572 northern pike, Esox lucius L., was removed from 25-ha West Long Lake, Nebraska from 2003 to 2006. The northern pike population was reduced from 36 fish ha )1 and 22 kg ha )1 in 2002 to 20 fish ha )1 and 9 kg ha )1 in 2006. The northern pike population shifted to dominance by smaller individuals. Relative abundance increased for bluegill, Lepomis macrochirus Rafinesque, but remained similar between years for largemouth bass, Micropterus salmoides (Lacepe`de), and yellow perch, Perca flavescens (Mitchill). Bluegill and yellow perch size structure increased probably because of reduced predation by northern pike. The effects of reduced northern pike density on largemouth bass were less evident. The largemouth bass population may be returning to higher density with smaller size structure observed before pike were introduced. The sport fish community responded positively to the removal of northern pike in this small lake.

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