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Introduced species are a threat to biodiversity. Burbot, Lota lota, a fish native to the Wind River Drainage, Wyoming and a species of conservation concern, have been introduced into the nearby Green River Drainage, Wyoming, where they are having negative effects on native fish species. We compared these native and introduced burbot populations to evaluate potential mechanisms that could be leading to introduction success. We examined genetic ancestry, physical habitat characteristics, community composition, and burbot abundance, relative weight, and size structure between the native and introduced range to elucidate potential differences. The origin of introduced burbot in Flaming Gorge Reservoir is most likely Boysen Reservoir and several nearby river populations in the native Wind River Drainage. Burbot populations did not show consistent differences in abundance, size structure, and relative weight between drainages, though Fontenelle Reservoir, in the introduced drainage, had the largest burbot. There were also limited environmental and community composition differences, though reservoirs in the introduced drainage had lower species richness and a higher percentage of non-native fish species than the reservoir in the native drainage. Burbot introduction in the Green River Drainage is likely an example of reservoir construction creating habitat with suitable environmental conditions to allow a southwards range expansion of this cold-water species. An understanding of the factors driving introduction success can allow better management of species, both in their introduced and native range.

Passive integrated transponder tags are commonly used in fisheries science to individually identify fish in studies that assume high fish survival and tag retention rates, and have recently been used in studies on burbot Lota lota, although information on retention and survival rates is unavailable. Burbot (310–676-mm TL) surgically implanted with 23-mm PIT tags had 93% survival and 100% retention over 60 d; the survival of these burbot was not significantly different from that of a control group. This suggests that this marking method is a viable means of individually identifying burbot for short-term studies. Received January 21, 2012; accepted July 4, 2012

Lepak JM, Fetherman ER, Pate WM, Craft CD, Gardunio EI. 2012. An experimental approach to determine esocid prey preference in replicated pond systems. Lake Reserv Manage. 28: 224–231. Competitive interactions between salmonids and white suckers (Catostomus commersonii) often result in poor salmonid growth, condition, and ultimately angler catch-per-unit-effort. Fisheries managers frequently introduce hybrid northern pike (Esox lucius) and muskellunge (E. masquinongy), known as tiger muskellunge, as biological control agents to reduce the abundance of undesirable species including white suckers, while simultaneously attempting to create viable recreational fisheries with stocked salmonids. In this study, northern pike were used to evaluate esocid prey preference between naive, hatchery-reared rainbow trout (Oncorhynchus mykiss) and wild white suckers. Enclosures containing northern pike were stocked with rainbow trout and white suckers at 2 densities (50:50 and 20:80, respectively) to represent di...

Altering food web structure has been shown to influence mercury (Hg) concentrations in sport fish. Here, we describe a whole-system manipulation designed to assess the effectiveness of stocking relatively high-quality, low-Hg prey (rainbow trout, Oncorhynchus mykiss ) as a means of increasing northern pike ( Esox lucius ) growth to reduce Hg concentrations. A replicated pond experiment served as a reference for the lake experiment and provided information to parameterize bioenergetics simulations. Results indicate that stocking relatively high-quality, low-Hg prey is a rapid and effective method to reduce sport fish Hg concentrations by up to 50% through an increase in individual northern pike biomass. Large northern pike, the fish that tend to be the most contaminated, were affected most by the manipulation. The observed declines in northern pike Hg concentrations indicate that stocking might be used to reduce Hg concentrations in sport fish prior to harvest. However, after 1 year, northern pike Hg concentrations rebounded, suggesting that reductions would be temporary without continuous stocking. Thus, perhaps the most effective method of perpetually reducing sport fish Hg concentrations would be to manage for the development of a naturally reproducing forage fish population with relatively high energy content and low Hg concentrations.

Summary Illegally introduced burbot (Lota lota) populations have spread throughout the Green River drainage (GRD) of the upper Colorado River Basin in Wyoming and Utah, USA where they are having adverse effects on native and sport fisheries. We analyzed existing data to evaluate the status of burbot in southwestern Wyoming. Burbot appear to have been illegally introduced into Big Sandy Reservoir in the early- to mid-1990’s, based on capture of burbot in 2003 that included one 16 year old fish and several between 7 and 12 years of age. Burbot began expanding throughout the Green River Drainage in the early 2000s and, with the assistance of a secondary introduction into Fontenelle Reservoir, have successfully invaded most portions of the GRD upstream of the Flaming Gorge Dam. Only one burbot has been captured downstream of Flaming Gorge Reservoir, but this detection indicates potential for downstream establishment in the future. Burbot are difficult to sample, especially in large rivers, so we recommend sampling techniques to monitor the expansion of burbot in lotic and lentic habitats of the upper Colorado River Basin as well as highlight research opportunities associated with this invasion.