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.
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.
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 naïve, 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 different ratios of forage. Weekly sampling by beach seine was used to determine rainbow trout and white sucker mortality. When the experiment was complete, enclosures were drained to determine overall survival of the forage species. Rainbow trout numbers declined precipitously to zero, while 60-75% of white suckers remained across all treatments. This study demonstrated a clear difference in survival of rainbow trout and white suckers (rainbow trout having lower survival) in the presence of northern pike under these conditions. We suggest fisheries managers consider these findings when stocking or managing for piscivores to control undesirable fish species, or to create recreational fisheries, while simultaneously stocking naïve sport fish vulnerable to predation.
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
Non-native populations of Pacific oysters Crassostrea gigas (Thunberg 1793) are established around the United Kingdom (UK), with two genetically different stocks originating from separate introductions to the UK and France. In this study, we use a coupled biophysical model to simulate Pacific oyster larval transport, in order to investigate the dispersal of the species from a known population near their northern limit on the west coast of the UK (in the Milford Haven Estuary). The model included a pelagic phase, simulating different swimming behaviours, and a settlement phase based on a hydrospatial substrate map. Following successful settlement elsewhere, subsequent releases simulated potential population spread over successive generations. Our results suggest that, should there be sufficiently warm sea temperatures to allow reproduction, dispersal away from Milford Haven Estuary would most be southeast ward towards the Bristol Channel; but dispersal north and west to Ireland is also possible, depending heavily on pelagic swimming behaviour. Seasonal modifications to circulation were less influential. Our study increases understanding of factors that contribute to oyster population spread, and suggests methods for improved management through numerical predictions.
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