Joseph L Thorley | bioRxiv Science

bioRxiv2015

The Abundance of Large Piscivorous Ferox Trout (Salmo trutta) in Loch Rannoch, Scotland

BackgroundFerox Trout are large, long-lived piscivorous Brown Trout (Salmo trutta). Due to their exceptionally large size, Ferox Trout are highly sought after by anglers while their life-history strategy, which includes delayed maturation, multiphasic growth and extended longevity, is of interest to ecological and evolutionary modelers. However, despite their recreational and theoretical importance, little is known about the typical abundance of Ferox Trout.\n\nMethodsTo rectify this situation a 16 year angling-based mark-recapture study was conducted on Loch Rannoch, which at 19 km2 is one of the largest lakes in the United Kingdom.\n\nResultsA hierarchical Bayesian Jolly-Seber analysis of the data suggest that if individual differences in catchability are negligible the population of Ferox Trout in Loch Rannoch in 2009 was approximately 71 fish. The results also suggest that a single, often unaccompanied, highly-experienced angler was able to catch roughly 8% of the available fish on an annual basis.\n\nDiscussionIt is recommended that anglers adopt a precautionary approach and release all trout with a fork length [≥] 400 mm caught by trolling in Loch Rannoch. There is an urgent need to assess the status of Ferox Trout in other lakes.

Ecology↗

bioRxiv2015

Recent Greater Sage Grouse (Centrocercus urophasianus) Population Dynamics in Wyoming Are Primarily Driven by Climate, not Oil and Gas Development

BackgroundSpatial scale is important when studying ecological processes. The Greater sage-grouse (Centrocercus urophasianus) is a large sexually dimorphic tetraonid that is endemic to the sagebrush biome of western North America. The impacts of oil and gas development at individual leks has been well-documented. However, no previous studies have quantified the population-level response.\n\nMethodsHierarchical models were used to estimate the effects of the areal disturbance due to well pads as well as climatic variation on individual lek counts and Greater sage-grouse populations (management units) over 32 years. The lek counts were analyzed using General Linear Mixed Models while the management units were analyzed using Gompertz Population Dynamic Models. The models were fitted using frequentist and Bayesian methods. An information-theoretic approach was used to identify the most important spatial scale and time lags. The relative importance of oil and gas and climate at the local and population-level scales was assessed using information-theoretic (Akaikes weights) and estimation (effect size) statistics.\n\nResultsAt the local scale, oil and gas was an important negative predictor of the lek count. At the population scale, there was only weak support for oil and gas as a predictor of density changes but the estimated impacts on the long-term carrying capacity were consistent with summation of the local impacts. Regional climatic variation, as indexed by the Pacific Decadal Oscillation, was an important positive predictor of density changes at both the local and population-level (particularly in the most recent part of the time series).\n\nConclusionsAdditional studies to reduce the uncertainty in the range of possible effects of oil and gas at the population scale are required. Wildlife agencies need to account for the effects of regional climatic variation when managing sage-grouse populations.

Ecology↗