Natural and marine environment
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Browsing Natural and marine environment by Author "Allen, Michelle"
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Item Does phenology influence predation rate on Salmo trutta parr during lake migration?(Wiley, 2024-03-16) Kennedy, Richard; Barry, James; Boyd, Adele; Allen, Michelle; Fisheries and Aquatic EcosystemsAcoustic tags fitted with predation sensors, which trigger following ingestion by piscivorous predators, were used to compare direct predation rates during downstream migration (out-migration) of potamodromous (freshwater) brown trout (Salmo trutta L.) parr from their natal river into a large freshwater lake system during spring and autumn. Thirty-eight spring migrants were tagged across two study years (2021 and 2022) of which 13 individuals (34%) were predated. By contrast 40 autumn migrants were tagged (2020 and 2021) of which three individuals (7.5%) experienced predation. The overall predation loss rate for spring migrants was 0.342% day−1 and was 0.075% day−1 for autumn migrants. Most predation events during spring (77%) occurred within the lower river before tagged fish entered the lake, whilst no predation events were recorded within the river in the autumn. Predation events were significantly linked to tagging season (spring or autumn), with the probability of tags remaining untriggered (as a proxy for survival) being higher 93% (95% confidence interval [CI] [87%, 100%]) in autumn than in spring 66% (95% CI [53%, 83%]). The spring migration periods showed significantly lower river discharge (0.321 m3/s mean daily discharge, April 1 to May 31) to those measured during autumn (1.056 m3/s mean daily discharge, October 1 to November 30) (Mann–Whitney U-test, U = 1149, p < 0.001). Lower flows, clearer water, and longer sojourn in the river may have contributed to greater predation losses in the spring relative to the autumn.Item Investigating the phenology of juvenile potamodromous brown trout (Salmo trutta L.) in two large lake catchments(Wiley, 2022-01-05) Kennedy, Richard; Rosell, Robert; Allen, MichelleThere is growing interest in the phenology of juvenile Salmo trutta and evidence of significant downstream migration during the autumn in some anadromous populations. The present study used acoustic telemetry to examine the phenology of potamodromous trout parr across a region encompassing two large lake catchments. One hundred sixty-seven trout parr were tagged in late summer across four lake tributaries between 2018 and 2020. In total, 75 tagged parr migrated into the lakes with 67 (89%) migrating between September and December and 8 (11%) migrating between March and June. Autumn migration was highly prevalent across all the tributaries, with 16%–66% of each tagged sample exhibiting autumn migration, and 0%–15% of each tagged sample exhibiting spring migration. Autumn migrants were significantly longer and heavier than spring migrants, but condition factor was similar. Autumn migrants were associated with higher river discharge levels and lower water temperatures than spring migrants. The management challenges posed by extensive autumn migration behaviour in migratory trout stocks are examined and discussed.Item The long-term response of lake nutrient and chlorophyll concentrations to changes in nutrient loading in Ireland's largest lake, Lough Neagh(Royal Irish Academy, 2021-04-29) McElarney, Yvonne; Rippey, Brian; Miller, Claire; Allen, Michelle; Unwin, AntonyThe long-term response of chlorophyll-a (chl-a) to changing lake water nutrient concentrations and increasing water temperature was investigated in Lough Neagh, a large, hypereutrophic lake in Northern Ireland. Trends in external and internal nutrient loading and their relation to lake nutrient concentrations were also established. Lake water concentrations of total P (TP) have increased since the 1990s but were not correlated with catchment inputs, which showed no trend. The characteristics of internal loading of P have changed since the mid-1990s, with an earlier and larger mass of P released from the sediments each summer. Catchment inputs of total oxidised N (NOx) decreased from the peak value of 10,186T/yr in 1995 to 5,396T/yr in 2011, coinciding with a reduction in lake water concentrations. External inputs and lake concentrations of NOx were highly correlated (R=0.88). Water temperature increased approximately 1C and was a predictor of variation in chl-a from 1974 to 2012. After the peak chl-a concentration in 1993, dissolved inorganic N (DIN) also became an important predictor, accounting for almost half of the 44% variance explained by a hierarchical partition model. Decreasing log (DIN:TP) ratios suggest that N limitation of chl-a has become more important in the lake recently.Item Recovery targets and timescales for Lough Neagh and other lakes(Elsevier, 2022-06-12) Rippey, Brian; McElarney, Yvonne; Thompson, James; Allen, Michelle; Gallagher, Mary; Douglas, Richard; Fisheries and Aquatic EcosystemsThe framework, model and methods of Nürnberg were applied and evaluated in Lough Neagh and 19 other lakes in order to establish inflow phosphorus concentrations that support target lake values. Supporting concentrations, in the absence of an internal load, were derived and the effect of uncertainty in the model retention coefficient was relatively small, ±11-20 % in Lough Neagh and an average (n = 17) of ±9.7 % in the other lakes. There was further support for the model and methods from an independent estimate of the net internal load in Lough Neagh (13 % difference) and from another model in the other lakes (Supporting concentrations, which should be lower, were by an average of 11 mg P m−3). In the framework, steady state with the phosphorus load is assumed, but, based on a generic lake model, is not likely if the hydraulic residence time>0.5-0.8 yr and should lead to a decrease in phosphorus retention, which was found during three periods in Lough Neagh. Based on a compilation of internal load recovery times from 23 lakes in the literature, it could take between 8 and 20 years for lakes with an internal load to approach their targets.