Abstract:Previous investigations into factors influencing incubation success of salmonid progeny have largely been limited to the development of empirical relationships between characteristics of the incubation environment and survival to emergence. It is suggested that adopting a process-based approach to assessing incubation success aids identification of the precise causes of embryonic mortalities, and provides a robust framework for developing and implementing managerial responses.Identifying oxygen availability within the incubation environment as a limiting factor, a comprehensive review of trends in embryonic respiration, and processes influencing the flux of oxygenated water through gravel riverbeds is provided. The availability of oxygen to incubating salmonid embryos is dependent on the exchange of oxygenated water with the riverbed, and the ability of the riverbed gravel medium to transport this water at a rate and concentration appropriate to support embryonic respiratory requirements. Embryonic respiratory trends indicate that oxygen consumption varies with stage of development, ambient water temperature and oxygen availability. The flux of oxygenated water through the incubation environment is controlled by a complex interaction of intragravel and extragravel processes and factors. The processes driving the exchange of channel water with gravel riverbeds include bed topography, bed permeability, and surface roughness effects. The flux of oxygenated water through riverbed gravels is controlled by gravel permeability, coupling of surface-subsurface flow and oxygen demands imposed by materials infiltrating riverbed gravels. Temporally and spatially variable inputs of groundwater can also influence the oxygen concentration of interstitial water.
Abstract:Oxygen fluxes through artificially created salmon redds within four UK rivers were quantified and assessed against survival to hatching of Atlantic salmon embryos. All sites recorded high spatial variability in survival. Minimum survival to hatching was zero at all sites. Maximum survival to hatching ranged from 35% to 91%. Mean survival to hatching ranged from 8Ð7% to 71%.Intra-and inter-site variations in rates of oxygen supply were observed. Generally, interstitial dissolved oxygen concentrations declined over the incubation period from a maximum recorded directly after redd creation, although localized fluctuations were recorded. Similarly, interstitial flow velocities declined over the incubation period from a maximum directly after redd creation to a minimum at hatching. With respect to the causes of embryo mortalities, oxygen supply was shown to be a stronger determinant of survival than interstitial oxygen concentration or interstitial flow velocity.To improve delineation of potential causes of embryo mortalities in the field, the statistical analysis was integrated within mass transfer theory of the processes controlling respiration to determine the likely mechanisms inhibiting respiration. Based on this analysis, mortalities were assessed to have resulted from periods of lethal oxygen concentrations, from periods of interstitial flow velocities that were insufficient to remove metabolic waste, or from combinations of oxygen concentration and interstitial flow that did not support respiratory requirements. A set of oxygen-supply-related thresholds for assessing incubation habitat quality are proposed.
Rates of oxygen consumption for Atlantic salmon Salmo salar embryos approaching hatching were determined. Values were recorded using a 'closed system' experimental set-up. A magnetic stirrer was used to ensure that zones of oxygen depletion did not develop in the microenvironment surrounding the respiring eggs. Recorded values of oxygen consumption ranged from 0Á0024 to 0Á0038 mg O 2 egg À1 h À1 , with a mean consumption rate of 0Á0032 mg O 2 egg À1 h À1 . The values of oxygen consumption were similar to those reported in other studies using a closed system experimental set-up, however, they were lower than those reported in a study adopting a flow-through system. The introduction of clay-sized sediment to the incubation chamber created a thin film (<1 mm) of sediment on the egg surface, and resulted in reduced rates of oxygen consumption. The additional 0Á3 g of clay sediment reduced oxygen consumption by an average of 41% and the addition of a further 0Á2 g of clay sediment reduced consumption by an average of 98%. Two explanations for the recorded reduction in consumption were proposed: (i) the creation of a low permeability seal around the eggs restricted the availability of oxygen to the incubating embryos and (ii) the clay-sized fine sediment physically blocked the micro-pore canals in the egg membrane, thereby restricting oxygen uptake. # 2005 The Fisheries Society of the British Isles
A refinement to the conductiometric standpipe method for determining interstitial flow velocities is described. Three modifications to the original calibration are presented: (i) development of calibration curves for gravels of varying permeability; (ii) statistical validation of a practicable field run time; and (iii) integration of zero velocity flow data to the calibration procedure. These modifications are shown to improve the conductiometric probe's ability to delineate interstitial flow velocities considered critical to salmonid incubation success. Field deployment of the probe highlighted its practical application for determining interstitial flow velocities in salmonid spawning gravels.
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