The Atlantic salmon in fresh water: spawning, rearing and production

摘要: Fluvial salmonids have evolved to use the diversity of habitats in natural streams for different life history stages and at seasons. Required freshwater habitat Atlantic salmon can be classified generally as that suitable (i) spawning, (ii) feeding during major growing period, (iii) overwintering. Spawning is usually rapid water tail pools on upstream edge a gravel bar, ideally with depths about 25 cm, mean velocities 30–45 cm s-1, maximum 2 body lengths substrate irregularly shaped stones cobble, pebble, gravel. Underyearling ( 7 TL) are riffles deeper than 20 coarse substrate. Depth preference increases size. Multiple linear regression models quantifying parr identified an important variable, positive relationship index coarseness. Negative relationships were found stream width, range discharge, overhanging cover. Water chemistry, especially alkalinity, nitrates, phosphates, regulators production. Although similar variables had importance, coefficients among rivers differed. Interactions occur variables. Further studies required quantify productive capacity parr. Results suggest useful derived if river system mapped, stratified by habitat, then smolt yield could predicted egg deposition estimated. In winter, young shelter or move pools, but continue feeding, larger being more active. Feeding general opportunistic. Food consists mainly insects, taken primarily column, also from surface bottom. Young flowing highly territorial less so slow still waters. fast water, their large pectoral fins apply themselves substrate, allowing them occupy this type little expenditure energy. Height above decreases velocity, temperature social status. preferred relatively productive, lentic waters occupied where there few predators severe competitors may provide significant some systems. Selective segregation minimizes competition between brook charr brown trout, trout negative effects underyearling salmon, whereas small flats. Competition both interference exploitation results interactive when resource, food, becomes limiting. Limited downstream movement summer. Older juveniles make movements, migrate downstream, most movements spring, lesser peak activity autumn. Dispersal tends indicating full distribution, spawning areas best located upstream. High densities yearling growth survival underyearlings systems, apparently not others, future research regard. Density-dependent evident food limiting, indicator cohorts quantitative has been derived, size sample give estimate density station, minimum occurring carrying capacity. Such regressions vary differing capabilities, assessing optimum densities. Life strategies change changes density-dependent rates. Present stock-recruitment functions do take environmental into consideration, limited applicability. determine requirements types systems geographical areas.