Showing papers by "Government of Canada published in 1995"

Intestinal microflora of salmonids: a review

Abstract: Microflora isolated from fish intestines have been described for a limited number of salmonid fish species. The size of the microbial population of salmonids appears to vary within different regions of the gastrointestinal tract. The genera present in the gastrointestinal tract seem to be those which can survive and multiply in the intestinal tract. The predominant bacteria isolated from the salmonid gut are aerobes or facultative anaerobes. Few investigations have evaluated obligate anaerobes in the digestive tract of salmonids, and these studies have suggested that the population levels of obligate anaerobes are lower than those of facultative anaerobes. The bacterial genera isolated from fish intestines vary with salinity, antibiotics, chromic oxide, diet and dietary components such as linoleic acid, and display day-to-day fluctuations. Acinelobacter spp., Enterobacter spp. and Pseu-domonas spp. are regarded as autochthonous in Oncorhynchus species, while Aeromonas spp., Flavobacterium spp., Pseudomonas spp. and Lactobacillus spp. are suggested as autochthonous in Arctic charr, Salvelinus alpinus(L.).

Sources of methyl mercury to freshwater ecosystems: A review

Abstract: The recent development of sensitive analytical techniques for the determination of MeHg concentrations in water has resulted in a rapid advancement in our understanding of MeHg production and transport in lake and reservoir systems. Results from three recent whole-ecosystem studies have shown that there are three important sources of MeHg to aquatic systems — precipitation, runoff from wetlands, and in-lake methylation. Data from these three studies are used to construct a simple model that illustrates how the relative importance of these sources can vary with rates of atmospheric deposition of MeHg, lake type, percentage of wetlands in the terrestrial catchment and the percentage of water surface area that covers flooded terrain.

Is Total Mercury Concentration a Good Predictor of Methyl Mercury Concentration in Aquatic Systems

Abstract: Methyl mercury (MeHg) concentrations were compared to total mercury (THg) concentrations in a variety of types of aqueous samples collected at the Experimental Lakes Area during 1991 through 1993. In several streams, an experimentally flooded wetland, and peat pore water, there was no relationship between MeHg and THg concentrations. %MeHg (compared to THg) ranged from < 1% to over 90%. In three ELA lakes, as in groups of lakes from other regions, a linear relationship between MeHg and THg concentration was found. However, these relationships differed by a factor of three from one region to another. This study shows that THg inputs and/or concentrations are not very useful in predicting MeHg concentrations, and that factors within ecosystems are very important in controlling MeHg concentrations.

Mature males of Arctic charr, Salvelinus alpinus, release F-type prostaglandins to attract conspecific mature females and stimulate their spawning behaviour

Abstract: We examined the behavioural and biological functions of prostaglandins (PG) of F-type as a chemosensory signal during spawning in Arctic charr. Immunoassay revealed F-type PGs in water inhabited by ripe charr of both sexes performing spawning-related acts. High concentrations of immunoreactive PGFs seemed to coincide with male spawning activity. Ripe isolated males were more odorous to other charr (as assayed by EOG) than either females or immature charr. When these males received chemical cues from ovulated females, they increased their release of odorants, including F-type PGs, into the water. PGF2α at concentrations of 0.1 nM attracted ovulated females and ripe males. It also stimulated digging behaviour in mature females. It is concluded that F-type PGs or their derivatives are released by ripe males on the spawning grounds to attract females and elicit their spawning behaviour.

Scanning proton microprobe analysis of strontium in an arctic charr, Salvelinus alpinus, otolith: implications for the interpretation of anadromy

Abstract: Scanning proton microprobe imaging has been used to map the distribution of strontium (Sr) in an arctic charr, Salvelinus alpinus, otolith. X-ray maps show that Sr variation follows an oscillatory zoned pattern which correlates with optically resolved zones (annuli). The internal region of the otolith shows optical zonation but no significant Sr content. Comparison of the optical image with the Sr X-ray map provides evidence of when the fish entered a high Sr environment. This may be interpreted as when the fish migrated from fresh water to a marine environment; this particular fish first migrated to sea in its eighth year. Micro-PIXE point analysis was used to determine the abundance of Sr in annuli along a radius from the nucleus to an outer edge; Sr levels in the internal region were about 10 ppm and variation in the outer zoned region was between 62 and 175 ppm. Detection limits for Sr are in the 1–2 ppm range. Other trace elements, such as transition elements, were found to be present in some growth regions in the 1–20 ppm range. Proton beam analysis is a non-destructive analytical technique capable of preserving the spatial integrity of trace-element data in otoliths such that element distribution may be linked to the growth structure of the otolith.

Effects of zooplankton on sedimentation in pelagic ecosystems : theory and test in two lakes of the Canadian shield

Abstract: A simple heuristic theory based on conservation of matter and describing the fate of autotrophic production in pelagic ecosystems was developed to assist in conceptualizing how zooplankton affect sedimentation processes in lakes and oceans. The theory predicted that effects of zooplankton on the fraction of autotrophic incorporation that sediments (the “export ratio”) will be a function of factors related both to zooplankton digestion and egestion and to tendencies of particulate matter to sediment directly prior to mineralization. As a result, effects of zooplankton grazing on the export ratio were predicted to be site-dependent, a function of physical conditions and zooplankton communities characterizing an ecosystem. The theory was tested by monitoring autotrophic production of C, N, and P, sedimentation of C, N, and P, and zooplankton biomass in two lakes of the Canadian shield characterized by contrasting morphometry and food-web structure. In Lake 110, a small elongate lake protected from wind exposure, export ratios of C, N, and P declined strongly with zooplankton biomass. In contrast, in L240, a larger lake with considerably greater wind exposure, export ratios increased with zooplankton biomass. These results were consistent with predictions of our theory that effects of zooplankton on sedimentation processes will depend on the tendency of particulate matter to directly sediment relative to the tendency of egested materials to sediment. However, no significant differences in relationships between export ratios for C, N, and P and zooplankton biomass were found.

Why Has Inequality in Weekly Earnings Increased in Canada

Abstract: Inequality in weekly earnings increased in the eighties in Canada. The growth in inequality occurred in conjunction with three facts. First, real hourly wages of young workers dropped more than 10%. Second, the percentage of employees working 35-40 hours per week in their main job fell and the fraction of employees working 50 hours or more per week rose. Third, there was a growing tendency for highly paid workers to work long workweeks. We argue that any set of explanations of the increase in weekly earnings inequality must reconcile these three facts. Sectoral changes in the distribution of employment by industry and union status explain roughly 30% of the rise in inequality. The reduction in real minimum wages and the decline of average firm size explain very little of the growth in age-earnings differentials. Skill- biased technological change could have increased both the dispersion of hourly wages and the dispersion of weekly hours of work and, thus, is consistent a priori with the movements observed. Yet other factors may have played an equally important--if not more important--role. The growth in competitive pressures, possible shifts in the bargaining power (between firms and labor) towards firms, the greater locational mobility of firms, the increase in Canada's openness to international trade, the rise in fixed costs of labor and possibly in training costs may be major factors behind the growth in weekly earnings inequality in Canada.

Changes in the Inflation Process in Canada: Evidence and Implications

Abstract: L'economie canadienne est en transition entre une phase de desinflation et une periode caracterisee par un taux d'inflation tres bas et relativement stable. Dans ce contexte, l'auteur se demande s'il faut s'attendre a ce que les parametres d'une equation de forme reduite soient insensibles aux changements qui s'operent dans le processus d'inflation. Deux questions empiriques […]

The Duration of Unemployment: A User Guide

Abstract: The objective of this paper is to introduce a new measure of the average duration of unemployment spells using Canadian data. The paper summarizes the work of Corak (1993) and Corak and Heisz (1994) on the average complete duration of unemployment in a non-technical way by focusing on the distinction between it and the average incomplete duration of unemployment, which is regularly released by Statistics Canada. It is pointed out that the latter is a lagging cyclical indicator. The average complete duration of unemployment is a more accurate indicator of prevailing labor market conditions, but some assumptions required in its derivation also imply that it lags actual developments.

Growth and differentiation of the secondary palate in a teleostean fish, oncorhynchus kisutch

Abstract: A study was undertaken to examine the growth and differentiation of secondary palate in a teleostean fish, Oncorhynchus kisutch The rate, pattern, and time of synthesis of various macromolecules, which play a crucial role during palate development in higher vertebrates were examined in the developing palate of fish A spurt in DNA synthesis during midmorphogenesis of fish palate appeared to be related to temporal regulation of palate development RNA synthesis was high during the time of primordial appearance and increased again from day 4 post hatching (PH) to correspond with differentiation of palate Protein synthesis remained low initially but its trend paralleled that of RNA synthesis after day 4 PH Glycosaminoglycan synthesis increased initially with the cartilaginous growth and then with the appearance of mucous cells An increase in collagen synthesis corresponded with the thickening of collagen layer in the basement membrance Cyclic AMP activity increased initially prior to the increase in DNA synthesis and subsequently remained high indicating its involvement in both growth and differentiation of fish palate These profiles of synthesis of various macromolecules in teleostean fish differ considerably from that seen in higher vertebrates On the basis of comparative analysis, it was suggested that the timing of mesenchymal differentiation may be one of the features in determining the characteristics of palate development in different classes of vertebrates © 1995 Wiley-Liss, Inc

Alternative Measures of the Average Duration of Unemployment

Abstract: This paper examines the robustness of a measure of the average complete duration of unemployment in Canada to a host of assumptions used in its derivation. In contrast to the average incomplete duration of unemployment, which is a lagging cyclical indicator, this statistic is a coincident indicator of the business cycle. The impact of using a steady state as opposed to a non steady state assumption, as well as the impact of various corrections for response bias are explored. It is concluded that a non steady state estimator would be a valuable compliment to the statistics on unemployment duration that are currently released by many statistical agencies, and particularly Statistics Canada.