From the 1940s on, the Bay of Quinte was subjected to increased point-source phosphorus loading. This and other stresses (exploitation, fish species invasion, and perhaps climate fluctuation) altered the productivity of the ecosystem and community structure. In the late 1970s, point-source loading was greatly reduced. At the same time, walleye (Stizostedion vitreum vitreurn) produced the largest year class ever recorded and surged to abundance greater than those seen in the 1950s before its collapse. Also, the dominant invader white perch (Morone americana), which had flourished in the 1960s and 1970s, was almost eliminated by a low-temperature kill. Studies of the bay ecosystem before and after these events indicated that while nutrients and algae responded to changes in nutrient loadings, changes in secondary producers hinged on the changes in the fish community. Use of Borgmann's biomass size spectrum model provides a focus for the interpretation of nutrient- and predator-related changes in biomass distribution. Deviations of the biomass spectrum are interpreted. The biomass and production spectra are linked to both phosphorus concentrations, observed and predicted, and to fishery exploitation rates. The results suggest that while nutrients control the overall biomass of the ecosystem and the slope of the biomass spectrum, trophic interactions and perturbations (e.g. exploitation) determine the degree to which a smooth biomass spectrum is achieved.

The operation, design and performance of a microcomputer controlled spectrum overlap eraser and automatic sensitivity control (ASC) for a clinical mass spectrometer are described allowing calibration for up to eight anaesthetic gases in less than 15 s per gas. The critical design parameters are identified and the mathematical algorithm used discussed. Constructional details of the system are given with particular reference to the key components identified in the analysis of design parameters. The results of static and dynamic testing of the system are reported. The calibrator showed output linearities within +/- 1.7% first standard deviation (FSD) for a two part mixture of gases relevant in anaesthesia and a typical accuracy of 2.1% FSD for any point. Dynamic testing showed that the machine did not impede the overall speed of response of the system. Transient viscosity effects were adequately eliminated and ASC action effective for variation in source pressure between 11.3 X 10(-3) Pa and 2.7 X 10(-4) Pa. Mean drift with the calibrator was found to be less than 0.38% vol/vol h-1.

Available literature data on the relationship between freshwater copepod egg development time and temperature were summarized and fitted where possible to Bělehrádek's temperature function[Formula: see text]where D is development time, T is temperature, a, b, and α are fitted constants. In the calanoids, and to a lesser extent cyclopoids, a and α were predictably related as were α and in situ egg hatching temperature (TH) when b was assumed to be constant for all copepods. This information was used to describe a simple procedure whereby a curve relating egg development and temperature could be constructed by only knowing TH and applying it to Bělehrádek's temperature function. Key words: Calanoidea, Cyclopoidea, zooplankton, temperature, production assessment

The survivorship of each instar of three cohorts of Leptodiaptomus minutus from Bluff Lake, Nova Scotia, is presented. High naupliar mortality but low copepodite mortality occurred. The previously reported values for the predation rate and size selection of prey by omnivorous zooplankton are compared with the observed mortality rates for the different sizes of instars. We estimate that predation by the omnivorous zooplankton could account for most of the naupliar mortality. Our analysis supports Dodson's hypothesis that size-selective predation by zooplankton can be a significant factor determining the proportion of a cohort that reaches maturity.

The mean duration of each instar of planktonic copepods is obtained from field data