In 1971, changes were observed in the overwintering population sizes of Calanus plumchrus Marukawa, Galanus marshallae Frost and Calanus pacificus californicus Brodsky in the Strait of Georgia, British Columbia. Calanus plumchrus and C. pacificus were less common than in previous years, while C. marshallae was more common. Based on scattered data taken since the turn of the century, these changes appeared to be abnormal. Because Calanus plumchrus constituted a significant proportion of the biomass of the zooplankton community, it was possible that the observed fluctuations were indicative of changes in the structure of the zooplankton community within the Strait. Thus a unique opportunity was presented to study a zooplankton community and Its relationship to environmental parameters. Multiple correlation analysis, cluster analysis, multiple regression analysis, factor analysis and principal components analysis were used to analyse zooplankton concentrations and hydrographic data taken in overwintering periods from I969 to 1974. Additional hydrographic data were used to examine relationships between physical and biological data three and six months out of phase. The multivariate techniques allowed an efficient analysis of the relationships within and between the biological and physical data banks. More than one multivariate method was used as each method gives a slightly different viewpoint on the data. A combination of methods thus produces a more complete picture of the system being analysed, while points of overlap between the techniques act as internal checks on the consistency of the analysis. The analysis indicates a recent shift in the hydrographic regime of the Strait of Georgia. The shift is most obvious in the salinity, but can also be seen in the temperature, and in both cases is strongest in Strait of Georgia deep water. It involves subtle changes in salinity and temperature structure. These changes axe of uncertain biological significance but indicate fluctuations in the process of deep water formation. Deep water is formed in the Southern Passages by the mixing of incoming Strait of Juan de Fuca intermediate and deep water with outflowing near surface fresher water. Changes in either of these components, or in the degree of mixing, may produce some changes in the quality of the deep water, which intrudes into the Strait of Georgia in late summer. These changes in quality appear to affect the zooplankton community. Individual zooplankton species are strongly influenced by temperature and stability characteristics or related factors. Temperature and stability during the fall intrusion are particularly important to the overwintering zooplankton community three months later. The same two factors in spring also affect zooplankton in the following winter. The concentrations of Calanus plumchrus and C. marshallae have significant (p<O.05) linear regressions with concurrent temperature at 350 m. The regression lines have opposite slopes and intersect in the region of normal ambient temperature at 350 m. This result suggests that deep water temperature, or a temperature associated, factor, strongly affects the relative fluctuations in the numbers of both species. Principal components and factor analysis of the hydrographic data both suggest that the most important factor in the structure of the water column is its subdivision into near surface, intermediate and deep water. However, in both temperature and salinity components a portion of the variance is associated with a temporal trend within the deep water. Principal components of the zooplankton similarly associate 15% of the zooplankton variance with a temporal trend. No species is strongly weighted on these components, and the association appears to be a function of the whole community, rather than of individual species. As an adjunct to this investigation, ecological separation between Calanus plumchrus and C. marshallae was investigated. Both species have similar distributions and life histories. Feeding competition between them is minimized by a separation in their ability to filter small particles from the water. Calanus plumchrus can feed readily on particles above 3>5 ym in diameter, while C. marshallae can not efficiently filter particles below about 10.5 ym in diameter. Thus, Calanus plumchrus can exploit a potentially rich food source with no competition from Calanus marshallae. This advantage may maintain Calanus plumchrus within the Strait of Georgia despite the detrimental effect of a shift in deep water temperature or related factors. It also suggests that, given a more "normal" physical climate, Calanus plumchrus could revert to its traditional dominance. If Calanus plumchrus continues to drop, or remains at suppressed levels, the economically important fish species that utilize it as food will have to shift prey species, probably to Calanus marshallae. Feeding on C. marshallae will involve a greater energy expenditure to obtain the same ration, and may be detrimental to some predators. / Science, Faculty of / Zoology, Department of / Graduate

Populations of Euphausia pacifica Hansen in the Strait of Georgia region which have recently been commercially harvested were studied with respect to life history, distribution and population dynamics in order to examine aspects of the management of the resource. The potential use of local euphausiids as a food item for fish rearing was also evaluated through chemical analyses and feeding trials with juvenile coho salmon. The maximum life span in local populations was 19 months for males and 22 months for females. Spawning, which occurred from May to September, appeared to be closely related to phytoplankton abundance. First-year growth was maximal in summer (0.094 mm/day) but slowed in autumn and halted in winter. Growth in the following year showed a similar pattern. Males appeared to grow faster and experienced size-selective mortality following early maturity (11-12 mm). Survival increased with life phase changes between egg (6%/mo) and early adult stages (68%/mo) but declined sharply for individuals over 18 mm. Total biomass, B, in each population reached a maximum in October-November. Production by E. pacifica , P, in Saanich Inlet during July-November was 26.8 mgC/m²/day (P/B = 8.8), which is similar to that for herbivorous copepods, but higher than a previous estimate for E. pacifica . Juvenile coho salmon at 9 C showed mean growth rates of 3.8%/day on freeze-dried euphausiids compared to 3.0%, 2.7% and 3.1%/day on diets of euphausiid meal, frozen euphausiids and Oregon Moist Pellet, respectively. Local euphausiids have a well-balanced spectrum of amino acids in their proteins and high carotenoid concentrations (80-219 μ/g tissue) , making them suitable for use in aquacultural feeds. British Columbia's euphausiid fishery harvested about 100 metric tons during early 1977; the main uses are as an aquarium fish food and as a dietary supplement in salmon aquaculture. Yield calculations and other management considerations have indicated that the optimal harvesting time for E. pacifica is between October and December rather than from January to March as suggested by government guidelines on plankton harvesting, a limited and carefully monitored euphausiid fishery in the Strait of Georgia region appears to have potential value to the new plankton harvesting industry and to managers of associated fisheries who need further information on zooplankton population dynamics. / Science, Faculty of / Zoology, Department of / Graduate