Goal:
This program examines various facets of the reproductive ecologies of northern fishes. A central theme of this work is understanding how reproductive effort and success vary among individual adults in age- and size-structured fish populations, how this variation may influence recruitment, and ultimately, the implications for managing fisheries with size-selective harvesting. Much of the research has focussed on the quality of eggs, in terms of size, biochemical composition, and survival to hatch, for individual females of long-lived iteroparous species such as walleye (Sander vitreus), lake trout (Salvelinus namaycush) and lake whitefish (Coregonus clupeaformis).
General hypotheses and some current projects:
Research projects within the reproductive ecology program have primarily been field-based studies of wild populations, though some have also examined captively-reared populations (in fish culture facilities) or conducted laboratory-based rearing experiments with spawn collected from wild populations. Measured indices of egg quality have included size, nutrient composition (total lipids, fatty acid profiles, essential metals, thiamine), and deleterious substances (mercury, organochlorines, non-essential metals) as well as post-fertilization survival. Egg quality is then modelled as a function of female age, size and various indices of condition (liver size, body lipids). The potential influence of the environment on egg-female phenotypic relationships has been examined through comparative studies of populations occupying different habitats, and by manipulation of incubation conditions in laboratory-based rearing experiments.
Recent research in this program has been examining how the relationships between embryonic survival and development and maternal traits in walleye and lake whitefish may be modified by variation in incubation temperature regimes.
Experimental Findings (past projects):
Some recently published results from the reproductive ecology program:
i) sex-based differences in fatty acid compositions of various tissues, presumably arising from provisioning demands for oogenesis, were demonstrated in two walleye spawning stocks (Johnston et al. 2020. Ecology of Freshwater Fish 29: 654-664)
ii) lake trout egg size was shown to vary with female age and size within multiple populations and vary with environmental conditions among populations. Captive-rearing of lake trout from these same stocks altered the ontogenetic progression of egg size (Johnston. 2018. Canadian Journal of Fisheries and Aquatic Sciences 75: 2123-2135)
iii) despite considerable latitudinal variation in growth rate and body condition of naturalized rainbow trout populations across the Laurentian Great Lakes we did not observe similar variation in indices of egg size or lipid content, suggesting that local adaptation for this trait has thus far been limited (Johnston et al. 2016. Journal of Great Lakes Research 42: 861-870)