Fox, Michael

My study was primarily focused on the comparison of life history traits between stocked American eel and their naturally recruited conspecifics in Lake Ontario and the upper St. Lawrence River (USLR/LO). I found that stocked eels experienced faster annual growth than their naturally recruited conspecifics and were comprised of a greater proportion of males. These findings indicate that the life history patterns of American eel may be genetically predisposed. Additionally, my study served to characterize the diets of stocked American eel and examine possible associations between eel and prey size. The eels consumed a number of macroinvertebrate prey orders as well as fishes and macrocrustaceans, with the latter prey items being more prevalent in the diets of larger eel specimens. A disparity in eel growth and body condition was observed between two primary stocking locations and were likely attributable to differences in available forage and habitat. Lastly, growth, body condition, and stocked eel diet were compared between lentic and lotic habitats. Eels from lotic streams experienced slower annual growth and had reduced body condition, and their diets were comprised of smaller prey items. The results of this study suggest that the current stocking methods employed in the USLR/LO are not suitable to restore the natural recruitment of individuals that will exhibit desired life history traits.

Nitrogen is a major constituent of agricultural fertilizers, and nitrogen inputs to stream water via runoff and groundwater lead to a variety of negative environmental impacts. In order to quantify the movement of nitrogen through aquatic food webs, fourteen streams with varying land uses across South-Central Ontario were sampled for two species of fish, freshwater mussels, and water for measurement of isotope ratios of δ15N and δ13C. I found that nitrogen isotopes in fish, water, and mussels were related to the percentage of riparian monoculture, and that carbon isotopes were unrelated to monoculture. Though all species were enriched as monoculture increased, the rate of δ15N enrichment as monoculture increased did not vary between species. This study has improved our understanding of how monoculture affects nutrient enrichment in stream food webs, and assesses the validity of using nitrogen isotopes to measure trophic positions of aquatic organisms across an environmental gradient.

Author Keywords: agriculture, fish, food webs, nitrogen, stable isotopes, streams

Competition is known to impact population dynamics through both indirect and direct interactions, and direct interactions can often lead to injury in one or both parties. As such, response to injury through tissue regeneration can be important for surviving post-competitive interaction. However, the impacts of outside factors like temperature and genome size (e.g. polyploidy) are not well studied, especially in syntopic systems. We addressed this knowledge gap by comparing regeneration rates of diploid Ambystoma laterale and triploid unisexual Ambystoma at two ecologically-relevant temperatures. Environmental factors appeared to have stronger effects on regeneration than ploidy level, but overall mass was impacted more strongly by ploidy level. Interestingly, there was an interaction between temperature and time within unisexuals that was absent when comparing different ploidy levels, implying temperature has a more complex effect on polyploids. This study supports the hypothesis that polyploid organisms are better equipped to respond to shifts in their environments, which can give them a competitive advantage at the northern range limit of this species complex.

Author Keywords: Ambystoma, Genome dosage, Hybrid vigor, Polyploidy, Thermal optimum, Tissue regeneration

Blackfin Cisco (Coregonus nigripinnis), a deepwater cisco species once endemic to the Laurentian Great Lakes, was discovered in Algonquin Provincial Park in four lakes situated within a drainage outflow of glacial Lake Algonquin. Blackfin habitat preference was examined by analyzing which covariates best described their depth distribution using hurdle models in a multi-model approach. Although depth best described their distribution, the nearly isothermal hypolimnion in which Blackfin reside indicated a preference for cold-water habitat. Feeding structure differentiation separated Blackfin from other coregonines, with Blackfin possessing the most numerous (50-66) gill rakers, and, via allometric regression, the longest gill rakers and lower gill arches. Selection for feeding efficiency may be a result of Mysis diluviana affecting planktonic size structure in lakes containing Blackfin Cisco, an effect also discovered in Lake Whitefish (Coregonus clupeaformis). This thesis provides insight into the habitat preferences and feeding ecology of Blackfin and provides a basis for future study.

Author Keywords: allometric regression, blackfin cisco, habitat, hurdle models, lake whitefish, mysis