Understanding drivers and correlates of fish productivity: Finding optimal indicators in freshwater fishes

Abstract

Canadian freshwater commercial and recreational fisheries contribute $8.8 billion in revenue to the economy annually and are a significant subsistence food source for Indigenous communities. Fish production is recognized as the best indicator of fish population fitness and for assessing productive capacity at both the population and community levels and is legislatively required by the Canadian federal government to prevent, mitigate and/or monitor impacts of development in the Fisheries Act. However, empirical tests of correlates and drivers of fish productivity are lacking due to the extensive effort and monetary expense required to calculate estimates of production. Using approximately 20-years of data from disturbed and undisturbed freshwater fish populations and the environments that support them at the IISD-Experimental Lakes Area (ELA) this dissertation explored spatiotemporal correlates and drivers of freshwater fish production. Here, I (i) proposed modifications to current estimation methodologies through the use of von Bertalanffy growth models to allow for estimates of negative production, (ii) identified key fine-scale mechanisms of both population- and communitylevel fish production temporally, as well as population-level production over regional scales, and (iii) based on these analyses, provide recommendations for variables that can be used as surrogates of fish production. I show that physiochemical and limnological factors that influence habitat availability (i.e., total phosphorus, dissolved organic carbon) dictate lower food web dynamics (i.e., prey quantity and access to prey) and resulting life history strategies (i.e., mean weight, mean length, abundance, and body condition), to ultimately shape fish productivity, demonstrating that fish production is primarily driven by factors that shape individual- and population-level bioenergetics.