Lake sturgeon growth chronologies
This thesis tested lake sturgeon ('Acipenser fulvescens') growth rings, contained in cross sections of leading pectoral fin rays, against three criteria required of any structure used in development of growth chronologies relevant to ecophysiological research. First, widths of growth rings were related to overall somatic growth of the organism. Secondly, synchrony of interannual growth variations was quantified using growth chronologies. Finally, lake sturgeon growth rings and related chronologies were tested to determine if these demonstrated the influence of large scale extrinsic factors. The results indicated that radii of sturgeon fin ray cross sections do relate to variations in the somatic growth and satisfy the first criterion. Secondly, individual chronologies from sturgeon sampled in Lake St. Clair, Lake Temiskaming, Saskatchewan River, Lake Winnebago, and Lac St. Louis demonstrated significant synchrony of interannual growth variations and satisfied the second criterion. Finally, lake sturgeon ring widths and chronologies were related to variations in air temperatures, an environmental factor previously associated with sturgeon growth, thereby satisfying the third criterion and indicated that growth data extracted from these natural archives was consistent with that already known regarding sturgeon growth. Having established the validity of lake sturgeon growth chronologies this investigation explored the application of these as ecological tools. Sturgeon chronologies, from populations in which synchronous interannual growth variation was detectable, were negatively correlated with neighbouring tree growth chronologies, a relationship possibly driven by growth response of fish and trees to annual temperature variations. Importantly, these results demonstrate the usefulness of growth chronologies in comparisons among diverse organisms. Fluctuations in synchrony of individual chronologies from neighbouring fish and trees over time were also investigated. Based on assumptions that strength of environmental factors increases growth synchrony within a population, the results suggest that growth in nearby fish and trees responds similarly to environmental fluctuations yet these relations may differ between watersheds. Finally, annual fluctuations in sturgeon growth, documented by chronologies, were successfully modeled in two populations using past records of environmental and tree growth variation. The same environmental factors explained growth variation in both populations suggesting these factors are operating on sturgeon across large geographic scales.