Darren M. Gillis

Ecological niche specialization inferred from morphological variation and otolith strontium of Arctic charr Salvelinus alpinus L. found within open lake systems of southern Baffin Island, Nunavut, Canada

The presence of two morphotypes of Arctic charr Salvelinus alpinus was confirmed via morphological variation and otolith strontium (Sr) within three open-lake systems of southern Baffin Island, Nunavut, Canada: Qinngu (LH001), Iqalugaarjuit Lake (PG082) and Qasigiat (PG015). Analysis of otolith Sr indicates that a component of each S. alpinus population within lakes LH001 and PG082 is migratory (large-maturing S. alpinus), whereas another component is lake-resident (small-maturing S. alpinus). Alternatively, small and large maturing S. alpinus may both inhabit tidal habitats during their lifetime in lake PG015. Three morphological characters were identified by principal factor analysis (PFA) as characters that were different between maturity groups for all lakes studied: eye diameter, pectoral fin length and pelvic fin length. As well, upper jaw length (LH001 and PG082) and fork depth (PG015) were identified in PFA as traits that differed between morphs. Univariate tests of morphological characters identified by PFA demonstrated maturity group differences with the exception of eye diameter in Lake PG015 and upper jaw length and pelvic fin length in lake LH001. No difference was found in the MANOVA test of upper and lower gill raker number between small-maturing and undeveloped fish within all lakes studied. Clear morphological variation observed between small-maturing and undeveloped fish in all three lakes of the study suggests ecological niche separation between morphotypes. This is the first documented case of lake-resident S. alpinus use of the tidal habitat in the presence of a migratory large-maturing morphotype.

Maturation, growth and fecundity of Arctic charr, Salvelinus alpinus (L.), life-history variants co-existing in lake systems of Southern Baffin Island, Nunavut, Canada

Two life-history variants of Arctic charr (Salvelinus alpinus), anadromous and lake-resident, have been previously identified in lakes of Southern Baffin Island, Nunavut, Canada. In accordance with classical life-history theory, it is hypothesised that anadromous charr will delay maturation in both size and age, and have increased fecundity (per spawning event) in comparison with lake-resident charr. Sagittal otoliths and biological data were collected for both life-history variants within the three studied lakes: Iqalugaarjuit, Qasigiat and Qinngu. Sagittal otoliths were embedded in epoxy resin, cross-sectioned for age determination, and imaged for back-calculation (size and age). Back-calculated data in each lake were fit to von Bertalanffy growth models for each life-history variant and compared via analysis of residual sums of squares. Anadromous charr had greater mean size at maturity and experienced a delay in mean age at maturity in comparison with lake-residents. The relationship between size and fecundity or egg diameter did not differ between the two life-history variants. Growth models indicate that the overall growth coefficients of lake-resident and anadromous charr were different in all three studied lakes. The Brody growth coefficient for all lake-resident charr populations was greater than anadromous individuals indicating that maximum length was reached at a rapid rate, resulting in a smaller asymptotic length. Indirect evidence suggests that anadromous and lake-resident charr belong to one reproductive population. Future genetic analysis is necessary to further determine the degree of divergence between the life-history variants.

Stock Differentiation of Walleye Based on the Fourier Approximation of Averaged Scale Outline Signals

Abstract Fourier analysis of scale outlines has been successfully used as a first method of stock discrimination in a number of fish species. However, the refinement of methods that increase the ability to differentiate among stocks would improve its utility for fisheries management. Signals created from averaging the scales of several walleyes Stizostedion vitreum produced variables that formed significantly better discriminant functions for stock discrimination than the single-scale signals traditionally used due to the variability of scale outline shapes from individual fish. Fourier analysis was used to quantify scale outline shape; the variables produced violated the discriminant analysis assumption of multivariate normality. A nonparametric randomization procedure, new to stock discrimination studies, was developed to test the significance of the discriminant functions formed. All signal-comparison discriminant functions were significant. A modified jackknife procedure was also developed to test for...

A predictive model for water clarity following dreissenid invasion

Optical transparency, or water clarity, is a fundamental property of lake ecosystems which influences a wide range of physical, chemical and biological variables and processes. The establishment of non-native dreissenid mussels in lake and river ecosystems across North America and Europe has been associated with often dramatic, but highly variable, increases in water clarity. The objective of this study was to develop a predictive model for water clarity (Secchi depth, m) in lakes following the establishment of dreissenids. We compiled water clarity data before and after dreissenid invasion from North American lakes that varied in size and nutrient status. An AIC model averaging approach was used to generate post-invasion water clarity predictions based on pre-invasion water clarity and lake morphometric characteristics from a 53 lake dataset. The accuracy of the model was verified using cross-validation. We then extended this model to existing empirical models of lake mixing depth and Walleye (Sander vitreus) yield, to demonstrate that increased water clarity associated with dreissenid invasion may have far-reaching physical and ecological consequences in lakes, including deeper thermoclines and context-dependent changes in fish yields.

Statistical power: an important consideration in designing community-based monitoring programs for Arctic and sub-Arctic subsistence fisheries

Polar communities and management agencies require well-designed monitoring systems to determine whether harvesting is biologically sustainable. While it is known that life history traits such as length-at-age and fecundity will vary with population density, cost-efficient monitoring requires that these metrics be incorporated into monitoring programs only if their statistical power is high to detect change due to fishing. We present a simple computer-simulated power analysis technique to compare the ability of monitoring designs to detect changes in fish length-at-age and fecundity, after adding effects of exploitation. We developed a methodology for estimating statistical power from first principles using computer simulation techniques which can be applied regardless of the statistical variance pattern in the data. Statistical power increased when more fish were sampled and when larger effects were added. Initially, power increased rapidly by increasing the sample size, regardless of the effect added. However, after 40–50 fish were included in the sample, smaller increments of increased power were obtained; highlighting that a cost-benefit analysis would be necessary. When compared to exploitation experiments in the literature, the stock-specific power analysis used here was able to correctly predict the outcome (significant change observed or not) of the literature studies in most cases. This technique advances the ability of designers of monitoring programs to assess the efficiency of any type of monitoring metric. Further, the simplicity of this power analysis technique allows it to be tailored to different species, life history traits, or potential disturbances to the population.