Research Document - 2014/095

Temporal variation in a population biomass index for Cambridge Bay Arctic Char, Salvelinus alpinus (L.), in relation to large-scale climate variables

By Xinhua Zhu, A. Chris Day, Theresa J. Carmichael, and Ross F. Tallman

Abstract

Arctic Char, Salvelinus alpinus (L.), is an important target species for Commercial, Recreational and Aboriginal (CRA) fisheries around Cambridge Bay, Nunavut. Since 1972 a fishery-independent survey, involving experimental gillnet and weir enumeration, has been conducted in August and September at traditional fishing locations at the mouths of seven river systems. A population biomass index, weight-based catch per unit effort (CPUE), was generated using total numbers of individuals per census and length-weight relationships. Overall, a twelve year CPUE series was available. No significant differences in log-transformed CPUE were found between gear types (F=0.02, p=0.90) or months (F=2.96, p=0.08). August gillnet CPUE data were selected for standardization because it showed a stronger temporal variation in CPUE through the time series after CPUE data from the different gears were aggregated.

Three large-scale climate-related variables, the north Atlantic oscillation index (NAO), the Arctic oscillation index (AOI), and northern hemisphere sea surface temperature (NHSST), were included to estimate Arctic Char CPUE when enumeration information was not available. Significantly positive correlations between log-transformed CPUE and wintertime (March) NAO (r=0.76, p=0.01) and AOI (r=0.79, p<0.005), with a five-year lag, were found. No significant relationship was found between CPUE and NHSST (p>0.05). Using posterior parameters in a robust normal regression model, estimates of CPUE from wintertime AOI were generated with contingent agreement between observed and predicted values (χ²=0.01, p>0.99). This approach is promising for further application of harvest statistics and the population biomass index to a population production model for Arctic Char integrating uncertainties from temporal variation in gear operations, stock status, and large-scale climate indices. Nevertheless, the potential associations between large-scale climate indices and local climate variability, and between climate variability and Arctic fish populations, remain to be demonstrated and established.

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