Development of A Life-History Framework for the Assessment of Arctic Charr Stocks in the Canadian Arctic

Arctic Charr (Salvelinus alpinus) fisheries are key to the economic development of Arctic communities. The assessment and management of Arctic Charr stocks however remain complicated by their numbers, widespread distribution and complex life-histories, which factor into a paucity of data and problem of generalization for the species in arctic environments. Here we demonstrate how diversity in Arctic Charr populations may be used to develop alternative assessment methods that focus on monitoring stock productivity as it determines resilience to harvesting. These include (1) a semi-quantitative productivity-susceptibility risk analysis (PSA) and (2) a fully quantitative model for Charr assessment. Both methods are based on a single sample of life-history traits for a stock, including age-at-maturity, fecundity, individual growth rate, longevity, and mortality. Within PSA, life-history information is used to score and rank individual stock productivity, and is coupled with measurements of susceptibility to fishing in order to evaluate the relative sustainability of a fishery. Using data for >90 Arctic Charr stocks from throughout Nunavut, we demonstrate the utility of PSA for distinguishing between regions where stocks are more or less vulnerable to harvest (on a broad geographical scale), and between more and less vulnerable stocks (on regional scales). The method is especially useful for the identification of area-specific indicator stocks (i.e. those stocks having highest vulnerability scores within a particular area). A fully-quantitative model for Charr assessment will relate life-history traits with harvest history and population response information in a model structure permitting to assess an appropriate, sustainable harvest level for a stock. In this context, life-history information is used to define a stock-productivity index (SPI). Functional relationships between SPI and harvest levels require to be characterized and standardized for varying stock size using environmental proxies for carrying capacity. Sustainable harvest will corresponded to a limited range of variation in SPI within which life-history traits are in balance and changes in some of the traits can be expected to be reversible. Together, a risk-analysis tool and a fully quantitative model for Charr assessment using life history information offer a promising alternative for fisheries development and management, and for ensuring conservation of Arctic Charr resources in Arctic Canada, with limited sampling. Because the life-history traits of Arctic Charr also tend to reflect the characteristics of their environment, a life-history framework for Charr assessment will further serve to monitor how Charr populations respond to environmental change.