Temperature-dependent growth as a function of size and age in juvenile Arctic cod (Boreogadus saida)

Forecasting climate-driven ecosystem impacts in the Arctic is currently limited by the availability of biological data on key species. In this study, we carried out a series of temperature-dependent growth experiments on juvenile Arctic cod (Boreogadus saida), an important forage fish species at the Atlantic-and Pacific-Arctic interface. Multi-week growth experiments were conducted across a range of temperatures (-1 to 16 degrees C), ages (age-0 and age-1) and sizes (45-125 mm SL) to determine best-fit temperature-dependent growth models. Temperature-dependent growth models considered were 1) a single model using pooled fish of mixed ages and sizes (Model A), separate models for age 0 and age 1 fish (Model B-0 and B-1), and a Lorentzian three-dimensional model incorporating size but not age (Model C). All juvenile Arctic cod demonstrated relatively high growth at cold temperatures (< 2 degrees C; similar to 0.75-1.00% d(-1)) with a deceleration in growth rate above 6.4 degrees C and 9.0 degrees C for age-1 and age-0 cod respectively. As such, Model A did not explain as much temperature-dependent growth (R-2 = 51%) as Model B-0 (R-2 = 98%) and Model B-1 (R-2 = 93%). Model C did reasonably well in explaining growth over a continuous range of sizes (R-2 = 71%) but explained less variance than either of the age models (Model B). These results stress the importance of considering the early ontogenetic effects on temperature-dependent growth variation in juvenile Arctic cod when projecting climate-driven changes in Arctic marine ecosystems.