The interplay of fall and winter environments on overwintering potential in age-0 Pacific cod ( <i>Gadus macrocephalus</i> )

Fish in higher latitudes must accumulate sufficient size and energy in fall to survive winters of low productivity. In this study, we measured the growth, condition, and survival of age-0 Pacific cod held in the laboratory under varying fall and winter food-temperature scenarios. Individually tagged fish were held for 6 weeks in the fall at either 7.0 or 10.0 °C under a “low” or “high” food ration (1.9%–2.6% vs. 4.2%–5.9% body weight d –1 , respectively) and redistributed into a series of new tanks to track survival and lipid loss in the absence of food across four winter temperatures (1.0, 2.5, 4.0, and 6.0 °C). Cooler winters and larger body size improved winter survival but were less important when fall conditions were unsuitable for lipid accumulation and growth, e.g., warm, low food scenarios. Lipid reserves explained overwintering winter survival, and survival outcomes were better predicted using environmental proxies and fall condition indices than simple size-based models. These results suggest that winter is a high mortality period, but the odds for winter survival are more likely predetermined by feeding conditions in the fall.