Gulf of Alaska | Fishes and Fish Habitats
Size shifts and changing overwintering success of age-0 Pacific cod ( Gadus macrocephalus ) in the post-heatwave era Presenter: Ben Laurel , ben.laurel@noaa.gov, NOAA Alaska Fisheries Science Center Mary Beth Rew Hicks , marybeth.rew.hicks@noaa.gov, NOAA Alaska Fisheries Science Center
Steve Barbeaux , steve.barbeaux@noaa.gov, NOAA Alaska Fisheries Science Center Louise Copeman , louise.copeman@noaa.gov, Alaska Fisheries Science Center
Ocean warming is reshaping the demographics of juvenile fish in ways that will likely alter their survival and recruitment to the adult population. This is particularly important in cold-ocean seasonal environments where fish must accumulate sufficient size and energy in fall to survive winters of low productivity. In this study, we tracked the growth, lipid content and survival of age-0 Pacific cod held in the laboratory under varying fall and winter food-temperature scenarios. During the fall experimental phase, individually tagged and measured fish were held for 6 weeks across a series of replicate tanks maintained at two temperatures (7.0 or 10.0°C) and two food rations (~1% or 3% body weight d-1). Fish were measured and subsampled for lipids after which remaining fish were 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, 6.0°C). As expected, cooler winters provided a survival advantage for juvenile cod, but only when fall environments had sufficient food to promote rapid growth and lipid storage. When fall conditions were metabolically costly (e.g., warm, low food treatments), winter survival was temperature-independent and determined by individual growth and lipid content prior to winter. Size was a poor predictor of overwintering success overall, although measurements closer to winter explained more variance than size measures conducted in early fall. Collectively, these results suggest survival trajectories will become increasingly difficult to predict from summer demographic information alone, especially as fall conditions warm and productivity scenarios change. It is also likely that heatwave events that contribute to warm falls and winters will magnify overwintering mortality for age-0 juvenile cod and potentially lead to new population bottlenecks in regions already experiencing high rates of warming.
Alaska Marine Science Symposium 2023 16
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