Escape from the heat: thermal stratification in a well-mixed estuary and implications for fish species facing a changing climate

Abstract Climate change may cause organisms to seek thermal refuge from rising temperatures, either by shifting their ranges or seeking microrefugia within existing ranges. We evaluate the potential for stratification provide two fish species in San Francisco Estuary (Estuary): Chinook Salmon ( Oncorhynchus tshawytscha Walbaum, 1792) and Delta Smelt Hypomesus transpacificus McAllister, 1963). compiled water temperature data multiple monitoring programs spatial, daily, hourly, intra-annual, inter-annual trends using generalized additive models. used our models predict locations periods of time that bottom column could function as salmon smelt. Periods which was cooler than surface primarily occurred during peak summer afternoons, with more prominent warmer years. Although is often exceedingly warm well-mixed overall, we identified refugia a long deep terminal channel Smelt, bordering Salmon. Thermal increase climate warms, pockets at depth, though limited, become important at-risk fishes future.