The effect of Crassostrea gigas size on survival following Pacific Northwest heat dome

Abstract

Following a heat dome event in late June- early July 2021, mass shellfish mortalities were reported in Washington State. It is important to study this mortality event given the economic and ecological value of shellfish, particularly in the context of climate change. We chose to contribute to this research by surveying Crassostrea gigas in San Juan Island, Washington, to estimate percent mortality and to investigate a relationship between size and survival following the heat dome. We surveyed four sites on San Juan Island, sampling 70 at each. We recorded whether each individual was living or recently dead, and measured total shell length. We compiled the data and generated a logistic regression to model the relationship between size and survival, and calculated percent mortality between the 4 sites and overall. We found a positive association between greater length (cm) and predicted probability of the individual being alive. We calculated an overall percent mortality of 8.57%, which is consistent with other estimates following the heat dome. While these data suggest that the heat dome was a major contributor to the observed shellfish mortality in Washington State, investigations into other potential factors characteristic of “summer mortalities” would contribute to a broader understanding of these events.