Oceanic and Atmospheric Correlations to Cetacean Mass Stranding Events in Cape Cod, Massachusetts, USA

Groups of pelagic dolphins and whales (order Cetacea) regularly strand on beaches throughout the world. These strandings are referred to as mass stranding events (MSEs). MSEs have been observed for centuries, however the underlying causes remain unclear. In Cape Cod, Massachusetts, USA, MSEs usually involve only a few species of cetaceans. We investigated possible connections between MSEs in Cape Cod and regional wind and ocean currents. The seasonal MSE distribution is strongly correlated to both wind and ocean current strengths, and correlation is maximized when MSEs are compared to environmental data one month in the past. Furthermore, a superposed epoch analysis (a Chree analysis) indicates significant shifts in ocean current strength for months surrounding MSEs. These results may indicate that atmospheric and oceanic effects are possible underlying factors influencing MSEs. These factors could generate environments conducive for prey assemblages that attract cetaceans, or perhaps by driving seasonal production of prey species. Plain Language Summary Two species of dolphins and pilot whales are regularly found stranded on the beaches of Cape Cod, Massachusetts. These events often occur with several animals stranded together and sometimes with much larger numbers. It is not clear what causes these animals to beach. We analyzed 18 years of stranding reports and found that more mass stranding events occur during the time of year when there are stronger winds and ocean currents. This could mean that the winds and ocean currents contribute to causing these stranding events. We conjecture that winds and ocean currents create a favorable environment for the animals these dolphins feed on, and that these offshore dolphins and whales strand while chasing this prey into shallower inshore waters. Key Points Cetacean stranding events are concentrated along the SE shores of Cape Cod Bay Wind speeds and ocean current speeds are strongly correlated to the seasonal number of cetacean mass stranding events in Cape Cod Wind and ocean interactions may cause near-shore upwelling conducive to prey assemblages attracting cetaceans and creating mass strandings