Coastal evacuations by fish during extreme weather events.

An increase in the intensity and frequency of extreme events is predicted to occur as a result of climate change. In coastal ecosystems, hurricanes and flooding can cause dramatic changes in water quality resulting in large mortality events in estuarine fauna. Facultative migration behaviors represent a key adaptation by which animals can evacuate ecological catastrophes, but remain poorly studied in marine systems. Here we identify coastal evacuations by otherwise resident riverine striped bass in the Hudson River Estuary, New York, USA, caused by an intense period of tropical storms in autumn 2011. These storms produced record rainfall and high water discharges into the Hudson River Estuary that increased the water level and reduced the water temperature, salinity and dissolved oxygen levels. Striped bass moved out of the estuary, exhibiting novel migration behaviours, that may have been in response to the strong flow and unsuitable conditions. In the months following the storms, some fish demonstrated exploratory trips back to the estuary, which may have been to assess the conditions before returning for the remainder of the winter. Behavioural adaptions to weather events by striped bass and other coastal fishes will depend on maintenance of key population segments and unimpeded evacuation routes.