Cold Water Anomaly May Explain 2011 Unusual Bottlenose Dolphin Mortalities
While climate change is often associated with global warming and rising seawater temperatures, there are other climate-related anomalies that can adversely affect marine life. From February 27 to May 26, 2011, 37 bottlenose dolphins were found dead on South Carolina beaches primarily in the central and southern sections of the state. This level of mortality exceeded twice the historical average for that time period and, at the recommendation of NCCOS researchers, prompted a NOAA Fisheries working group to declare an Unusual Mortality Event for South Carolina.
During the preceding period from late December 2010 to mid-February 2011, mean water temperatures in the area had dropped below 8 degrees Celsius, a critical low temperature threshold for the survival of many species of fish and shrimp that are primary food sources for dolphins. Mass fish kills also occurred in the region during January-February 2011. It is believed that disease-compromised and starved dolphins with weakened immune systems, eventually succumbed to the effects of opportunistic viral or bacterial pathogens.
A similar pattern occurred in the winter of 2001, revealing that the two coldest winters in the last 20 years coincided with the two highest incidences of dolphin mortality in South Carolina since records have been kept, emphasizing the need for consistent monitoring of dolphin mortality to determine trends and establish predictive models.