Inferring Survival and Mortality of Stranded Common Dolphins Off Cape Cod, MA Using Satellite Telemetry Data

Over the past decade, post-release monitoring of stranded cetaceans has been facilitated by the use of satellite-linked telemetry. On Cape Cod, 76 stranded common dolphins, (Delphinus delphis) have been released with satellite tags since 2012, leading to new discoveries about their behavior and habitat use. However, these tags seldom transmit for their entire battery life, leading to questions about the survival and mortality of animals following rescue. My project examined whether or not it is possible to infer post-release mortality through an analysis of three behavioral parameters: swim speed; turning angle; and number of messages received per day. Three individuals in this data set are known to have died because their carcasses were recovered on shore. I used data from these three animals to characterize behavioral patterns associated with known mortality. These three individuals had transmission periods ranging from less than one day to six days. I assume that 36 dolphins with transmission periods of longer than 21 days survived, and I examined the three behavioral parameters for signs of mortality in 27 dolphins for which transmission period was less than 21 days. Dolphins that were known to have died following release exhibited slower swim speeds (Kolmogorov-Smirnov=0.27, p=0.0002) and a smaller turning angle (KS=0.2, p=0.0047). The number of messages received per day was complicated by inconsistent duty cycling and limitations in maximum number of messages allowed per day and results from this analysis were inconclusive. Understanding the post-release survival and mortality of stranded and rescued marine mammals will help stranding programs determine which animals are good candidates for release and improve rescue techniques on the beach.