When and how much disturbance will cause populations to decline? That is one of the main questions researchers and decision-makers face when they have concerns about changes in the environment or human impacts on species. The question becomes more difficult to answer when the sources of disturbance become more subtle and varied because, oftentimes, these disturbances do not directly cause mortality or lowered reproduction. Instead, the effects are seen through longer-term changes in individuals’ health. Our goal is to determine when reduced health leads to lower reproduction and survival as well as understand the characteristics of disturbances that lead to reduced health. Instead of experimentally manipulating individuals and populations, long-term datasets allow us to investigate how natural environmental variability affects health and populations. The unique suite of mark-recapture and dolphin prey data (see Allen, p.18) collected by the Sarasota Dolphin Research Program provides us with an unprecedented ability to look at long-term trends in a bottlenose dolphin population with fluctuations in red tide and water temperature. We are also able to begin to look at how red tide and temperature affect dolphin prey species. We have found that dolphin survival declines with longer red tides the year before. When there are no red tides, survival declines as winter water temperatures decline. Lower reproduction and earlier mother-calf separation were also correlated with longer red tides in winter. In addition, longer red tides are associated with lower overall available energy for the dolphins as their prey decline. Using the long-term health assessment data, the next step is to determine how these changes in red tide, temperature, survival, and reproduction are reflected in the health of the dolphins. This research is supported by the Office of Naval Research.
This article appeared on page 8 of the 2017 SDRP Annual Report, Nicks n Notches.