Natural variation in multiple factors can make it difficult to understand links in large ecosystems like Sarasota Bay, particularly when changes are occurring over long periods. However, the unique suite of mark-recapture and dolphin prey data 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 temperature. We are also able to begin to look at how red tide and temperature affect dolphin prey species. We have found that red tides are themselves connected with temperature. The duration of red tides declines with higher winter temperatures as competing non-toxic organisms flourish. Summer 2009 was the second warmest summer on record, followed by the coldest winter. While no red tide was present, dolphin survival was the lowest on record, suggesting dolphins may have been experiencing thermal stress during that year. Longer red tides are followed by lower dolphin survival the next year. Reproduction and mother-calf separation were not strongly connected to red tide. Longer red tides are also associated with lower prey availability and lower overall prey energy. The results indicate that longer-term loss of prey due to red tides may affect dolphins more than direct exposure to red tide toxins. Results also allow us to understand the link between lost foraging energy and survival. That link is a key component in quantifying the effects of human disturbance on dolphin populations when the disturbance reduces foraging.
This article appeared on page 6-7 of the 2018 SDRP Annual Report, Nicks n Notches.