2020 Dolphin Movements in the Keys
Why are there slower movement rates? There is no question that dolphin are influenced by oceanography but correctly modeling how closely dolphin do or do not orient with major ocean currents is a difficult task. The Straits of Florida, however, afford a unique geographic region where one of the world’s most powerful western boundary currents, the Gulf Stream, flows northward along the eastern Florida shelf and ultimately toward the north Atlantic. The Straits of Florida is also the region where 68.9% (n = 16,030) of all dolphinfish tag deployments have occurred for the Dolphinfish Research Program (DRP) through the end of 2017. Of those deployments, 236 fish were recovered off eastern Florida, with days at liberty < 60 days within the Straits of Florida. While there are a number of different analyses that can be done using these data, recently, we reached out to the Marine Program Leader and Lead Meteorologist Chris Rothwell at the Key West branch of the National Weather Service who, working with Ph.D. candidate Caitlin Dirkes at Florida State University, has produced preliminary results on the climatology of the offshore position of the Florida Current/Gulf Stream (in nautical miles) from eight key reef points in the Straits of Florida (From west to east: Dry Tortugas Light, Cosgrove Shoal Light, Sand Key Light, Looe Key Light, Sombrero Key Light versus Alligator Reef Light, Molasses Reef Light, and Carysfort Reef Light). In other words, they are responsible for producing the following text and graphical report on the approximate shoreward edge of the Gulf Stream. One of their preliminary findings is that the north wall of the Gulf Stream is generally closer to the shore/reef in winters and summers, with greater variability for western sites within the Straits of Florida. Based on these observations and preliminary results, our program intends to compare dolphinfish release sites and movements within the Keys relative to the seasonal and interannual variability in Gulf Stream position along this reef tract. The question is do dolphin move faster if tagged and released well within the main flow of the Gulf Stream. Over the years we have documented an overall northern movement trend for dolphinfish along the U.S. East Coast. Many recaptures over the past few years, however, have led us to focus on the variability in movement speeds for dolphin along the Lower Florida Keys. Last year, a number of lingering movements were observed and recently John Anderson of Lexington, South Carolina, added another to the list. He recaptured a Killin’ Time II tagged dolphin 6 days after and west of its release site. Yet another recent slow movement is the fish recaptured by Camron Jaques, 5 days after it was released by Killin’ Time II, while fishing out of Hawks Cay off Duck Key. Connecting the release and recapture sites puts this straightline movement rate at just over 10 miles per day. Yet, two days after Camron reported this fish, Alejandro Batista, while fishing off Islamorada recaptured a different Killin’ Time II tagged fish less than a day after it was a released off Cudjoe Key. Does this variability relate at all to the variability in position of the northern edge of the Gulf Stream current in the Straits of Florida with relation to where these fish were caught, tagged, and released? Stay tuned for future updates as we delve further into this analysis. A special thanks to all the anglers who reported recoveries of tagged dolphin in Florida this June.