Final Report: Analyzing Genetic Connectivity of Caribbean and Florida Mutton

Riley’s Hump, in the recently created South Tortugas Ecological Reserve, is the historical site of a spawning aggregation of mutton snapper (Lutjanus analis), perhaps the only site in the southeastern United States. The aggregation was exploited heavily by commercial fishermen for decades prior to the area being declared an ecological reserve in 2001. Fishery managers hope that the population of mutton snapper will rebound now that the area is closed to all uses, including fishing. In Year 1of a related study, we established stations for monitoring abundance of snappers and groupers to provide baseline estimates of abundance for comparison with future years’ estimates in order to establish trends in populations. Protection from fishing pressure should allow the populations to increase, leading to “spillover”, or increased recruitment of these fishes to areas outside the boundaries of the reserves. An important question to ask is: is the population at Riley’s Hump the source of all recruits to the rest of the southeastern U. S? Previous detailed studies of the region’s physical oceanography (Lee et al. 1994) show that the potential exists for the Tortugas Reserve to supply larvae to nearby waters. The effects of the Florida Current, onshore flow of surface waters, and the cyclonic circulation in the Tortugas gyre should combine to aid local retention and recruitment of larvae into the Florida Keys. Additional drifter studies show that larvae spawned in the Dry Tortugas may end up along the southeastern coast of Florida after entrainment in the Gulf Stream (Domeier 2004, Hare). We need to address an equally relevant question: Where do the adult fish on Riley’s Hump come from? Is the adult population at Riley’s Hump dependent solely on itself to replenish the population, or is significant recruitment coming in from other upstream areas? In addition to the historical spawning aggregation at Riley’s Hump, there are known aggregations further upstream in Belize (Domeier and Colin, 1997). We also know anecdotally from fishermen in Honduras (from the islands of Roatan and Utila) that aggregations of mutton snapper have been exploited there during the spawning season for a number of years. Both of these locations could conceivably be a source of recruits to the Riley’s Hump/Tortugas population of mutton snapper, given oceanic circulation patterns in the region (Cowen et al. 2002). Proper management of a species, especially one exploited as heavily as mutton snapper have been in the past, requires knowing the source of recruits to the fishery, and what kind of pressure these source populations experience. In this report we present the results of our ongoing FY03 work examining the connectivity between the Dry Tortugas and upstream sources such as the Mesoamerican Barrier Reef system off Belize and Honduras, as well as the connectivity of the Dry Tortugas with downstream areas along the Florida Keys and southeast Florida. The expected outcomes of this project were 1) knowledge about the effectiveness of marine protected areas in rebuilding exploited fish stocks, and 2) the development of scientific information about recruitment sources and sinks for U. S. populations of mutton snapper. This information should be useful to management agencies such as the South Atlantic Fishery Management Council (SAFMC)