South Florida's seagrass and mangrove dominated estuaries serve prominently as nursery habitats for the pink shrimp (Penaeus duorarum), supporting both the Tortugas and Sanibel fisheries. The Tortugas pink shrimp fishery is the larger of the two and is the second largest commercial fishery in Florida with landings of approximately 9 million pounds annually prior to 1980. The Sanibel fishery is small by comparison averaging about 4 percent of the Tortugas catch annually. Early tagging studies suggested that western and southwestern Florida Bay, the middle Florida Keys, Whitewater Bay, Coot Bay, and the Ten Thousand Islands are nursery grounds supporting the Tortugas fishery; nursery areas for the Sanibel fishery are thought to include at least estuaries extending from Indian Key along the southwest coast of Florida to Pine Island Sound north of Fort Myers; and, juvenile shrimp in east coast estuaries (for example, Barnes Sound and Biscayne Bay) may not enter either fishery (Costello and Allen, 1966).

Linkages between inshore nursery grounds and offshore fishing grounds are complex and apparently poorly understood. Recruitment of pink shrimp into the offshore fishery occurs throughout the year with two peaks of recruitment; a fall recruitment period measured from July through December, peaking between August and October; and a spring recruitment period measured from January through June, peaking between March and May. The spring peak is larger than the fall and may be increasing. It is the fall peak that has declined during the 1980's in the Tortugas fishery. In contrast, available data on inshore abundance of juvenile pink shrimp in Florida Bay and Whitewater Bay suggests the prominence of single, late summer to early winter (August-December) peaks of abundance contributing to the spring peak on the offshore grounds (Costello and others, 1986; Robblee and others, 1991).

Questions regarding the relative importance of inshore nursery areas in south Florida and the timing of movements between inshore nurseries and offshore fishing grounds are considered critical for evaluating the cause of recent declines in Florida's pink shrimp fishery and for establishing the pink shrimp as a performance measure for evaluating restoration alternatives for Florida Bay. We are using natural stable C, N, and S isotope ratios to evaluate the relation between inshore shrimp stocks and offshore Tortugas and Sanibel fisheries. Stable isotopes have been used successfully as tracers to address similar questions in other shrimp populations, including south Florida (Fry, 1983). Shrimp assume isotopic signatures that reflect their nutritional base. The isotopic composition of the pink shrimp differs between seagrass and mangrove habitats as defined by ¹³C and ¹⁵N ratios (Harrigan and others, 1989). As shrimp migrate offshore, their isotopic composition gradually shifts with feeding and growth to reflect an open-water food web. Shrimp with different inshore isotopic compositions would tend to converge on open-water values with growth. Samples collected in the late 1970's show that young recruits to the Tortugas fishery have ¹³C values consistent with a recent past in seagrass meadows, such as those found in Florida Bay at that time (Fry, 1983).

Exploratory sampling was completed previously (Fry and others, 1997; Fry and others, in preparation). Based on these data, continuing efforts have been focused on Whitewater Bay/Ponce de Leon Bay and Johnson Key Basin in western Florida Bay. Sampling continues on both the Tortugas and Sanibel grounds with the assistance of Ed Little and Tom Herbert of the National Marine Fishery Service.

Funding for this research was provided from the U.S. Department of the Interior, South Florida Ecosystem Restoration Program "Critical Ecosystems Studies Initiative" (administered through the National Park Service); and, in part, from the U.S. Geological Survey, Florida Caribbean Science Center for the "Empirical and Modeling Studies in Support of Florida Bay Ecosystem Restoration Program."

REFERENCES

Costello, T.J,. and Allen, D.M., 1966, Migrations and geographic distribution of the pink shrimp, Penaeus duorarum, of the Tortugas and Sanibel grounds, Florida: U.S. Fish and Wildlife Service, Fishery Bulletin 65, p. 449-459.

Costello, T.J., Allen, D.M., and Hudson, J.H., 1986, Distribution, seasonal abundance, and ecology of juvenile northern pink shrimp, Penaeus Duorarum, in the Florida Bay area: Miami, Florida, U.S. Department of Commerce, NOAA Technical Memorandum, NMFS-SEFC-161, 84 p.

Fry, B., 1983, Fish and shrimp migrations in the northern Gulf of Mexico analyzed using C, N, and S isotope ratios. Fishery Bulletin, v. 81, no. 4, p. 789-801.

Fry, B., Mumford, P.L., and Robblee, M.B., (in preparation) Stable isotope studies of pink shrimp (Penaeus duorarum Burkenroad) migrations on the southwestern Florida shelf.

Fry, B., Robblee, M.B., and Mumford, P.L., 1997, Relationships between inshore nursery habitats of the pink shrimp, Penaeus duorarum, and offshore Tortugas and Sanibel fisheries, in U.S. Geological Survey Program on the South Florida Ecosystem--Proceedings of the Technical Symposium in Ft. Lauderdale, Florida, August 25-27, 1997: U.S. Geological Survey Open-File Report 97-385, p. 15-16.

Harrigan, P., Zieman, J.C., and Macko, S.A., 1989, The base of nutritional support for the gray snapper (Lutjanus griseus): An evaluation based on combined stomach content and stable isotope analysis: Bulletin of Marine Science, v. 44, p. 65-77.

Robblee, M.B., Jewell, S.D., and Schmidt, T.W., 1991, Temporal and spatial variation in the pink shrimp, Penaeus duorarum, in Florida Bay and adjacent waters of Everglades National Park, Annual Report, October 1, 1991: Homestead Florida, South Florida Research Center, Everglades National Park, 34 p.

¹U.S. Geological Survey, Florida International University, OE Building, Room 148, University Park Campus, Miami, Florida 33199.

²Coastal Ecology Institute, Louisiana State University, Baton Rouge, Lousiana 70803-7503.

³Southeast Environmental Research Program, Florida International University, OE Building, Room 148, University Park Campus, Miami, Florida 33199.

(This abstract was taken from the Proceedings of the South Florida Restoration Science Forum Open File Report)

Back to Project Homepage