744 



Fishery Bulletin 94(4), 1996 



Tortugas 

 Grounds 



D 



The predictive model(s) was intended 

 to provide an estimate of a future 12- 

 month total pink shrimp catch with a 

 forecast issued in advance of the main 

 shrimping season. For the Tortugas 

 fishery, monthly catches generally rise 

 sharply in November and taper off af- 

 ter April (Nance and Patella, 1989). Ide- 

 ally, the forecast should be released to 

 the industry no later than October. In 

 practice, however, there are time delays 

 between data collection for a given 

 month and availability of final data. My 

 goal was to release a forecast by Octo- 

 ber Yr.t f° r tne November Yrt through 

 October Yrt+1 "fishing year." 



Since the fishery's inception in 1949, 

 researchers have postulated that land- 

 ings from the Tortugas Grounds were 

 dependent on survival and growth of 

 postlarval and juvenile pink shrimp in 

 primary nursery habitats of Florida Bay 

 and Whitewater Bay (Fig. 1). Female 

 shrimp in spawning condition were 

 found all year on the Tortugas Grounds 

 west of Key West, with the highest frequency of ripe 

 females occurring April through July (Ingle et al., 

 1959; Cummings, 1961). Larval stages were found 

 all year in waters west and south of Florida Bay but 

 were generally most abundant in the same months 

 as ripe females (Munro et al., 1968; Jones et al., 

 1970). Postlarval stages also were found all year, but 

 late postlarval stages were found primarily near the 

 coast and in Florida Bay and Whitewater Bay (Tabb 

 et al., 1962; Jones et al., 1970; Roessler and Rehrer, 

 1971; Allen et al., 1980). Larval and postlarval stages 

 were first thought to migrate into Florida Bay by 

 riding surface waters on the eastward tidal excur- 

 sion and by dropping to the bottom either during 

 westward tidal movement (Koczy et al., 1960) or af- 

 ter detecting lower salinities (Hughes, 1969). Alter- 

 natively, currents were hypothesized to sweep lar- 

 vae south and east of the spawning grounds and along 

 the south side of the Florida Keys until larvae en- 

 tered Florida Bay through passes between the keys 

 (Rehrer et al., 1967; Munro et al., 1968). Recent re- 

 search on larval shrimp distributions in relation to 

 currents has indicated that both immigration meth- 

 ods may be effective (Criales and Lee, 1995). 



Postlarvae reaching coastal seagrass and man- 

 grove nurseries encounter several distinctive envi- 

 ronments: Florida Bay seagrass beds are frequently 

 hypersaline, the Whitewater Bay ecosystem is estua- 

 rine, and the Florida Keys are oceanic (Tabb et al., 

 1962; Mclvor et al., 1994). Catches of postlarval and 



Gull ol Mexico 



^ 



Whitewater Bay 



Cape Sable 



Everglades 

 National 

 Park 



>si-^C 



Flamingo* 



Florida Bay 



^$tff 



.*«** 



9%o'' 



Atlantic Ocean 



Figure 1 



Location of the Tortugas pink shrimp grounds in relation to the southern Florida 

 environmental data sources. P35, P37, and P38 are wells in Everglades National 

 Park. Rain gauges are located at Flamingo, Royal Palm, and Tamiami Trail. Sur- 

 face water discharge gates are located at L-67 to 40-Mile Bend and at L-30 to L-67. 



juvenile pink shrimp were highest in seagrasses of 

 western Florida Bay and the middle Florida Keys, 

 moderate in central Florida Bay and the lower Keys, 

 and low to absent in eastern Florida Bay (Costello et 

 al., 1986; Holmquist et al., 1989). Pink shrimp also 

 recruit to the mangrove-lined Whitewater Bay sys- 

 tem and were found to be more abundant in sub- 

 merged aquatic vegetation than in nonvegetated ar- 

 eas during trawl surveys (Idyll and Yokel, 1970). 

 Higher densities of pink shrimp are associated with 

 seagrass (Thalassia testudinum and Halodule 

 wnghtu) habitats than with algal, red mangrove 

 (Rhizophora mangle) prop root, or nonvegetated habi- 

 tats (Sheridan, 1992; Sheridan et al. 3 ). Widespread 

 mortality of seagrasses (Robblee et al., 1991) thus 

 might be expected to reduce subsequent pink shrimp 

 harvests. 



Juvenile pink shrimp exhibit early spring and late 

 summer peaks in abundance in western Florida Bay 

 (although only a single summer peak has been ob- 

 served for the last decade 4 ) and move out of coastal 

 habitats on ebb tides, at night, during full and new 

 moons (Tabb et al., 1962; Hughes, 1968; Yokel et al., 



3 Sheridan, P.. G. McMahan, G. Conley, A. Williams, and G. 

 Thayer. 1996. Response of macrofaunal communities to 

 seagrass mortality in Florida Bay (Florida, USA). I. Shallow 

 bank-top habitats. In review 



4 Robblee, M. 1995. National Biological Service, Southeast rrn 

 Research Program, Florida International University, Miami, Fl 

 33199 Unpubl. data. 



