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Fishery Bulletin 93(3), 1995 



25.0 



24.0 



-84.0 -83.0 -82.0 -81.0 -80.0 



Figure 1 



Location of transects and 1-m 2 MOCNESS sampling stations (*) of the South- 

 east Florida and Caribbean Recruitment Project (SEFCAR) cruise LH3, 29 

 May-30 June 1991 at the Dry Tortugas and Lower Florida Keys. Shaded area 

 indicates spawning area of pink shrimp, Penaeus duorarum, in southeast 

 Florida. Solid lines are the CTD temperatures at 100 m depth in late May 

 1991. Dashed line indicates the continuation of the Florida Current. 



hypothesized that P. duorarum larvae migrate from 

 where they are spawned in the Dry Tortugas by means 

 of the Florida Current and return to Florida Bay 

 through passes in the middle Keys. However, they had 

 difficulty in explaining the exact migratory path in light 

 of inconsistencies between the prevailing currents and 

 the abundance of larvae in the pathway to the coast. 



Penaeoid shrimps other than Penaeus are abun- 

 dant in the Dry Tortugas and may occur in commer- 

 cial catches (Eldred, 1959), but they are of little or 

 no economic value. Such is the case for the rock 

 shrimp, Sicyonia spp., the humpback shrimp, Solen- 

 ocera spp., and the roughneck shrimp, Trachypenaeus 

 spp. Life histories of these species are poorly known, 

 and larval research in the Gulf of Mexico has focused 

 on trends of seasonal distribution (Eldred et al., 1965; 

 Temple and Fisher, 1967; Subrahmanyam, 1971b). 



The Southeast Florida and Caribbean Recruitment 

 Project (SEFCAR) has investigated the effect of 

 oceanographic processes on plankton and regional 

 recruitment of fishes and other reef species along the 

 continental shelf in southeast Florida. The hydro- 

 graphic conditions in the Straits of Florida are domi- 

 nated by the strong Florida Current. In the south- 

 western part of the Florida Keys, the Florida Cur- 

 rent is highly variable, often associated with mean- 

 ders and gyres (Lee et al., 1992). The Dry Tortugas 

 are located near the turning point where the south- 



ward-flowing Loop Current swerves 

 abruptly east to enter the Straits of 

 Florida (Gaby and Baig, 1983). A cy- 

 clonic gyre over the slope off the Dry 

 Tortugas with horizontal dimensions 

 of approximately 200 km has been 

 described by Lee et al. (1994). The 

 gyre, which persisted for about 100 

 days from mid-May to late August 

 1994, was observed to move eastward 

 to the region of the Pourtales Terrace 

 (Lee et al., 1994). Lee et al. (1992) 

 called this gyre the Pourtales Gyre, 

 and its effect on lobster Scyllarus sp. 

 and shrimp larvae was demonstrated 

 by the high abundance of larvae 

 nearshore in the path of the westward 

 flow of the gyre (Yeung and McGowan, 

 1991; Criales and McGowan, 1994). 



The objective of this study is to 

 describe the horizontal and vertical 

 distribution patterns of the three 

 most abundant penaeoid shrimp lar- 

 vae in the Dry Tortugas and lower 

 Florida Keys during the presence of 

 the cyclonic Tortugas Gyre. This work 

 will form a basis for later comparisons 

 with surveys under different hydrographic conditions. 



Materials and methods 



Plankton and hydrographic sampling 



Samples were collected between 29 May and 30 June 

 1991, as part of the cruise LH3 of the RV Longhorn, 

 by using a 1-m 2 MOCNESS (multiple opening-clos- 

 ing net and environmental sensing system [Wiebe et 

 al., 1976]) with 0.333-mm net mesh size. The nine 

 nets of the MOCNESS were towed in an aperture 

 along an oblique path at a speed of approximately 

 2 m-s' 1 , and samples from the surface to near the 

 bottom were collected. Net 1 in the set was towed 

 obliquely from the surface down to about 200 m or to 

 the closest multiple of 20 m if the water depth was 

 less than 200 m. Net 2 (deepest) to net 9 (uppermost) 

 sequentially opened or closed at controlled depths of 

 200-160 m, 160-130 m, 130-100 m, 100-80 m, 80- 

 60 m, 60-40 m, 40-20 m, and 20-0 m for the deeper 

 stations, and 50-40 m, 40-30 m, 30-20 m, 20-10 m, 

 and 10-0 m, or 45-30 m, 30-15 m, and 15-0 m depth 

 intervals for the shallow stations (<50 m). A flowmeter 

 and conductivity- temperature depth (CTD) sensors 

 were attached to the net frame. The volume of water 

 filtered in each layer varied from 130 to 593 m 3 , de- 

 pending on the depth strata sampled. 



