Cnales et al Variability in supply and cross-shelf transport of Farfontepenaeus duoroium postlarvae into Florida Bay 



67 



rent speed; highest catches occurred 

 at the maximum speed and lowest 

 catches at the minimum speed (Fig. 

 5B). From 8 to 9 August, the highest 

 peak of postlarvae occurred at the 

 end of the dark-flood period when 

 the current had decreased in speed 

 (Fig. SCI. 



Transport simulations 



Results of channel net sampling 

 showed that the greatest postlarval 

 influx occurred at the northwestern 

 border of the bay, where there was a 

 strong seasonal pattern with maxima 

 from July through September each 

 year. Postlarval concentrations at 

 the northwestern stations were cor- 

 related with the alongshore winds 

 and with surface temperature but 

 did not correlate with the cross-shelf 

 winds. However, postlarvae need to 

 travel up to 150 km across the shelf 

 to reach their nursery grounds. 



Cross-shelf transport mechanisms 

 were explored by using a Lagrang- 

 ian trajectory model that simulated 

 the maximum distance traveled by 

 planktonic stages moving at night 

 for a 30-day period. Four scenarios 

 of transport were modeled under dif- 

 ferent assumptions of behavior: 



600x10-" 



400x10' 



200x103 . 



-100x10' 



-200x10-' 



-300x10' 



-400x10' • 



-500x10' 



20x10' 



Mooring B 



"-V 



r -20x10'  



-40x10'  



-60x10'  



-80x10^ 



-100x10' 



Long Key CMAN 



Scenario 1 With the assumption 

 that planktonic stages (larvae and 

 postlarvae) of pink shrimp respond 

 to light and salinity changes (Hughes 

 1969a, 1969b). the first simulation 

 postulates that larvae and postlar- 

 vae move horizontally with a vertical 

 migratory behavior cued by changes 

 in salinity. Larvae and postlarvae 

 swim to the surface at night when 

 an increase in salinity is detected 

 and remain near the bottom when 

 the salinity decreases. 



Onshore mooring The maximum distance traveled in 

 the cross-shelf direction was 98 km eastward and 70% 

 of larvae traveled up to 30 km (Fig. 6A). The average 

 eastward distance in all simulations was 22 km. The 

 maximum displacement occurred in fall-winter. Along- 

 shore distances were as much as 25 km northward 

 (70% of larvae) and 15 km southward (30%) (Fig. 6, A 

 and B). 



Offshore mooring The maximum distances traveled 

 in the cross-shelf direction was 100 km (84%^ of larvae 

 traveled 40 km). Alongshore distances were as much as 

 15 km northward (70%) and 20 km southward (30%) 

 (Fig. 6, C and D). 



1011121 23456789 101 1121 23456789 101 1121 2345678910 

 1997 1998 1999 2000 



Figure 4 



Time series of current and wind displacement. October 1997-October 2000. 

 Current data are from two ADCPs located at the SW Florida shelf, and wind 

 data are from Long Key CMAN station; lA) onshore ADCP mooring A, (B) 

 offshore ADCP mooring B; see ADCP locations in Figure 1. (C) Wind displace- 

 ment. Alongshore constituents are represented by interrupted lines (N=north 

 l-^], S=south [-]) and cross-shelf by continuous lines (E = east [+], W=west [-]). 



Scenario 2 The second simulation assumes that plank- 

 tonic stages travel at night using the instantaneous 

 current. 



Onshore mooring Distances traveled in the cross- 

 shelf direction reached a maximum of 68 km and 75% 

 of larvae traveled only 30 km eastward (Fig 6A). The 

 average eastward distance in all simulations was 15 km. 

 The maximum displacement occurred in spring-summer 

 (May to September 1998) during the first year and in 

 fall-winter (October 1999 to February 2000) during the 

 second and third year. Distances recorded in the along- 

 shore direction were as far as 40 km northward (48% of 

 larvae) and 30 km southward (52%) (Fig. 6, A and B). 



