70 



Fishery Bulletin 104(1) 



(Criales et al., 2005). Therefore, pink shrimp and other 

 fish and invertebrate species that use tidal currents 

 for transport with a daily vertical behavior may take 

 advantage of this annual tidal cycle to improve their 

 chances of reaching coastal nursery habitats. 



The monthly influx of postlarvae through the Mid- 

 dle Florida Keys channels exhibited a highly variable 

 seasonal pattern from year to year and from station 

 to station. This section of the Keys coastal waters is 

 frequented by coastal cyclonic eddies that originate 

 at the Dry Tortugas and move downstream at 5-17 

 km/day along the edge of the shelf at intervals of 1 to 

 3 months (Fratantoni et al., 1998; Yeung et al., 2001). 

 For planktonic stages, these eddies may serve as a 

 delivery mechanism from offshore spawning grounds 

 to the southeastern border of Florida Bay, allowing an 

 onshore transport by the coastal countercurrent flow 

 generated by the cyclonic circulation (Lee et al., 2001; 

 Yeung et al., 2001; Criales et al., 2003). Episodic, me- 

 soscale events associated with boundary current fronts 

 and eddies may cause high variability in transport (Lee 

 et al., 1994; Limouzy-Paris et al., 1997; Yeung and Lee, 

 2002). This variability was reflected in the influx of 

 pink shrimp postlarvae through Middle Keys channels 

 (Criales et al., 2003). The influx of postlarvae at WH 

 and PH channels in the present study was also highly 

 variable and there was no correlation with winds or sea 

 surface temperature. Therefore, we hypothesized that 



the high variability in postlarval influx detected at 

 the Florida Keys channels reflects the temporal and 

 spatial variability associated with the passage of coastal 

 eddies. 



Simulations of transport based on current observa- 

 tions indicated that passive larvae could not consistent- 

 ly be advected the estimated 150 km eastward across 

 the shelf between spawning and nursery grounds in 

 30 days. This is true primarily because of the weak 

 eastern current and the reversing nature of tides. In 

 contrast, planktonic stages (larvae and postlarvae) mov- 

 ing at night with the eastward current (flood tide) can 

 consistently travel 100 to 200 km in 30 days. Hypotheti- 

 cally, 85% of the larvae can be transported far enough 

 from the known spawning grounds of Dry Tortugas to 

 the nursery grounds in western Florida Bay in 30 days. 

 Previous works conducted inside Florida Bay (Tabb et 

 al., 1962; Roessler and Rehrer, 1971) and our own data 

 obtained along the western border of Florida Bay dem- 

 onstrated the ability of pink shrimp postlarvae to re- 

 spond to the dark flood tide and to distinguish between 

 day and night. Over 90% of postlarvae were caught in 

 the dark flood period and only a few postlarvae were 

 caught during daylight hours. This behavior needs to be 

 investigated for early larval stages to define the exact 

 age at which larvae begin reacting to change in tides 

 and to environmental cues that trigger the vertical 

 movement in relation to tidal stage. For other penaeid 



