Concentration and Upstream Migration of Postlarval Pink Shrimp in Northern Florida Bay Maria M. Criales Joan A. Browder Michael B. Robblee Thomas L. Jackson Hernando Cardenas
Outline Question Hypothesis Hypothesis Testing Finding Support for finding Conclusions
Question: Is the observed lower density of juvenile pink shrimp in north-central Florida Bay due to the chronic hypersalinity in that part of the bay or to lack of influx of postlarvae?
Tides in Florida Bay M 2 tidal constituent is highest at the northwestern border of the Bay. Initial Hypothesis If postlarvae use flood-tide transport (FTT) for upstream movement into the Bay, postlarval influxes will be greatest at the western margin of the Bay where tidal amplitudes are highest and will decrease with distance into the Bay.
Evidence of flood-tidal transport at the entrance of Florida Bay Current speed (cm*sec -1 ) 4 Flood 2 Ebb -2 July 9-1, 22-4 4 2-2 -4 4 2-2 -4 Flood new Storm full Ebb July 23-24, 22 Flood new Ebb August 8-9, 22 18h19h2h21h22h23h24h 1h 2h 3h 4h 5h 6h 7h 3 2 1-1 -2.9.6.3. -.3 -.6 -.9 1.6 1.2.8.4. -.4 -.8 Concentration (postlarvae* m -3 ) 9% of postlarvae were collected during the dark flood tide, an indication of flood-tide transport (FTT).
Evidence for flood-tidal transport into the Bay interior Postlarvae 2-hr -1 Postlarvae hr -1 5 4 3 2 1 1 8 6 4 2 St.4 h 19h 21h 23h 1h 3h 5h 7h July 6-7, 25 Sta. 4 Ebb Ebb Flood Flood 2 21 22 23 24 1 2 3 4 5 6 7 6 4 2-2 -4-6 -8-1 -12 1 8 6 4 2-2 -4-6 -8-1 current speed cm*sec -1 Current speed cm*sec -1 Factor p-exp1 p-exp2 p-exp3 p-exp4 p-exp5 New M Full M Full M Full M New M Tide (ebb, flood).4*.1**.3*.1**.2* Depth (subsurface, intermediate) ---.24.95.28.15 Current speed (low, medium, high).3*.17.4*.6.4* 18 16 14 12 1 8 6 4 2 August 18-19, 25 Sta.3 Flood Ebb 2 21 22 23 24 1 2 3 4 5 6 7 6 4 2-2 -4-6 Current speed cm*sec -1 August 18-19, 25 subsurface intermedia C speed
Sampling on a transect across the northern Bay We sampled monthly two or three nights around the new moon in summer-early fall of 24 and 25 using moored channel nets
Highest postlarval concentrations were at midtransect stations in shallow channels surrounded by dense seagrass beds and moderate tidal amplitudes (15-2 cm).
Tidal excursion and cumulative displacement Distance from station1 (km)\ Cumulative Eastward displacement (km) Tidal Excursion (km) 3 25 2 15 1 5 6 5 4 3 2 1 T P A i Π = i 1 2 3 4 5 6 Stations Cumulative Eastward displacement Distance from Station 1 8 6 4 2 1 2 3 4 5 6 Stations i T P Π i i = Ai Postlarvae* 1 3 m -3 Our finding: Postlarvae accumulate little by little during successive nights until eastward tidal transport fails.
Support for our finding 3. 9 CL (mm) 2.5 2. 1.5 mean CL mean DRS 8 7 6 5 Number DRS 1. 4.5 1 2 3 4 5 6 3 Stations Carapace length (CL) and number of rostral spines (DRS) show a west-east progression from station 1 to 4 indicating an increase in size and age to the site where postlarvae concentrate.
Our finding is supported by studies by other investigators, who refer to a saltatory movement. Rothlisberg et al. (1995) - Penaeus plebejus postlarvae Christy and Morgan (1998) blue crab Callinectes sapidus and Uca spp. megalopae
But what influences the abundance of pink shrimp in the interior-most bay? Effect Degrees of MS F p freedom precipitation 1.33.8.772 temperature 1 1.25.32.572 salinity 1 18.48 4.64.35* water level 1.2..946 wind speed 1 17.53 4.49.36* cross-shelf wind stress 1 17.57 4.51.36* alongshore wind stress 1 2.99.77.383 Error 118 3.933
Wind strength and direction Mean postlarvae*1 m -3 Wind U, V 1 8 6 4 2 1 5-5 -1 24 25 + to N, E - to S, W postlarvae wind speed Jl Jl A A A S S O O N NJnJnJnJl Jl A A A S S S O 24 25 U V 1 8 6 4 2 Wind speed (m*sec -1 ) Peaks of postlarvae were positively correlated with wind strength, although not with wind direction.
Salinity Mean postlarvae*1 m -3 1 8 6 4 2 postlarvae sal MK sal BK Mean salinity Jl Jl A A A S S O O N N JnJnJn Jl Jl A A A S S S O 5 45 4 35 3 Salinity 24 25 Peaks of postlarvae often corresponded with days of low salinity at nearby ENP stations.
New sampling with a Renfro trawl To search for firstsettlement shrimp.
Sampling settlement stages with Renfro trawl n=4 n=4 n=2 n=31
Preliminary results =small CL<4.5 mm =large CL>4.5 mm
Darkness enhances capture of smallest size group, but not older stages. 12 16 1 14 Small CL<4.5 mm 8 6 4 2 Large CL >4.5 mm 12 1 8 6 4 2-2 -4 L TW D light Mean Mean±SE Mean±SD -2 L TW D light Mean Mean±SE Mean±SD
Conclusions Tidal currents and FTT behavior are major factors affecting transport and recruitment of pink shrimp. Postlarvae may advance eastward with floodtide transport (FTT) during successive nights until tidal transport fails. Highest concentration and largest postlarvae occur midway into the interior bay where tidal amplitude is moderate, not at the boundary of the bay, where tidal amplitude is highest. Winds and salinity may affect postlarval transport and concentration in the estuarine Florida Bay.
Future Research Define environmental factors associated with the FTT. Investigate settlement and post-settlement. Apply the pink shrimp survival, growth, and potential harvest model to management issues.
Acknowledgment We would like to thank Ned Smith for his advice on the tidal analysis. We thank Everglades National Park and DeWitt Smith for the time series data on water stage and salinity. We thank Jeremy Hall, Destiny Hazra, Joe Contillo, Andre Daniels, and others at NOAA and USGS for assistance with field sampling. This project was supported by NOAA South Florida Ecosystem Restoration and Modeling Program and the Habitat Program at NOAA Fisheries for supporting this research.