Sanchez-Rubio et al.: Climate-related hydrological regimes and their effects on abundance of |uvenile Callinectes sapidus 
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30°N 
2<fN 
9?W 9?W 91°W 90° W 89° W 
Figure 1 
Trawl stations surveyed by Louisiana Department of Wildlife and Fisheries (47 solid circles) 
and Gulf Coast Research Laboratory (four solid squares), stations from the U.S. Army Corps 
of Engineers (two sea level gauges: open squares), and the wind station from the National Cli- 
matic Data Center (open circle). Coastal study areas (CSAs): I=Lake Borgne-Chandeleur Sound 
estuary; II = Breton Sound estuary; III = Barataria Bay estuary; IV=Terrebonne-Timbalier Bay 
estuary; V=Lake Mechant-Caillou Lake estuary; VI=Vermilion Bay estuary; VII = Calcasieu 
Lake estuary; and VIII = Biloxi estuary. 
abundance, a wind momentum time series was formed 
by year from the difference between east and west and 
north and south winds. Two data sets were generated 
showing the east-west and north-south wind momentum 
values. To identify wind directions (angle with respect 
to the coast) influencing water level in the northcen- 
tral GOM, PV-Wave, vers. 6.21 (Visual Numerics Inc., 
Boulder, CO) software was used to correlate the Kessler 
Airport wind direction (vector) and water level from one 
gauge west (Cocodrie) and one gauge east (Rigolets) of 
the Mississippi River Delta. 
Annual PDSI and precipitation values were calculated 
for each of the four divisions (southwest, southcentral, 
and southeast Louisiana, and coastal Mississippi) in 
the northcentral GOM. For each of the four divisions, 
an annual precipitation anomaly was calculated by 
subtracting the average value by year from the yearly 
values of precipitation. Annual PDSI (Pearson r>0.649, 
P<0.001) and precipitation (Pearson r>0.646, P<0.001) 
values were highly correlated among the four divisions 
and thus allowed calculation of regional annual ( 1967 — 
2005 ) data for both variables. 
Long-term, fishery-independent, biological data were 
acquired from 47 stations in Louisiana (Louisiana De- 
partment of Wildlife and Fisheries) and four stations in 
Mississippi (Gulf Coast Research Laboratory and Mis- 
sissippi Department of Marine Resources). This region 
was divided into eight coastal study areas (CSAs): seven 
in Louisiana and one in Mississippi (Fig. 1). Louisiana 
data (CSAs I— VII ) cover the period 1967 to 2005 and 
samples were collected weekly from March to October 
and biweekly from November to February. Mississippi 
data (CSA VIII) extended from 1973 to 2005 and sam- 
ples were taken monthly. Both states, by agreement, 
use standard gear and sampling protocols: a 4.9-m 
otter trawl (1.9-cm bar mesh with a 6.35-mm mesh 
liner in the codend) pulled for 10 minutes. Crabs were 
counted and measured to the nearest carapace width 
(mm). Monthly surface salinities were calculated from 
trawl stations west (CSA III, V-VII) and east (CSA I 
and VIII) of the Mississippi River Delta. Monthly salini- 
ties were averaged to obtain single data sets of annual 
(1973-2004) salinity for each CSA. The annual salinity 
of each CSA was multiplied by the number of samples 
taken annually and the products for all CSAs were 
added and then divided by the total number of samples 
collected in the eight CSAs. The yearly regional salinity 
was a weighted average by sample size, which gives to 
the CSAs where few samples were collected less weight 
than those where large numbers of samples were taken 
in the calculation of the regional salinity data set. An 
annual weighted salinity anomaly was calculated by 
subtracting the average value by year from the yearly 
values of weighted salinity. The variability of salinity 
can be considered regionally, because two major riv- 
ers in the west (Mississippi and Atchafalaya rivers) 
and two in the east (Pearl and Pascagoula rivers) of 
the Mississippi River Delta are responsible for 90% of 
freshwater discharge to the northern GOM (Eleuterius, 
1978; Perret et ah, 1971). 
Although the biological data for Louisiana cover the 
period 1967 to 2005, trawl sampling effort and areal 
