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Years 
-Observed 
Predicted 
Figure 4 
Observed (black line) and predicted (gray line) yearly values for 
(A) numbers of postlarval Gulf menhaden (Brevoortia patronus) 
in surveys conducted with beam plankton trawls (BPLs) during 
1981-2008 in Mississippi and Alabama, (B) numbers of age-1 Gulf 
menhaden in commercial landings (millions of fish per vessel-ton/ 
week [vtw]), and (C) proportion of age-1 Gulf menhaden in land- 
ings per vtw taken in the purse-seine fishery in the northern Gulf 
of Mexico in 1964-2010. 
The steady decreases in age-0 and -1 Gulf menhaden 
that have been observed since 1964 may have been a 
function of the fishery-dependent and fishery-indepen- 
dent sampling strategies and changes in the physiogra- 
phy of nearshore environments in the northern G0M. 
Fixed fishery-independent sampling stations may ac- 
count for some portion of the perceived decline in abun- 
dance of early juvenile Gulf menhaden as fish moved 
farther up into estuaries in response to elevated salini- 
ties (Vanderkooy and Smith 4 ). The downward trend of 
age-1 Gulf menhaden in commercial landings (numbers 
and proportions) from 1964 to 2010 was accompanied 
by a steady rise of sea level in the study area. Num- 
bers and proportions of age-1 Gulf menhaden 
in commercial landings were high (10 million 
fish/vtw; 74%/vtw) during the decadal aver- 
age hydrological regime characterized by low 
(6954 mm) sea level. Proportion of age-1 Gulf 
menhaden in commercial landings was aver- 
age (61%/vtw) during the decadal cold, wet 
regime characterized by high (0.56) PDSI 
and high (401.6 above average) river flows. 
Numbers and proportions of age-1 Gulf men- 
haden in commercial landings were low (6.2 
million fish/vtw; 44%/vtw) during the decadal 
warm, dry regime with high (7016 mm) sea 
level, low (-0.57) PDSI, and low (247.6 below- 
average) river flows. 
Changes in the physiography of estuaries 
due to sea level rise and conversion of wet- 
lands to open water may play a major role 
in structuring inshore nursery habitats for 
Gulf menhaden, and declining numbers of 
age-1 fish in the commercial harvest may 
reflect a response to those changes. The sta- 
ble numbers of age-2 fish in the commercial 
harvest indicate that age-1 Gulf menhaden 
were remaining in nearshore waters and en- 
tering the fishery at a later age (SEDAR 3 ). 
Air temperature and sea level in the western 
and central regions and PDSI in the western 
region explained 46% and 32% of the vari- 
ability in numbers and proportions of age-1 
Gulf menhaden. Only an additional 1% of the 
variability in proportion of age-1 Gulf menha- 
den was explained by adding meteorological 
and hydrological factors, such as PDSI from 
the central region and precipitation and river 
flows from the central and western regions. 
The influence of Mississippi River dis- 
charge on annual recruitment of Gulf menha- 
den has been analyzed over the last 30 years. 
Previous studies found an inverse annual as- 
sociation between Mississippi River discharge 
(November-March) and estimates of juvenile 
recruits (Guillory et al., 1983; Govoni, 1997; 
Vaughan et ah, 2000, 2007). Govoni (1997) ex- 
plained this relationship by suggesting that 
high flow of the Mississippi River and the re- 
sultant plume pushed larvae farther offshore, 
prolonging shoreward transport of larvae and increas- 
ing larval vulnerability to predation. Results of this 
study indicate a positive association between ENSO- 
related meteorological (e.g., northerly cold winds) and 
hydrological (e.g., river discharge and flooding events) 
conditions and the recruitment of Gulf menhaden — a 
finding that is contradictory to the results of these 
previous studies. 
The influence of ENSO on recruitment of Gulf men- 
haden can be explained by its effect in structuring suit- 
able offshore and inshore nursery habitats. In offshore 
waters, high seaward projection and areal coverage of 
the nutrient-rich plume of the Mississippi River are 
