396 
Fishery Bulletin 113(4) 
The monthly values of T were multiplied by the pro- 
portion of monthly hours to obtain wind momentum. 
To encompass transport-recruitment processes, annual 
average values of wind momentum (north-south and 
east-west wind directions) were calculated from Octo- 
ber of the previous year to March of the following year, 
the months when larvae inhabit offshore nursery habi- 
tats and early juveniles recruit to estuaries. 
Riverine influx of nutrients 
The predicted monthly loads of nutrients for the Mis- 
sissippi River from October 1974 through September 
2011 were obtained from the U.S. Geological Survey 
(USGS, data available from website). Monthly influx 
of nutrients (in metric tons) for the mainstem Missis- 
sippi River Basin was based on approved water quality 
data near St. Francisville, Louisiana, and represented 
stream flows from the Mississippi River at Tarbert 
Landing, Mississippi, and near Knox Landing, Loui- 
siana, and Thebes, Illinois, and from the Ohio River 
at Metropolis, Illinois. Monthly concentrations of nu- 
trients were averaged for the water year (September 
of the previous year to August of the following year). 
Those months covered the period of early offshore and 
inshore development of Gulf menhaden. The potential 
conditions limiting the availability of nutrients were 
evaluated by calculating the annual average ambient 
N:P ratio in water (Smith, 1984) and by comparing 
that value with the average value of ambient N:P ratio 
in phytoplankton (Redfield, 1958). 
Biological data 
Fishery-independent data on abundances of menha- 
den postlarvae and juveniles were acquired from BPL 
samples in Mississippi and Alabama and from seine 
surveys conducted by state agencies in all the major 
coastal bay systems of Texas (Texas Parks and Wild- 
life Commission), Louisiana (Louisiana Department 
of Wildlife and Fisheries), Mississippi (Mississippi 
Department of Marine Resources), and Alabama (Ala- 
bama Marine Resources monitoring programs) (Table 
1). Biological data were analyzed by region (central 
and western). Within these 2 regions, 19 coastal study 
areas or bay systems were identified: Lake Borgne- 
Chandeleur Sound; Breton Sound; Barataria Bay; 
Terrebonne-Timbalier Bay; Lake Mechant-Caillou 
Lake; Vermilion Bay; Calcasieu Lake; Biloxi; Mobile 
Bay; Sabine Lake; Galveston Bay; Cedar Lakes; East 
Matagorda Bay; West Matagorda Bay; San Antonio 
Bay; Aransas Bay; Corpus Christi Bay; Upper Laguna 
Madre; and Lower Laguna Madre. 
Data from seine surveys in Alabama, Mississippi, 
and Louisiana were grouped into a single data set 
for the central region (sampling gear and protocols 
used for surveys in these states are similar and fol- 
low those of Christmas [1973]), and data from seine 
surveys in Texas were placed in the western region. 
Detailed specifications for seine collections are found 
in SEDAR. 67891011 In Alabama and Mississippi, small- 
mesh BPLs with 1.6-mm-mesh wings and a 750-n co- 
dend were used, and data from sampling with these 
BPLs were grouped to form a single data set. The BPL 
is described in Renfro (1963). Catches in BPL hauls 
comprised late-stage larvae and postlarvae (11-20 mm 
standard length [SL] ); catches in seine hauls were pri- 
marily postlarvae and early juveniles (17-49 mm SL). 
According to Shaw et al. (1988), lengths for postlar- 
val Gulf menhaden range between 15 and 25 mm SL. 
Transformation to the juvenile stage begins at ~20 mm 
SL and ends at ~30 mm SL (Suttkus, 1956; Hettler, 
1984). 
Fishery-independent surveys have been conducted 
in Texas estuaries from 1977 to the present, in Loui- 
siana since 1986, in Alabama since 1981, and in Mis- 
sissippi from 1973 to the present. Disparity in survey 
periods, sampling effort, and areal coverage between 
years and among and within bay systems complicated 
comparisons of abundance among and within areas in 
early years with the result that periods of abundance 
were restricted to those years with adequate sampling 
coverage and effort. The following years and months 
were analyzed for this study: seine data, all states, 
1985-2008 (January-August); BPL data, Mississippi 
and Alabama, 1981-2008 (November-May). Yearly 
catch was calculated by month and gear mentioned 
above. Annual catch by station within each bay sys- 
tem was calculated by dividing the total catch by the 
total number of hauls. To obtain yearly catch for each 
of the 19 bay systems, the annual catches from the sta- 
tions within a bay system were added and then divided 
by the number of stations in that system. The catches 
from bay systems within a region were added and then 
divided by the number of bay systems within that re- 
gion to produce a regional annual catch for relevant 
gear types. Data were analyzed regionally in a manner 
that ensured equality across each study area (the same 
weight was given to each station and each bay system). 
The purse-seine fishery for menhaden has been in 
operation since the late 1940s. Gulf menhaden domi- 
nate this fishery, and finescale and yellowfin menhaden 
compose less than 1% of the annual landing (Ahren- 
holz, 1981). The fishery is prosecuted from the state 
6 SEDAR (Southeast Data, Assessment, and Review). 2011. 
Fishery-independent sampling: Alabama. SEDAR27-RD-01, 
2 p. [Available at website.] 
7 SEDAR (Southeast Data, Assessment, and Review). 2011. 
Fishery-independent sampling: Mississippi. SEDAR27- 
RD-02, 5 p. [Available at website.] 
8 SEDAR (Southeast Data, Assessment, and Review). 2011. 
Fishery-independent sampling: Florida SEDAR27-RD-03, 
57 p. [Available at website.] 
9 SEDAR (Southeast Data, Assessment, and Review). 2011. 
Fishery-independent sampling: Texas. SEDAR27-RD-04, 11 
p. [Available at website.] 
10 SEDAR (Southeast Data, Assessment, and Review). 2011. 
Fishery-independent sampling: SEAMAP trawl. SEDAR27- 
RD-05, 6 p. [Available at website.] 
n SEDAR (Southeast Data, Assessment, and Review). 2011. 
Fishery-independent sampling: Louisiana. SEDAR27- 
RD-06, 9 p. [Available at website.] 
