98 
Fishery Bulletin 116(1) 
Table t 
Mean seasonal occurrence, with 95% confidence intervals, of pelagic species of Sargassum across 
the U.S. Gulf of Mexico and by western and eastern regions during the coupling of phases of the 
Atlantic Multidecadal Oscillation (AMO) and North Atlantic Oscillation (NAO) from 1982 through 
2012. Occurrence represents the percentage of ichthyoplankton samples associated with pelagic 
Sargassum. n= the total number of square degree areas (1 degree latitude by 1 degree longitude) 
that were compared. Numbers in parentheses are the number of square degree areas (1 degree 
latitude, 1 degree longitude) with higher percentages of Sargassum species occurrence during the 
coupling of AMO and NAO phases. NS=nonsignificant. 
Season 
U.S. Gulf 
of Mexico 
n 
Cold AMO, 
positive NAO 
phases 
Warm AMO, 
negative NAO 
phases 
Summer 
Whole 
71 
2.54 ±0.75% (9) 
5.51 ±0.90% (55) 
Pj= 0 
(May-Jul) 
Western 
33 
3.63 ±1.39% (5) 
6.84 ±1.46% (26) 
P,<0.0001 
Eastern 
38 
1.59 ±0.58% (4) 
4.35 ±0.96% (29) 
Pj=Q 
Fall 
Whole 
55 
0.58 ±0.31% (5) 
0.96 ±0.52% (2) 
P ; =0 
(Sep-Nov) 
Western 
24 
0.96 ±0.52% (2) 
2.56 ±0.85% (19) 
P 7 <0.0001 
Eastern 
31 
0.29 ±0.36% (3) 
2.20 ±0.83% (24) 
P ; <0.0001 
Summer 
Western 
33 
3.63 ±1.39% 
6.84 ±1.46% 
(May-Jul) 
Eastern 
38 
1.59 ±0.58% 
4.35 ±0.96% 
P 2 =0.0060 
P 2 =0.0075 
Fall 
Western 
24 
Q.96±0.52% 
_ 
(Sep-Nov) 
Eastern 
31 
0.29±0.36% 
— 
P,=0.0036 
p 2 =ns 
P/-values given by the Wilcoxon signed rank test for the analysis between AMO and NAO phases. 
P 2 -values given by the Mann-Whitney U test for the analysis within AMO and NAO phases. 
hurricane tracks during the Atlantic Ocean hurricane 
season (June to November) for each of the 2 AMO-NAO 
phases were downloaded as maps from 1980 through 
2009 (NOAA National Ocean Service, data available 
from website, accessed October 2015). A hurricane is 
a tropical cyclone with maximum sustained (1-min) 
10-m winds of 33 m/s (65 kt) or greater. The number 
of hurricanes that occurred from June to November in 
the NERR and GOM were enumerated for the periods 
1980-1994 (AMOc and NAOp phases) and 1995-2009 
(AMOw and NAOn phases). Hurricanes were included 
only when sustained wind speed during at least part of 
their track in the NERR and GOM was classified as a 
hurricane. A historical list of monthly shedding of LC’s 
spin-off eddies was obtained from Vukovich (2012). 
The spin-off eddies were enumerated for the periods 
1979-1994 (AMOc and NAOp phases) and 1995-2010 
(AMOw and NAOn phases). 
To statistically compare monthly and seasonal val¬ 
ues of the AMM and wind momentum among weather- 
related hydrographic regimes imposed by the coupling 
of AMO and NAO phases and ENSO events, 2 non- 
parametric rank-sum tests were carried out with SPSS 
Statistics software. A nonparametric multiple samples 
test (Kruskal-Wallis H test) was performed to compare 
the values of the indices among 3 contrasting weather- 
related hydrographic regimes associated with ENSOw, 
ENSOn, and ENSOc events. A nonparametric 2-sample 
test (Mann-Whitney U test) was performed to compare 
values of the indices between 2 contrasting weather- 
related hydrographic regimes associated with the 
couplings of AMOc and NAOp and AMOw and NAOn 
phases, ENSOw and ENSOn events, ENSOw and EN¬ 
SOc events, and ENSOn and ENSOc events. To adjust 
the P-values for multiple comparisons, the a level of 
each individual test was adjusted downward by using 
the Bonferroni correction method (Bonferroni, 1935). 
No statistical test was used to compare the number 
of years with above or below Amazon River discharge 
in the NERR, the total number of hurricanes in the 
NERR and GOM, and LC’s spin-off eddies in the GOM 
waters between the coupling of AMO and NAO phases. 
Results 
Variability of seasonal occurrence of pelagic Sargassum 
in USGOM regions in response to the coupling of AMO 
and NAO phases and ENSO events 
Occurrence of species of Sargassum differed by season, 
region, water depth, and climate (Tables 1-4). High- 
