96 
Fishery Bulletin 116(1) 
phases. The 1077 samples were further characterized 
as collected after ENSOc (n- 394), ENSOn (n=302), and 
ENSOw (n=381) events. Sargassum species occurred 
in samples from February to November after ENSOc 
years, from April to December after ENSOn years, and 
from January to November after ENSOw years. 
Samples associated with species of Sargassum were 
subdivided temporally by month of collection and spa¬ 
tially within square degree areas of 1 degree latitude 
and 1 degree longitude across the USGOM. Monthly 
samples associated with Sargassum species within 
each square degree area were further subdivided by 
the weather-related hydrographic regime in place when 
samples were collected. Monthly samples collected 
duringl982-1994 and 1995-2012 were classified un¬ 
der the influence of the couplings of AMOc and NAOp 
and AMOw and NAOn phases, respectively. The same 
monthly samples were also classified by the ENSO 
event (warm, neutral, or cold) that was present from 
May of the previous year to February of the year in 
which samples were collected. The final data set rep¬ 
resented the monthly ichthyoplankton samples associ¬ 
ated with species of Sargassum within square degree 
areas (1 degree of latitude by 1 degree of longitude) 
across the USGOM under the influence of the coupling 
of AMO and NAO phases and ENSO events. 
Samples from May to July and from September 
to November associated with the Sargassum species 
within each square degree area and weather-related 
hydrographic regime were added to obtain the total 
number of samples associated with the Sargassum spe¬ 
cies within each square degree area, weather-related 
hydrographic regime, and summer and fall seasons. 
Samples associated with species of Sargassum within 
each square degree area, weather-related hydrographic 
regime, and season were added, multiplied by 100, and 
then divided by the total number of SEAMAP ichthyo¬ 
plankton samples collected within each square degree 
area, weather-related hydrographic regime, and season. 
If the number of samples collected was fewer than 8 per 
square degree area, the percentage of seasonal samples 
associated with Sargassum species was not calculated. 
The calculated values represented the percentage of 
seasonal SEAMAP samples associated with species of 
Sargassum within each square degree area across the 
USGOM, weather-related hydrographic regime, and 
season. Percentages were used because differences in 
sampling effort (total number of samples and sampling 
years) existed among hydrographic regimes. The num¬ 
ber of samples collected was 7768 (summer) and 5939 
(fall) during the coupling of AMOc/NAOp phases, 7910 
(summer) and 9196 (fall) samples during the coupling 
of AMOw/NAOn phases, 6532 (summer) and 5820 (fall) 
samples after ENSOw events, 4389 (summer) and 4396 
(fall) samples after ENSOn events, and 4757 (sum¬ 
mer) and 4919 (fall) samples after ENSOc events. The 
number of samples collected under the AMO and NAO 
phases and after ENSO events were 15,678 (summer) 
and 15,135 (fall). After spatially comparing the season¬ 
al occurrences of pelagic species of Sargassum ., analy¬ 
sis was restricted to data calculated from more than 9 
square degree areas per regime. Because the ichthyo¬ 
plankton surveys did not specifically target areas with 
Sargassum macroalgae, the percentage of samples as¬ 
sociated with species of Sargassum was considered a 
measure of occurrence across the USGOM. 
Data analysis was limited spatially to survey areas 
between 81°W to 97°W and 24°N to 29°N and an area 
that extended from 86°W to 88°W and 30°N. The 90 th 
parallel west divided the general area into western and 
eastern regions. The study area was also divided into 
deep basin and continental shelf waters. The deep basin 
was limited spatially to survey areas between 85°W to 
95°W and 24°N to 26°N and an area that extended from 
86°W to 88°W and 27°N. To statistically compare the 
seasonal occurrence of Sargassum species within square 
degree areas in USGOM regions between 2 or more 
contrasting weather-related hydrographic regimes, 3 
nonparametric tests were performed by using SPSS 
Statistics 2 software, vers. 20.0 (IBM Corp., Armonk, 
NY). Using the Kruskal-Wallis H test, we compared 
seasonal occurrences of pelagic species of Sargassum in 
USGOM regions among 3 contrasting weather-related 
hydrographic regimes associated with ENSO events. 
With the Mann-Whitney U test, we compared seasonal 
occurrences of pelagic species of Sargassum in USGOM 
regions between 2 contrasting weather-related hydro- 
graphic regimes associated with the coupling of AMO 
and NAO phases and ENSO events. With the Wilcox- 
on signed rank test, we compared seasonal occurrences 
of Sargassum species from identical square degree ar¬ 
eas in USGOM regions between 2 contrasting weather- 
related hydrographic regimes associated with the cou¬ 
plings of AMO and NAO phases and ENSO events. 
Environmental data 
The AMM index was downloaded as monthly values 
from 1981 through 2009 from the NOAA Earth Sys¬ 
tem Research Laboratory (data available from web¬ 
site, accessed October 2015). This index represents the 
variations in SST and sea level pressure between the 
tropical Atlantic Ocean north and south of the ITCZ. 
The ITCZ is an area where the northeast and south¬ 
east trade wind systems meet, creating a rain band in 
the tropical North Atlantic Ocean (Vimont and Kossin, 
2007). Monthly data for Amazon River discharge were 
downloaded from SO HYBAM (streamflow data avail¬ 
able from website, accessed December 2015). The data 
from 1982 through 2013 were limited to the months 
(from April to August) of highest river discharge. Wind 
speed and direction data were downloaded from the 
NOAA National Data Buoy Center (data available from 
website, accessed October 2015). These data were re¬ 
corded hourly at the western (buoy 42002: 1978-2011), 
central (buoy 42001:1979-2011), and eastern (buoy 
2 Mention of trade names or commercial companies is for iden¬ 
tification purposes only and does not imply endorsement by 
the National Marine Fisheries Service, NOAA. 
