Tolan and Fisher: Biological response of Lut/anus griseus to climate patterns in Texas bays and estuaries 
39 
Table 2 
Percent and cumulative percent of the total variation explained by the eight empirical orthogonal function (EOF) modes. The 
eight modes correspond to the eight major Texas estuaries, spatially interpolated by means of an objective analysis scheme by 
means of a series consisting of 288 monthly averaged mean salinity readings collected from the Resource Monitoring Program of 
the Texas Parks and Wildlife Department. 
EOF 
1 2 3 4 5 6 7 8 
Percent 96.40 0.81 0.65 0.55 0.47 0.41 0.39 0.33 
Cumulative percent 96.40 97.21 97.86 98.26 98.73 99.14 99.53 100 
p 
CD 
ro 
CD 
o. 
E 
0 ) 
c 
ro 
CD 
E 
CD 
■D 
5 
5 - 1 -! 1 1 1 1 1 1 1 1 1 1 1 r 
82 84 86 88 90 92 94 96 98 00 02 04 06 
Year 
Sabine-Neches 
Mission-Aransas 
Trinity-San Jacinto 
Nueces 
Lavaca-Colorado — — 
Laguna Madre 
— • - 
- — 
Guadalupe 
Figure 2 
Time series of mean yearly temperatures (summer maximum and winter 
minimums, in °C) of Texas coastal estuaries. The solid horizontal line iden- 
tifies the lower lethal limit (12°C) for gray snapper (Lutjanus griseus). 
to the Nueces Estuary; see Table 1). 
Given the affinity of this species for 
structured habitats, it is no surprise 
that the otter trawl was the least effec- 
tive gear for capturing this species. 
Environmental data during this 
same period demonstrated increasing 
annual water temperatures, although 
these increases were not seasonally 
uniform. Summer maximum water 
temperatures remained relatively 
stable, whereas winter minimums 
increased through time. The largest 
proportion of temperature increases 
were attributed to higher winter 
temperature minimums since 1993 
(Fig. 2). Before 1993, winter minimum 
temperatures routinely fell below the 
lower lethal limit for gray snapper, 
and these events were especially com- 
mon in the upper coast estuaries of 
Sabine-Neches, Trinity-San Jacinto, 
and Lavaca-Colorado. Since 1993, 
winter temperatures along the coast 
of Texas have generally been mild, 
although particularly powerful polar 
fronts caused dramatic declines in 
surface water temperatures in both 
1997 and 2001. 
The 288 months of average surface 
temperatures from the seven major 
estuaries along the Texas coast were 
combined into a data matrix and interpreted with a 
spatial EOF. The variance pattern for the principal EOF 
mode is shown in Figure 3. The fundamental periodicity 
within the first mode (capturing 96% of the total vari- 
ability, Table 2) represents the yearly signal inherent in 
the series (0.083 cycles per month, or 1 cycle per year). 
Temperature structure in each estuary was effectively 
described by the first mode of the EOF, and positive 
component loadings ranged from 0.976 to 0.985 for each 
estuary. Seasonally detrended EOF mode 1 revealed 
that increases in winter minimum temperatures, espe- 
cially after 1993, corresponded to the largest positive 
amplitude values seen in the series. Before 1993, the 
slope of the detrended temperature record was not sig- 
nificantly different from zero (F 1 143 = 1.194; P=0.276), 
whereas after 1993, the trend in water temperature 
was significantly upward and warmer (F l 153 = 5.055; 
P=0.026). 
Before 1993, gray snapper were generally uncommon 
in all estuaries on the Texas gulf coast, but since then, 
increases in abundances have ranged from near 3- to 
over 20-fold (see Table 1). The temporal pattern of in- 
creasing abundances, especially within the mid-coast 
estuaries where gray snapper are most prevalent, is 
shown in Figure 4. A winter temperature minimum 
near or below the lower lethal limit appears to inhibit 
