42 
Fishery Bulletin 107(1 ) 
and Able (2007) presented for what the authors term 
as “outbursts” of Atlantic croaker (Micropogonias un- 
dulatus) populations along the east coast of the United 
States. Warmer winters result in higher juvenile sur- 
vival, which allows for the formation of larger year 
classes. Sequential warm winters lead to sequentially 
large year classes that extend the duration of an out- 
burst. In the Atlantic croaker example, the outburst 
allowed population ranges to expand north and, as a 
result, spawning extended farther north, supplying 
larvae to estuaries not normally inhabited. The out- 
burst was continued as a result of additional juvenile 
habitat that was then available to the population. This 
appeared to be the case for gray snapper populations 
in the western Gulf of Mexico. A decade of nearly un- 
interrupted warm winters has allowed this species to 
flourish in estuaries where they were not historically 
encountered in great numbers. Following the winter 
temperature shift of 1993, the only precipitous dips 
in the exponential rise in gray snapper population 
numbers (declines seen in 1998 and 2002) followed 
years with sharply colder winters (1997 and 2001, see 
Fig. 3). 
In the Hare and Able (2007) model, the role of larval 
supply was minimal, because the spatial expansion 
of the spawning range was a direct consequence of 
the outburst, not the cause. Temperature-related over- 
wintering mortality of juvenile fish establishes year- 
class strength, and these strong year classes carry 
the population for 3-5 years. Based on established von 
Bertalanffy growth parameters (derived separately from 
Louisiana recreational harvest [Fischer et al., 2005] and 
eastern Florida commercial harvest | Burton, 2001]), the 
mean size of Texas gray snapper collected with gill nets 
represents 3-4 year-old fully mature fish. Fischer et al. 
(2005) found a multimodal distribution in gray snapper 
age structure from Louisiana and attributed the varia- 
tion in year-class strength to intraspecific competition 
among juveniles for resources within the estuaries be- 
fore recruiting to the offshore fisheries. The successive 
peaks in age-class abundance (strong year classes every 
2-3 years) could also be attributed to juvenile overwin- 
tering mortality associated with thermal limits within 
the estuaries. Interestingly, year of birth distributions 
from Louisiana recreational catches from 1998 through 
2002 (Fig. 5B in Fischer et al., 2005) showed that the 
largest percentage of gray snapper came from 1994, 
around the same time that the slope of seasonally de- 
trended EOF mode 1 turned positive. 
An alternative explanation for the exponential rise 
in the landings of gray snapper recorded from the 
northern Gulf may be attributed to a directed rec- 
reational fishing effort. To reverse the condition of 
overfishing of red snapper (Lutjanus campechanus), 
increasingly restrictive fish-size limits and bag limits 
were placed on the recreational fishing sector for red 
snapper in 1991. Anglers began to target the more 
nearshore populations of gray snappers once their bag 
limits of red snapper were reached. Peak landings of 
gray snapper in Louisiana generally coincided with the 
red snapper recreational season ( April-October), and 
as a result, landings of gray snapper increased expo- 
nentially from 3.25 metric tons in 1983 to 175 metric 
tons in 2002 (Fischer et al., 2005). Even though the 
landing data for both Texas and Louisiana presented 
in Figure 5 were not adjusted for effort, it should be 
noted that both the fishery-indepen- 
dent and fishery-dependent indices 
of population abundance for each 
state both showed similar increases 
after the winter temperature shift of 
the mid-1990s. From 2000 to 2006, 
increasingly restrictive limits on red 
snapper have dramatically increased 
the fishing effort for gray snapper; 
yet the trends of the fishery-indepen- 
dent index (determined from TPWD 
gillnet effort over the period of re- 
cord (1978-2007) has displayed simi- 
lar temperature-related fluctuations 
as those displayed by the fishery-de- 
pendent indices. 
Gray snapper are particularly sus- 
ceptible to cold weather; their lower 
thermal limits range from 11° to 
14°C (Starck and Schroeder, 1971). 
The effects of cold weather on marine 
organisms in Texas bays vary sub- 
stantially, depending on how rapidly 
the temperature drops, on the sever- 
ity and duration of the cold tempera- 
tures, on the physiographic charac- 
teristics of the affected area, and on 
Year 
Figure 5 
Time series of landing of adult gray snapper (Lutjanus griseus) from gill 
nets (Texas estuaries) and recreational landings (both Texas and Louisi- 
ana) from 1982 to 2006. To allow direct comparisons, each series has been 
standardized to a mean of zero and a unit variance of 1. 
