Burton: Age, growth, and mortality of Lut/anus griseus 
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Length interval starting point 
Figure 5 
Length frequencies for gray snapper measured by fishery and area, 
1986-97. 
latter scenario would be aggravated by the sus- 
pected tendency of gray snapper to undertake 
spawning migrations to offshore reefs (Domeier 
et ah, 1997). This behavior, resulting in higher 
fish densities on these reefs, would increase their 
vulnerability to fishery harvest during summer 
months, a time of maximum fishing effort due to 
favorable weather conditions. 
Another effect of long-term heavy fishing pres- 
sure could be a genetic shift in growth charac- 
teristics of the fish. Size-selective mortality could 
result in slower growing individuals in the popu- 
lation. Buxton ( 1993) found growth rates for Chry- 
solephus cristiceps (Sparidae) to be significantly 
lower in exploited than in protected populations. 
Zhao et al. (1997) found that mean back-calculat- 
ed lengths at age for vermilion snapper, Rhom- 
boplites aurorubens, declined from 1979 to 1987, 
concluding that this result was a true change 
in growth, posssibly caused by overfishing. Har- 
ris and McGovern (1997) attributed decreases in 
growth and maturity rates of red porgy ( Pagrus 
pagrus ), over time, to sustained heavy fishing 
pressure. Zhao and McGovern (1997) found sim- 
ilar decreases in size and age at maturity for 
vermilion snapper over time, attributing the de- 
clines to increasing fishing pressure. Other inves- 
tigators, however, have hypothesized that these 
results were caused by size selectivity charac- 
teristics of different gears used during different 
sampling periods (e.g. Potts et al., 1998). 
An alternate explanation for the lack of larger, 
older gray snapper in south Florida is emigration. 
An argument might be made that the inshore 
to offshore spawning migrations (Domeier et al., 
1997) previously mentioned might take them be- 
yond the range of the fisheries and make gray 
snapper less vulnerable to fishing gear in the 
south Florida area. This hypothesis seems highly 
unlikely given the range and technology of modern fisher- 
ies. Moreover, most reef fishes are thought to exhibit a sed- 
entary lifestyle as adults, staying close to the same general 
reef area (Ehrlich, 1975; Heemstra and Randall, 1993; Sam- 
oilys, 1997). However, Moe (1969) found that red grouper 
(. Epinephelus morio ) showed some migratory behavior — 
22 individuals moved 29 km in 50 days, and another indi- 
vidual moved 76 km. Most of these movements were from 
inshore to offshore. A comprehensive tagging study could 
be designed to address the question of whether significant 
numbers of gray snapper migrate out of the south Florida 
area. 
Management of gray snapper is the responsibility of the 
South Atlantic Fishery Management Council (SAFMC), 
whose current strategy is to manage this species, and most 
others in the snapper-grouper complex, as a single stock 
throughout their management area. It is very unlikely 
that gray snapper in north and south Florida are geneti- 
cally distinct because of the northward flow of the Gulf 
Stream and the resulting widespread distribution of prog- 
eny. However, this study in conjunction with that of Ma- 
nooch and Matheson (1981) strongly suggests that gray 
snapper have been exploited at higher rates of F in south 
Florida than in north Florida for at least two decades. 
As a result, gray snapper reach a smaller maximum size 
and younger maximum age in the population, as well as 
smaller sizes at most ages. These biological features carry 
implications for overall population health because fecun- 
dity is usually proportional to size or age, or to both. Fish- 
ery managers attempting to assess stocks of gray snapper 
should perform area-specific analyses in order to manage 
this species in the most effective manner. Given the re- 
sults of this study, it seems that managing gray snapper as 
a stock unit could worsen overfishing conditions in south 
Florida. 
Acknowledgments 
I gratefully acknowledge the many port samplers whose 
efforts made this study possible: headboat samplers Dan 
Theisen, Pamela Washnock, and Peggy Kirwin, NMFS 
