Burton: Age, growth, and mortality of Lut/anus griseus 
261 
atures of 25.0°C and 26.1°C for north and south Florida, 
estimated M at 0.43 and 0.38 for the two areas. The regres- 
sion method of Ralston (1987) estimated M = 0.37 and M 
= 0.29 for north Florida and south Florida, respectively. I 
used a variety of estimation methods to give the reader 
a sense of the variation associated with estimating M, a 
parameter we often know little about but which is a very 
important variable in stock assessments. 
Estimates of total mortality derived from catch curves 
differed substantially by area (Fig. 4). Estimates of Z for 
gray snapper from north Florida averaged 0.35 during 
1986-97 for all fisheries combined. Gray snapper were ful- 
ly recruited to the headboat fishery between ages 5 and 6, 
to the commercial fishery between ages 7 and 8, and to the 
private recreational fishery between ages 4 and 5. The av- 
erage value of Z for 1986-97 for gray snapper from south 
Florida was 0.94, almost three times that of north Florida. 
Full recruitment occurs between ages 4 and 5 in all fisher- 
ies in south Florida. 
Discussion 
Differences in growth rates and size at age between areas 
were great enough to argue against pooling the data for 
growth analysis. However, the pooled data set does provide 
the opportunity for comparing my results against a previ- 
ous similar study for the purpose of validating my aging 
estimates. Back-calculated lengths at age were in close 
agreement with lengths estimated previously by Manooch 
and Matheson (1981). Estimated lengths (mm) for ages 1, 
5, 10, and 15 with measurements to the last annulus, were 
87 vs. 89, 370 vs. 370, 559 vs. 556, and 630 vs 680 (pres- 
ent study vs. previous study). The close agreement in size 
Table 4 
Back-calculated total lengths (mm) of gray snapper aged by sectioned otoliths for South Florida. 
Annulus number 
Obs. age 
n 
1 
2 
3 
4 
5 
6 
7 
8 
9 
10 
11 
12 
13 
14 
15 
1 
2 
20 
100 
227 
3 
136 
89 
195 
272 
4 
258 
90 
184 
253 
305 
5 
174 
94 
190 
254 
303 
341 
6 
81 
97 
192 
256 
305 
346 
383 
7 
32 
96 
212 
283 
337 
382 
424 
461 
8 
10 
99 
203 
262 
313 
355 
391 
422 
451 
9 
3 
71 
179 
248 
286 
317 
342 
367 
392 
414 
10 
3 
77 
164 
210 
253 
281 
311 
336 
358 
380 
404 
11 
1 
70 
152 
197 
243 
279 
316 
343 
370 
397 
425 
443 
12 
— 
13 
2 
84 
198 
244 
280 
307 
335 
358 
385 
408 
431 
454 
473 
491 
14 
— 
15 
1 
73 
138 
213 
260 
288 
307 
335 
354 
382 
401 
420 
438 
457 
475 
495 
No. of calculations 
721 
721 
701 
565 
307 
133 
52 
20 
10 
7 
4 
3 
3 
1 
1 
Weighted means 
Annual mean 
92 
191 
258 
306 
346 
389 
432 
412 
398 
414 
443 
461 
480 
475 
495 
growth increment 
92 
99 
67 
48 
40 
43 
43 
(20) 
(14) 
16 
29 
18 
19 
(5) 
20 
Table 5 
Von Bertalanffy growth parameters and associated statistics for gray snapper by area and sex, 1994-1997. 
Data set 
L«, 
SE (LJ 
95% Cl 
K 
SE (K) 
95% Cl 
to 
SE (t Q ) 
95% Cl 
n 
North Florida 
716 
11.33 
693-738 
0.17 
0.01 
0.16-0.19 
-0.001 
0.11 
-0.22-0.22 
520 
South Florida 
625 
56.33 
515-736 
0.13 
0.02 
0.08-0.18 
-1.33 
0.41 
-2.12-0.53 
721 
Males 
697 
22.93 
652-742 
0.18 
0.017 
0.15-0.21 
0.49 
0.21 
0.08-0.89 
339 
Females 
768 
35.7 
697-838 
0.15 
0.017 
0.1 -0.18 
0.16 
0.26 
-0.36-0.67 
272 
