704 
Fishery Bulletin 95(4), 1997 
are consistent features of king mackerel populations. 
Assuming that these differences persisted from 1977 
to 1992, during which time exploitation rates varied 
considerably (Mackerel Stock Assessment Panel 4 ), we 
suggest that these differences are not just tempo- 
rary density-dependent responses to varying popu- 
lation sizes or exploitation rates. 
Our findings of regional (stock) growth differences 
are also consistent with those of Gold et al. (in press), 
who compared mtDNA haplotypes and found weak 
genetic differences between Atlantic and Gulf king 
mackerel. Although our results are not indicative of 
genetic discontinuity, our data demonstrate that the 
three groups of fish experience sufficiently different 
environmental and fishery conditions to produce 
identifiable and consistent differences in growth. 
Contrary to our finding of regional differences in 
growth within sexes, Beaumariage (1973) reported 
that growth rates did not differ for either sex between 
the Gulf and Atlantic coasts of Florida. His results 
may reflect that many of his Atlantic fish were col- 
lected off southeast Florida during winter and thus 
may have been Gulf-group fish. In addition, the use 
of whole otoliths for ageing undoubtedly introduced 
error in length-at-age estimates, possibly obscuring 
regional differences. 
Johnson et al. (1983) reported that female king 
mackerel from Louisiana grew faster than females 
from other areas of the Gulf and from the Atlantic. 
However, their predicted sizes-at-age for Louisiana 
females ages 4-8, the ages with adequate sample 
sizes (n = 16-78) that could be accurately aged with 
whole otoliths, were no more than 3.1 cm different 
from our eastern Gulf fish. For fish older than age 8, 
their estimates were increasingly larger than ours, 
most likely because the use of whole otoliths resulted 
in underageing these larger fish. 
The growth differences between 1977-78 and 
1986-92, i.e. lower growth during the former period 
seen in both sexes in the Atlantic and eastern Gulf 
(Fig. 6), could be a density-dependent response. Popu- 
lations were much larger in the late 1970’s and early 
1980’s than during 1986-92 (Mackerel Stock Assess- 
ment Panel 4 ). The key point to remember is that 
within sexes, the growth differences among regions 
clearly present in 1986-92 apparently existed as far 
back as 1977-78. 
Acknowledgments 
We would like to thank the Institute Nacional de la 
Pesca for the cooperation of their personnel at the 
fishery laboratories in Yucalpeten, Campeche, 
Alvarado, and Tampico for obtaining samples and 
data from the Mexican fisheries. K. Burns and her 
Table 6 
Von Bertalanffy parameters and 95% asymptotic confidence intervals for male and female king mackerel by region for fish col- 
lected during 1986-92 and 1977-78, calculated using quarterly observed sizes-at-age. 
Collection 
years 
Para- 
meter 
Females 
Males 
n 
Estimate 
Asymptotic 95% 
confidence interval 
n 
Estimate 
Asymptotic 95% 
confidence interval 
1986-92 Atlantic 
3,407 
126.7 
125.0 to 128.5 
2,083 
96.4 
95.7 to 97.1 
E. Gulf 
L„ 
2,796 
137.8 
135.8 to 139.8 
1,330 
102.6 
101.1 to 104.1 
W. Gulf 
L x 
1,662 
134.1 
130.6 to 137.7 
995 
102.8 
100.5 to 105.2 
Atlantic 
K 
3,407 
0.145 
0.137 to 0.154 
2,083 
0.262 
0.248 to 0.276 
E. Gulf 
K 
2,796 
0.172 
0.163 to 0.181 
1,330 
0.247 
0.227 to 0.267 
W. Gulf 
K 
1,662 
0.150 
0.136 to 0.164 
995 
0.203 
0.180 to 0.226 
Atlantic 
to 
3,407 
-3.15 
-3.41 to -2.90 
2,083 
-1.98 
-2.19 to -1.78 
E. Gulf 
t a 
2,796 
-1.83 
-1.98 to -1.67 
1,330 
-1.84 
-2.09 to -1.59 
W. Gulf 
to 
1,662 
-2.69 
-3.02 to -2.37 
995 
-2.74 
-3.16 to -2.32 
1977-78 Atlantic 
323 
122.7 
115.5 to 129.9 
128 
95.9 
92.3 to 99.6 
E. Gulf 
1,011 
137.1 
133.4 to 140.8 
343 
99.0 
96.6 to 101.3 
W. Gulf 
188 
151.5 
138.2 to 164.8 
40 
116.0 
93.1 to 138.9 
Atlantic 
K 
323 
0.124 
0.096 to 0.151 
128 
0.211 
0.159 to 0.262 
E. Gulf 
K 
1,011 
0.160 
0.145 to 0.175 
343 
0.269 
0.229 to 0.309 
W. Gulf 
K 
188 
0.127 
0.080 to 0.175 
40 
0.094 
0.026 to 0.163 
Atlantic 
t 0 
323 
-4.54 
-5.59 to -3.49 
128 
-3.14 
-4.26 to -2.02 
E. Gulf 
t Q 
1,011 
-2.12 
-2.39 to -1.85 
343 
-1.63 
-2.04 to -1.22 
W. Gulf 
to 
188 
-2.78 
-4.52 to -1.03 
40 
-6.78 
-11.1 to -2.45 
