DeVries and Grimes: Spatial and temporal variation in age and growth of Scomberomorus cavalla 
695 
Several studies have examined spatial, temporal, 
and gear-related variation in life history and fishery 
parameters of king mackerel. The parameters have 
included mean back-calculated sizes, (Beaumariage, 
1973; Manooch et al., 1987), von Bertalanffy growth 
rates (Johnson et al., 1983; Manooch et al., 1987), 
and size, age, and sex composition of the catch 
(Beaumariage, 1973; Johnson et al., 1983; Trent et 
al., 1983; Trent et al., 1987). The usefulness of this 
information for current stock assessments is limited 
for several reasons. Much of the previous work was 
based on data collected 15 to 25 years ago when ex- 
ploitation was much lower, the species unmanaged, 
and population size, at least in the eastern Gulf of 
Mexico, higher. In addition, all age estimates were 
based on examination of whole otoliths, which re- 
sults in considerable under-ageing of older, larger fish 
(Collins et al., 1989). In addition, some studies were 
geographically limited (Beaumariage, 1973; Trent et 
al., 1987), and because stock boundaries were un- 
known when the data were collected, none of the data 
were partitioned according to stock boundaries. 
The primary objective of this study was to exam- 
ine variation in age and growth in relation to space, 
time, and sex of king mackerel collected during 1977- 
78 and 1986-92. 
Methods 
Most king mackerel used in this study were collected 
during 1986-92 as part of a continuing cooperative 
program between the states from North Carolina to 
Texas and the National Marine Fisheries Service that 
was designed to provide age and length-frequency 
data needed to conduct annual stock assessments. 
Samples from 1977 and 1978 were collected by 
Johnson et al. ( 1983) for their age and growth study. 
All fish were measured to the nearest centimeter fork 
length (FL) and are reported in our study in those 
units. 
Three regions, which reflect stock boundaries ac- 
cording to current hypotheses (Grimes et al., 1987; 
Johnson et al., 1994; Gulf of Mexico and South At- 
lantic Fishery Management Councils 3 ), were sampled 
during 1986-92. The regions were 1) Atlantic: North 
Carolina to about Miami, FL; 2) eastern Gulf: Florida 
Keys through Mississippi, and, during April-Octo- 
ber, Louisiana; and 3) western Gulf: Mexico, Texas, 
and, during November-March, Louisiana. All Loui- 
siana samples were collected during April-October; 
therefore they were classified as eastern Gulf. We 
did not adjust the Atlantic-eastern Gulf boundary 
seasonally, as the current fishery management plan 
does, because only 378 of the 5,490 Atlantic fish aged 
were collected in the area of mixing off eastern 
Florida during November-March. These 378 fish 
were used in the analyses. 
For the 1986-92 samples, taken from North Caro- 
lina to Yucatan, Mexico, we used stratified sampling 
(Ketchen, 1950), attempting to collect sagittal otoliths 
from 20 fish from each unique year, region, sex, and 
10-cm size-interval combination. That quota was of- 
ten exceeded for abundant size intervals and not 
reached for rarer size intervals. 
The fish from Johnson et al.’s (1983) study were 
collected from recreational hook-and-line catches 
from North Carolina to Texas. Johnson et al. also 
used stratified sampling, with each sex and 10-cm 
size-interval combination comprising a stratum. For 
the analysis, regional classifications were the same 
as those used for the 1986-92 samples. 
In most cases, heads were shipped to our labora- 
tory where otoliths were removed and stored dry. The 
majority (>90%) of otoliths collected in the United 
States were taken from recreational hook-and-line 
catches, and the remainder from various commer- 
cial fisheries. All Mexican samples were collected 
from commercial fisheries. 
For the 1986-92 samples, otoliths from males <80 
cm and females <90 cm were read whole. The whole 
otoliths were placed in a black-bottomed dish con- 
taining glycerin and examined with a dissecting mi- 
croscope at 12-25x with reflected light. For larger 
fish (males >80 cm and females >90 cm), three trans- 
verse sections about 0.7 mm thick were made about 
the focus with a Beuhler Isomet low-speed saw. Sec- 
tions were mounted on glass slides with FLO-TEXX, 
a clear polymer mounting medium. Sections were 
examined under transmitted, polarized light at 50 
or 125x with a compound microscope. Annuli of whole 
otoliths were identified according to the criteria of 
Johnson et al. (1983), and sections according to the 
criteria of Waltz. 5 The dorsal half of the section was 
usually read because it was clearer than the ven- 
tral. Otoliths collected during 1986-88 were read 
independently by two readers, and if there was dis- 
agreement, a second reading was made. If the sec- 
ond reading disagreed with the first, the otolith was 
excluded from analysis. After 1988, otoliths were read 
by the senior author alone. 
Ageing methods for the 1977 and 1978 collections 
were basically the same, except that we sectioned 
males >75 cm and females >80 cm FL and used whole 
ages from Johnson et al. (1983) for fish below these 
sizes. 
5 Waltz, W. 1986. Data report on preliminary attempts to as- 
sess and monitor size, age, and reproductive status of king mack- 
erel in the south Atlantic Bight. South Carolina Wildl. Mar. 
Res. Dep. MARMAP rep. for contract 6-35147. 
