164 
. ~ 
cS : handeleur 
72,4 4slands 
< 7777 Gill-net study 
- t———-l area 
S Sesscces State-federal 
= boundary 
Fishery Bulletin 120(2) 
Gulf of Mexico 
Figure 1 
Map of the study areas in the north-central Gulf of Mexico where red drum (Sciaenops ocellatus) 
were collected during fishery-independent bottom longline (BL) and gill-net surveys from 2006 
through 2018. The dashed line that follows the coastline indicates the boundary between state and 
federal waters. Gray lines indicate depth contours. LA=Louisiana; MS=Mississippi; AL=Alabama; 
FL=Florida. 
Otolith processing and aging 
All otoliths were processed following procedures detailed 
in Powers et al. (2012) and VanderKooy et al.' A portion of 
the fish aged in Powers et al. (2012) were also included in 
our study; however, these fish were aged again as part of 
this study for consistency. Once otoliths were processed, 
aging was conducted by 2 readers independently (without 
consultation between readers) and blindly (without 
knowledge of fish capture date or size). Each otolith sec- 
tion was viewed with an Olympus” SZX16 stereomicro- 
scope (Olympus Corp., Tokyo, Japan) with transmitted 
light (brightfield illumination). The number of opaque 
zones was counted along the ventral edge of the sulcus 
acusticus. A margin code (1—4) was assigned to the otolith 
' VanderKooy, S., J. Carroll, S. Elzey, J. Gilmore, and J. Kipp (eds.). 
2020. A practical handbook for determining the ages of Gulf of 
Mexico and Atlantic Coast fishes, 3rd ed. Gulf States Mar. Fish. 
. Comm., Publ. 300, 248 p. [Available from website.] 
2 Mention of trade names or commercial companies is for identi- 
fication purposes only and does not imply endorsement by the 
National Marine Fisheries Service, NOAA. 
margin, according to the otolith manual of the Gulf States 
Marine Fisheries Commission (VanderKooy et al.’). 
Whole age, in years, was calculated for each fish accord- 
ing to guidelines of the Gulf States Marine Fisheries Com- 
mission. If the collection month was January—June and the 
margin code was 3 or 4, the whole age equaled the number 
of opaque zones, plus 1. If the collection month was October— 
December and the margin code was 1 or 2, the whole age 
equaled the number of opaque zones, minus 1. For all other 
combinations of capture month and margin code, the whole 
age equaled the number of opaque zones. Next, the num- 
ber of days between the capture date and October 1 (the 
assumed birth date of red drum; Ditty, 1986) of the previous 
year was calculated. This number was then divided by the 
total number of days in the capture year, and the result was 
added to the whole age to yield the fractional age. 
If the readers assigned different whole ages to any oto- 
lith, the readers consulted with each other or a third reader 
aged the otolith. If the 2 initial readers did not reach an 
agreement or if the third reader did not agree with 1 of the 
2 initial ages, the otolith was excluded from further analysis. 
Average percent error was calculated for all whole ages to 
