NMFS NUMBER: 93-SER-023
Location and Stock Identification of Spawning Aggregations
of Gag, Mycteroperca microlepis, along the Southeast
Coast of the United States
South Carolina Department of Natural Resources
August 29, 1996
Marine Fisheries Service, Southeast Region, 9721 Executive
Center Drive, North Koger Building, St. Petersburg, FL
33702. PHONE: (813) 570-5324
The goal of
this project was to use rapid survey methods to locate
gag (Mycteroperca microlepis) spawning aggregations
and determine the relationship between spawning adults
and juveniles recruited to nursery habitats. Using side-scan
sonar to locate, and underwater TV (UWTV), and plankton
sampling to confirm, spawning aggregations were located.
The identity of stocks was determined by tagging and genetic
work. DNA amplification techniques were used to identify
individuals from specific spawning sites, and to determine
if juveniles in estuarine nursery habitats can be identified
as progeny form particular spawning aggregations.
Finally, the project determined sex ratios of gag in spawning
aggregations throughout the South Atlantic Bight. The
data indicated that gag are spawning north of Florida.
Large adult gag in spawning condition were collected at
the shelf edge off Charleston, South Carolina. UWTV noted
the presence of few gag during the spawning season, but
occasional groups were seen at the shelf edge. Plankton
tows collected only one Mycteroperca spp. larva.
Genetic analysis indicated no clear pattern of stock structure
in gag, and suggested year class differences in microsatellite
allele frequencies. To resolve this, a large sample size
(at least 50 fish from each year class and from each area)
and ageing data are needed. Sex ratios of gag off
the southeastern Atlantic coast have changed over the
last 20 years, perhaps as a result of fishing pressure.