Gag are
a relatively common species of grouper in waters offshore
of Louisiana, and are avidly pursued by both recreational
and commercial fishermen. They are a mottled gray color with
no outstanding distinguishing features. They are most similar
to scamp grouper, but lack the streamer points that scamp
have on their dorsal (back), anal (belly), and caudal (tail)
fins, and the scamp's bright yellow markings around its mouth.
Because
of its popularity and its biology, the gag are considered
susceptible to overfishing. Gag, like many groupers, change
sex, starting life as females and changing to males as they
become older and larger. This means that there are fewer males
than females in any population, so fishing pressure can affect
one sex more than the other.
Gag have
been well-researched on the South Atlantic coast, but very
little work has been done on their biology in the Gulf of
Mexico. One Gulf study, done in the late 1980s, took place
off of the west central Florida Gulf Coast. A total of 1,331
gag ranging in size from 0.7 - 48.9 inches long were captured.
Larger fish were captured by recreational and commercial fishermen
from waters 119 to 594 feet deep. Smaller fish nearshore and
in Tampa Bay were captured using seines, pushnets, hooks,
traps and spearguns. All fish were weighed, measured and their
age determined by counting the rings in their otoliths (ear
bones).
Gag in
the study increased in size as the water became deeper, out
to 265 feet deep. For example, the average size was 20 inches
at 33 foot depths and 40 inches at 265 feet. This may be due
to more fishing pressure in shallower waters, or to the fact
that gag migrate to deeper waters as they mature.
The oldest
fish in the study was 21 years old and 45.6 inches long. The
largest fish (48.9 inches) was 17 years old. Gag grew rapidly
until they were 10 years old and an average size of 44 inches.
From 10 to 21 years old, growth rates were very slow. Growth
rates were most rapid the first year, with the average gag
being almost 17 inches long by its first birthday.
Overall,
females outnumbered males by more than six-to-one. Gag under
32 inches and five years old were all females. By 42 inches
and 11 years old the sex ratio was about even. Between five
and 11 years old, male fish were larger than female fish,
most likely because the larger fish in each age group had
changed sex from female to male. After 11 years old, the average
size of males and females was about the same.
Females
usually became mature enough to spawn between ages three and
four. At four years old, 70 percent were mature. By age six,
all females were mature. Spawning takes place between December
and May, with a peak in February and March.
Download:
gaggrouper.pdf
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