STOCK ASSESSMENT OF WHITE GRUNT FROM THE WEST ...

otoliths (Padgett 1997, Murie and Parkyn 1999, Potts and Manooch In review). Alternative
methods of aging white grunt, including breaking-and-burning sagittal otoliths and thinsectioning
of fin rays, have also been investigated (Murie and Parkyn 1999).
Manooch (1976) reported that ages of white grunt read using scales and surface readings
of whole otoliths agreed 75% of the time for fish 2 to 12 years of age, with most of the
disagreement occurring in fish 9 to 10 years old. In comparison with sectioned otoliths, whole
otoliths underestimated the age of white grunts from 0 to 18 years of age after 8-10 years (Murie
and Parkyn 1999). Percent agreement between whole and sectioned otoliths changed from 91%
for grunt less than 10 years old to only 14% for fish older than 10 years, with differences between
ages as high as 4-5 years in older fish (Murie and Parkyn 1999). It was therefore necessary to use
thin-sectioned otoliths to reliably age white grunt from the eastern Gulf of Mexico. Using this
method, Murie and Parkyn (1998, 1999) obtained an average estimate of aging precision
between two independent readers of 98% (n=1,015), with a concordance correlation of 0.997.
Similar aging precision has been obtained by Padgett (1997) aging white grunt from the South
Atlantic Bight using sectioned otoliths (97%).
Aging methodology using sectioned otoliths has only recently been validated for white
grunt from the eastern Gulf of Mexico, using both marginal-increment analysis and chemical
marking (Murie and Parkyn 1999). Murie and Parkyn (1999) observed that the mean monthly
index of completion for the marginal increment (the distance from the last annulus to the margin
of the otolith as a proportion of the last complete increment) was unimodal (Fig. 6), indicating
that white grunt in the eastern Gulf of Mexico were depositing only one annulus each year. In
addition, the index of completion was at a minimum in May and June, which indicated that white
grunt deposited their annulus during this time period. The formation of one annulus in an
intervening 12-month period was also confirmed using oxytetracycline as a chemical mark
injected into white grunts that were subsequently held in captivity for one year (Murie and
Parkyn 1999).
Based on marginal-increment analysis, Padgett (1997) and Potts and Manooch (In
review) have recently determined that white grunt in the Atlantic also deposit one annulus each
year. In the South Atlantic Bight (primarily northern Georgia and the Carolinas) and the
Carolinas, white grunt form their annulus in March/April (Padgett 1997 and Potts and Manooch
In review, respectively). Similar to white grunt from the west coast of Florida, white grunt from
southeastern Florida form their annulus primarily in May (range of March-June) (Potts and
Manooch In review).
White grunt from the west coast of Florida reach a maximum age of 18 years (Murie and
Parkyn 1998). Both female and male white grunts show very rapid growth in length in their first
three years, after which their growth slows and plateaus at around 12-13 inches total length (Murie
and Parkyn 1999) (Fig. 7). Growth curves of female and male white grunt collected from either
research samples (primarily hook-and-line gear) and the commercial fishery (traps) from the eastern
Gulf of Mexico were described by von Bertalanffy growth models (Table 1) (modified from Murie
and Parkyn 1999). Although there was an overall trend in male white grunts being slightly larger
than females at any age beyond 2 years, especially for males collected in the commercial trap
fishery, there was also a lot of variability in the growth of grunts (Fig. 7) (Murie and Parkyn 1999).
Minor differences observed between research and commercial samples were probably due to both
differences in gear and depth, since the trap fishery operates in >60 feet of water whereas the
research sampling was carried out in 18-37 feet of water. Padgett (1997) also found that fish
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