Details of our sampling for early juvenile gag grouper appear in Table 1 and Table 1b. During the field season, all of the time of the personnel of this subproject was taken up with sampling, so we preserved the fish. We will analyze their growth rates and diets during the winter.
Stable Isotope Component Accomplishments
We achieved our objective of determining the maximum turnover rates for gag liver, gonad, and muscle tissue. Four adult gag (1 male and 3 females) were captured in traps during late June of 2006, a time when according to our model, they should be feeding on water-column (pelagic) fish (Table 2). The fish were transported to holding tanks at the Florida State University Coastal and Marine Laboratory at St. Teresa, FL, and held under a natural photoperiod at temperatures and salinities occurring offshore. The fish were fed a pelagic-derived diet of known carbon ratios (mackerel 13C(PDB) = -21.3%) for eight weeks in order to acclimate them and ensure that their tissue had a pelagic-like value. The gag's diet was then switched to an estuary-derived diet (pinfish 13C(PDB) = -16.6%). Their liver, muscle, and gonad tissues were then sampled via biopsy once a month for 9 months. The turnover rates we found for the three tissues sampled ranged from 0.09% to 0.52% per month (Table 3).
As we hypothesized, liver tissue had the most rapid turnover followed by gonad and then muscle. We observed a significant slope for all the tissue in the study with p-values of 0.001 for gonad, 0.033 for liver, and < 0.0001 for muscle (Figs. 9a-c). However, the liver tissue was much more variable than either gonad or muscle, changing as much as 9.7% in a month (Fig. 9b). We hypothesized that this variability was related to the fat content of the liver, but preliminary results from a lipid-correction experiment suggest that lipid content was not the only factor causing the observed variability. This observation is consistent with other studies that have attempted to correct for the fat content in livers (Post et al., 2007).