Validation of yellowedge grouper, Epinephelus flavolimbatus, age using nuclear bomb-produced radiocarbon

Abstract

Age validation and estimates of longevity of yellowedge grouper (Epinephelus flavolimbatus) from the Gulf of Mexico (GOM) are needed to inform fishery management decisions. Yellowedge grouper sagittal otoliths (n=100) were collected, aged using conventional means, and cores were submitted for radiocarbon ( 14 C) measurement. Radiocarbon values of yellowedge grouper otoliths were compared to established radiocarbon chronologies in the region to validate the age and ageing methodology of this species. The yellowedge grouper chronology displayed a similar sigmoidal trend as previously published chronologies. In addition to the core analysis, multiple areas on otolith sections from eight specimens were analyzed for Δ 14 C to validate age estimates for fish born prior to the 14 C increase. Our results indicate that yellowedge grouper live longer than previously reported (minimum of 40 years based on radiocarbon measurements). The validated ageing methodology supported an estimated maximum longevity of 85 years and established that yellowedge grouper have the longest lifespan currently known for any species of grouper in the GOM. Results also indicate a depth-age interaction in that material extracted from adult otolith sections assigned to post-bomb dates exhibited lower Δ 14 C values than cores (juvenile material) assigned to the same postbomb dates. This finding is likely explained by lower 14 C levels reported from water masses at deeper depths (>100 m) which are inhabited by adults.

A California Current bomb radiocarbon reference chronology and petrale sole (Eopsetta jordani) age validation

“…The onset of the radiocarbon increase is consistent with those of other northern hemisphere chronologies (e.g., Hamel et al 2008;Cook et al 2009) as well as those from other upwelling ecosystems (Druffel 1981;Druffel 1987;Druffel 1991). In comparison to many previous studies (Campana 1997;Piner and Wischniowski 2004;Hamel et al 2008), the CC reference chronology derived from petrale sole otoliths is more variable and has a notable lag in the rate of radiocarbon increase during what is generally considered to be the period of bomb radiocarbon increase, and may not have reached an asymptote.…”

“…The model estimated the timing and pattern of increase in ⌬ 14 C given both the reference and test data series, allowing the estimation of bias and variability in ageing (Hamel et al 2008). The model consistently fits bomb radiocarbon chronologies reasonably well as evidenced in Hamel et al (2008), Cook et al (2009), andFriess andSedberry (2011). Tests analogous to two-sample t tests were used to compare values of (with all other parameters fixed) between the reference and test chronologies.…”

Age estimation and lead-radium dating of golden tilefish, Lopholatilus chamaeleonticeps

“…To account for differences in growth zone interpretation, the validated age estimation criteria (as described above) were applied to the sectioned otoliths from the tilefish bomb 14 C study (Harris 2005) and the birth years were adjusted. Even though the adjusted birth years differed slightly (earliest birth year of 1958 was shifted to 1955 and the latest birth year of 1975 was shifted to 1973), the Δ 14 C levels for the U.S. South Atlantic were considerably lower than the Δ 14 C levels established for the Gulf of Mexico (GOM; Andrews et al 2013a) and the deeper-dwelling yellowedge grouper (Epinephelus flavolimbatus, Cook et al 2009), but similar to the Northwestern Atlantic otolith reference (NWA;Campana et al 2008) late in the Δ 14 C record (Fig. 7).…”

“…7 Time series of bomb radiocarbon data plotted as Δ 14 C to facilitate comparisons of golden tilefish measurements made previously (Harris 2005) with other Δ 14 C from regional fishes and temporal references. Δ 14 C measurements from yellowedge grouper (Epinephelus flavolimbatus, Cook et al 2009) and barrelfish (Hyperoglyphe perciformis, Filer and Sedberry 2008) provided an offset context of Δ 14 C values, relative to the regional time-specific Δ 14 C references from the Northwestern Atlantic (Loess -NWA otolith, Campana et al 2008) and the Gulf of Mexico (Loess -GOM coral, Andrews et al 2013a), and a basis for exploring the possible reasons for the anomalous Δ 14 C values measured for golden tilefish (Harris 2005). Loess curves are a smoothed function to provide a visual representation of the trends provided by the original data series burrows (Jones et al 1989).…”

“…Loess curves are a smoothed function to provide a visual representation of the trends provided by the original data series burrows (Jones et al 1989). Even though juvenile yellowedge grouper can recruit to shallower depths (25-125 m; Cook et al 2009), reduced Δ 14 C levels in otoliths of this species indicate it may typically recruit to greater depths with a prompt migration to even greater depths (Andrews et al 2013a). In addition, golden tilefish Δ 14 C levels were similar in timing, if traditional age estimates are correct, to those reported for barrelfish (Hyperoglyphe perciformis) collected from off South Carolina (Filer and Sedberry 2008; Fig.…”