Age underestimation of many shark species, such as the sandbar shark (Carcharhinus plumbeus), has been proven with age validation methods including bomb radiocarbon dating, oxytetracycline (OTC) injection, and tagrecapture data. Validation studies indicate that band-pair deposition in vertebral centra may not be directly related to time, especially in older individuals of a species. In this study, vertebrae from tagged, OTCinjected, and recaptured sandbar sharks were examined to determine if band-pair deposition past the OTC mark matched time at liberty. In 6 of 8 OTC-injected sharks at liberty for >1 year, band-pair count past the OTC mark underestimated time at liberty by 24-58%. Additionally, growth rates derived from tag-recapture data were slower than those described by previously published vertebral band-pair growth curves but were similar to those predicted by previous bomb radiocarbon dating and OTC results from this study. Together, the results from these studies indicate that modeling tag-recapture data may be more accurate for age determination in elasmobranchs given that band-pair counts on vertebral centra do not coincide with age throughout life. Analyses indicate that sandbar sharks may be less productive than previously understood.Research has shown that the rate of vertebral band-pair deposition in elasmobranchs is variable and not necessarily related to time (Harry, 2018;Natanson et al., 2018). At least 30% of studies attempting to validate the periodicity of vertebral band-pair deposition in elasmobranchs in relation to age have shown that ages were underestimated (Harry, 2018).

The porbeagle (Lamna nasus) is a slow-growing, late-maturing, long-lived pelagic shark that inhabits cold temperate waters. Previous research based on specimens collected from the western North Atlantic Ocean has indicated that this lamnid shark has an annual reproductive cycle. However, the results of a recent evaluation of reproductive tracts from a geographically segregated group of porbeagles within the western North Atlantic Ocean indicate the presence of females in a resting stage of maturity. The observation of a resting stage has implications not only in the reproductive cycle, biennial versus annual, of this species but also in the lifetime productivity. This finding indicates that this shark follows the typical lamnid resting period between pregnancies, a period that would decrease the lifetime output of young sharks and their resilience to direct and indirect fishing pressure.

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