Reproductive and age data were collected for Blacktip Sharks Carcharhinus limbatus in the Gulf of Mexico from fishery‐dependent and ‐independent sources from 2006 to 2011 for stock assessment. A total of 757 Blacktip Sharks were sampled for reproductive analysis (399 females, 358 males), of which 741 were aged. Additional length and age data from a previous age and growth study on Blacktip Sharks in the Gulf of Mexico (207 females, 161 males) were incorporated into the size‐ and age‐at‐maturity analyses. The results indicated that Blacktip Sharks in the Gulf of Mexico have a synchronous, seasonal reproductive cycle and that females exhibit a biennial ovarian cycle. Male and female mating and parturition peaked from March to May. Length at 50% maturity was estimated to be 105.8 and 119.2 cm FL for males and females, respectively, while age at 50% maturity was calculated as 4.8 and 6.3 years. Near‐term pups averaged 38 cm FL, and gestation was approximately 12 months. Litter size was 4.5 pups per female, and fecundity was found to increase with both maternal size and age. Maternal body size—but not age—had a positive influence on offspring fitness. This represents the first comprehensive reproductive study of Blacktip Sharks in the Gulf of Mexico. Received October 1, 2012; accepted December 5, 2012

The great hammerhead shark, Sphyrna mokarran, is a cosmopolitan species that is caught in a variety of fisheries throughout much of its range. The apparent decline of great hammerhead shark populations has reinforced the need for accurate biological data to enhance fishery management plans. To this end, age and growth estimates for the great hammerhead were determined from sharks (n = 216) ranging in size from 54- to 315-cm fork length (FL), captured in the Gulf of Mexico and north-western Atlantic Ocean. Growth curves were fitted using multiple models and evaluated using Akaike’s information criterion. The von Bertalanffy growth model was the best fitting model, with resulting growth parameters of L∞ = 264.2-cm FL, k = 0.16 year–1, t0 = –1.99 year for males, and L∞ = 307.8-cm FL, k = 0.11 year–1, t0 = –2.86 year for females. Annual band pair deposition was confirmed through marginal-increment analysis and a concurrent bomb radiocarbon validation study. Great hammerheads have one of the oldest reported ages for any elasmobranch (44 years) but grow at relatively similar rates (on the basis of von Bertalanffy k value) to other large hammerhead species from this region. The present study is the first to provide vertebral ages for great hammerheads.

Bomb radiocarbon analysis of vertebral growth bands was used to validate lifespan for sand tiger sharks (Carcharias taurus) from the western North Atlantic (WNA) and southwestern Indian Oceans (SIO). Visual counts of vertebral growth bands were used to assign age and estimate year of formation (YOF) for sampled growth bands in eight sharks from the WNA and two sharks from the SIO. Carbon-14 results were plotted relative to YOF for comparison with regional Δ14C reference chronologies to assess the accuracy of age estimates. Results from the WNA validated vertebral age estimates up to 12 years, but indicated that ages of large adult sharks were underestimated by 11–12 years. Age was also underestimated for adult sharks from the SIO by 14–18 years. Validated lifespan for C. taurus individuals in the present study reached at least 40 years for females and 34 years for males. Findings indicated that the current age-reading methodology is not suitable for estimating the age of C. taurus beyond ~12 years. Future work should investigate whether vertebrae of C. taurus record age throughout ontogeny, or cease to be a reliable indicator at some point in time.