Biological parameters of the Atlantic sharpnose shark Rhizoprionodon terraenovae in the northern Gulf of Mexico were re-examined to test for potential changes due to density dependent responses. Biological data from published studies in the Gulf of Mexico collected during the period 1979–1984 were compared with data collected during the period 1998–2001. For combined sexes, the von Bertalanffy growth parameters were L∞ = 110.8 cm total length, K = 0.39 year–1 and to = –0.86 year during 1984 and L∞ = 94.0 cm total length, K = 0.73 year–1 and to = –0.88 year during 1998–2001. Median size for males and females at maturity decreased from approximately 78.3 and 80.2�cm total length (TL), respectively, in 1979–1980 to 72.6 and 75.8 cm TL, respectively, in 1998–2001. Age at maturity for combined sexes also decreased from 2.3 years in 1979–1980 to 1.4 years in 1998–2001. Litter size was similar between periods (5.0 embryos), as was the average size of embryos close to parturition (32 cm TL; 130–150�g). Growth rates using observed mean size-at-age data were higher from 1998–2001 for early ages (0–2.5 years). The observed decrease in maturity and increased growth rate lends support to the hypothesis of a compensatory response, although it could not be fully determined whether the response was due to differences in methodology among studies, anthropogenic influences or natural causes.

The reproductive parameters of 1,194 sandbar sharks Carcharhinus plumbeus (701 females, 493 males) were examined for stock assessment. Size and age at 50% maturity was 151.6 cm FL (12.1 years) for males and 154.9 cm (13.1 years) for females; however, the size and age at which 50% of females were in maternal condition was 162.0 cm FL (15.5 years). Males and females showed distinct seasonal reproduction patterns, with peak mating and parturition occurring from April through July. The majority of near‐term pregnant and postpartum females were observed in the Florida Keys, which is an extension of the previously reported nursery grounds for sandbar sharks in the western North Atlantic Ocean. Female fecundity averaged 8.0 pups, and there was a significant increase in fecundity with length and age. The ovarian cycle is at least biennial, although there is evidence that some females have triennial cycles. Received November 3, 2011; accepted June 1, 2012

SynopsisWe examined life history traits (e.g., mean length-at-age, growth rate, age-at-maturity) for blacktip sharks collected from two separate geographical areas (eastern Gulf of Mexico and South Atlantic Bight) to address the potential for separate stocks in southeastern US waters. Samples were obtained from fishery-dependent and independent sources. Growth and logistic models were fitted to observed length-at-age and reproductive data, respectively. von Bertalanffy growth parameters derived for blacktip shark from the Gulf of Mexico show that they attain a statistically smaller theoretical maximum length (L ¥ = 141.6 cm vs. L ¥ = 158.5 cm for female and L ¥ = 126.0 cm FL and L ¥ = 147.4 cm FL for male) and have a faster growth rate (k = 0.24 yr -1 vs. k = 0.16 yr -1 for female and k = 0.27 yr -1 vs. k = 0.21 yr -1 for male) than conspecifics in the South Atlantic Bight. Median length-and age-atmaturity were significantly different between sex and area. Length at which 50% of the population is mature was 117.3 cm FL for females and 103.4 cm FL for males in the Gulf of Mexico and 126.6 cm FL for females and 116.7 cm FL for males in the South Atlantic Bight. Median age-atmaturity was 5.7 yrs and 4.5 yrs for females and males in the Gulf of Mexico, respectively, while age-at-maturity was 6.7 yrs for females and 5.0 yrs for males for sharks from the South Atlantic Bight. Due to varying statistical results, temporal problems of sampling, and potential for gear bias, we could not definitively conclude that differences in life history characteristics exist.

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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