Regional differences in reproduction of Blacktip Shark in the northern Gulf of Mexico

Abstract

Objective: Blacktip Sharks Carcharhinus limbatus are common in the U.S. Gulf of Mexico and are targeted in both recreational and commercial fisheries. Recent studies have supported biological separation between the eastern and western Gulf of Mexico for Blacktip Sharks, which are currently managed through separate quotas. However, comprehensive reproductive information throughout these areas is lacking. To further investigate the potential for separate stocks in the Gulf of Mexico, reproductive data were examined for Blacktip Sharks collected from the eastern and western regions. Methods: A total of 236 Blacktip Sharks (146 females, 90 males) were collected from July 2020 to October 2021 using both fishery-independent and fishery-dependent methods. Additional length, age, and maturity data from 2006 to 2021 were incorporated into the analysis for a total of 1,308 Blacktip Sharks (726 females, 382 males). Results: Results confirmed a seasonal and synchronous reproductive cycle for Gulf of Mexico Blacktip Sharks. Females exhibited a biennial ovarian cycle, and peak mating activity occurred in March–May followed by a 12-month gestational period. Some variability was observed within the reproductive cycle compared with past studies, indicating that some Blacktip Sharks may demonstrate a more protracted mating and ovulation period than previously described. Median size and age at maturity differed significantly by sex and region. Median length at maturity was 94.7 cm FL for males and 100.6 cm FL for females in the western Gulf of Mexico (n= 452) and 105.7 cm FL for males and 116.1 cm FL for females in the eastern Gulf of Mexico (n= 856). Median age at maturity was 3.1 years for males and 3.5 years for females in the western Gulf of Mexico and 4.7 years for males and 6.4 years for females in the eastern Gulf of Mexico. Conclusions: These results suggest that there are significant Blacktip Shark life history differences between the eastern and western Gulf of Mexico and that separate quotas may need to be implemented for effective fisheries management.