The Reproductive Biology of the Common Thresher Shark in the Western North Atlantic Ocean

Abstract

Reproductive organs from 130 male and 256 female Common Thresher Sharks Alopias vulpinus were examined to describe the reproductive characteristics and determine size at maturity and reproductive seasonality for the species in the western North Atlantic Ocean. Males ranged in size from 78 to 237 cm FL and females ranged from 62 to 263 cm FL. The onset of maturity in males was best described by an inflection in the relationship of clasper length to FL in combination with the degree of clasper calcification. Males matured between 181 and 198 cm FL, and estimated median size at maturity was 188 cm FL. In females, changes in the relationship between ovary and uterus length and width with FL were used to estimate the size at maturity. Females matured between 208 and 224 cm FL; the estimated median size at maturity was 216 cm FL. Litter sizes averaged 3.7 young. The period of parturition is protracted, spanning late spring to late summer (May–August). As in other Lamniformes, young are nourished through oophagy. The proportion of mature females in the resting, pregnant, and postpartum stages provides evidence that indicates that the Common Thresher Shark does not reproduce annually.

Received August 22, 2012; accepted May 21, 2013

ACKNOWLEDGMENTS

We thank the officials and participants of the many shark tournaments between southern New Jersey and Maine for allowing us to sample their landed Common Thresher Sharks. The members of the Apex Predators Program (past and present) provided much help in all phases of this work. We also thank Nancy Kohler, Dave Ebert, and Sabine Wintner for reviewing early drafts and the two anonymous reviewers who reviewed the final manuscript and whose input made this a far more comprehensive overview. Megan Winton also reviewed the final manuscript and was a great sounding board for revision process. Last but not least, L.J.N. would like to particularly thank H. Wes Pratt for bequeathing such an amazing data set and providing the copious instruction needed to maintain it in a consistent form.