Using reproductive hormone concentrations from the muscle of white sharks Carcharodon carcharias to evaluate reproductive status in the Northwest Atlantic Ocean

Abstract

Novel, non-lethal approaches are needed to improve our current understanding of the reproductive biology and ecology of the white shark Carcharodon carcharias. Previous studies have demonstrated that concentrations of reproductive hormones in muscle tissue can be used as reliable indicators of reproductive status for many vertebrate species, including elasmobranchs. Here, we applied this method to assess the concentrations of testosterone (T) and estradiol (E2) in muscle biopsies from free-swimming white sharks at a known aggregation site off the coast of Cape Cod, Massachusetts (USA), in the Northwest Atlantic Ocean, to determine whether this technique could be used to evaluate the reproductive status of this species. A total of 14 muscle samples from 13 white sharks (7 males [1 sampled twice], 6 females), ranging in size from 3.3 to 4.2 m total length, were analyzed for this study. T and E2 were present in sufficient amounts to be quantified in 7 of the 8 (87.5%) male and 1 of the 6 (16.7%) female samples, respectively. As expected, most samples collected from immature individuals were below minimum detection thresholds. Hormone concentrations in males presumed to be adults were also generally low, suggesting these individuals were not actively producing sperm at the time of sample collection. Overall, the results herein are similar to those found in other species and indicate that concentrations of hormones in the skeletal muscle of subadult and adult white sharks can provide information on the reproductive status of individuals. This technique could have wide-ranging applications for the study of white shark reproduction in the future.