Research Description:

Reproduction in the Blacknose Shark, Carcharhinus acronotus, Off the Southeastern Coast of the United States

The blacknose shark, Carcharhinus acronotus, is a relatively small shark that inhabits the coastal shorelines of the western Atlantic from North Carolina to the southern edge of Brazil. It is very common off the shores of Florida where it is targeted by commercial shark fishers. C. acronotus is the second most commonly caught small coastal shark taken in the fishing monitored by the Commercial Shark Fishery Observer Program, University of Florida. Despite being a commercially important shark, research on this species is rather sparse. Some studies have examined reproduction but research is lacking for Florida populations.

Better understanding of blacknose shark reproduction, particularly in the heavily fished Florida waters, is paramount to properly managing the species. My goal is to elucidate the reproductive cycle of female C. acronotus through analysis of the ovary (egg development) and nidamental gland (sperm storage). My examination of the ovary will include development of a gonadosomatic index (GSI). This index is used to monitor the activity of the gonad throughout the year. In seasonal reproducers an increase in GSI indicates an increase in gonadal activity. Analyzing the change in GSI can help determine the timing of reproductive events, such as folicle development in females or sperm production in males. Additionally, I will measure ovarian egg diameters to determine the cycle of egg development and possibly indicate fecundity by quantifying the amount of active eggs per ovary. Using immunohistochemistry I will examine the nidamental gland to determine if female C. acronotus store sperm. Some shark species, such as the blue shark, Prionace glauca, are known to store sperm in the nidamental gland. Sperm storage can increase reproductive success by making fertilization temporally independent of mating.