An Observation of Mating in Free-Ranging Blacktip Reef Sharks, Carcharhinus melanopterus

We describe the mating behavior of free-ranging Blacktip Reef Sharks, Carcharhinus melanopterus, at Palmyra Atoll. This is the first primary report of mating in C. melanopterus and the first direct observation of mating for an obligate swimming shark species. Similar to that in other nonobligate swimming shark species, mating in C. melanopterus was characterized by multiple males following a single female, a male grabbing the female near the pectoral fin and positioning her head down on the bottom, and the insertion of a single clasper. Copulation lasted 68 sec, which is shorter than the durations recorded for most other shark species. The mating of sharks has been observed for only a small number of species. All published primary accounts of shark mating come from species that are capable to some degree of buccally pumping water over their gills to obtain oxygen (i.e., not obligated to swim at all times under normal conditions to respire; buccal ventilators) (Pratt and Carrier 2001). It is currently unknown if and how the mating behavior of obligate swimming species (those that cannot, under normal circumstances, obtain sufficient oxygen while remaining stationary; obligate ram ventilators) may vary from that of their nonobligate swimming counterparts. It has been suggested that these obligate swimming sharks may mate in shallow water with copulation being brief, or that they may mate while swimming (Stevens 1974, Johnson and Nelson 1978, Ebert 1996, Francis 1996, HarveyClark et al. 1999). Here we describe a direct observation of mating in the obligate swimming Blacktip Reef Shark, Carcharhinus melanopterus (Quoi & Gaimard), and compare these observations to what is already known about mating in nonobligate swimming sharks. materials and methods The mating event we report was observed while scuba diving on the northern forereef of Palmyra Atoll (5 53 0 835 00 N, 162 05 0 919 00 W), a U.S. National Wildlife Refuge in the northern Line Islands (central Pacific Ocean). Temperature, depth, and light intensity at the time of the mating were recorded using multiple sensors affixed to the seafloor (Onset Computer Corp.). The density of C. melanopterus at nine sites on the forereef at Palmyra was measured during June–August 2006 using 50 8 m belt transects located at 10.5 m depth. Each transect was surveyed seven times at approximately 8-day intervals by observers using scuba.