Studies of the natural reproductive cycle of nurse sharks, Ginglymostoma
cirratum, are conducted in the Florida Keys. Wes Pratt, Staff Scientist
with the Center for Shark Research and his cooperators Dr. Jeff Carrier
of Albion College, and Dr. Ed Heist of the
University of Illinois have embarked on a systematic study of mating systems and strategies, using
G. cirratum as a template to understand the vital mating systems of large Atlantic sharks (see
Mote News). In June and July,
adult male and female nurse sharks, 210 to 275 cm long, mate on shallow grass flats.
The females utilize these shallows as a refuge to control male access and perhaps for mate selection. (Pratt and Carrier, 2001). The males
only visit the shallows during the time of mating. Some of the females return to the grassy mating area throughout the fall, using it as a
maternity refuge and perhaps as a primary nursery ground. After parturition and live birth of up to 50 young, the females stop visiting
the shallows and skip the next mating season. This shallow water mating and refuging is unusual among known shark mating
systems and affords a unique opportunity to investigate the dynamics of shark reproduction.
Using specially designed capture gear and the latest tagging and
monitoring methodology, Pratt, his wife Theo, a Mote volunteer, and his cooperators visit the mating area, refuge and nursery ground several
times a year to sample tag and observe shark behaviors.
Expeditions are made on privately owned support vessels and on the exploration vessel
Tiburon
of Key West. Past expeditions have teamed with the National Geographic Remote Imaging team utilizing
Crittercam
and other technologies to explore mating from the shark's point of view.
Our systematic studies of this benign, yet docile shark species will hopefully one day provide the necessary information to allow us not only
manage and conserve shark species, but to also understand and put in perspective the complex behaviors and life histories of all sharks, the
maligned, feared and misunderstood top oceanic predators.
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We
conduct periodic sampling investigations in the lower
Florida Keys to survey and tag sharks as they appear seasonally in key
habitats( flats, back reef, reef edge, channels around bridges), to identify species and collect CPUE data for various gear
types, and provide baseline information of shark populations in the
Lower Florida Keys.
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