Harold L. Pratt

A review of elasmobranch reproductive behavior with a case study on the nurse shark, Ginglymostoma cirratum

Elasmobranch reproductive behavior has been inferred from freshly caught specimens, laboratory examinations of reproductive structures and function, or determined from direct observations of captive or free swimming wild animals. Several general behaviors have been described including seasonal sexual segregation, courtship and copulation. Courtship behavior was inferred for many species from the presence of scars and tooth cuts on the females body, and noted in more detail from underwater observations. Copulation has been directly observed in captive settings for several species of elasmobranchs in large aquaria, and in the wild for three species of urolophids and for Triaenodon obesus and Ginglymostoma cirratum. A detailed ‘case history’ of nurse shark reproductive behavior is presented that may be used as a template for future work on shark reproductive behavior of other species. Our studies, using diver identifiable tags and in situ behavioral observations, provide unprecedented information on social structure and mating behavior in this species. Since 1993, 115 G. cirratum, 45 adults and 70 juveniles have been tagged in the Dry Tortugas, Florida. Observations show that adult males visit the study site every year with three males dominant. Individual adult females visit the study area to mate in alternate years. Polygyny and polyandry are common. Future research on reproductive behavior of elasmobranchs should address questions on male access to females, sexual selection and dominance hierarchies.

Group reproductive behaviors in free-living nurse sharks, Ginglymostoma cirratum

Fifty mating events in free-living nurse sharks (Ginglymostoma cirratum) were observed over a nine-day period in the Dry Tortugas island cluster in the Florida Keys. Four stages of mating were identified: precoupling, coupling, positioning and alignment, and insertion and copulation. Copulation was observed and filmed in four of the mating events. Seminal fluid released into the water was obtained following one copulation and showed the presence of free, nonpackaged sperm cells. At least 10 of the events involved multiple males attempting copulation with single females.

Multiple paternity in the nurse shark, Ginglymostoma cirratum

For over a decade, we have been studying the reproductive behavior of the nurse shark, Ginglymostoma cirratum, in the Dry Torugas off the Florida Keys, an important mating and nursery ground for this species. In the course of these studies, we have used a variety of tags and tagging protocols to monitor individual animals. Here we report the use of molecular methods for the genetic analysis of nurse sharks. Specifically we have analyzed genetic variation at the MHC II alpha locus using the polymerase chain reaction (PCR) followed by restriction fragment length polymorphism (RFLP) analysis of the amplified products. We found this technique to be a relatively rapid and reliable method for identifying genetic differences between individual sharks. Applying this method to a family of sharks consisting of a mother and 32 pups, we demonstrate that at least four fathers must have fathered this brood. Multiple paternity in the nurse shark suggests a mechanism by which populations of this species may maximize genetic variability. This seems especially valuable for philopatric species whose migratory movement, and thus potential for genetic diversity, is limited.

Habitat management and closure of a nurse shark breeding and nursery ground

Abstract The nurse shark ( Ginglymostoma cirratum ) is a common resident of Florida and Caribbean waters. In spite of its prevalence, details of nurse shark life history and ecology are not well known. Ongoing studies have identified a population that undergoes mating and parturition in one specific site in the Florida Keys. Our tagging, observation, and filming have demonstrated that reproductive activities occur preferentially for some animals in very shallow coastal waters, and one such site became the study area. From our continuing investigations we have learned that mating activities of the sharks in this area are vulnerable to the disruptive effects of wading, diving, photography (electronic flash), boat traffic, and human presence during the times when mating occurs. To reduce disruptive activities during the mating season, a proposal to protect this mating and nursery grounds was submitted to the National Park Service. Three elements of protection that we felt were critical to implement were to: (1) recognize a specific area as unique and critical to the breeding success of the sharks, (2) restrict the public during times identified by our research as essential for mating, and (3) implement a program of public education.

Seasonal Distribution and Historic Trends in Abundance of White Sharks, Carcharodon carcharias, in the Western North Atlantic Ocean

Despite recent advances in field research on white sharks (Carcharodon carcharias) in several regions around the world, opportunistic capture and sighting records remain the primary source of information on this species in the northwest Atlantic Ocean (NWA). Previous studies using limited datasets have suggested a precipitous decline in the abundance of white sharks from this region, but considerable uncertainty in these studies warrants additional investigation. This study builds upon previously published data combined with recent unpublished records and presents a synthesis of 649 confirmed white shark records from the NWA compiled over a 210-year period (1800-2010), resulting in the largest white shark dataset yet compiled from this region. These comprehensive records were used to update our understanding of their seasonal distribution, relative abundance trends, habitat use, and fisheries interactions. All life stages were present in continental shelf waters year-round, but median latitude of white shark occurrence varied seasonally. White sharks primarily occurred between Massachusetts and New Jersey during summer and off Florida during winter, with broad distribution along the coast during spring and fall. The majority of fishing gear interactions occurred with rod and reel, longline, and gillnet gears. Historic abundance trends from multiple sources support a significant decline in white shark abundance in the 1970s and 1980s, but there have been apparent increases in abundance since the 1990s when a variety of conservation measures were implemented. Though the white sharks inherent vulnerability to exploitation warrants continued protections, our results suggest a more optimistic outlook for the recovery of this iconic predator in the Atlantic.

Exact Enumeration of Sires in the Polyandrous Nurse Shark (Ginglymostoma cirratum)

Abstract Polyandry has been demonstrated in a number of shark species. Studies based on a small number of loci typically estimate the minimum number of sires, which may be much lower than the actual number of sires due to the sharing of alleles by parents. We genotyped three litters of Nurse Shark (Ginglymostoma cirratum) ranging in size from 29 to 39 pups at 12 DNA microsatellite loci to determine the number of sires for each litter. We analyzed the genotypes using two analytical methods, both of which indicated that each litter had five to seven sires with one to 17 pups per sire. Previous analyses of these litters based on MHC loci indicated a minimum of four sires. Because G. cirratum are not capable of long-term sperm storage and ovulate over several weeks, they may require multiple inseminations to fertilize an entire litter. The varying levels of developmental stage among embryos found within a single litter may reflect multiple fertilizations over a prolonged period. Exact enumeration of sires as demonstrated here can provide valuable information for understanding reproductive ecology of live-bearing vertebrates.

Use of Telemetry in Fisheries Management: Juvenile Sandbar Sharks in Delaware Bay

Sandbar shark (Carcharhinus plumbeus) populations on the US east coast have undergone several decades of decline due to fishing pressure. One strategy for rebuilding stocks is improved survival of young sharks through enhancement of nursery areas. A key element for understanding the dynamics of shark nursery areas is increased knowledge about essential habitat for young sharks that occupy these nurseries. This study was conducted to quantify habitat use and movement patterns of juvenile sandbar sharks in Delaware Bay, which is a major east coast nursery for this species. Twenty five sandbar sharks were tracked for 2.5 to 75 h using ultrasonic telemetry. Although the sharks moved throughout the lower portion of the bay, and several sharks crossed the entire bay, individuals predominantly remained close to shore and in shallow water. The majority of sharks tracked showed movements that were heavily influenced by tidal currents, and sharks tracked on the New Jersey side of the bay had larger activity spaces, occupied deeper water, and ranged farther from shore than sharks tracked on the Delaware side. Management measures such as area/time closures would provide protection for a large number of sharks in a relatively small portion of Delaware Bay and may be improved if behavior of sharks is taken into consideration. For example, area closures on the Delaware side of the bay are likely to protect more individuals per unit area than an equal area on the New Jersey side. Our study demonstrates the utility of telemetry studies for providing information that will allow more precisely focused and effectively implemented fisheries management practices.