National Shark Research Consortium
Florida Program for Shark Research - Florida Museum of Natural History
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NSRC-supported Initiatives
Studies of the age, growth, and reproduction of commercially important sharks
Reproduction of the sandbar shark (Carcharhinus plumbeus)
The sandbar shark is the most targeted species in the commercial shark bottom long-line fishery. Additionally, the sandbar shark comprises approximately 20% of the large shark fauna and is second only to the blue shark (Prionace glauca) in recreational catches along the U.S. East Coast. In addition to age and growth data, which have been examined in several studies for this species, information on the reproduction of the sandbar shark is needed for better management of the population. Currently there is a need for accurate and up to date information on the reproductive cycle (gonadosomatic indices, timing of gamete production, sperm storage, etc) of the sandbar shark in Florida waters. The most comprehensive study on sandbar shark reproduction in Florida waters is more than 40 years old. In our study, we are examining the reproductive cycle through both gross observations as well as histological observations of the reproductive track to pinpoint the timing of reproductive events. Growth of the oviducal gland and claspers will elucidate the size of maturity in female and male sandbar sharks respectively. Changes in the size of the gonads relative to the size of the sharks (gonadosomatic index) will provide information on the timing of gonadal activity. Changes in ovarian egg sizes will help to determine when ovulation occurs. Histological preparations of the testis and oviducal gland will further clarify the seasonality of sperm production and possible storage of sperm by females.
Shark embryo fitness
In some species of shark, litter size is positively correlated with the size of the mother shark; i.e. larger mature females produce more young. This study was designed to answer the question: do larger mature female sharks produce fitter young? We are assessing embryo fitness by examining the condition of the embryos through the relationship between embryo length and weight, specifically Fulton's condition. Embryos that have higher condition levels will be considered "more fit," in keeping with literature on other vertebrates. We will then determine if there is a relationship between embryo fitness and the size of the mother shark. Lengths of pregnant sharks are taken in the field. Embryos are dissected out, labeled as to which uterus they were taken from, and taken back to the lab on ice. Embryos are then weighed and measured in the lab. We have focused on two species, Rhizoprionodon terraenovae (sharpnose shark) and C. plumbeus (sandbar shark). The sharpnose shark was chosen due to its small size and abundance in the fishery. The sandbar shark was chosen also due to its relative abundance in the fishery and sample holding from our ongoing sandbar shark reproductive study. The data produced from this study will give insight into the energetics of reproduction, a topic that has not received much attention in sharks.
Fatty acid and lipid analysis of embryonic development
In viviparous placental sharks, such as the sandbar shark, during gestation embryos first utilize yolk reserves present in the yolk sac. However, once the yolk is fully ingested, the empty yolk sac attaches to the uterine wall to form a placental connection. This connection provides several functions: transfer of nutrients; transfer of macromolecules, such as immunoglobulins; respiration; and osmotic and ionic regulation. It has been shown that in placental shark species, as initial yolk stores in the yolk sac are depleted, the maternal liver produces yolk protein precursors that are secreted into the blood, where they are utilized by developing oocytes for the next reproductive cycle. These yolk precursors could also be transported across the uterus and fetal placenta to nourish embryos during gestation. It is probable that in addition to yolk protein precursors, the maternal liver also mobilizes fat stores for embryo nourishment. Studies have shown the livers of pregnant elasmobranchs such as Trygon violacea, Torpedo ocellata, Acanthias blainvillei, and Mustelus vulagris are reduced in size as embryos develop in utero. It has been suggested that mobilization of lipids may be a major factor in embryonic growth and maternal lipid reduction.
In this study we are analyzing the fatty acid composition and lipid levels of maternal and embryonic livers of sandbar sharks to determine which essential (dietary) fatty acids are mobilized for embryonic growth and whether mobilization of these fatty acids is reflected in maternal fatty acid composition and lipid levels. Comparing embryonic weights with lipid levels may provide insight into nutritional partitioning. The presence of runts (embryos significantly smaller than their litter mates) suggests that some partitioning of nutrients does occur. Genetic analysis has shown that these runts are not genetically different than some of their siblings, suggesting a maternal control of embryonic growth. Our hypothesis is that lipid levels will be lower in genetically indistinct runt sharks, which would support the idea that paternal fitness is not a major factor in determining embryonic fitness.
This study has not been previously conducted for any elasmobranch and will allow for increased knowledge of reproduction in placental shark species. Additional data on embryonic growth will allow for better understanding of factors that may contribute to pup survival, such as size at birth. If embryonic growth is not influenced by paternal genetics, then more focus on the mechanisms of gestation may be warranted. Further, if pup survival is not influenced by paternal genetic contribution, then polyandrous mating may not be advantageous for this species.
Paternity analysis of the Atlantic sharpnose shark (Rhizoprionodon terraenovae)
The paradigm that female monogamy is widespread across taxa and that polyandry is rare, is shifting. Parentage studies utilizing high resolution molecular markers have revealed that genetic polyandry is common, even in species with internal fertilization that had traditionally been considered monogamous or polygynous. Paternity analysis has only been conducted for a handful of shark species (e.g. C. plumbeus, Sphyrna tiburo, Negaprion brevirostris, Ginglymostoma cirratum), some with low sample sizes (Triakis scyllium). The majority of these studies have shown sharks to be largely polyandrous. However, a study on the bonnethead shark, S. tiburo, showed this species' mating habits to be mostly monogamous. Mating behavior in sharks may be plastic, depending on anthropogenic and natural factors and may vary by locality. The sharpnose shark is commonly caught in the commercial shark fishery as bycatch. Knowledge of the reproductive behavior of shark species impacted by fisheries is needed to fully understand how population level fluctuations may contribute to shifts in mating systems. For this study, DNA samples from pregnant sharpnose sharks and their embryos will be analyzed utilizing microsatellite genetic techniques. The occurrence or absence of polyandrous mating will be determined.
Age and growth of the great hammerhead shark (Sphyrna mokarran)
Populations of hammerhead sharks are believed to have severely declined in recent years. To properly regulate shark populations, fishery managers require life history data, particularly age and growth information for the species of sharks present in the fishery. Currently there is a need for accurate age and growth data for S. mokarran. Scientists at FPSR and NMFS Panama City labs, are currently finishing the analysis of 219 great hammerhead vertebrae for an age and growth study. This study will be the first to quantify growth in this exploited yet poorly understood species.
Reproduction of two congener shark species (Sphyrna lewini, S. mokarran)
In addition to accurate information on age and growth, fisheries managers also require data on the reproductive parameters for stock assessment. To date no study has provided accurate data on the reproduction of the scalloped hammerhead in coastal eastern U.S. waters. Further, no study on any aspect of the life history of the great hammerhead has been published for any population. The paucity of life history data on these species prohibits the use of species specific stock assessment models for managing current fished populations. We recently completed an age and growth study on the scalloped hammerhead shark and are currently finishing up a study on the age and growth of the great hammerhead shark (see above). Our results indicate significant differences in growth parameters between these two species. Species specific differences in reproduction have yet to be explored as good reproductive data are currently lacking.
Our goals for this project are to: 1) determine the size/age of maturity of male and female scalloped hammerhead and great hammerhead sharks in the northwest Atlantic Ocean; 2) determine the fecundity and reproductive cycle for scalloped hammerhead and great hammerhead sharks; 3) determine if female scalloped and great hammerhead sharks reproduce annually or biennially; 4) determine if significant differences in reproductive parameters occur between these two species of the same genera.
Life history and morphology of batoid species
Sexual dimorphism in skate tooth morphology
Sexual differences in tooth morphology of batoids (skates and rays) have been observed in several species. However, few comprehensive studies have been conducted on this phenomenon. These differences have been attributed to either differences in habitat or perhaps more likely as an adaptation to enhance the grasping ability of males during mating events. To study differences in tooth morphology skate teeth are removed from the jaw and examined microscopically. A picture of each tooth is taken and morphology software is used to denote landmarks and curve shapes found within each tooth. These data are compiled and ANOVA techniques are used to compare the tooth shape of males and females.
During the last year we initiated a study to examine sexual dimorphism in the tooth morphology of two skate species, the roundel skate (Raja texana) and the spreadfin skate (Dipturus olseni). During year six we will complete analysis of differences in the morphology of male and female R. texana teeth. In addition during this year we will study the differences in tooth morphology between immature and mature individuals of this species. Analysis of the differences in the morphology of male and female D. olseni teeth will also be completed. It has been hypothesized that sexual differences in skate teeth morphology are more pronounced in larger skate species. The results of this research will provide the opportunity to determine if sexual differences in skate teeth morphology are more prominent in the larger D. olseni. Future sampling may provide the opportunity to compare the time of year to changes in tooth morphology of R. texana allowing us to examine the role of the reproductive cycle in the onset of any changes in morphology that occur during mating season.
Age, growth, and reproductive biology of the smooth butterfly ray (Gymnura micrura)
The smooth butterfly ray is found in shallow coastal waters throughout the state of Florida. It appears to be a common resident in two of the University of Florida's targeted sampling localities on the Atlantic coast and in the Gulf of Mexico. Despite the relatively high abundance of this animal within shallow coastal waters of the southeastern United States little is known about its life history, movements, and migration. In year six of this program we will initiate a study of the age, growth, and reproductive biology of G. micrura. Vertebral and reproductive samples will be collected during sampling activities in the Mosquito Lagoon portion of the Indian River Lagoon system and the Cedar Key region of the Gulf of Mexico. Additional samples will be collected by researchers from the NMFS Panama City laboratory. These samples will be used to calculate growth curves, determine ages and sizes at maturity, and determine fecundity levels for G. micrura within these regions. The ability to collect samples from both the Atlantic and Gulf coasts will allow us to determine if there are differences in the age, or reproductive parameters of smooth butterfly rays found within each of these regions.
Age-structured simulation model for the dusky shark
The current Federal Fishery Management Plan for Atlantic sharks manages 39 species, which are separated into three management categories: large coastal (ridgeback and non-ridgeback), small coastal and pelagic sharks. In 1999, 14 of these species were moved to the prohibited species list, including the dusky shark. Commercial and recreational fishermen are no longer allowed to catch or land this species. Despite this change in management, dusky shark populations continue to remain low due to intrinsic biological characteristics and high hook mortality.
During year six, data will be added to two separate population models for the dusky shark. The first model is age structured and will be used to determine the status of this population now and in the future. Data for this model will include biological information, mortality rates, catches and catch rates. A base case scenario and several sensitivity analyses will be run using this model. The base case will incorporate catches and catch rates through 2006, current fishing and natural mortality, and known biological information while the sensitivity analysis will look at alternative scenarios such as no fishing mortality, area closures, reducing the number of discards and increasing fishing pressure.
The second model is a spatially stage structured model, which will be used to look at the effects of time/area closures on the population of the dusky shark. Movement rates, virgin recruitment, natural and fishing mortality and spatial cells are used in this model. A base case and several sensitivity analyses will be run using this model. The base case will include the current time/area closure, which exists off the coast of North Carolina, current mortality rates and estimates of this species movement rates and virgin recruitment. Sensitivity runs will look at both larger and smaller closures, different mortality rates, movement rates and virgin recruitment size. This project will be finished during this year of funding.
Taxonomy of the genus Centrophorus
In the face of dwindling shark numbers, shark taxonomy is becoming more important as scientists attempt to identify species in order to explain the subtle relationships and complex reactions of ecosystems threatened by human activities. The study of taxonomy provides a solid foundation for the research needed for the conservation of sharks and their habitat. Taxonomists recognize that the genus Centrophorus is in need of revision. Examination of the literature on Centrophorus reveals that much taxonomic uncertainty exists regarding this genus. Paucity of material and lack of data on developmental changes have resulted in wide differences of opinion about the validity of the species assigned to Centrophorus. Researchers differ in the choice of morphometric and meristic characters used as diagnostic features for the species. Coloration, placoid scales, and tooth configuration have all been used as diagnostic features of the genus in the past.
Morphometrics of the genus Centrophorus, from the Northwestern Atlantic have been analyzed in an effort to determine species validity. Initially, Discriminant Function Analysis (DFA) was performed using 65 morphological measurements of 59 museum specimens and 25 newly caught specimens from Jamaican waters. The key characters separating these 84 specimens are associated with snout length, pelvic fin inner margin length, length of the subterminal margin, and length of the caudal fin. The DFA supports the validity of Centrophorus acus, C. granulosus, C. uyato, and a C. sp. Recently, morphometrics of twelve specimens (provided by Jose Castro and Mote Marine Laboratory), also collected from the Northwestern Atlantic Ocean, were compared with results from the analysis of the initial 84 specimens. During year six a comparison of all 96 Centrophorus specimens, using the 12 most diagnostic measurements, will be completed. Future work involves collecting morphometrics from more Centrophorus specimens. This database will serve as a valuable tool for Centrophorus comparison and identification.
Habitat use and behavioral studies
Tagging and acoustic tracking of rays in the Indian River Lagoon
In cooperation with Dynamac, Inc. at the Kennedy Space Center, we are currently maintaining a passive acoustic monitoring system that includes 27 moored receiving stations (Vemco VR2 receivers) placed at key locations throughout the northern IRL. The system is currently set up for monitoring the movements of bluntnose stingrays (Dasyatis say), smooth butterfly rays (G. micrura), spotted eagle rays (Aetobatus narinari), cownose rays (Rhinoptera bonasus) (FPSR initiatives), adult red drum (Sciaenops ocellatus), and green sea turtles (Chelonia mydas) (Dynamac initiatives). This array of receivers is currently being used to track the movements of 20 bluntnose stingrays, 17 smooth butterfly rays, two spotted eagle rays and one cownose ray. We will continue this effort and will attach Vemco V13 or V9 coded transmitters to at least 20 more rays during the upcoming year. During year six we hope to concentrate our tagging efforts on pelagic species and attach at least 17 more transmitters to cownose or spotted eagle rays. Movements of ray species will be monitored by the passive system for up to 18 months. We currently have a grant pending to increase the number of animals transmittered to a total of 80 within the upcoming year and to expand our tagging efforts to include the other two Dasyatis species commonly found within the lagoon (D. sabina and D. americana). These data will help to identify both daily and seasonal movements of the tagged rays within the IRL, and enable us to isolate the timing of their migrations in and out of the system. In addition this study will allow us to compare the movements of pelagic (cownose rays and spotted eagle rays) and benthic species (bluntnose rays and smooth butterfly rays). Water quality measurements including temperature, salinity, and dissolved oxygen recorded at monitoring stations on a regular basis throughout the year will be used to determine if the rays' movements can be correlated to environmental cues.
Shark nursery delineation in the northeastern Gulf of Mexico
The Cedar Key area of the Gulf of Mexico consists of several small islands situated just offshore between the Suwannee River mouth to the northwest and the Waccassasa River mouth to the southeast. This area encompasses many diverse marine habitats including sea grass beds, mangroves, mud flats, oyster bars, tidal channels, and salt marshes. The incidental capture of numerous elasmobranch species within this area off the western Florida coast by scientists working for the University of Florida and the Florida Fish and Wildlife Conservation Commission indicates this region may support a diverse and abundant assemblage of sharks and rays. This recent work suggests that bull sharks, blacktip sharks, Atlantic sharpnose sharks, bonnethead sharks, smooth butterfly rays, cownose rays, southern stingrays, bluntnose stingrays, and Atlantic stingrays all commonly occur within this region. Little is known about the life history and ecology of many of these species, particularly the ray populations. In addition, neonate and juvenile bull sharks appear to be abundant in the Waccassasa River mouth and the southern portion of Waccassasa Bay indicating this area may function as a nursery ground for bull sharks and possibly other elasmobranch species. Nursery areas are thought to enhance survivorship of neonate and juvenile sharks due to the presence of increased resources and a lack of large predators. These areas tend to be closer to land and more vulnerable to pollution and environmental disturbances making the identification and conservation of nursery habitat critical to the health of shark populations.
In cooperation with NMFS South East Fishery Science Center we will continue a monitoring study in the Cedar Key area in the Gulf of Mexico this upcoming summer. Using standardized gillnetting gear, areas from the Waccassasa River mouth to the Suwannee River mouth will be sampled using stratified random sampling techniques. This will allow us to determine if this area functions as a nursery and Essential Fish Habitat for several elasmobranch species. The use of gear consistent with that used to study elasmobranch nursery areas in the western Gulf of Mexico and along the southern Gulf coast of Florida will allow us to compare the productivity of this area with nearby areas. To date this area of the Gulf of Mexico is largely unstudied and represents a significant gap in our knowledge of elasmobranch species within the Gulf of Mexico.
Maintenance and growth of the International Shark Attack File (ISAF) and public education about shark attack
The ISAF is a cooperative program administered by the American Elasmobranch Society and the Florida Museum of Natural History at the University of Florida. It is the international repository of scientific data on shark attacks, having served in that capacity since 1958. Approximately one hundred new cases are added each year and many older case files are modified by additions of new or altered data. The ISAF currently houses 4,227 cases. ISAF personnel coordinate the activities of a network of U.S. and international scientific cooperators who investigate attacks in their regions and forward their investigative data to the ISAF. ISAF support staff analyzes the data for short- and long-term trends, and recommends strategies to reduce the risk of attack to federal, state, and international governmental agencies. In addition, each year the ISAF staff respond to hundreds of inquiries from the media and general public about the subject, and take part in several shark education programs. Since shark attack, shark fishery management, and shark conservation have increasingly become interrelated topics, responses to these queries serve to further a broad understanding of shark-related issues in the public at large.
In year six we will continue to create a new ISAF database. This new database will have a web interface and will run through Microsoft Sequel Server. The new database will provide a standardized data entry format and be more user friendly than the current Microsoft Access database. In addition, we will be able to upload video, pictures, ISAF questionnaires, medical files and newspaper articles into the new database. Other projects for year six include rechecking all the case files, following up on open case files and continuing the documentation of all new shark attacks worldwide.
Web- and media-based public education focusing on shark biology, ecology, fishery management, and conservation
The shark section of the Florida Museum of Natural History's Ichthyology web site [http://www.flmnh.ufl.edu/fish/Sharks/sharks.htm] provides a rich source of information on sharks as well as other elasmobranchs and is the most highly utilized shark site on the World Wide Web. In addition to disseminating information on the Museum's own programs (FPSR and ISAF) and sharks in general, the site hosts the web pages of the American Elasmobranch Society and the IUCN/SSG (Shark Specialist Group), the world's foremost scientific society and conservation group, respectively, dedicated to elasmobranchs, and that of the Smalltooth Sawfish Recovery Team, a group working to restore this endangered species to former levels of abundance. The ISAF pages are the site's most highly utilized pages due to the public and media's almost insatiable interest in shark attacks. Viewers drawn to the site by fascination with shark attacks find complementary explanatory material dealing with shark biology and ecology, conservation, and fishery management. In addition, the site also includes informational pages focusing on sawfishes, spiny dogfishes, and white, whale, basking, and megamouth sharks; current shark news items; educational information and activities; organizational information; reference and resource lists; announcements for meetings and conferences on sharks; and links to other shark-related sites. The result is that interested viewers come away with a more balanced view of elasmobranchs and measures needed to insure their management and survival. We have found that providing a combination of web-based educational materials plus direct interplay with the media results in a very positive approach to educating the public about elasmobranch issues.
In year six, we will continue to add new information and features oriented to public education on sharks, sawfish, skates, and rays.
The shark attack statistics on the ISAF statistical pages will continue to be updated frequently due to the high degree of interest with new information added as it becomes available. Biological profiles of individual species of elasmobranchs represent one of the most important common threads between various sections of the web site, linking photographs in the Image Gallery, a major entry page of the site, to virtually all shark sections. These profiles provide summary information on the life history, distribution, ecology, behavior, and conservation/management status of each species. To date, we have a total of over 95 elasmobranch profiles available online to which we will continually add new species. The interactive educational component of the web site will continue to be updated and improved. In addition, an online exhibit consisting of a shark dissection and shark anatomy along with teaching materials will be developed and be available in the education section of the web site. We will continue to add detailed information regarding current research projects for each institutional member of the National Shark Research Consortium. Finally, ongoing maintenance activities will include every section of the shark web site including organizational information, news stories, image gallery, education, conferences and meetings, staff, outside links, and references.
Classroom-based elasmobranch education initiatives
Project Shark Awareness
Project Shark Awareness Student
Photo credit: Matthew Ratajczak
Scripps Treasure Coast Newspapers
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Project Shark Awareness is a classroom-based outreach program for educating school teachers and other educators about the myths and realities of shark behavior, biology, and conservation. This program consists of a series of workshops and training sessions augmented by a variety of teaching support materials. A teaching kit consisting of a PowerPoint presentation, teaching guide, handouts, methods to evaluate student learning (quiz, puzzles, question sheets). In addition, shark jaws, teeth, skin, and fossils in the teaching kits will provide hands-on learning opportunities. A companion web page within the FLMNH Ichthyology education web site is available online to accompany Project Shark Awareness materials.
During 2007, two separately funded Project Shark Awareness workshops for Florida secondary school educators were held at the FLMNH. In the new budget year, we hope to expand this outreach effort to include workshops for educators throughout the southeast United States due to the overwhelming response to the workshops held in previous years. This effort will be dependent upon external funding available through other granting agencies. This will further increase exposure of this program to educators and students throughout the southeast United States.
Sawfish In Peril
Sawfish in Peril is a new classroom-based education initiative which will be designed and implemented in a similar manner to Project Shark Awareness. Very little is known about sawfishes, which historically were very abundant in the tropics. Today, the U.S. distribution of the smalltooth sawfish (Pristis pectinata) is primarily restricted to the waters off the coast of southwest Florida. Although it is difficult to estimate the exact numbers of sawfish remaining in U.S. waters, it is likely that the population has declined at least 95% over the past century. As a result, the smalltooth sawfish has recently been listed for protection under the U.S. Endangered Species Act. The largetooth sawfish (Pristis perotteti), once found in low numbers in waters ranging from Texas to Florida, likely has been extirpated from U.S. waters. Sawfish In Peril will result in a better informed public concerning the plight and protection of sawfishes native to U.S. coastal waters, as well as the fate of sawfishes in general, which as a group are globally threatened. Workshops will be held for Florida educators dependent upon external funding availability which is currently being pursued.
In addition to the above program, we are currently distributing brochures on smalltooth sawfish detailing the conservation status as well as how to handle and release an accidentally captured sawfish. During year six, we will continue to distribute these brochures through marinas and tackle shops along the southwest coast of Florida as well as through educators in schools throughout the state. Also, sawfish signage is continuing to be posted in cooperation with the Florida Fish and Wildlife Conservation Commission at appropriate marinas and boat launches in southwest Florida.
Page updated May 2007
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