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Charles A. Manire - One of the best experts on this subject based on the ideXlab platform.
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organochlorine concentrations in Bonnethead sharks sphyrna tiburo from four florida estuaries
Archives of Environmental Contamination and Toxicology, 2005Co-Authors: James Gelsleichter, Charles A. Manire, John K Carlson, Enric Cortes, Nancy J Szabo, L LombardicarlsonAbstract:Because of their persistence in aquatic environments and ability to impair reproduction and other critical physiological processes, organochlorine (OC) contaminants pose significant health risks to marine organisms. Despite such concerns, few studies have investigated levels of OC exposure in sharks, which are fish particularly threatened by anthropogenic pollution because of their tendency to bioaccumulate and biomagnify environmental contaminants. The present study examined concentrations of 29 OC pesticides and total polychlorinated biphenyls (PCBs) in the Bonnethead shark (Sphyrna tiburo), an abundant species for which evidence of reproductive impairment has been observed in certain Florida populations. Quantifiable levels of PCBs and 22 OC pesticides were detected via gas chromatography and mass spectrometry in liver of 95 S. tiburo from four estuaries on Florida’s Gulf coast: Apalachicola Bay, Tampa Bay, Florida Bay, and Charlotte Harbor. In general, OC concentrations were significantly higher in Apalachicola Bay, Tampa Bay, and Charlotte Harbor S. tiburo in relation to the Florida Bay population. Because the rate of infertility has been shown to be dramatically higher in Tampa Bay versus Florida Bay S. tiburo, the present findings allude to a possible relationship between OC exposure and reproductive health that requires further investigation. Pesticide and PCB concentrations did not appear to significantly increase with growth or age in S. tiburo, suggesting limited potential for OC bioaccumulation in this species compared with other sharks for which contaminant data are available. Concentrations of OCs in serum and muscle were not correlated with those in liver, indicating that these tissues are poor surrogates for measuring internal OC burden in this species via nonlethal sampling procedures.
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predominance of genetic monogamy by females in a hammerhead shark sphyrna tiburo implications for shark conservation
Molecular Ecology, 2004Co-Authors: Demian D Chapman, Paulo A Prodohl, James Gelsleichter, Charles A. ManireAbstract:There is growing interest in the mating systems of sharks and their relatives (Class Chondrichthyes) because these ancient fishes occupy a key position in vertebrate phylogeny and are increasingly in need of conservation due to widespread overexploitation. Based on precious few genetic and field observational studies, current speculation is that polyandrous mating strategies and multiple paternity may be common in sharks as they are in most other vertebrates. Here, we test this hypothesis by examining the genetic mating system of the Bonnethead shark, Sphyrna tiburo, using microsatellite DNA profiling of 22 litters (22 mothers, 188 embryos genotyped at four polymorphic loci) obtained from multiple locations along the west coast of Florida. Contrary to expectations based on the ability of female S. tiburo to store sperm, the social nature of this species and the 100% multiple paternity observed in two other coastal shark species, over 81% of sampled Bonnethead females produced litters sired by a single male (i.e. genetic monogamy). When multiple paternity occurred in S. tiburo, there was an indication of increased incidence in larger mothers with bigger litters. Our data suggest that sharks may exhibit complex genetic mating systems with a high degree of interspecific variability, and as a result some species may be more susceptible to loss of genetic variation in the face of escalating fishing pressure. Based on these findings, we suggest that knowledge of elasmobranch mating systems should be an important component of conservation and management programmes for these heavily exploited species.
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maternal serum and yolk hormone concentrations in the placental viviparous Bonnethead shark sphyrna tiburo
General and Comparative Endocrinology, 2004Co-Authors: Charles A. Manire, James Gelsleichter, Lois E L Rasmussen, David L HessAbstract:Abstract Among vertebrates, maternal transfer of hormones to offspring has been studied extensively in mammals (placental transfer) and more recently in oviparous birds and reptiles (yolk transfer). The placental viviparous Bonnethead shark, Sphyrna tiburo, allows the investigation of both yolk and placental hormone transfers in a single organism. In this species, yolk provides nutrition for the first half of embryonic development and placental transfer provides the second half. As sex determination is complete prior to development of placental connections, it was postulated that yolk hormones would have a prominent role in embryonic regulation. The goal of the current study was to determine serum and yolk hormone concentrations during five reproductive stages, from pre-ovulatory through pre-implantation (pre-placental) stages. Radioimmunoassay was used to determine 17β-estradiol, progesterone, and testosterone concentrations in both serum and yolk. When yolk and serum concentrations were compared, the yolk had significantly higher concentrations of both estradiol and progesterone during post-ovulation and early pregnancy. Yolk concentrations of testosterone were significantly less than serum at pre-ovulation, but there were no differences after that stage. When yolk concentrations were compared between stages, significantly higher concentrations of estradiol were present in ovulatory, post-ovulatory, and pre-implantation stages, while progesterone was significantly higher in post-ovulatory, early pregnancy, and pre-implantation stages and testosterone was higher in pre-ovulation. Most of these results are consistent with the published findings in birds and reptiles. Further, in the Bonnethead shark, they suggest that yolk transfer of hormones is adequate for sexual differentiation in embryonic development and that estradiol probably has a significant developmental role.
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latitudinal variation in life history traits of Bonnethead sharks sphyrna tiburo carcharhiniformes sphyrnidae from the eastern gulf of mexico
Marine and Freshwater Research, 2003Co-Authors: Linda A Lombardicarlson, Enric Cortes, Glenn R Parsons, Charles A. ManireAbstract:Life-history traits (size at age, growth rates, size and age at maturity, size of near-term embryos and litter sizes) of Bonnetheads, Sphyrna tiburo, were analysed to test for latitudinal differences by comparing data collected from three areas along Florida's Gulf of Mexico coastline between March 1998 and September 2000. A total of 539 sharks were collected during the study: 207 in north-west Florida (latitude ~30°N), 176 in Tampa Bay (~28°N) and 156 in Florida Bay (~25°N). Male and female Bonnetheads in north-west Florida had the largest predicted asymptotic sizes (1007 mm and 1398 mm TL, respectively) and attained the largest estimated median size at maturity (830 mm and 944 mm, respectively) and the oldest estimated median age at maturity (3.0+ years and 4.0+ years, respectively). The largest near-term embryos (297 mm TL) were also collected at the highest latitude, but no latitudinal difference in litter size was found. These differences in life-history traits provide supporting evidence that a pattern of latitudinal variation exists. Male and female Bonnetheads in north-west Florida also had the fastest growth rate compared with the other locations, supporting the hypothesis that growth rate is inversely related to the length of the growing season (i.e. a pattern of countergradient variation exists).
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serum relaxin concentrations and reproduction in male Bonnethead sharks sphyrna tiburo
General and Comparative Endocrinology, 2003Co-Authors: James Gelsleichter, Charles A. Manire, B G Steinetz, Cristal AngeAbstract:Relaxin is a 6-kd polypeptide hormone that is responsible for regulating several reproductive processes in female vertebrates, but its role in male reproduction remains unclear. To aid in clarifying this role, the objective of the present study was to investigate changes in endogenous relaxin levels associated with reproductive events in male elasmobranchs, which represent one of only three vertebrate groups known to possess this hormone. Serum relaxin concentrations were measured in 27 immature and 66 mature male Bonnethead sharks (Sphyrna tiburo), a species with a well-characterized, seasonal reproductive cycle. Temporal changes in serum relaxin concentrations of immature male S. tiburo were not observed. In contrast, a temporal cycle in serum relaxin concentrations of mature male S. tiburo was observed in individuals from two sampling locations. Significant increases (P<0.05) in serum relaxin concentrations of mature male S. tiburo from both collection sites occurred during late spermatogenesis and the mating period, two critical stages of the reproductive cycle. The results from this study suggest that relaxin may play an important role in regulating semen quality, or other aspects of reproduction in male sharks. This is the first study to demonstrate a temporal pattern in endogenous serum Rlx concentrations associated with reproductive events in feral vertebrates. As such, it strengthens earlier hypotheses that suggested a role for this hormone in regulating male vertebrate fertility and copulatory success.
James Gelsleichter - One of the best experts on this subject based on the ideXlab platform.
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Molecular identification and functional characteristics of peptide transporters in the Bonnethead shark (Sphyrna tiburo)
Journal of Comparative Physiology B, 2016Co-Authors: Hannah R. Hart, James Gelsleichter, Andrew N Evans, Gregory A. AhearnAbstract:Elasmobranchs are considered to be top marine predators, and in general play important roles in the transfer of energy within marine ecosystems. Despite this, little is known regarding the physiological processes of digestion and nutrient absorption in these fishes. One topic that is particularly understudied is the process of nutrient uptake across the elasmobranch gastrointestinal tract. Given their carnivorous diet, the present study sought to expand knowledge on dietary nutrient uptake in elasmobranchs by focusing on the uptake of products of protein digestion. To accomplish this, a full-length cDNA encoding peptide transporter 1 (PepT1), a protein previously identified within the brush border membrane of vertebrates that is responsible for the translocation of peptides released during digestion by luminal and membrane-bound proteases, was isolated from the Bonnethead shark ( Sphyrna tiburo ). A cDNA encoding the related peptide transporter PepT2 was also isolated from S. tiburo using the same methodology. The presence of PepT1 was then localized in multiple components of the Bonnethead digestive tract (esophagus, stomach, duodenum, intestine, rectum, and pancreas) using immunohistochemistry. Vesicle studies were used to identify the apparent affinity of PepT1 and to quantify the rate of dipeptide uptake by its H^+-dependent cotransporter properties. The results of this study provide insight into the properties of peptide uptake within the Bonnethead gut, and can facilitate future work on physiological regulation of protein metabolism and absorption including how these processes may vary in elasmobranchs that exhibit different feeding strategies.
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population structure and cryptic speciation in Bonnethead sharks sphyrna tiburo in the south eastern u s a and caribbean
Journal of Fish Biology, 2016Co-Authors: Andrew T Fields, C. Pfoertner, Kevin A Feldheim, James Gelsleichter, Demian D ChapmanAbstract:Population structure and lineage diversification within a small, non-dispersive hammerhead shark species, the Bonnethead shark Sphyrna tiburo, was assessed. Sphyrna tiburo is currently described as one continuously distributed species along the Atlantic continental margins of North, Central and South America, but recent genetic analysis of an insular population (Trinidad) suggests the possibility of cryptic speciation. To address this issue S. tiburo were sampled at six sites along c. 6200 km of continuous, continental coastline and from one island location (Grand Bahama) across a discontinuity in their distribution (the Straits of Florida), in order to test if they constitute a single lineage over this distribution. A total of 1030 bp of the mitochondrial control region (CR) was obtained for 239 S. tiburo, revealing 73 distinct haplotypes, high nucleotide diversity (0·01089) and a pair of highly divergent lineages estimated to have separated 3·61–5·62 million years ago. Mitochondrial cytochrome oxidase I and nuclear internal transcribed spacer loci show the same pattern. Divergence is similar within S. tiburo to that observed between established elasmobranch sister species, providing further evidence of cryptic speciation. A global AMOVA based on CR confirms that genetic diversity is primarily partitioned among populations (ΦST = 0·828, P < 0·001) because the divergent lineages are almost perfectly segregated between Belize and North America–The Bahamas. An AMOVA consisting solely of the North American and Bahamian samples is also significantly different from zero (ΦST = 0·088, P < 0·001) and pairwise FST is significantly different between all sites. These findings suggest that S. tiburo comprises a species complex and supports previous research indicating fine population structure, which has implications for fisheries management and biodiversity conservation.
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androgen receptors in the Bonnethead sphyrna tiburo cdna cloning and tissue specific expression in the male reproductive tract
General and Comparative Endocrinology, 2015Co-Authors: John P. Tyminski, James Gelsleichter, Philip J. MottaAbstract:As demonstrated in past studies, androgens appear to play critical roles in regulating reproduction in male sharks. However, little is known about the cell-specific actions of androgens in these fishes. To address this, this study examined androgen targets in reproductive organs of a seasonally reproducing shark, the Bonnethead (Sphyrna tiburo). A partial Bonnethead AR cDNA clone was isolated and found to exhibit strong homology with known vertebrate ARs. Using RT-PCR and in situ hybridization, AR was found to be expressed in multiple cell types in the male Bonnethead testis (premeiotic germ cells, Leydig-like interstitial cells, Sertoli cells, peritubular myoid cells, and mature spermatozoa) and gonadal ducts (stromal cells, luminal epithelial cells, mature spermatozoa). Furthermore, AR expression in these organs was found to vary temporally in relation to the seasonal reproductive cycle. Based on immunocytochemistry, the presence of AR protein in male Bonnethead reproductive organs was largely consistent with patterns of AR gene expression with the single exception of mature spermatozoa, which exhibited consistently strong mRNA expression but only inconsistent and weak AR protein immunoreactivity. These results suggest important roles for androgens in regulating germ cell proliferation, hormone production, spermatid elongation, spermiation, and gonadal duct function in male Bonnetheads. In addition, high abundance of AR mRNA in Bonnethead spermatozoa suggest the potential for de novo protein synthesis following spermiation/copulation and/or a role for AR mRNA in early embryonic development, both of which have been proposed to explain the occurrence of mRNA transcripts in spermatozoa from various vertebrates.
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organochlorine concentrations in Bonnethead sharks sphyrna tiburo from four florida estuaries
Archives of Environmental Contamination and Toxicology, 2005Co-Authors: James Gelsleichter, Charles A. Manire, John K Carlson, Enric Cortes, Nancy J Szabo, L LombardicarlsonAbstract:Because of their persistence in aquatic environments and ability to impair reproduction and other critical physiological processes, organochlorine (OC) contaminants pose significant health risks to marine organisms. Despite such concerns, few studies have investigated levels of OC exposure in sharks, which are fish particularly threatened by anthropogenic pollution because of their tendency to bioaccumulate and biomagnify environmental contaminants. The present study examined concentrations of 29 OC pesticides and total polychlorinated biphenyls (PCBs) in the Bonnethead shark (Sphyrna tiburo), an abundant species for which evidence of reproductive impairment has been observed in certain Florida populations. Quantifiable levels of PCBs and 22 OC pesticides were detected via gas chromatography and mass spectrometry in liver of 95 S. tiburo from four estuaries on Florida’s Gulf coast: Apalachicola Bay, Tampa Bay, Florida Bay, and Charlotte Harbor. In general, OC concentrations were significantly higher in Apalachicola Bay, Tampa Bay, and Charlotte Harbor S. tiburo in relation to the Florida Bay population. Because the rate of infertility has been shown to be dramatically higher in Tampa Bay versus Florida Bay S. tiburo, the present findings allude to a possible relationship between OC exposure and reproductive health that requires further investigation. Pesticide and PCB concentrations did not appear to significantly increase with growth or age in S. tiburo, suggesting limited potential for OC bioaccumulation in this species compared with other sharks for which contaminant data are available. Concentrations of OCs in serum and muscle were not correlated with those in liver, indicating that these tissues are poor surrogates for measuring internal OC burden in this species via nonlethal sampling procedures.
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predominance of genetic monogamy by females in a hammerhead shark sphyrna tiburo implications for shark conservation
Molecular Ecology, 2004Co-Authors: Demian D Chapman, Paulo A Prodohl, James Gelsleichter, Charles A. ManireAbstract:There is growing interest in the mating systems of sharks and their relatives (Class Chondrichthyes) because these ancient fishes occupy a key position in vertebrate phylogeny and are increasingly in need of conservation due to widespread overexploitation. Based on precious few genetic and field observational studies, current speculation is that polyandrous mating strategies and multiple paternity may be common in sharks as they are in most other vertebrates. Here, we test this hypothesis by examining the genetic mating system of the Bonnethead shark, Sphyrna tiburo, using microsatellite DNA profiling of 22 litters (22 mothers, 188 embryos genotyped at four polymorphic loci) obtained from multiple locations along the west coast of Florida. Contrary to expectations based on the ability of female S. tiburo to store sperm, the social nature of this species and the 100% multiple paternity observed in two other coastal shark species, over 81% of sampled Bonnethead females produced litters sired by a single male (i.e. genetic monogamy). When multiple paternity occurred in S. tiburo, there was an indication of increased incidence in larger mothers with bigger litters. Our data suggest that sharks may exhibit complex genetic mating systems with a high degree of interspecific variability, and as a result some species may be more susceptible to loss of genetic variation in the face of escalating fishing pressure. Based on these findings, we suggest that knowledge of elasmobranch mating systems should be an important component of conservation and management programmes for these heavily exploited species.
Timothy S Gross - One of the best experts on this subject based on the ideXlab platform.
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serum steroid hormones including 11 ketotestosterone 11 ketoandrostenedione and dihydroprogesterone in juvenile and adult Bonnethead sharks sphyrna tiburo
Journal of Experimental Zoology, 1999Co-Authors: Charles A. Manire, Timothy S Gross, L E L RasmussenAbstract:Previous studies in the placental viviparous Bonnethead shark, Sphyrna tiburo, have correlated 17 β-estradiol, progesterone, testosterone, and dihydrotestosterone with reproductive events in both males and females. However, several key reproductive events, including implantation, maintenance of pregnancy, and parturition, did not correlate with these four steroid hormones. Therefore, the present study investigated three steroid hormones, 11-ketotestosterone, 11-ketoandrostenedione, and dihydroprogesterone, which have demonstrably important roles in the reproductive cycles of teleosts. It was hypothesized that one or more of these three hormones would correlate with specific reproductive events in S. tiburo. Concurrently, developmental (growth and/or maturation) analyses of these three steroids plus 17 β-estradiol, progesterone, testosterone, and dihydrotestosterone were investigated in juvenile Bonnethead sharks. Serum dihydroprogesterone concentrations were highest in mature females and 11-ketotestosterone concentrations were highest in mature males. In mature females, 11-ketoandrostenedione levels were elevated from the time of mating, through six months of sperm storage and another four months of gestation. At parturition concentrations became significantly lower and remained lower until mating occurred again in another two to three months. Serum 11-ketotestosterone concentrations were the highest at implantation though not significant. In mature males, significantly elevated serum levels of dihydroprogesterone occurred in April and May, near the start of annual testicular development. During growth in males, testosterone and dihydrotestosterone increased progressively and in females, testosterone increased progressively. At maturity in males, significant increases occurred in testosterone and 11-ketotestosterone concentrations while, in females, dihydroprogesterone, 11-ketotestosterone, 17 β-estradiol, progesterone, testosterone, and dihydrotestosterone concentrations increased. This study shows that although testosterone may be the primary androgen in the Bonnethead shark, other derived androgens may have important functions in growth, maturation, and reproduction. J. Exp. Zool. 284:595–603, 1999. © 1999 Wiley-Liss, Inc.
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serum steroid hormones including 11 ketotestosterone 11 ketoandrostenedione and dihydroprogesterone in juvenile and adult Bonnethead sharks sphyrna tiburo
Journal of Experimental Zoology, 1999Co-Authors: Charles A. Manire, Timothy S Gross, L E L RasmussenAbstract:Previous studies in the placental viviparous Bonnethead shark, Sphyrna tiburo, have correlated 17 β-estradiol, progesterone, testosterone, and dihydrotestosterone with reproductive events in both males and females. However, several key reproductive events, including implantation, maintenance of pregnancy, and parturition, did not correlate with these four steroid hormones. Therefore, the present study investigated three steroid hormones, 11-ketotestosterone, 11-ketoandrostenedione, and dihydroprogesterone, which have demonstrably important roles in the reproductive cycles of teleosts. It was hypothesized that one or more of these three hormones would correlate with specific reproductive events in S. tiburo. Concurrently, developmental (growth and/or maturation) analyses of these three steroids plus 17 β-estradiol, progesterone, testosterone, and dihydrotestosterone were investigated in juvenile Bonnethead sharks. Serum dihydroprogesterone concentrations were highest in mature females and 11-ketotestosterone concentrations were highest in mature males. In mature females, 11-ketoandrostenedione levels were elevated from the time of mating, through six months of sperm storage and another four months of gestation. At parturition concentrations became significantly lower and remained lower until mating occurred again in another two to three months. Serum 11-ketotestosterone concentrations were the highest at implantation though not significant. In mature males, significantly elevated serum levels of dihydroprogesterone occurred in April and May, near the start of annual testicular development. During growth in males, testosterone and dihydrotestosterone increased progressively and in females, testosterone increased progressively. At maturity in males, significant increases occurred in testosterone and 11-ketotestosterone concentrations while, in females, dihydroprogesterone, 11-ketotestosterone, 17 β-estradiol, progesterone, testosterone, and dihydrotestosterone concentrations increased. This study shows that although testosterone may be the primary androgen in the Bonnethead shark, other derived androgens may have important functions in growth, maturation, and reproduction. J. Exp. Zool. 284:595–603, 1999. © 1999 Wiley-Liss, Inc.
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serum steroid hormones including 11 ketotestosterone 11 ketoandrostenedione and dihydroprogesterone in juvenile and adult Bonnethead sharks sphyrna tiburo
Journal of Experimental Zoology, 1999Co-Authors: Charles A. Manire, Timothy S Gross, L E L RasmussenAbstract:Previous studies in the placental viviparous Bonnethead shark, Sphyrna tiburo, have correlated 17 beta-estradiol, progesterone, testosterone, and dihydrotestosterone with reproductive events in both males and females. However, several key reproductive events, including implantation, maintenance of pregnancy, and parturition, did not correlate with these four steroid hormones. Therefore, the present study investigated three steroid hormones, 11-ketotestosterone, 11-ketoandrostenedione, and dihydroprogesterone, which have demonstrably important roles in the reproductive cycles of teleosts. It was hypothesized that one or more of these three hormones would correlate with specific reproductive events in S. tiburo. Concurrently, developmental (growth and/or maturation) analyses of these three steroids plus 17 beta-estradiol, progesterone, testosterone, and dihydrotestosterone were investigated in juvenile Bonnethead sharks. Serum dihydroprogesterone concentrations were highest in mature females and 11-ketotestosterone concentrations were highest in mature males. In mature females, 11-ketoandrostenedione levels were elevated from the time of mating, through six months of sperm storage and another four months of gestation. At parturition concentrations became significantly lower and remained lower until mating occurred again in another two to three months. Serum 11-ketotestosterone concentrations were the highest at implantation though not significant. In mature males, significantly elevated serum levels of dihydroprogesterone occurred in April and May, near the start of annual testicular development. During growth in males, testosterone and dihydrotestosterone increased progressively and in females, testosterone increased progressively. At maturity in males, significant increases occurred in testosterone and 11-ketotestosterone concentrations while, in females, dihydroprogesterone, 11-ketotestosterone, 17 beta-estradiol, progesterone, testosterone, and dihydrotestosterone concentrations increased. This study shows that although testosterone may be the primary androgen in the Bonnethead shark, other derived androgens may have important functions in growth, maturation, and reproduction. J. Exp. Zool. 284:595-603, 1999.
Enric Cortes - One of the best experts on this subject based on the ideXlab platform.
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organochlorine concentrations in Bonnethead sharks sphyrna tiburo from four florida estuaries
Archives of Environmental Contamination and Toxicology, 2005Co-Authors: James Gelsleichter, Charles A. Manire, John K Carlson, Enric Cortes, Nancy J Szabo, L LombardicarlsonAbstract:Because of their persistence in aquatic environments and ability to impair reproduction and other critical physiological processes, organochlorine (OC) contaminants pose significant health risks to marine organisms. Despite such concerns, few studies have investigated levels of OC exposure in sharks, which are fish particularly threatened by anthropogenic pollution because of their tendency to bioaccumulate and biomagnify environmental contaminants. The present study examined concentrations of 29 OC pesticides and total polychlorinated biphenyls (PCBs) in the Bonnethead shark (Sphyrna tiburo), an abundant species for which evidence of reproductive impairment has been observed in certain Florida populations. Quantifiable levels of PCBs and 22 OC pesticides were detected via gas chromatography and mass spectrometry in liver of 95 S. tiburo from four estuaries on Florida’s Gulf coast: Apalachicola Bay, Tampa Bay, Florida Bay, and Charlotte Harbor. In general, OC concentrations were significantly higher in Apalachicola Bay, Tampa Bay, and Charlotte Harbor S. tiburo in relation to the Florida Bay population. Because the rate of infertility has been shown to be dramatically higher in Tampa Bay versus Florida Bay S. tiburo, the present findings allude to a possible relationship between OC exposure and reproductive health that requires further investigation. Pesticide and PCB concentrations did not appear to significantly increase with growth or age in S. tiburo, suggesting limited potential for OC bioaccumulation in this species compared with other sharks for which contaminant data are available. Concentrations of OCs in serum and muscle were not correlated with those in liver, indicating that these tissues are poor surrogates for measuring internal OC burden in this species via nonlethal sampling procedures.
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latitudinal variation in life history traits of Bonnethead sharks sphyrna tiburo carcharhiniformes sphyrnidae from the eastern gulf of mexico
Marine and Freshwater Research, 2003Co-Authors: Linda A Lombardicarlson, Enric Cortes, Glenn R Parsons, Charles A. ManireAbstract:Life-history traits (size at age, growth rates, size and age at maturity, size of near-term embryos and litter sizes) of Bonnetheads, Sphyrna tiburo, were analysed to test for latitudinal differences by comparing data collected from three areas along Florida's Gulf of Mexico coastline between March 1998 and September 2000. A total of 539 sharks were collected during the study: 207 in north-west Florida (latitude ~30°N), 176 in Tampa Bay (~28°N) and 156 in Florida Bay (~25°N). Male and female Bonnetheads in north-west Florida had the largest predicted asymptotic sizes (1007 mm and 1398 mm TL, respectively) and attained the largest estimated median size at maturity (830 mm and 944 mm, respectively) and the oldest estimated median age at maturity (3.0+ years and 4.0+ years, respectively). The largest near-term embryos (297 mm TL) were also collected at the highest latitude, but no latitudinal difference in litter size was found. These differences in life-history traits provide supporting evidence that a pattern of latitudinal variation exists. Male and female Bonnetheads in north-west Florida also had the fastest growth rate compared with the other locations, supporting the hypothesis that growth rate is inversely related to the length of the growing season (i.e. a pattern of countergradient variation exists).
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gillnet selectivity of small coastal sharks off the southeastern united states
Fisheries Research, 2003Co-Authors: John K Carlson, Enric CortesAbstract:Abstract Gillnet selectivity parameters for the Atlantic sharpnose, Rhizoprionodon terraenovae , blacknose, Carcharhinus acronotus , finetooth, Carcharhinus isodon , and Bonnethead, Sphyrna tiburo , sharks were estimated from fishery-independent catches in multi-panel gillnets with stretched mesh sizes ranging from 8.9 to 14.0 cm in steps of 1.3 cm, with an additional size of 20.3 cm. Mesh selectivities were estimated using a maximum-likelihood model, which fits a gamma distribution to length data for each mesh size using the log-likelihood function. The Atlantic sharpnose and finetooth shark exhibited the broadest selection curves. Peak selectivities for the Atlantic sharpnose were reached from 750 mm FL for the 8.9 cm mesh to 1150 mm FL for the 14.0 cm mesh in 50 mm FL increments per mesh. Peak selectivity for the finetooth shark was reached at 550 mm FL for the 8.9 and 10.2 cm meshes, increased to 650 mm FL for the 11.4 mesh, and 750 mm FL for the 12.7 and 14.0 cm meshes. Selectivity was highest at 1150 mm FL for the 20.3 cm mesh. The Bonnethead and blacknose shark exhibited narrower selection curves, with peak selectivity occurring at 450 mm FL for the 8.9 cm mesh, 750 mm for the 12.7 cm mesh in 100 mm FL increments per mesh. Maximum selectivity for the 20.3 cm mesh was 950 and 1050 mm FL for Bonnethead and blacknose shark, respectively. The θ 1 values for blacknose and finetooth shark were most similar (140.58 and 141.25), whereas the value calculated for Atlantic sharpnose was the highest (211.95) and that for the Bonnethead (131.77) was the lowest. Values calculated for θ 2 , a parameter that describes the variance of sizes by mesh, ranged from 27,259 for the Bonnethead to 189,873 for the finetooth shark. Although gillnets used in this study were not directly constructed for use in estimation of gillnet selectivities, information on mesh selectivities estimated herein has direct applicability to commercial gillnets with meshes of similar sizes.
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Stock Assessment of Small Coastal Sharks in the U.S. Atlantic and Gulf of Mexico
2002Co-Authors: Enric Cortes, Sustainable Fisheries, Division Contribution Sfd, National Marine, Fisheries ServiceAbstract:Several species of small coastal sharks are caught in directed fisheries and as bycatch in waters off the eastern coast of the U.S.A. This management group presently includes the Atlantic sharpnose (Rhizoprionodon terraenovae), Bonnethead (Sphyrna tiburo), blacknose (Carcharhinus acronotus), and finetooth (Carcharhinus isodon) sharks. A stock assessment of the small coastal shark complex was conducted over a decade ago and the ensuing management plan classified this group as being fully utilized. A substantial amount of information has become available since then, including biological data, improved fisheries statistics, and bycatch estimates from the shrimp trawl fishery. A number of fishery-independent and fishery-dependent catch rate series have also become available or their duration been extended. In all, there is now sufficient information to conduct stock assessments of the small coastal shark complex and the individual species. The objective of the current study is thus to assess the status of small coastal shark stocks in the southeastern U.S. region. Commercial and recreational landings represent only a small fraction of all catches, because small coastal sharks are also caught as bycatch and discarded in a variety of fisheries, in particular the shrimp trawl fishery. Commercial landings in numbers exceed recreational harves
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demographic analysis as an aid in shark stock assessment and management
Fisheries Research, 1998Co-Authors: Enric CortesAbstract:Abstract The use of demographic analyses incorporating life history information on validated age and growth, reproduction, and natural mortality is proposed to gain insight into the population dynamics of sharks under a variety of scenarios and to assess their vulnerability to varying exploitation rates. This approach provides a useful framework for comparison with other currently used methods of assessment, especially those that rely only on fishery-dependent data, and thus can be helpful to stock assessments and to the rational exploitation and management of shark stocks. A review of demographic analyses of large coastal sharks on the east coast of the US indicates that the lemon and sandbar sharks have very low rates of population increase ( r −1 ) and are thus extremely vulnerable to exploitation. In contrast, one of the small coastal group species of lesser importance to the fisheries, the Bonnethead shark, has some of the highest r values yet calculated for any shark. Preliminary demographic analyses using nonvalidated age estimates indicate that two other common and economically valuable large coastal species, the blacktip and dusky sharks, may also exhibit relatively slow rates of population change and be very vulnerable to overexploitation. Improved assessment of shark stocks requires increased collection of biological and fishery data, and a much better understanding of their population dynamics, especially stock–recruitment relationships.
John P. Tyminski - One of the best experts on this subject based on the ideXlab platform.
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androgen receptors in the Bonnethead sphyrna tiburo cdna cloning and tissue specific expression in the male reproductive tract
General and Comparative Endocrinology, 2015Co-Authors: John P. Tyminski, James Gelsleichter, Philip J. MottaAbstract:As demonstrated in past studies, androgens appear to play critical roles in regulating reproduction in male sharks. However, little is known about the cell-specific actions of androgens in these fishes. To address this, this study examined androgen targets in reproductive organs of a seasonally reproducing shark, the Bonnethead (Sphyrna tiburo). A partial Bonnethead AR cDNA clone was isolated and found to exhibit strong homology with known vertebrate ARs. Using RT-PCR and in situ hybridization, AR was found to be expressed in multiple cell types in the male Bonnethead testis (premeiotic germ cells, Leydig-like interstitial cells, Sertoli cells, peritubular myoid cells, and mature spermatozoa) and gonadal ducts (stromal cells, luminal epithelial cells, mature spermatozoa). Furthermore, AR expression in these organs was found to vary temporally in relation to the seasonal reproductive cycle. Based on immunocytochemistry, the presence of AR protein in male Bonnethead reproductive organs was largely consistent with patterns of AR gene expression with the single exception of mature spermatozoa, which exhibited consistently strong mRNA expression but only inconsistent and weak AR protein immunoreactivity. These results suggest important roles for androgens in regulating germ cell proliferation, hormone production, spermatid elongation, spermiation, and gonadal duct function in male Bonnetheads. In addition, high abundance of AR mRNA in Bonnethead spermatozoa suggest the potential for de novo protein synthesis following spermiation/copulation and/or a role for AR mRNA in early embryonic development, both of which have been proposed to explain the occurrence of mRNA transcripts in spermatozoa from various vertebrates.
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Androgen Receptors in the Bonnethead Shark, Sphyrna tiburo: cDNA Cloning and Tissue-Specific Expression in the Male Reproductive Tract
2007Co-Authors: John P. TyminskiAbstract:Androgen receptors in the Bonnethead shark, Sphyrna tiburo: CDNA cloning and tissue-specific expression in the male reproductive trac
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Residency and movement patterns of Bonnethead sharks, Sphyrna tiburo, in a large Florida estuary
Environmental Biology of Fishes, 2006Co-Authors: Michelle R Heupel, Angela B. Collins, Colin A Simpfendorfer, John P. TyminskiAbstract:The use of a coastal estuary by Bonnethead sharks, Sphyrna tiburo, was examined by acoustic monitoring, gillnet sampling and tag-recapture studies. Acoustic monitoring data were used to define the residency and movement patterns of sharks within Pine Island Sound, Charlotte Harbor, Florida. Sharks were monitored for periods of 1-173 days with individuals regularly moving in and out of the detection range of the acoustic system. Patterns of movement could not be correlated with tidal level or time of day. Home range sizes within the Pine Island Sound population were typically small with individuals using core areas on a daily basis. However, core areas shifted within the study site over time resulting in eventual usage of most of the available habitat. Gillnet sampling revealed that S. tiburo were abundant in shallow water near seagrass beds, but that presence of individuals at specific sites was variable. Tag-recapture data showed that most individuals remained within the Pine Island Sound region over time and did not appear to undergo long coastal migrations. The movement and residence patterns of S. tiburo suggest that individuals are resident within the estuary, but do not show site fidelity to specific areas within the estuary.
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serum steroid concentrations and development of reproductive organs during puberty in male Bonnethead sharks sphyrna tiburo
Fish Physiology and Biochemistry, 2002Co-Authors: James Gelsleichter, John P. Tyminski, L E L Rasmussen, Charles A. Manire, B Chang, L LombardicarlsonAbstract:Puberty is a critical, hormone-mediated event during which an animal acquires the ability to breed and propagate. Despite the importance of this stage in animal reproduction, little is known regarding the physiological factors that regulate and/or accompany puberty in several vertebrate groups including elasmobranchs. To address the need for such information, the present study investigated morphological and hormonal changes that occur during puberty in male Bonnethead sharks (Sphyrna tiburo). Serial changes in development of claspers, paired copulatory organs in male elasmobranchs, and serum steroid concentrations during puberty were evaluated in captive-held male S. tiburo. Captive-animal studies were supplemented by observations on gonadal development, gonaduct morphology, and serum steroid concentrations in feral, peripubertal male S. tiburo. Changes in size and histological architecture of testes and gonaducts of peripubertal sharks mirrored the seasonal progression of events that occur in these structures in mature males. Claspers grew in length continuously during puberty, but sharks did not reach functional maturity until a short period before mating activity commences in the mature population. Clasper growth appeared to be strictly regulated in S. tiburo, perhaps to ensure growth of these organs to sizes deemed critical for reproductive success. Serum concentrations of testosterone, dihydrotestosterone, progesterone, and 17β-estradiol increased in both captive and feral sharks during pubertal development, and may be associated with development of the gonads and gonaducts. Differences in hormone profiles of captive and feral sharks were observed at certain periods during puberty, but their origin remains unclear.