Reproductive aspects of the Atlantic angel shark Squatina dumeril in the southern Caribbean Sea

The maturity and reproduction of the Atlantic angel shark Squatina dumeril were assessed using 77 females (29·2–110·4 cm total length; L_T) and 269 males (58·7–108·2 cm L_T) harvested by artisanal gillnetters off Venezuela. The biased sex ratio implied segregation or sex‐specific gear selectivity. Based on the development of the reproductive tract, 50% L_T at sexual maturity (L_T50, mean ± s.e .) for females and males were estimated at 86·14 ± 0·64 and 81·55 ± 0·12 cm, respectively. Uterine fecundity ranged between one and six and with a maximum embryo size of 25·7 cm L_T. Gravid females were observed from August to December, including those close to parturition and while the gestation period was not confirmed, the size of ovarian follicles among some specimens implied protraction. The low fecundity of the species supports close monitoring of catches.     

Biological observations on the broadfin shark Lamiopsis temminckii (Carcharhiniformes: Carcharhinidae)

Biological information was collected from 214 individuals of the broadfin shark Lamiopsis temminckii measuring 418 to 1782 mm total length, L_T. Size at maturity (L₅₀) for females and males was estimated at 1430 and 1368 mm L_T, respectively, while mature and gravid females were observed from 1350 mm L_T with litter sizes 2–8 and size at birth 418–650 mm L_T. Analysis of stomach contents revealed a variety of prey, primarily crustaceans (54·0%), teleosts (42·7%) and cephalopods.     

Development and microstructure of tooth histotypes in the blue shark,Prionace glauca (Carcharhiniformes: Carcharhinidae) and the great white shark,Carcharodon carcharias (Lamniformes: Lamnidae)

Elasmobranchs exhibit two distinct arrangements of mineralized tissues in the teeth that are known as orthodont and osteodont histotypes. Traditionally, it has been said that orthodont teeth maintain a pulp cavity throughout tooth development whereas osteodont teeth are filled with osteodentine and lack a pulp cavity when fully developed. We used light microscopy, scanning electron microscopy, and high‐resolution micro‐computed tomography to compare the structure and development of elasmobranch teeth representing the two histotypes. As an example of the orthodont histotype, we studied teeth of the blue shark, Prionace glauca (Carcharhiniformes: Carcharhinidae). For the osteodont histotype, we studied teeth of the great white shark, Carcharodon carcharias (Lamniformes: Lamnidae). We document similarities and differences in tooth development and the microstructure of tissues in these two species and review the history of definitions and interpretations of elasmobranch tooth histotypes. We discuss a possible correlation between tooth histotype and tooth replacement and review the history of histotype differentiation in sharks. We find that contrary to a long held misconception, there is no orthodentine in the osteodont teeth of C. carcharias. J. Morphol. 276:797–817, 2015. © 2015 Wiley Periodicals, Inc.     

Bioenergetics of juvenile whitespotted bamboo shark Chiloscyllium plagiosum [Anonymous (Bennett)]

This study establishes the bioenergetics budget of juvenile whitespotted bamboo shark Chiloscyllium plagiosum by estimating the standard metabolic rate (R_S), measuring the effect of body size and temperature on the R_S, and identifying the specific dynamic action (R_SDA) magnitude and duration of that action in juvenile whitespotted bamboo sharks. The mean ±s .d . (R_S) of six fish (500–620 g) measured in a circular closed respirometry system was 30·21 ± 5·68 mg O₂ kg^?1 h^?1 at 18° C and 70·38 ± 14·81 mg O₂ kg^?1 h^?1 at 28° C, respectively. There were no significant differences in R_S between day and night at either 18 or 28° C (t‐test, P > 0·05). The mean ±s .d . Q₁₀ for 18–28° C was 2·32 ± 0·06 (n = 6). The amount of oxygen consumed per hour changed predictably with body mass (M; 295–750 g) following the relationship: (n = 40, r²= 0·92, P < 0·05). The mean magnitude of R_SDA was 95·28 ± 17·55 mg O₂ kg^?1 h^?1. The amount of gross ingested energy (E_I) expended as R_SDA ranged from 6·32 to 12·78% with a mean ±s .d . of 8·01 ± 0·03%. The duration of the R_SDA effect was 122 h. The energy content of juvenile whitespotted bamboo shark, squid and faeces determined by bomb calorimeter were 19·51, 20·3 and 18·62 kJ g dry mass^?1. A mean bioenergetic budget for juvenile whitespotted bamboo sharks fed with squid at 18° C was 100C = 29·5G + 31·9R_S+ 28·2R_SDA+ 6·7F + 2·1E + 1·6U, where C = consumption, G = growth, F = egestion, E = excretion and U = unaccounted energy.     

Performance of shark teeth during puncture and draw: implications for the mechanics of cutting

The performance of an organism's feeding apparatus has obvious implications for its fitness and survival. However, the majority of studies that focus on chondrichthyan feeding have largely ignored the role of teeth. Studying the functional morphology of shark teeth not only elucidates the biological role that teeth play in feeding, but also provides insight specifically into the evolution of shark feeding because teeth are often the only structures available in the fossil record. In the present study, we investigate the puncture and draw performance of three general categories of extant teeth, tearing‐type, cutting‐type, and cutting–clutching type, as well as three fossil morphologies, utilizing a universal testing system. Differences in puncturing performance occurred among different prey items, indicating that not all ‘soft’ prey items are alike. The majority of teeth were able to puncture different prey items, and differences in puncture performance also occurred among tooth types; however, few patterns emerged. In some cases, broader triangular teeth were less effective at puncturing than narrow‐cusped teeth. There were no differences between the maximum draw forces and maximum puncture forces. Many of the shark teeth in the present study were not only able to perform draw and puncture equally well, but also many tooth morphologies were functionally equivalent to each other. The findings obtained in the present study lend little support to the belief that shark tooth morphology is a good predictor of biological role. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100 , 271–286.     

Restricted movements and mangrove dependency of the nervous shark Carcharhinus cautus in nearshore coastal waters

This study used a network of acoustic receivers deployed around a no‐take zone in Mangrove Bay, within the Ningaloo Reef Marine Park in Western Australia, to study residency and habitat preference of a small coastal shark, the nervous shark Carcharhinus cautus. Twelve C. cautus were tagged with acoustic tags and monitored for up to 579 days. Based on individuals detected within the receiver array for at least 2 months, C. cautus had small core (50% kernel utilization distribution, KUD) and home ranges (95% KUD) of 0·66 and 3·64 km², respectively, and showed a strong habitat preference for mangroves, which are only found in the no‐take zone. This resulted in C. cautus spending most of their detected time within the no‐take zone boundaries (mean = 81·5%), showing that such a protected area could be beneficial to protect this species from extensive fishing pressure and local depletion, where required. Not all C. cautus remained within the acoustic array, however, suggesting that individual variations occur and that not all individuals would benefit from such protection. This study provides important information about the habitat, residency and movements of C. cautus that can be used for management and conservation. The strong affinity and residency of C. cautus within a mangrove‐fringing coastline, emphasizes the importance of mangrove habitat to the species and suggests that such preferences can be used to design appropriate no‐take zones for this species or others with similar habitat preferences.     

Population biology of the little gulper shark Centrophorus uyato in Lebanese waters

A total of 38 individuals of the heavily exploited little gulper shark Centrophorus uyato were collected from Lebanese coastal waters using bottom longlines and trammel nets of different meshes at depths ranging from 115 to 600 m between May 2013 and February 2014. Their total lengths were between 45 and 94 cm and their total mass was from 870 to 6700 g. The sex ratio was not significantly different from 1:1, with 20 males and 18 females, but bathymetric sexual segregation occurred. Catch per net setting (CNS) was used as a relative abundance index to detect spatial distribution; trammel nets showed largest CNS ranging from 4·9 to 5·45 kg per unit effort in the north and south, at depths from 120 to 200 m, during spring and summer. The mass–length relationships demonstrated negative allometric growth (b < 3) (males: M_T = 0.3585L_T^2·071, r² = 0·94; females: M_T = 0.0239L_T^2·735, r² = 0·64). The condition factor as well as the gonado‐somatic and hepato‐somatic indices of C. uyato in the study area were also calculated. The results are discussed in relation to the distribution, growth and reproduction as well as the management of C. uyato.     

On the geometry and mechanics of tooth position in the white shark,Carcharodon carcharias

The teeth of captured specimens, of prepared museum specimens, and of high-speed videotape images of the white shark, Carcharodon carcharias, were compared with respect to (1) deviation of each tooth from the animal's midline and (2) the crown angle of the functional teeth along the jaw margin. Tooth position was measured either directly using a meter stick apparatus or derived from tracings of the video footage. Tooth positions were not statistically unique in any region of the upper or lower jaw but demonstrated less variability in crown angle within 30° of the midline (71.48° ± 10°). Videotape analysis of feeding sharks indicated an 8.7° increase in crown angle of the centermost teeth during bites where the jaws were closed through an angle of 20–35° and a 15.7° reduction in this same parameter during jaw adduction through 35° or more. Such changes in tooth orientation (relative to the rear of the buccal cavity) are ascribed to flexure of the cartilaginous jaws and cranium by the cranial musculature and possibly also to sliding of the tooth bed over the jaw. Outward rotation of the teeth and jaw rami describes a plucking action during feeding or prey sampling, while larger bites rotate the frontmost teeth inward towards the gullet. Functionally, this may make the teeth more effective at grasping small prey items or gouging chunks from larger prey. However, testing of the load required to remove teeth showed no significant increase in tensile resistance with reduced crown angle. © 1995 Wiley-Liss, Inc.     

Assessing multiple paternity in three commercially exploited shark species: Mustelus mustelus,Carcharhinus obscurus and Sphyrna lewini

In this study, multiple paternity (MP) was investigated in three commercially important shark species, common smoothhound Mustelus mustelus, dusky shark Carcharhinus obscurus and scalloped hammerhead Sphyrna lewini occurring in southern Africa. Reduced marker panels of between five and six microsatellite loci were constructed for each species and used to genotype and assess the presence of MP in a total of 60 M. mustelus individuals from six litters, 90 C. obscurus individuals from 14 litters and 54 S. lewini individuals from 13 litters. Analysis in GERUD and COLONY revealed the presence of MP in all three species. Multiple paternities were observed in 67, 35 and 46% of the litters of M. mustelus, C. obscurus and S. lewini, with corresponding average sire size of 1·6, 1·4 and 2·0, respectively. The variation in the rate of MP among the three species is in accordance with previous studies whilst the comparatively high frequency of MP observed for M. mustelus, matches what has previously been reported for shark species demonstrating aggregation behaviour.     

A minimally invasive technique to assess several life‐history characteristics of the endangered great hammerhead shark Sphyrna mokarran

A dorsal‐fin photo‐identification technique paired with a non‐invasive parallel laser photogrammetry technique was used to non‐invasively identify individual Sphyrna mokarran over time. Based on the data collected over a duration of 59 days, 16 different S. mokarran (mean ± s.d . pre‐caudal length: 220·82 ± 13·66 cm; mean ± s.d . cephalofoil width: 71·38 ± 7·94 cm) were identified using dorsal‐fin photo‐identification, with a mean ± s.d . shark re‐sighting frequency of 4·05 ± 3·06 at‐sea days. The results illustrate a high S. mokarran sighting rate and therefore, the utilization of parallel laser photogrammetry and dorsal‐fin photo‐identification may be a plausible multi‐year approach to aid in non‐invasively determining the growth rate and inter‐annual site fidelity of these animals.     

Using genetic inference to re‐evaluate the minimum longevity of the lemon shark Negaprion brevirostris

A combination of mark–recapture and genetic sampling was used to extend the minimum longevity of an elasmobranch species and the life span estimate of the lemon shark Negaprion brevirostris was increased conservatively from 20·2 to 37 years. This increase in longevity means higher vulnerability and a longer recovery time from exploitation.     

Quantifying the impact of environmental variables upon catch per unit effort of the blue shark Prionace glauca in the western English Channel

The effect of environmental variables on blue shark Prionace glauca catch per unit effort (CPUE) in a recreational fishery in the western English Channel, between June and September 1998–2011, was quantified using generalized additive models (GAMs). Sea surface temperature (SST) explained 1·4% of GAM deviance, and highest CPUE occurred at 16·7° C, reflecting the optimal thermal preferences of this species. Surface chlorophyll a concentration (CHL) significantly affected CPUE and caused 27·5% of GAM deviance. Additionally, increasing CHL led to rising CPUE, probably due to higher productivity supporting greater prey biomass. The density of shelf‐sea tidal mixing fronts explained 5% of GAM deviance, but was non‐significant, with increasing front density negatively affecting CPUE. Time‐lagged frontal density significantly affected CPUE, however, causing 12·6% of the deviance in a second GAM and displayed a positive correlation. This outcome suggested a delay between the evolution of frontal features and the subsequent accumulation of productivity and attraction of higher trophic level predators, such as P. glauca.     

Catch composition,reproductive biology and diet of the bramble shark Echinorhinus brucus (Squaliformes: Echinorhinidae) from the south‐eastern Arabian Sea

Fishery and biological data are presented for the poorly known bramble shark Echinorhinus brucus (Squaliformes: Echinorhinidae), from the deep waters of the south‐eastern Arabian Sea. A total of 5318 individuals from by‐catch landings of deep‐water bottom set longlines, gillnets and shrimp trawl fisheries operating at depths of 200–1200 m were recorded between January 2008 and December 2011 at the Kochi Fisheries Harbour (Kerala). A total of 431 individuals, from 46 to 318 cm total length (L_T) and 0·8 to 132 kg total mass (M_T), were examined to determine biological data for this species. The L_T at which 50% were mature (L_T50) for females and males was estimated at 189 and 187 cm L_T. Litter size ranged from 10 to 36 and size at birth was between 42 and 46 cm L_T. Dietary analysis of stomach contents revealed E. brucus feeds on a variety of prey including crustaceans (69% index of relative importance, I_RI), teleosts (25·8% I_RI), cephalopods (1·7% I_RI) and elasmobranchs (0·7% I_RI). This study provides the first detailed biological data for this species and also highlights the extent of the by‐catch fishery for this species in Indian waters.     

Three decades of longlining in Bimini,Bahamas, reveals long‐term trends in lemon shark Negaprion brevirostris (Carcharhinidae) catch per unit effort

In Bimini, Bahamas, the consistent employment of longlines, beginning in 1982, provided a rare opportunity to explore population trends for large resident sharks. This study assessed three shallow water longline survey periods at this location; 1982–1989, 1992–2002 and 2003–2014, with the aim of determining trends in annual catch per unit effort (CPUE) for an IUCN listed near‐threatened species, the lemon shark Negaprion brevirostris. A general additive model (GAM) was used to analyse the non‐linear annual CPUE values over the entire 32‐year research period. The GAM displayed high variability of annual CPUE, with a peak value of 0·026 N. brevirostris per hook day (hooks day^?1) in 2000. The temporal pattern of CPUE indicated an abundance trend with a complete cycle, from trough to trough, occurring over a period of approximately 18 years. The 1982–1989 survey period saw the highest proportion of mature individuals (19·8%) and the smallest average pre‐caudal length (L_PC; 124·8 cm). The 1992–2002 survey period had the highest average annual CPUE (0·018 hooks day^?1), while the 2003–2014 research period saw largest average L_PC size (134·8 cm) and the lowest average CPUE values (0·009 hooks day^?1) of the entire research period. The long‐term trend identified in this study provides a baseline for future assessment.     

Genetic and reproductive evidence for two species of ornate wobbegong shark Orectolobus spp. on the Australian east coast

This study reports on evidence for reproductive isolation among Orectolobus ornatus and Orectolobus halei, two previously cryptic and recently redescribed species of wobbegong shark (Orectolobiformes: Orectolobidae) from the east coast of Australia. The evidence is based on disparity in size at sexual maturity, diagnostic nuclear and mitochondrial DNA variants, and marked phylogenetic divergence. Plots of total length (L_T) and maturity for the two species were non‐overlapping and illustrative of statistically significant size dimorphism. Genetic analyses and phylogenetic reconstruction did not provide indication of hybridization between O. ornatus and O. halei. In fact, sequence divergence between them was higher than in comparisons with another congeneric and largely co‐distributed wobbegong species (Orectolobus maculatus). The assumption of a molecular clock revealed that the two species have evolved in isolation for c. 3·9 million years. These results challenge a paradigm often mentioned in the biodiversity literature that most cryptic species are the product of recent speciation events and will contribute to the development of effective management strategies for wobbegong sharks.     

Antimicrobial susceptibilities and resistance genes in Campylobacter strains isolated from poultry and pigs in Australia

Aims

To evaluate the phenotypic and genotypic profiles of Campylobacter spp. from poultry faecal samples from free range or intensively raised meat chickens and free range egg layers. In addition, a case‐comparison study of antibiotic resistance genes from different groups of poultry and some pig strains previously collected was carried out.

Methods

Resistance to different antibiotics was assessed using the agar dilution method. In addition, all the strains were tested for ampicillin (bla_OXA‐61), erythromycin (aph‐3‐1), tetracycline tet(O), streptomycin (aadE), and the energy‐dependent multi‐drug efflux pump (cmeB) resistance genes using multiplex polymerase chain reaction.

Results

The evaluation of phenotypic resistance revealed all of the strains from poultry were sensitive to ciprofloxacin, gentamicin, erythromycin or tylosin. But, widespread resistance to lincomycin (51–100%), extensive resistance to ampicillin (33·3–60·2%) and less resistance to tetracycline (5·6–40·7%) were observed in the different groups of chickens. Antibiotic resistance genes bla_OXA‐61, cmeB and tet(O) were found in 82·6–92·7%, 80·3–89% and 22·3–30·9% Camp. coli isolates from pigs, whilst 59–65·4% and 19·2–40·7% Camp. jejuni from chickens were found to encode bla_OXA‐61 and tet(O), respectively.

Conclusion

No significant difference between isolates from free range egg layers and meat chickens (P < 0·05) was found. However, there were significant differences between the pig strains and all the groups of poultry strains (P < 0·05) with regard to carriage of resistance genes. In addition, pulsed field gel electrophoresis of selected resistant isolates from the poultry and pig revealed closely related clonal groups.

Significance and Impact of the study

Our results suggest the resistant strains are persisting environmental isolates that have been acquired by the different livestock species. Furthermore, the different treatment practices in poultry and pigs have resulted in differences in resistance profiles in Campylobacter isolates.     

Reproductive parameters of the Pacific angel shark Squatina californica (Selachii: Squatinidae)

Reproductive characteristics of the Pacific angel shark, Squatina californica, were evaluated from 420 specimens obtained from the artisanal fishery in La Paz Bay, Gulf of California, Mexico. Females (99 cm, 6000 g) were larger than males (95 cm, 5000 g) in terms of both total length (L_T) and body mass (M_T). The overall sex ratio was significantly different from the expected 1:1, suggesting sexual segregation of mature individuals in La Paz Bay. Males had developed reproductive organs and calcified claspers from 72 cm L_T; the median size at maturity (L_T50) was 75·6 cm. In females, only the left ovary was functional and mature ovarian follicles were present from 77 cm L_T; the estimated L_T50 was 77·7 cm. For the 10 gravid females sampled, uterine fecundity was between two and 10 embryos. Mature, non‐gravid females with small and large ovarian follicles appeared simultaneously with gravid females with follicles that did not exceed 1·9 cm diameter.     

Dental ontogeny of a white shark embryo

Unlike most viviparous vertebrates, lamniform sharks develop functional teeth during early gestation. This feature is considered to be related to their unique reproductive mode where the embryo grows to a large size via feeding on nutritive eggs in utero. However, the developmental process of embryonic teeth is largely uninvestigated. We conducted X‐ray microcomputed tomography to observe the dentitions of early‐, mid‐, and full‐term embryos of the white shark Carcharodon carcharias (Lamniformes, Lamnidae). These data reveal the ontogenetic change of embryonic dentition of the species for the first time. Dentition of the early‐term embryos (∼45 cm precaudal length, PCL) is distinguished from adult dentition by 1) the presence of microscopic teeth in the distalmost region of the paratoquadrate, 2) a fang‐like crown morphology, and 3) a lack of basal concavity of the tooth root. The “intermediate tooth” of early‐term embryos is almost the same size as the adjacent teeth, suggesting that lamnoid‐type heterodonty (lamnoid tooth pattern) has not yet been established. We also discovered that mid‐term embryos (∼80 cm PCL) lack functional dentition. Previous studies have shown that the maternal supply of nutritive eggs in lamnoid sharks ceases during mid‐ to late‐gestation. Thus, discontinuation of functional tooth development is likely associated with the completion of the oophagous (egg‐eating) phase. Replacement teeth in mid‐term embryos include both embryonic and adult‐type teeth, suggesting that the embryo to adult transition in dental morphology occurs during this period. J. Morphol. 278:215–227, 2017. © 2016 Wiley Periodicals,Inc.     

Stable‐isotope comparisons between embryos and mothers of a placentatrophic shark species

Stable nitrogen (δ¹⁵N) and carbon (δ¹³C) isotopes of Atlantic sharpnose shark Rhizoprionodon terraenovae embryos and mothers were analysed. Embryos were generally enriched in ¹⁵N in all studied tissue relative to their mothers' tissue, with mean differences between mother and embryo δ¹⁵N (i.e. Δδ¹⁵N) being 1·4‰ for muscle, 1·7‰ for liver and 1·1‰ for cartilage. Embryo muscle and liver were enriched in ¹³C (both Δδ¹³C means = 1·5‰) and embryo cartilage was depleted (Δδ¹³C mean = ?1·01‰) relative to corresponding maternal tissues. While differences in δ¹⁵N and δ¹³C between mothers and their embryos were significant, muscle δ¹⁵N values indicated embryos to be within the range of values expected if they occupied a similar trophic position as their respective mothers. Positive linear relationships existed between embryo total length (L_T) and Δδ¹⁵N for muscle and liver and embryo L_T and Δδ¹³C for muscle, with those associations possibly resulting from physiological differences between smaller and larger embryos or differences associated with the known embryonic nutrition shift (yolk feeding to placental feeding) that occurs during the gestation of this placentatrophic species. Together these results suggest that at birth, the δ¹⁵N and δ¹³C values of R. terraenovae are likely higher than somewhat older neonates whose postpartum feeding habits have restructured their isotope profiles to reflect their postembryonic diet.     

Killing in the Pliocene: shark attack on a dolphin from Italy

Abstract: Shark bite marks, including striae, sulci and abrasions, in a well‐preserved fossil dolphin skeleton referred to Astadelphis gastaldii (Cetacea, Delphinidae) from Pliocene sediments of Piedmont (northern Italy), are described in detail. The exceptional combination of a fossil dolphin having a significant part of the skeleton preserved and a large number of bite marks on the bones represents one of the few detailed documentations of shark attack in the past. Most bite marks have been referred to a shark about 4 m long with unserrated teeth, belonging to Cosmopolitodus hastalis, on the basis of their shape and their general disposition on the dolphin skeleton. According to our hypothesis, the shark attacked the dolphin with an initial mortal bite to the abdomen from the rear and right, in a similar way as observed for the living white shark when attacking pinnipeds. A second, less strong, bite was given on the dorsal area when the dolphin, mortally injured, probably rolled to the left. The shark probably released the prey, dead or dying, and other sharks or fishes probably scavenged the torn body of the dolphin.