应用脂肪酸组成研究热带东太平洋同域中上层鲨鱼营养生态位分化

物种对食物资源利用方式的差异,即营养生态位分化是物种共存的先决条件之一,对种间营养生态位的比较研究有助于了解同域分布物种的共存机制。脂肪酸组成可反映生物较长时间尺度的摄食信息,对探讨物种间营养生态位分化具有重要指示作用。热带东太平洋主要栖息有8种大型中上层鲨鱼,大青鲨(Prionace glauca)、大眼长尾鲨(Alopias superciliosus)、镰状真鲨(Carcharhinus falciformis)、长鳍真鲨(Carcharhinus longimanus)、浅海长尾鲨(Alopias pelagicus)、尖吻鲭鲨(Isurus oxyrinchus)、路氏双髻鲨(Sphyrna lewini)和锤头双髻鲨(Sphyrna zygaena),通过比较其肌肉脂肪酸组成,分析种间食性差异,营养关系及营养生态位分化。结果表明,尖吻鲭鲨营养级相对较高,大青鲨相对较低。3种鼠鲨与5种真鲨存在食性差异或栖息地隔离。浅海长尾鲨与大眼长尾鲨营养生态位重叠程度较高,存在激烈的资源竞争。大青鲨与镰状真鲨生态位宽度较大,表征其对环境的可塑性较强;尖吻鲭鲨和路氏双髻鲨生态位宽度较小,表现为其食性的特化。本研究解释了脂肪酸组成分析在鲨鱼摄食研究中的潜在应用,对分析大洋性鲨鱼的营养生态位分化,资源分配方式及同域共存机制有一定的应用价值。     

Diversity of dermal denticle structure in sharks: Skin surface roughness and three‐dimensional morphology

Shark skin is covered with numerous placoid scales or dermal denticles. While previous research has used scanning electron microscopy and histology to demonstrate that denticles vary both around the body of a shark and among species, no previous study has quantified three‐dimensional (3D) denticle structure and surface roughness to provide a quantitative analysis of skin surface texture. We quantified differences in denticle shape and size on the skin of three individual smooth dogfish sharks (Mustelus canis) using micro‐CT scanning, gel‐based surface profilometry, and histology. On each smooth dogfish, we imaged between 8 and 20 distinct areas on the body and fins, and obtained further comparative skin surface data from leopard, Atlantic sharpnose, shortfin mako, spiny dogfish, gulper, angel, and white sharks. We generated 3D images of individual denticles and measured denticle volume, surface area, and crown angle from the micro‐CT scans. Surface profilometry was used to quantify metrology variables such as roughness, skew, kurtosis, and the height and spacing of surface features. These measurements confirmed that denticles on different body areas of smooth dogfish varied widely in size, shape, and spacing. Denticles near the snout are smooth, paver‐like, and large relative to denticles on the body. Body denticles on smooth dogfish generally have between one and three distinct ridges, a diamond‐like surface shape, and a dorsoventral gradient in spacing and roughness. Ridges were spaced on average 56 µm apart, and had a mean height of 6.5 µm, comparable to denticles from shortfin mako sharks, and with narrower spacing and lower heights than other species measured. We observed considerable variation in denticle structure among regions on the pectoral, dorsal, and caudal fins, including a leading‐to‐trailing edge gradient in roughness for each region. Surface roughness in smooth dogfish varied around the body from 3 to 42 microns.     

Virtual reconstruction of the skeletal labyrinth of two lamnid sharks (Elasmobranchii,Lamniformes)

The first virtual reconstruction of the skeletal labyrinth of the porbeagle shark Lamna nasus and the shortfin mako shark Isurus oxyrinchus is presented here using high‐resolution micro‐computed tomography. The results, in comparison with previously published information, suggest relationships between skeletal labyrinth morphology and locomotion mode in chondrichthyans, but also show that further studies are required to establish such connections. Nevertheless, this study adds to the knowledge of the skeletal labyrinth morphology in two apex elasmobranch species.     

New insights on the trophic ecology of blue (Prionace glauca) and shortfin mako sharks (Isurus oxyrinchus) from the oceanic eastern South Pacific

The blue shark (Prionace glauca) and the shortfin mako shark (Isurus oxyrinchus) are two large and highly migratory sharks distributed in most oceans. Although they are often caught in the south Pacific Ocean long-line fisheries, their trophic ecology is poorly understood. Stable isotopes with Bayesian mixing and dependence concentration models were performed to determine the diet and trophic differences between the two species in the South-eastern Pacific Ocean. According to the mixing models, fishes are the most important prey of these sharks. Dolphin calves and remains were found in the stomachs of both species, which represents a novel finding in trophic ecology of South Pacific sharks. Intra-specific differences were found in P. glauca, but not in specimens of I. oxyrinchus. The two sharks showed a high degree of diet overlap (73%), primarily over mackerel and dolphin carcasses. Our results indicate that blue and shortfin mako sharks have a generalist feeding strategy in the eastern Pacific Ocean, with a strong preference for teleost fishes and also for dolphin carcasses. Therefore, trophic studies are useful to understand energy flow through the food web, and the trophic position of key species.     

Ventricle morphology in pelagic elasmobranch fishes

Ventricle weights of the warm-bodied great white shark, Atlantic shortfin mako, and the common thresher shark (the latter presumed to be warm-bodied) are similar to those of ectothermic blue sharks, sandbar sharks, dusky sharks, tiger sharks and scalloped hammerhead sharks. Ventricle muscularity, as estimated by the ratio of cortical to spongy layer thickness, is almost twice as great in the former three species than in the latter elasmobranchs. Measurements of ventricular volumes suggest that the ventricles of the great white, Atlantic shortfin mako and common thresher sharks are better adapted to respond to demands for increases in cardiac output via increased heartbeat frequency in comparison with ectothermic species of shark.     

Biological characterization of the skin of shortfin mako shark Isurus oxyrinchus and preliminary study of the hydrodynamic behaviour through computational fluid dynamics

This study characterized the morphology, density and orientation of the dermal denticles along the body of a shortfin mako shark Isurus oxyrinchus and identified the hydrodynamic parameters of its body through a computational fluid‐dynamics model. The study showed a great variability in the morphology, size, shape, orientation and density of dermal denticles along the body of I. oxyrinchus. There was a significant higher density in dorsal and ventral areas of the body and their highest angular deviations were found in the lower part of the mouth and in the areas between the pre‐caudal pit and the second dorsal and pelvic fins. A detailed three‐dimensional geometry from a scanned body of a shark was carried out to evaluate the hydrodynamic properties such as drag coefficient, lift coefficient and superficial (skin) friction coefficient of the skin together with flow velocity field, according to different roughness coefficients simulating the effect of the dermal denticles. This preliminary approach contributed to detailed information of the denticle interactions. As the height of the denticles was increased, flow velocity and the effect of lift decreased whereas drag increased. The highest peaks of skin friction coefficient were observed around the pectoral fins.     

Functional morphology of the gills of the shortfin mako,Isurus oxyrinchus,a lamnid shark

This study examines the functional gill morphology of the shortfin mako, Isurus oxyrinchus, to determine the extent to which its gill structure is convergent with that of tunas for specializations required to increase gas exchange and withstand the forceful branchial flow induced by ram ventilation. Mako gill structure is also compared to that of the blue shark, Prionace glauca, an epipelagic species with lower metabolic requirements and a reduced dependence on fast, continuous swimming to ventilate the gills. The gill surface area of the mako is about one‐half that of a comparably sized tuna, but more than twice that of the blue shark and other nonlamnid shark species. Mako gills are also distinguished from those of other sharks by shorter diffusion distances and a more fully developed diagonal blood‐flow pattern through the gill lamellae, which is similar to that found in tunas. Although the mako lacks the filament and lamellar fusions of tunas and other ram‐ventilating teleosts, its gill filaments are stiffened by the elasmobranch interbranchial septum, and the lamellae appear to be stabilized by one to two vascular sacs that protrude from the lamellar surface and abut sacs of adjacent lamellae. Vasoactive agents and changes in vascular pressure potentially influence sac size, consequently effecting lamellar rigidity and both the volume and speed of water through the interlamellar channels. However, vascular sacs also occur in the blue shark, and no other structural elements of the mako gill appear specialized for ram ventilation. Rather, the basic elasmobranch gill design and pattern of branchial circulation are both conserved. Despite specializations that increase mako gill area and efficacy relative to other sharks, the basic features of the elasmobranch gill design appear to have limited selection for a larger gill surface area, and this may ultimately constrain mako aerobic performance in comparison to tunas. J. Morphol. 271:937–948, 2010. © 2010 Wiley‐Liss, Inc.     

Polymorphic microsatellite markers for studies of the conservation and reproductive genetics of imperilled sand tiger sharks (Carcharias taurus)

We report on the isolation of eight microsatellites from the sand tiger shark, Carcharias taurus, using an enrichment protocol. All loci, with the exception of Cta45–183, were in Hardy–Weinberg equilibrium. Loci exhibited three to 15 alleles, and observed and expected heterozygosities of 0.095–1.000 and 0.284–0.924, respectively. An additional marker (Iox‐12) developed from a shortfin mako library was variable in sand tigers. These markers will be used to examine population genetics and mating patterns of this imperilled species.     

Movements and Swimming Behavior of Three Species of Sharks in La Jolla Canyon, California

We tracked six individuals of three shark species, the shortfin mako, Isurus oxyrinchus, great white, Carcharodon carcharias, and blue, Prionace glauca, near the submarine canyon off La Jolla, southern California during the summers of 1995 and 1997. The duration of tracking ranged from 2 to 38 h per shark. The mode of travel differed in one respect among species. The rate of movement of the endothermic species, the mako and white shark, exceeded that of the ectothermic species, the blue shark. Similarities among species were more common. Firstly, individuals of all three species swam in a directional manner. Secondly, individuals constantly moved up and down in the water column, exhibiting oscillatory or yo-yo swimming. Thirdly, members of the three species swam at the surface for prolonged periods. Finally, the movements of the mako and white sharks were at times loosely associated with bottom topography. We discuss the various adaptive advantages that have been proposed for these behavioral patterns. Oscillatory swimming has been attributed to the following: (1) heating the body in the warm surface waters after swimming in cold, deep water, (2) alternating between two strata of water, one carrying chemical information as to its source, and deriving a direction to that stratum's origin, (3) conserving energy by quickly propelling oneself upward with many tail beats and slowly gliding downward with few beats, and (4) descending to where magnetic gradients are steeper, more perceptible, and useful to guide migratory movements. At the surface, an individual would be able to swim in a straight line by using following features as a reference: (1) celestial bodies, (2) polarized light, or (3) the earth's main dipole field. Furthermore, an individual would conserve energy because of the greater ease to maintaining a warm body in the heated surface waters.     

Food habits of the shortfin mako, Isurus oxyrinchus, off the southwest coast of Portugal

The shortfin mako, Isurus oxyrinchus, is caught in the eastern North Atlantic as a regular bycatch of the surface-drift longline fishery, mainly directed towards swordfish, Xiphias gladius. Stomachs of 112 shortfin mako sharks, ranging in size from 64 cm to 290 cm fork length, showed teleosts to be the principal component of the diet, occurring in 87% of the stomachs and accounting for over 90% of the contents by weight. Crustaceans and cephalopods were also relatively important in this species’ diet, whereas other elasmobranchs were only present in lower percentages. Meal overlap was observed in half of the sampled sharks. No clear trend of prey size selectivity was found, despite smaller individuals seeming incapable of pursuing larger and faster prey. The retention of small prey was also observed in the diet of all sizes of shark. Seasonality in food habits was in accordance with the current availability of food items. The observed vacuity index of 12% is comparable to foraging ecology studies using gillnetting and appears not to be influenced by baited longline gear. Morphological relationships of the digestive system might add important information to the foraging ecology studies and to ecosystem modelling.     

Application of bomb radiocarbon chronologies to shortfin mako (Isurus oxyrinchus) age validation

Age estimation is an issue for the shortfin mako, Isurus oxyrinchus, because of disagreement on vertebral band-pair deposition periodicity. In the 1950s–1960s, thermonuclear testing released large amounts of radiocarbon into the atmosphere, which diffused into the ocean through gas exchange. This influx created a time-specific marker that can be used in age validation. Annual band-pair deposition in the porbeagle, Lamna nasus, was validated in a previous study and indicated preliminary annual deposition in the shortfin mako, using four samples from one vertebra. In the present study, age estimates from 54 shortfin mako vertebrae collected in 1950–1984 ranged 1–31 years. Ageing error between readers was consistent, with 76% of the estimates ranging within 2 years. Twenty-one Δ¹⁴C values from eight shortfin mako vertebrae (collected in the western North Atlantic in 1963–1984) ranged −154.8‰ to 86.8‰. The resulting conformity with the Δ¹⁴C timeline for the porbeagle supported annual band-pair deposition in vertebrae of the shortfin mako.     

Comparative squamation of the lateral line canal pores in sharks

The current study collected the first quantitative data on lateral line pore squamation patterns in sharks and assessed whether divergent squamation patterns are similar to experimental models that cause reduction in boundary layer turbulence. In addition, the hypothesis that divergent orientation angles are exclusively found in fast‐swimming shark species was tested. The posterior lateral line and supraorbital lateral line pore squamation of the fast‐swimming pelagic shortfin mako shark Isurus oxyrinchus and the slow‐swimming epi‐benthic spiny dogfish shark Squalus acanthias was examined. Pore scale morphology and pore coverage were qualitatively analysed and compared. In addition, pore squamation orientation patterns were quantified for four regions along the posterior lateral line and compared for both species. Isurus oxyrinchus possessed consistent pore scale coverage among sampled regions and had a divergent squamation pattern with multiple scale rows directed dorsally and ventrally away from the anterior margin of the pore with an average divergent angle of 13° for the first row of scales. Squalus acanthias possessed variable amounts of scale coverage among the sampled regions and had a divergent squamation pattern with multiple scale rows directed ventrally away from the anterior margin of the pore with an average angle of 19° for the first row of scales. Overall, the squamation pattern measured in I. oxyrinchus fell within the parameters used in the fluid flow analysis, which suggests that this pattern may reduce boundary layer turbulence and affect lateral line sensitivity. The exclusively ventral oriented scale pattern seen in S. acanthias possessed a high degree of divergence but the pattern did not match that of the fluid flow models. Given current knowledge, it is unclear how this would affect boundary layer flow. By studying the relationship between squamation patterns and the lateral line, new insights are provided into sensory biology that warrant future investigation due to the implications for the ecology, morphology and sensory evolution of sharks.     

Quantification of red myotomal muscle volume and geometry in the shortfin mako shark (Isurus oxyrinchus) and the salmon shark (Lamna ditropis) using T1-weighted magnetic resonance imaging

T1-weighted magnetic resonance imaging (MRI) in conjunction with image and segmentation analysis (i.e., the process of digitally partitioning tissues based on specified MR image characteristics) was evaluated as a noninvasive alternative for differentiating muscle fiber types and quantifying the amounts of slow, red aerobic muscle in the shortfin mako shark (Isurus oxyrinchus) and the salmon shark (Lamna ditropis). MRI-determinations of red muscle quantity and position made for the mid-body sections of three mako sharks (73.5-110 cm fork length, FL) are in close agreement (within the 95% confidence intervals) with data obtained for the same sections by the conventional dissection method involving serial cross-sectioning and volumetric analyses, and with previously reported findings for this species. The overall distribution of salmon shark red muscle as a function of body fork length was also found to be consistent with previously acquired serial dissection data for this species; however, MR imaging revealed an anterior shift in peak red muscle cross-sectional area corresponding to an increase in body mass. Moreover, MRI facilitated visualization of the intact and anatomically correct relationship of tendon linking the red muscle and the caudal peduncle. This study thus demonstrates that MRI is effective in acquiring high-resolution three-dimensional digital data with high contrast between different fish tissue types. Relative to serial dissection, MRI allows more precise quantification of the position, volume, and other details about the types of muscle within the fish myotome, while conserving specimen structural integrity.     

Microsatellite Analyses of Blacktip Reef Sharks (Carcharhinus melanopterus) in a Fragmented Environment Show Structured Clusters

The population dynamics of shark species are generally poorly described because highly mobile marine life is challenging to investigate. Here we investigate the genetic population structure of the blacktip reef shark (Carcharhinus melanopterus) in French Polynesia. Five demes were sampled from five islands with different inter-island distances (50–1500 km). Whether dispersal occurs between islands frequently enough to prevent moderate genetic structure is unknown. We used 11 microsatellites loci from 165 individuals and a strong genetic structure was found among demes with both F-statistics and Bayesian approaches. This differentiation is correlated with the geographic distance between islands. It is likely that the genetic structure seen is the result of all or some combination of the following: low gene flow, time since divergence, small effective population sizes, and the standard issues with the extent to which mutation models actually fit reality. We suggest low levels of gene flow as at least a partial explanation of the level of genetic structure seen among the sampled blacktip demes. This explanation is consistent with the ecological traits of blacktip reef sharks, and that the suitable habitat for blacktips in French Polynesia is highly fragmented. Evidence for spatial genetic structure of the blacktip demes we studied highlights that similar species may have populations with as yet undetected or underestimated structure. Shark biology and the market for their fins make them highly vulnerable and many species are in rapid decline. Our results add weight to the case that total bans on shark fishing are a better conservation approach for sharks than marine protected area networks.     

DNA barcoding of fresh seafood in Australian markets reveals misleading labelling and sale of endangered species

Flake and shark samples were purchased from outlets in several coastal Australian regions and genetically barcoded using the cytochrome oxidase subunit 1 (CO1) gene to investigate labelling reliability and species-specific sources of ambiguously labelled fillets. Of the 41 shark fillet samples obtained, 23 yielded high-quality CO1 sequences, out of which 57% (n = 13) were labelled ambiguously (misleading) and 35% (n = 8) incorrectly. In contrast, barramundi fillets, which are widely available and sought after in Australian markets, were shown to be accurately labelled. Species identified from shark samples, including the shortfin mako (n = 3) and the scalloped hammerhead (n = 1), are assessed by the IUCN as endangered and critically endangered, respectively, with several others classified as vulnerable and near threatened.     

东太平洋中部中上层鲨鱼群落营养生态位分化

鲨鱼在大洋生态系统中占据着重要的生态地位,其作为顶级捕食者,通过下行效应直接影响生态系统的稳定.稳定同位素技术是目前研究摄食生态学强有力的手段之一,可利用碳氮稳定同位素在食物网中的特性分别指示鲨鱼的食物来源和营养级.本研究选取8种130尾采集自东太平洋中部的中上层鲨鱼,应用稳定同位素绘制其种群生态位图谱,比较不同种群间的生态地位及资源分配方式上的差异.结果表明:不同鲨鱼种群碳、氮稳定同位素比值存在显著差异;8种鲨鱼在东太平洋生态系统中的营养级为4.3~5.4,大青鲨、尖吻鲭鲨与其他6种鲨鱼存在摄食隔离,表现出独特的营养生态地位.这些结果充分证明大洋性中上层鲨鱼并非生态系统的冗余种,其营养生态位的独特性不会被其他捕食者简单地替代和弥补.     

A case of genetic polyandry in the shortfin mako Isurus oxyrinchus

This article documents a case of genetic polyandry in the oceanic and pelagic shortfin mako Isurus oxyrinchus and briefly comments on the implications of this finding.     

A mitochondrial species identification assay for Australian blacktip sharks (Carcharhinus tilstoni, C. limbatus and C. amblyrhynchoides) using real-time PCR and high-resolution melt analysis

Tropical Australian shark fisheries target two morphologically indistinguishable blacktip sharks, the Australian blacktip (Carcharhinus tilstoni) and the common blacktip (C. limbatus). Their relative contributions to northern and eastern Australian coastal fisheries are unclear because of species identification difficulties. The two species differ in their number of precaudal vertebrae, which is difficult and time consuming to obtain in the field. But, the two species can be distinguished genetically with diagnostic mutations in their mitochondrial DNA ND4 gene. A third closely related sister species, the graceful shark C. amblyrhynchoides, can also be distinguished by species‐specific mutations in this gene. DNA sequencing is an effective diagnostic tool, but is relatively expensive and time consuming. In contrast, real‐time high‐resolution melt (HRM) PCR assays are rapid and relatively inexpensive. These assays amplify regions of DNA with species‐specific genetic mutations that result in PCR products with unique melt profiles. A real‐time HRM PCR species‐diagnostic assay (RT‐HRM‐PCR) has been developed based on the mtDNA ND4 gene for rapid typing of C. tilstoni, C. limbatus and C. amblyrhynchoides. The assay was developed using ND4 sequences from 66 C. tilstoni, 33. C. limbatus and five C. amblyrhynchoides collected from Indonesia and Australian states and territories; Western Australia, the Northern Territory, Queensland and New South Wales. The assay was shown to be 100% accurate on 160 unknown blacktip shark tissue samples by full mtDNA ND4 sequencing.     

Characterization of microsatellite loci isolated from the blacktip shark and their utility in requiem and hammerhead sharks

We isolated and characterized 16 microsatellite loci from the blacktip shark, Carcharhinus limbatus, and tested cross‐species amplification in 11 Carcharhinus species and five additional shark genera. Thirty‐six (1.6%) and 180 (48%) colonies were positive for dinucleotide repeat motifs from unenriched and enriched libraries, respectively. Heterozygosities of polymorphic loci ranged from 0.04 to 0.96 with two to 22 alleles per locus. Amplification products were observed at nine to 13 loci (five to 11 of which where polymorphic) in 10 Carcharhinus species. Several loci were also polymorphic in each of the additional genera examined.