THE PHYLOGENETIC RELATIONSHIPS AMONG REQUIEM AND HAMMERHEAD SHARKS: INFERRING PHYLOGENY WHEN THOUSANDS OF EQUALLY MOST PARSIMONIOUS TREES RESULT

Abstract— Protein variation among 37 species of carcharhiniform sharks was examined at 17 presumed loci. Evolutionary trees were inferred from these data using both cladistic character and a distance Wagner analysis. Initial cladistic character analysis resulted in more than 30 000 equally parsimonious tree arrangements. Randomization tests designed to evaluate the phylogenetic information content of the data suggest the data are highly significantly different from random in spite of the large number of parsimonious trees produced. Different starting seed trees were found to influence the kind of tree topologies discovered by the heuristic branch swapping algorithm used. The trees generated during the early phases of branch swapping on a single seed tree were found to be topologically similar to those generated throughout the course of branch swapping. Successive weighting increased the frequency and the consistency with which certain clades were found during the course of branch swapping, causing the semi-strict consensus to be more resolved. Successive weighting also appeared resilient to the bias associated with the choice of initial seed tree causing analyses seeded with different trees to converge on identical final character weights and the same semi-strict consensus tree.
The summary cladistic character analysis and the distance Wagner analysis both support the monophyly of two major clades, the genus Rhizoprionodon and the genus Sphyrna. . The distance Wagner analysis also supports the monophyly of the genus Carcharhinus . However, the cladistic analysis suggests that Carcharhinus is a paraphyletic group that includes the blue shark Prionace glauca .     

Spatial distribution of sharks captures in the Pacific of Nicaragua and its relationship with several oceanographic variables

Between August 1995 and August 1997 long line fishing techniques and a bathythermograph were used to correlate some physical variables with the spatial distribution of four shark species in 26 fishing cruises off the Nicaraguan Pacific Coast. They were the thresher (Alopias vulpinus), blue (Prionace glaucea), gray (Carcharhinus falciformis) and hammer (Sphyra lewini). All species concentrated in the southeastern Nicaraguan Pacific, at the seasonal upwelling area of Papagayo Gulf. The range of sea surface temperatures in which the sharks were captured was 25-28 degrees C. We could clearly associate this physical parameter with shark availability. The vertical distribution of the captured sharks suggests that they occupy termocline levels above the 15 degrees C isotherm. Although these species are oceanic, the blue shark was captured in ocean waters over the 1800 m isobar, while the grey and thresher sharks where close to the continental shelf. Body length in decreasing order are: thresher (210-290 cm, SN = 21), blue (60-240 cm, SN = 13) and gray (80-200 cm, SN = 17).     

Identification of factors influencing shark catch and mortality in the Marshall Islands tuna longline fishery and management implications

Recent average annual catches of sharks by tuna longline vessels fishing in the Republic of the Marshall Islands (RMI) are estimated to be between 1583 and 2274 t. Although 22 shark species have been recorded by the observer programme for this fishery, 80% of the annual catch comprises only five species: blue shark Prionace glauca, silky shark Carcharhinus falciformis, bigeye thresher shark Alopias superciliosus, pelagic thresher shark Alopias pelagicus and oceanic whitetip shark Carcharhinus longimanus. Wire leaders (i.e. branch lines or traces) were also used by nearly all observed vessels. Generalized additive model (GAM)-based analyses of catch rates indicated that P. glauca and A. superciliosus are caught in higher numbers when vessels fish in relatively cooler waters, at night, close to the full moon, when the 27° C thermocline is close to the surface and during El Ni?o conditions. In contrast, C. falciformis, A. pelagicus and C. longimanus are caught in higher numbers when shark lines are used (all three species) or hooks are set at a shallow depth (A. pelagicus and C. longimanus and, also, P. glauca). These findings are generally consistent with current knowledge of these species' habitat preferences, movement and distribution. The results of these analyses were combined with information pertaining to shark condition and fate upon capture to compare the likely effectiveness of a range of potential measures for reducing shark mortality in the longline fishery. Of the options considered, the most effective would be to combine measures that reduce the catch rate (e.g. restrictions on the use of wire leaders, shark baits and shark lines) with measures that increase survival rates after post-capture release (e.g. finning bans).     

Foundations of the method of dating global fluctuations of abundance of oceanic sharks on the basis of the amount of fossil teeth in bottom sediments

A method for dating fluctuations in abundance of Elasmobranchii based on three parameters: density of fossil teeth on the ocean floor, density of modern species, and the rate of teeth replacement in modern species is proposed. As a model event, the substitution by the blue shark Prionace glauca of sharks of the genus Isurus that dominated from the Pliocene to the Late Holocene was used. It was determined that, at various values of the aforementioned parameters, the blue shark occupied a dominant position in the eastern Pacific between 302 and 3940 years ago. It is suggested that, in case of a large amount of material in geological collections using this method, a great number of paleoreconstructions of the development and changes in the oceanic biota may be carried out.     

Catch composition and reproductive biology of whaler sharks (Carcharhiniformes: Carcharhinidae) caught by fisheries in Indonesia

The first detailed information on the biological aspects of members of the economically important shark family Carcharhinidae in Indonesian waters is given. Carcharhinids dominated the landings of sharks at sites visited, comprising almost 60% of the total biomass of all sharks recorded, over an intensive 5 year sampling period. A total of 26 species of carcharhinids, representing half of the species in the Carcharhinidae, were recorded. The most abundant species, in terms of numbers recorded, were Scoliodon laticaudus and Carcharhinus falciformis , while the most abundant in terms of biomass were Prionace glauca , C. falciformis and Carcharhinus obscurus . Biological data are presented for 22 of the 26 species. The total length at which males attain maturity ( L ₅₀) was determined for 10 species. The biological aspects of a number of species, most notably Carcharhinus sorrah and Loxodon macrorhinus , were found to differ from those recorded in the literature for other regions.     

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。     

北大西洋大青鲨种群统计分析

大青鲨是金枪鱼延绳钓渔业中最主要的兼捕鱼种,在海洋食物网中属于顶端物种,在海洋生态系统中处于重要地位.由于数据限制,传统的资源评估方法很难准确描述大青鲨的资源动态.本研究基于大青鲨的生活史参数,应用种群统计分析法评估大青鲨的种群参数和资源状态,并探讨了内禀增长率为0时对应的临界捕捞死亡系数F_c与开捕年龄t_c的关系.结果表明： 未开发状态下,大青鲨存活率为0.719～0.820;大青鲨的内在瞬时增长率(r₀)为0.250～0.381,种群倍增时间(t_x2)为1.819～2.773年,种群的净繁殖力(R₀)为6.600～22.255,世代间期时间(G)为8.498～〖JP2〗10.162年,种群资源状态良好.生活史参数的敏感性检验显示,大青鲨初始年龄的自然死亡系数、种群性成熟年龄及寿命的不确定性对种群统计参数的意义影响不大;临界捕捞死亡系数伴随开捕年龄的增大而增大,当t_c≥5时,F_c值与t_c无显著相关关系.     

Morphological abnormalities in a blue shark Prionace glauca (Chondrichthyes: Carcharhinidae) foetus from southern Brazil

This study records the occurrence of a blue shark Prionace glauca foetus, with morphological abnormalities in the trunk and cephalic region, from a female caught by a pelagic longline in October 2003, in southern Brazil.     

On the Capture of a Blue Shark,Prionace glauca (Carcharhinidae), in Peter the Great Bay,Sea of Japan

Journal of Ichthyology - The capture of a blue shark, Prionace glauca, with a body length of 108.5 cm in Peter the Great Bay, Sea of Japan, is reported. Its measurable traits, dental formula, and...     

Length‐weight relationships of four sharks caught in the Northern Persian Gulf and Oman Sea

The length–weight relationships (LWRs) for four little‐known shark species collected in the Persian Gulf and Oman Sea from March 2014 to September 2015 are presented, namely: Carcharhinus dussumieri, Carcharhinus macloti, Chiloscyllium arabicum, and Chaenogaleus macrostoma.     

Spiral valve parasites of blue and common thresher sharks as indicators of shark feeding behaviour and ecology

This study documented the parasite faunas of the spiral valves of blue sharks Prionace glauca (L. 1758) and common thresher sharks Alopias vulpinus (Bonnaterre, 1788) caught in the California Current Large Marine Ecosystem (CCLME) north of the Mexican border. The spiral valves of 18 blue and 19 thresher sharks caught in the CCLME from 2009 to 2013 were examined for parasites. Seven parasite taxa were found in blue sharks and nine in threshers. The tetraphyllidean cestode Anthobothrium sp. (78% prevalence) was the most common parasite in blue sharks, and the phyllobothriid cestode Paraorygmatobothrium sp. (90% prevalence) was the most common in threshers. An adult nematode of the genus Piscicapillaria was found in threshers for the first time and may be a new species. Adult individuals of Hysterothylacium sp. were found in both shark species. The adult acanthocephalan Rhadinorhynchus cololabis and remains of the parasitic copepod Pennella sp. – both parasites of Pacific saury, Cololabis saira – were found in the intestines of threshers, indicating recent feeding on saury. This study paves the way for a more comprehensive examination, including more samples and a wider variety of shark species, to provide a greater understanding of shark feeding behaviour and possibly provide information on shark population biology.     

Biomagnification of Mercury and Selenium in Blue Shark Prionace glauca from the Pacific Ocean off Mexico

The aim of this study was to determine the biomagnification of mercury through the principal prey of the blue shark, Prionace glauca, off the western coast of Baja California Sur, Mexico, as well as the relationship between mercury and selenium in blue sharks. High levels of mercury were found in shark muscle tissues (1.39?±?1.58?μg/g wet weight); these values are above the allowed 1.0?μg/g for human consumption. The mercury to selenium molar ratio was 1:0.2. We found a low correlation between mercury bioaccumulation and shark size. Juveniles have lower concentrations of mercury than adults. Regarding the analyzed prey, the main prey of the blue shark, pelagic red crab, Pleuroncodes planipes, bioaccumulated 0.04?±?0.01?μg/g Hg wet weight, but the prey with higher bioaccumulation was the bullet fish Auxis spp. (0.20?±?0.02?μg/g wet weight). In terms of volume, the red crab P. planipes can be the prey that provides high levels of mercury to the blue shark.     

Migration pathways, behavioural thermoregulation and overwintering grounds of blue sharks in the Northwest Atlantic

The blue shark Prionace glauca is the most abundant large pelagic shark in the Atlantic Ocean. Although recaptures of tagged sharks have shown that the species is highly migratory, migration pathways towards the overwintering grounds remain poorly understood. We used archival satellite pop-up tags to track 23 blue sharks over a mean period of 88 days as they departed the coastal waters of North America in the autumn. Within 1-2 days of entering the Gulf Stream (median date of 21 Oct), all sharks initiated a striking diel vertical migration, taking them from a mean nighttime depth of 74 m to a mean depth of 412 m during the day as they appeared to pursue vertically migrating squid and fish prey. Although functionally blind at depth, calculations suggest that there would be a ~2.5-fold thermoregulatory advantage to swimming and feeding in the markedly cooler deep waters, even if there was any reduced foraging success associated with the extreme depth. Noting that the Gulf Stream current speeds are reduced at depth, we used a detailed circulation model of the North Atlantic to examine the influence of the diving behaviour on the advection experienced by the sharks. However, there was no indication that the shark diving resulted in a significant modification of their net migratory pathway. The relative abundance of deep-diving sharks, swordfish, and sperm whales in the Gulf Stream and adjacent waters suggests that it may serve as a key winter feeding ground for large pelagic predators in the North Atlantic.     

Size and distribution of Pandarus satyrus (Copepoda: Pandaridae) on the blue shark Prionace glauca (Carcharhiniformes: Carcharhinidae) in Costa Rica.

A total of 80 specimens of Pandarus satyrus, a cosmopolitan ectoparasitic copepod, were taken from fishery catches of blue sharks (Prionace glauca) in the Eastern Pacific coast of Costa Rica. All specimens were found in the dorsal surface of pectoral fins (8-30 per shark). Longer specimens were most abundant.     

Assessment of multiple paternity in single litters from three species of carcharhinid sharks in Hawaii

We tested for presence or absence of multiple paternity in single litters from each of three congeneric shark species in Hawaii: the sandbar shark, Carcharhinus plumbeus, bignose shark, Carcharhinus altimus, and Galapagos shark, Carcharhinus galapagensis. Based on eight polymorphic microsatellite loci, we excluded paternity by a single sire in sandbar and bignose sharks, but could not exclude a single sire for the litter from the Galapagos shark. This study doubles the number of shark species tested for multiple paternity, and is the first demonstration of multiple paternity in sandbar and bignose sharks.     

Long-Term Changes in Species Composition and Relative Abundances of Sharks at a Provisioning Site

Diving with sharks, often in combination with food baiting/provisioning, has become an important product of today’s recreational dive industry. Whereas the effects baiting/provisioning has on the behaviour and abundance of individual shark species are starting to become known, there is an almost complete lack of equivalent data from multi-species shark diving sites. In this study, changes in species composition and relative abundances were determined at the Shark Reef Marine Reserve, a multi-species shark feeding site in Fiji. Using direct observation sampling methods, eight species of sharks (bull shark Carcharhinus leucas, grey reef shark Carcharhinus amblyrhynchos, whitetip reef shark Triaenodon obesus, blacktip reef shark Carcharhinus melanopterus, tawny nurse shark Nebrius ferrugineus, silvertip shark Carcharhinus albimarginatus, sicklefin lemon shark Negaprion acutidens, and tiger shark Galeocerdo cuvier) displayed inter-annual site fidelity between 2003 and 2012. Encounter rates and/or relative abundances of some species changed over time, overall resulting in more individuals (mostly C. leucas) of fewer species being encountered on average on shark feeding dives at the end of the study period. Differences in shark community composition between the years 2004–2006 and 2007–2012 were evident, mostly because N. ferrugineus, C. albimarginatus and N. acutidens were much more abundant in 2004–2006 and very rare in the period of 2007–2012. Two explanations are offered for the observed changes in relative abundances over time, namely inter-specific interactions and operator-specific feeding protocols. Both, possibly in combination, are suggested to be important determinants of species composition and encounter rates, and relative abundances at this shark provisioning site in Fiji. This study, which includes the most species from a spatially confined shark provisioning site to date, suggests that long-term provisioning may result in competitive exclusion among shark species.     

Observations of newborn blue sharks Prionace glauca in shallow inshore waters of the north‐east Atlantic Ocean

The anomalous presence of numerous blue shark Prionace glauca neonates and juveniles in shallow inshore waters of Galicia, north‐west Spain, during the summers of 2014 and 2015 is reported. Changes in oceanographic conditions, high recruitment events or changes in the pupping area are discussed as possible causes of this unusual behaviour.     

Blue shark Prionace glauca fin-to-carcass-mass ratios in Spain and implications for finning ban enforcement

This study examines the processing of fins from blue sharks Prionace glauca caught by the Spanish longline fleet and landed in Vigo, Spain, and implications of these practices for enforcing the E.U. ban on shark finning, which relies on a maximum fin-to-carcass-mass ratio. Two major sources of variability in fin-to-carcass ratios are quantified and discussed: (1) the fin set (type and number of fins retained from each shark) and (2) the cutting method used to separate fins from carcasses. The significant differences in fin-to-carcass-mass ratios between fin sets or cutting procedure demonstrates that the ratio limit is problematic and, conclusively, in order to facilitate proper enforcement, fishermen should be required to land all sharks with the fins still naturally attached to the bodies.     

The early stages of development in Carcharhinus plumbeus

Six embryos of the sandbar shark, Carcharhinus plumbeus , were found in a gravid female caught at Ras Muhammad, southern tip of Sinai peninsula, in October 1975. Their external morphology, internal organs, and the structure of the egg case and the uterus are described. Embryos were estimated to be two months old and all were in a stage of development between the end of the external-gill phase and before the beginning of the pseudoplacenta formation. The foetomaternal interrelation is based on oxygen supply from the maternal uterus mucosa and some mucus is produced by tubular glands also in the uterus mucosa. The compartments formation and the septum generation are described. An embryonic-membrane-storage chamber has been found for each embryo and we assume that this structure is common, at least, to all the genus Carcharhinus .     

Diet,trophic interactions and possible ecological role of commercial sharks and batoids in northern Peruvian waters

The Peruvian sea represents one of the most productive ocean ecosystems and possesses one of the largest elasmobranch fisheries in the Pacific Ocean. Ecosystem-based management of these fisheries will require information on the trophic ecology of elasmobranchs. This study aimed to understand the diet, trophic interactions and the role of nine commercial elasmobranch species in northern Peru through the analysis of stomach contents. A total of 865 non-empty stomachs were analysed. Off northern Peru, elasmobranchs function as upper-trophic-level species consuming 78 prey items, predominantly teleosts and cephalopods. Two distinctive trophic assemblages were identified: (a) sharks (smooth hammerhead shark Sphyrna zygaena, thresher shark Alopias spp. and blue shark Prionace glauca) that feed mainly on cephalopods in the pelagic ecosystem; and (b) sharks and batoids (Chilean eagle ray Myliobatis chilensis, humpback smooth-hound Mustelus whitneyi, spotted houndshark Triakis maculata, Pacific guitarfish Pseudobatos planiceps, copper shark Carcharhinus brachyurus and school shark Galeorhinus galeus) that feed mainly on teleosts and invertebrates in the benthonic and pelagic coastal ecosystem. This study reveals for the first time the diet of T. maculata and the importance of elasmobranchs as predators of abundant and commercial species (i.e., jumbo squid Dosidicus gigas and Peruvian anchovy Engraulis ringens). The results of this study can assist in the design of an ecosystem-based management for the northern Peruvian sea and the conservation of these highly exploited, threatened or poorly understood group of predators in one of the most productive marine ecosystems.