1,721,269 research outputs found
Near-infrared spectroscopy for shark ageing and biology
No full textAccurate and reliable age estimates of sharks are important for informing management that will achieve sustainable outcomes for populations. Age is the foundation of many of the essential parameters, such as growth rate and productivity, that are used in demographic analyses and fisheries assessments (Cailliet et al., 2006; Campana, 2001). Here, "sharks" is used as a general term to refer to sharks, rays, and chimaeras, therwise known as chondrichthyans. Traditionally, to estimate age in sharks, growth bands are counted in their hard parts. Vertebrae or dorsal fin spines are primarily used, although caudal thorns have also been found suitable for ageing in a few species of skates (Cailliet, 2015; Goldman et al., 2012; Serra-Pereira et al., 2008). As sharks age, calcified material accumulates in these structures and can produce visible band pairs that, when formation periodicity has been validated, enable age determination (Goldman et al., 2012; see also Chapter 10 in this volume).
Counting these band pairs requires experience and time to achieve consistent results, and repeated reads are necessary to ensure precision of the counts (Cailliet et al., 2006). It also can require time-consuming preparation, such as sectioning of the structures and enhancement with stains to improve clarity and readability of the band pairs (Irvine et al., 2006b; Matta et al., 2017). In addition, this approach normally requires the lethal removal of the structures used for ageing from an individual. Given the vulnerability of many shark species to exploitation (Dulvy et al., 2014), nonlethal methods for ageing would be beneficial. These issues prompted investigation of near-infrared spectroscopy (NIRS) as a complementary approach to shark ageing. Although NIRS requires traditional band counts of some age structures, it can greatly reduce the time taken to estimate age from a structure and has the potential to be nonlethal (Rigby et al., 2014, 2016b). This chapter reviews how NIRS works and the application and considerations for use of NIRS in shark ageing
FIGURE 1 in Range, sexual dimorphism and bilateral asymmetry of rostral tooth counts in the smalltooth sawfish Pristis pectinata Latham (Chondrichthyes: Pristidae) of the southeastern United States
No full textFIGURE 1. Relative frequency of total rostral tooth counts for Pristis pectinata from the southeastern United States (n=105).Published as part of Wiley, Tonya R., Simpfendorfer, Colin A., Faria, Vicente V. & Mcdavitt, Matthew T., 2008, Range, sexual dimorphism and bilateral asymmetry of rostral tooth counts in the smalltooth sawfish Pristis pectinata Latham (Chondrichthyes: Pristidae) of the southeastern United States, pp. 51-59 in Zootaxa 1810 (1) on page 54, DOI: 10.11646/zootaxa.1810.1.3, http://zenodo.org/record/512508
Acoustic telemetry
No full textAcoustic telemetry involves the use of sound to convey information relating to the presence of an animal as it moves from one location to another in the aquatic environment. In the context of shark research, this most commonly reflects using acoustic transmitters and receivers to track movement of individuals. Originally, acoustic transmitters simply emitted a pulse that could be detected by a receiving device; researchers followed the sound using a directional hydrophone as the shark swam through the environment and recorded positions every few minutes to represent the movement track of an individual (Holland et al., 1992; Morrissey and Gruber, 1993). As technology developed, information was encoded into acoustic signals by using a series of pings that could be decoded by the receiver. This led to the capacity to provide unique identification codes for an individual tag, which allowed simultaneous tracking of multiple individuals. By combining coded transmitters with data-logging acoustic receivers that could be moored in study sites for long periods, the need for animals to be actively followed was removed. This revolutionized the field of acoustic telemetry by allowing researchers to establish arrays of receivers to detect and track sharks automatically (Heupel et al., 2006). Sensors are also being developed and integrated with transmitters to provide information on the environments that tagged sharks encounter (e.g., depth, temperature) and their behavioral state (e.g., acceleration). Similarly, advances in receiver systems, collaborations, and modes to access stored data provide new ways to examine shark behavior and distribution at broad scales. In this chapter, we discuss the application of acoustic telemetry to track sharks, advances to the technology over time, and the challenges and opportunities this technology has provided to shark research
Prediciendo los efectos del ENSO y el cambio climático en la distribución del tiburón martillo juvenil en el norte de Perú
Full text linkEl tiburón martillo (Sphyrna zygaena) está amenazado de extinción debido a las pesquerías del sudeste del Pacífico. Sin embargo, existen pocos esfuerzos para manejar sus pesquerías sosteniblemente, para lo cual se requiere conocer el uso de su hábitat. Por lo tanto, esta investigación tiene como objetivo predecir la distribución espacial del tiburón martillo en los escenarios actuales de La Niña y El Niño y su distribución en el cambio climático futuro. 2994 ocurrencias de tiburones juveniles (2009 y 2017), y ocho factores ambientales fueron modelados utilizando Maxent. Los resultados indican que los predictores ambientales de distribución más importantes fueron la profundidad, la temperatura de la superficie del mar y la clorofila-a (indicador disponibilidad de presas). La mayor idoneidad del hábitat se predijo en la región central oceánica durante La Niña y en zona costera del norte en El Niño. Estos hábitats presentan condiciones oceanográficas y batimétricas únicas que resultan en zonas de alta productividad marina. En escenarios futuros de cambio climático, se predice que la idoneidad del hábitat será más costera, aumentando su vulnerabilidad a la pesca. Para mejorar la conservación del tiburones martillo y su ecosistema, estas áreas de alta idoneidad deberían ser una prioridad para futuras investigaciones y manejo.The smooth hammerhead shark (Sphyrna zygaena) is one of most captured
shark species by southeastern Pacific fisheries. Their distribution and habitat use
is poorly understood hindering the identification of critical habitats for their
conservation and the possible impacts of environmental change on species
distribution. The aim of this research was to predict the spatial distribution of
smooth hammerheads based on habitat suitability from the Northern Humboldt
Upwelling System (NHUS) off northern Peru. (06ºS-11ºS). To achieve this, three
analyses were performed: i) characterize their population structure, ii) identify
environmental factors that affect their distribution, and iii) predict their spatially
and environmentally suitable habitat under current La Niña and El Niño scenarios
and projected to a future scenario of ocean warming between the years 2040-
2050. Between the years 2009 and 2017, 7485 sharks were measured and
georeferenced obtained from a small-scale driftnet fishery. Their ecological niche
was modelled using the program MaxEnt. The results indicate that neonate and
juvenile smooth hammerheads are the dominant life-stage in the northern part of
NHUS where this area probably represents a nursery area. The spatial
distribution of sharks varies according to their ontogeny, and at seasonal and El
Niño Southern Oscillation (ENSO) conditions. Sharks were closer to the coast
during warmer (summer and El Niño conditions) periods. Four environmental
variables were identified as important predictors of species distribution: depth,
sea surface temperature (SST), chlorophyll-a, as a proxy of prey availability-,
and, to a lesser degree, salinity. During current conditions, the highest suitable
habitat was predicted in the central-offshore and shifted to northern-coastal part
of the study area (close to the ecotone zone; 6ºS) in La Niña and El Niño
conditions- respectively- as the coastal upwelling area, during El Niño warm
conditions, offers the coolest environment and the highest productivity. Unique
bathymetric conditions are associated with these areas (i.e. shelf break, marine
canyons, narrow continental shelf, and coastal topography) generating
oceanographic conditions (i.e. marine fronts, upwelling) which result in zones of
exceptional high marine productivity. Under future climate change scenarios, the
habitat suitability of smooth hammerheads will shift to a more coastal distribution.
To enhance the conservation of smooth hammerheads and their supporting
ecosystem, these areas of high suitability should be a priority for fishery
management and under future scenarios of climate change, their coastal
distribution could increase their catchability. Furthermore, these areas of highest
suitability should be considered as candidates for a dynamic pelagic marine
protected area
Utility of a multi-faceted approach in determining the habitat use of endangered euryhaline elasmobranchs in a remote region of northern Australia
Full text linkThe overriding aim of this thesis was to explore the habitat use of the critically endangered freshwater sawfish (Pristis microdon) and northern river shark (Glyphis garricki) in the remote Kimberley region of northern Western Australia. This information has been largely lacking and is critical for the management and conservation of these species. Habitat use of these species was documented through the use of long-term catch, environmental and tagging (conventional, acoustic and satellite) data, which was acquired between 2005 and 2009 in the Fitzroy River and King Sound, Western Australia. Monitoring of the various environmental parameters demonstrated that the study area is extremely dynamic, with significant seasonal changes in abiotic variables such as water flow, depth, temperature, turbidity and salinity. Catch data demonstrated that juvenile P. microdon inhabit the Fitzroy River for three to five years, at which time individuals begin to emigrate from the river, prior to maturation. Catch data also demonstrated that juvenile and adult male G. garricki inhabit highly turbid nearshore waters throughout the upper King Sound. Relative abundance of P. microdon in the river varied seasonally and annually, and differed between size classes. A decrease in relative abundance between the early and late dry season, which was only significant with young of the year P. microdon, was attributed to mortality as well as dispersal of individuals. Catches of G. garricki were rare, although this species was relatively abundant in highly turbid waters in King Sound. Foraging, depth use and inter-pool movements of P. microdon in the Fitzroy River were influenced by depth, flow and light intensity/turbidity and potentially by salinity and/or water temperature. However, the response to environmental variables differed between P. microdon size classes, possibly due to differences in trophic and habitat requirements of the various size classes. Results from this study demonstrated that P. microdon is sensitive to environmental change, but appear to endure/recover from short-term (months) negative impacts through behavioural regulation. It is not possible at this time to positively conclude about the impacts of specific environmental changes on G. garricki habitat use, due to the limited data from G. garricki captures and tagging. However, as all G. garricki captured in this study were observed to inhabit tidal creeks and river mouth areas, the destruction of such areas or restriction to and from such areas is likely to negatively impact this species
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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