1,721,225 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
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
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
Environmental DNA (eDNA): a valuable tool for ecological inference and management of sharks and their relatives
No full textKnowledge of spatial and temporal variation in abundance is critical for the implementation of effective protective measures for organisms that are both naturally rare and vulnerable to exploitation. The development of management and conservation strategies for elasmobranchs depends on accurate assessment and monitoring of the distribution and abundance of target species in the field, but detecting species occurrences is often even more challenging in the aquatic environment than on land (Webb and Mindel, 2015). Consequently, as is the case for many large, mobile and rare vertebrates, shark detection is inherently difficult.
All organisms continuously leave traces of themselves behind in the environment in the form of shed skin cells, bodily fluids, metabolic waste, gametes, or blood. Any of these materials can contain pieces of the organism's DNA. Environmental DNA (eDNA) analysis is based on the retrieval of this naturally released genetic material from the environment. It generally refers to bulk DNA extracted from an environmental sample such as water but also from soil, sediment, snow, or even from air (Taberlet et al., 2012a). In aquatic systems, macroorganismal-derived eDNA can be present as free DNA, cellular debris, or particle-bound DNA and is mostly present in small fragments, due to rapid degradation (Barnes et al., 2014); however, much of the eDNA is retrieved from cellular material and may therefore contain still relatively undamaged nucleic acid molecules. Nevertheless, eDNA studies focus primarily on the detection of short fragments, as currently available parallel sequencing and qPCR platforms have short-read capabilities limited to a few hundred base pairs. When DNA is present at low concentrations, mitochondrial DNA (mtDNA) is often targeted, as there are substantially more mitochondrial than nuclear DNA copies per cell (Wilcox et al., 2013). Commonly employed mtDNA genes include cytochrome b, cytochrome c oxidase subunit 1 (COI), 12S rRNA, and 16S rRNA (Kelly et al., 2014; Thomsen et al., 2012b; Valentini et al., 2016), and targeted fragments typically fall within the range of 79 to 285 bp (Ficetola et al., 2008; Minamoto et al., 2012). The level of target specificity is often the main determining factor when choosing or designing primers for eDNA analysis
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
Citizen science in shark and ray research and conservation: strengths, opportunities, considerations and pitfalls
No full textCitizen science programs are growing around the world in number, diversity, and prominence, and they are arguably now accepted as a mainstream scientific methodology (Dickinson et al., 2012; Silvertown, 2009). Modern citizen science programs range from observation-based programs, such as recording local sightings of specific species or phenomena, to global efforts to collect "big data," such as the National Aeronautics and Space Administration (NASA) program Global Learning and Observations to Benefit the Environment (GLOBE), where citizen scientists from around the world use a smartphone app to photograph clouds and record data on mosquitoes. In the fields of biology and ecology, citizen scientists are collecting data on changes in species distributions, pollution, invasive species, threatened species, disease, phenology, biodiversity, habitats, and landscapes and are making tangible conservation contributions (Bonney et al., 2009, 2014; Dickinson et al., 2010; Edgar et al., 2017; Robinson et al., 2015; Silvertown, 2009). In situations where citizen science participants are numerous and widely distributed, these initiatives can help professional scientists greatly expand their spatial and temporal sampling capability, and thus the scope and scale of research questions they can address. In terms of biodiversity monitoring alone, citizen science programs have been estimated to include 1.5 million volunteers that contribute over $2.5 billion worth of in-kind contributions to biodiversity science every year (Theobald et al., 2015)
Social science and its application to the studies of shark biology
No full textMeeting the needs of people while sustaining ecosystems and the benefits they deliver is a global challenge. Coastal marine systems present a particularly important case, given that over half of the world's population lives within 100 km of the ocean, and fisheries provide the primary source of protein for over a billion people worldwide (Leslie et al., 2015). Sharks and rays play important roles in many of these fisheries and coastal communities, as not only do they provide food and income but they can also have strong social and cultural value (Dulvy et al., 2017). However, pressures on sharks and rays from fishing, habitat loss, and other factors are increasing, resulting in global declines in some species and raising concerns that up to a quarter of the world's sharks and rays are threatened with extinction (Dulvy et al., 2008).
At a time when many shark and ray species are experiencing ongoing population declines from these growing pressures, the need to engage in research that bridges the human-shark interface to better inform conservation and fisheries management and policy is becoming increasingly recognized (Jacques, 2010; Simpfendorfer et al., 2011). With the possible exception of work related to "shark attacks" on humans, social science research that focuses on sharks has not kept pace with biophysical science, despite knowledge that understanding people is pivotal to effective natural resource management (Gutierrez et al., 2011; Reid, 2016; Twyman, 2017)
A review on the morphology of ovarian follicles in elasmobranchs: A case study in Rhizoprionodon taylori
Full text linkThe identification of the elasmobranch secondary ovarian follicles and their function can be challenging and the inconsistent use of terminology derived from other taxa is a matter of ongoing debate. In this study, the available information on the histology of the elasmobranch secondary ovarian follicles derived from atresia (preovulatory follicles) or ovulation (postovulatory follicles) is reviewed highlighting their morphology and steroidogenic capacity. Based on this literature review, the ovarian follicles of the Australian sharpnose shark Rhizoprionodon taylori were classified according to their preovulatory or postovulatory origin. Two types of secondary follicles originating from atresia of developing follicles (atretic previtellogenic follicles) and ripe follicles (atretic vitellogenic follicles), and one type of postovulatory follicle were identified throughout the reproductive year of this species. Morphological similarities of the elasmobranch secondary ovarian follicles and their variations in different species denote the difficulty to classify them. Given the multiple origins of ovarian follicles, their poorly understood functions and capacity to supply steroids, visual identification of these structures and the use of terminology derived from mammalian and other vertebrate studies (with the exception of the corpora lutea as a temporary endocrine gland) is not advisable. J. Morphol. 278:486–499, 2017.Fil: Waltrick, Daniela S.. James Cook University; Australia. Western Australian Fisheries and Marine Research Laboratories; AustraliaFil: Simpfendorfer, Colin A.. James Cook University; AustraliaFil: Awruch, Cynthia Andrea. James Cook University; Australia. University of Tasmania; Australia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; Argentin
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
- …
