How Close is too Close? The Effect of a Non-Lethal Electric Shark Deterrent on White Shark Behaviour

This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.Sharks play a vital role in the health of marine ecosystems, but the potential threat that sharks pose to humans is a reminder of our vulnerability when entering the ocean. Personal shark deterrents are being marketed as the solution to mitigate the threat that sharks pose. However, the effectiveness claims of many personal deterrents are based on our knowledge of shark sensory biology rather than robust testing of the devices themselves, as most have not been subjected to independent scientific studies. Therefore, there is a clear need for thorough testing of commercially available shark deterrents to provide the public with recommendations of their effectiveness. Using a modified stereo-camera system, we quantified behavioural interactions between white sharks (Carcharodon carcharias) and a baited target in the presence of a commercially available, personal electric shark deterrent (Shark Shield Freedom7™). The stereo-camera system enabled an accurate assessment of the behavioural responses of C. carcharias when encountering a non-lethal electric field many times stronger than what they would naturally experience. Upon their first observed encounter, all C. carcharias were repelled at a mean (± std. error) proximity of 131 (± 10.3) cm, which corresponded to a mean voltage gradient of 9.7 (± 0.9) V/m. With each subsequent encounter, their proximity decreased by an average of 11.6 cm, which corresponded to an increase in tolerance to the electric field by an average of 2.6 (± 0.5) V/m per encounter. Despite the increase in tolerance, sharks continued to be deterred from interacting for the duration of each trial when in the presence of an active Shark Shield™. Furthermore, the findings provide no support to the theory that electric deterrents attract sharks. The results of this study provide quantitative evidence of the effectiveness of a non-lethal electric shark deterrent, its influence on the behaviour of C. carcharias, and an accurate method for testing other shark deterrent technologies

The Digital Fish Library: Using MRI to Digitize, Database, and Document the Morphological Diversity of Fish

Museum fish collections possess a wealth of anatomical and morphological data that are essential for documenting and understanding biodiversity. Obtaining access to specimens for research, however, is not always practical and frequently conflicts with the need to maintain the physical integrity of specimens and the collection as a whole. Non-invasive three-dimensional (3D) digital imaging therefore serves a critical role in facilitating the digitization of these specimens for anatomical and morphological analysis as well as facilitating an efficient method for online storage and sharing of this imaging data. Here we describe the development of the Digital Fish Library (DFL, http://www.digitalfishlibrary.org), an online digital archive of high-resolution, high-contrast, magnetic resonance imaging (MRI) scans of the soft tissue anatomy of an array of fishes preserved in the Marine Vertebrate Collection of Scripps Institution of Oceanography. We have imaged and uploaded MRI data for over 300 marine and freshwater species, developed a data archival and retrieval system with a web-based image analysis and visualization tool, and integrated these into the public DFL website to disseminate data and associated metadata freely over the web. We show that MRI is a rapid and powerful method for accurately depicting the in-situ soft-tissue anatomy of preserved fishes in sufficient detail for large-scale comparative digital morphology. However these 3D volumetric data require a sophisticated computational and archival infrastructure in order to be broadly accessible to researchers and educators

Study of pallial neurogenesis in shark embryos and the evolutionary origin of the subventricular zone

The dorsal part of the developing telencephalon is one of the brain areas that has suffered most drastic changes throughout vertebrate evolution. Its evolutionary increase in complexity was thought to be partly achieved by the appearance of a new neurogenic niche in the embryonic subventricular zone (SVZ). Here, a new kind of amplifying progenitors (basal progenitors) expressing Tbr2, undergo a second round of divisions, which is believed to have contributed to the expansion of the neocortex. Accordingly, the existence of a pallial SVZ has been classically considered exclusive of mammals. However, the lack of studies in ancient vertebrates precludes any clear conclusion about the evolutionary origin of the SVZ and the neurogenic mechanisms that rule pallial development. In this work, we explore pallial neurogenesis in a basal vertebrate, the shark Scyliorhinus canicula, through the study of the expression patterns of several neurogenic markers. We found that apical progenitors and radial migration are present in sharks, and therefore, their presence must be highly conserved throughout evolution. Surprisingly, we detected a subventricular band of ScTbr2-expressing cells, some of which also expressed mitotic markers, indicating that the existence of basal progenitors should be considered an ancestral condition rather than a novelty of mammals or amniotes. Finally, we report that the transcriptional program for the specification of glutamatergic pallial cells (Pax6, Tbr2, NeuroD, Tbr1) is also present in sharks. However, the segregation of these markers into different cell types is not clear yet, which may be linked to the lack of layering in anamniotesThis work was supported by the Spanish Ministerio de Economía y Competitividad-FEDER (BFU2014-5863-1P)S

Variation in brain organization and cerebellar foliation in chondrichthyans: Sharks and holocephalans

The widespread variation in brain size and complexity that is evident in sharks and holocephalans is related to both phylogeny and ecology. Relative brain size (expressed as encephalization quotients) and the relative development of the five major brain areas (the telencephalon, diencephalon, mesencephalon, cerebellum, and medulla) was assessed for over 40 species from 20 families that represent a range of different lifestyles and occupy a number of habitats. In addition, an index (1-5) quantifying structural complexity of the cerebellum was created based on length, number, and depth of folds. Although the variation in brain size, morphology, and complexity is due in part to phylogeny, as basal groups have smaller brains, less structural hypertrophy, and lower foliation indices, there is also substantial variation within and across clades that does not reflect phylogenetic relationships. Ecological correlations, with the relative development of different brain areas as well as the complexity of the cerebellar corpus, are supported by cluster analysis and are suggestive of a range of 'cerebrotypes'. These correlations suggest that relative brain development reflects the dimensionality of the environment and/or agile prey capture in addition to phylogeny

Variation in Brain Organization and Cerebellar Foliation in Chondrichthyans: Batoids

Interspecific variation in relative brain size (encephalization), the relative size of the five major brain areas (the telencephalon, diencephalon, mesencephalon, cerebellum, and medulla) and the level of cerebellar foliation was assessed in over 20 representative species of batoid (skates and rays), from eight families. Using species as independent data points and phylogenetically independent contrasts, relationships among each of the neuroanatomical variables and two ecological variables, habitat and lifestyle, were assessed. Variation in relative brain size and brain organization appears to be strongly correlated with phylogeny. Members of the basal orders Rajiformes and Torpediniformes tend to have relatively small brains, with relatively small telencephalons, large medullas, and smooth, unfoliated cerebellums. More advanced Myliobatiformes possess relatively large brains, with relatively large telencephalons, small medullas, and complex, heavily foliated cerebellums. Increased brain size, telencephalon size, and cerebellar foliation also correlate with living in a complex habitat (such as in association with coral reefs) and an active, benthopelagic lifestyle, but as primary habitat and lifestyle also closely match phylogenetic relationships in batoids, it is difficult to separate the influence of phylogeny and ecological factors on brain organization in these animals. However, the results of two forms of multivariate analysis (principal component analysis and cluster analysis) reveal that certain species are clustered with others that share ecological traits, rather than with more closely related species from the same order. This suggests that ecological factors do play a role in defining patterns of brain organization and there is some evidence for 'cerebrotypes' in batoids

Degradation of Ru(bpy) <inf>3</inf>²⁺-based OLEDs

Analysis of the possible mechanisms of degradation of Ru(bpy) 32+-based OLEDs has led to the idea of quencher formation in the metalloorganic area close to the cathode. It has been suggested that the quencher results from an electrochemical process where one of the bipyridine (bpy) groups is replaced with two water molecules or from reduction of Ru(bpy) 32+ to Ru(bpy) 30. We have tested these and other degradation ideas for Ru(bpy) 32+-based OLEDs, both prepared and tested with considerable exposure to the ambient environment and using materials and procedures that emphasize cost of preparation rather than overall efficiency. In order to understand the mechanisms involved in these particular devices, we have correlated changes in the devices' electrical and optical properties with MALDI-TOF mass spectra and UV-vis absorption and fluorescence spectra. © 2005 Materials Research Society