Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 13 of 13 for “"chondrichthyans"”.
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Baited remote underwater survey of chondrichthyans in False Bay, South Africa
… the period of June-July 2012. Fifteen species of chondrichthyans were recorded, of which Haploblepharus edwardsii was the most abundant, being observed at 83 of 95 sites. One hour was sufficient to capture all the chondrichthyans within the observed area as the average time of arrival was about …
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The historical exploitation of chondrichthyans in False Bay, South Africa and assessment of their conservation status
… Bay, South Africa, began in the 1600s. Today chondrichthyans are regularly taken in multiple fisheries throughout the Bay. Using time series data and life history information I assessed the vulnerability of chondrichthyans to exploitation in False Bay. Extensive time series from five fishing …
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The Impact of Fishing on Populations of Deep-water Chondrichthyan Fishes of the Northeast Atlantic
… impact on several species of deep-water chondrichthyans from the area were assessed. Landings from a three-year market sampling programme showed that the deep-water fishery is highly seasonal in nature operating at greater depths in the summer months. The depth fished by vessels is …
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An assessment of the long-term changes in chondrichthyan abundance on the inshore trawl grounds of the Agulhas Bank, South Africa
… fish abundance. This dissertation focuses on the chondrichthyans, which are believed to be the group of fishes most at risk from intense exploitation. Despite some problems associated with changes in taxonomy and the efficiency of gear, this analysis was able to compare two distinct periods at …
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Interazioni trofiche tra Condroitti in Mediterraneo
Chondrichthyans play an important ecological role, they tend to be high in the food web being very often predators at the top of marine food webs (Cortés, 1999; Ebert e Bizzarro, 2007). Sharks and rays appear to be particularly vulnerable to over-exploitation because of their K-selected …
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From brain development to reproductive axis: an integrated study of the nervous system in cartilaginous fish
… on postnatal brain development in Mediterranean chondrichthyans; (ii) the limited availability of comparative neuroecological analyses testing habitat-related brain organization within the Mediterranean Sea; and (iii) the poor understanding of interactions between dopaminergic and …
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Effects of the late Permian mass extinction on chondrichthyan palaeobiodiversity and distribution patterns
… explores the authenticity of extinction among chondrichthyans and possible explanations for the observed patterns, because extinction severities on the taxonomic and ecological levels may be decoupled or the quality of the fossil record may be variable. The presented analyses are based on a …
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The trophic dynamics of the broadnose sevengill shark (Notorynchus cepedianus) in False Bay, South Africa, using multiple tissue stable isotope analysis
… including cephalopods, crustaceans, teleosts, chondrichthyans and marine mammals. In addition, seven white shark, Carcharodon carcharias, muscle samples were collected from False Bay and analysed for comparison with those of sevengills. Sevengills in False Bay had the highest δ15N values of all …
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Axial patterning of the chondrichthyan pharyngeal endoskeleton and the origin of the jaw
… were based largely on the skeletal anatomy of chondrichthyans (sharks, skates and holocephalans), but remain largely untested from a developmental perspective. Here, I test 1) whether jaws and gill arches ancestrally shared common developmental patterning mechanisms, and 2) whether the …
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Quantitative fish survey of the submarine canyons of the iSimangaliso Wetland Park
… Only three Myliobatidae species represented the Chondrichthyans. Variation in Shannon-Wiener species diversity (H') was influenced by the diversity of habitat (Kruskall†Wallis p<0,0001) and depths (Kruskall†Wallis p<0,0001). Mann†Whitney post hoc tests showed cave to have a higher H' than …
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A baited remote underwater video survey of the Goukamma Marine Protected Area's ichthyofauna and a subsequent community structure comparison with the Betty's Bay, Stilbaai, and Tsitsikamma Marine Protected Areas
… species richness and abundance of sparids, chondrichthyans, and other reef-associated species than CAS and UVC samples. Over 90% more chondrichthyans were recorded in the BRUV samples than by the other two methods. BRUVs are therefore considered to be a suitable replacement for CAS and UVC …
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Quantifying variation in teeth of Late Triassic vertebrates: implications for identification, palaeoecology, and biostratigraphy
… taxa in combination, from pseudosuchians to chondrichthyans and highlights the importance of small and isolated fossils in reconstructing vertebrate communities.
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The evolution and function of pharyngeal arch signalling centres in jawed vertebrates
Pharyngeal arches are paired columns of tissue that form when pouches of foregut endoderm contact surface ectoderm on either side of the embryonic vertebrate head. In fishes, endodermal pouches fuse with surface ectoderm to form gill slits. Once delineated, pharyngeal arches undergo morphogenesis …