Thesis (M.S.)--George Mason University, 2009. / Vita: p. 127. Thesis director: Chris Parsons. Submitted in partial fulfillment of the requirements for the degree of Master of Science in Environmental Science and Policy. Title from PDF t.p. (viewed Oct. 11, 2009). Includes bibliographical references (p. 121-126). Also issued in print.

No description available.

This study was undertaken to investigate the taxonomy, biogeography and biology of cow and frilled sharks (Chondrichthyes: Hexanchiformes). This taxon comprises two families, four genera and six extant species. The hexanchoids are a distinctive group of sharks characterized by six or seven paired gill openings, a single dorsal fin and an anal fin. Adult males of this group lack a siphon sac, but have in its place a clasper sac. This structure, which develops along the claspers, is unique to the Hexanchiformes. Hexanchoid sharks are widely distributed in area and depth. This group ranges from coastal bays and harbors along the open coast out across the continental shelf and down along the slopes to considerable depths. They occur from the equatorial zone to sub-polar regions. However, little is known about the ecology and life history of these sharks. Intraspecific variation of meristic counts were generally low for the Hexanchidae, but high for the Chlamydoselachidae, indicating that subpopulations, subspecies or even additional, new species exist within this family. Based on the indicators used in this study, maturity in male frilled sharks was attained at 916 mm TL, perlon sharks between 700 and 800 mm TL, sixgill sharks approximately 3140 mm TL, bigeyed sixgill sharks at about 1250 mm TL and sevengill sharks at approximately 1550 mm TL. Male reproductive success did not appear to be seasonal since males were found to contain viable sperm all year round. Female perlon sharks begin maturing between 950 mm and 1100 mm TL. Gravid females and newborns were absent from the other size classes and it is suspected that they aggregate in different locations to those of adult males and non-breeding females. Adult females are known at 4210 mm TL and immature at 3500 mm TL, However, a more accurate estimate of the size at maturity is wanting. Newborn sixgills were caught off southern Namibia during mid to late summer over three successive seasons. The occurrence of gravid females carrying term embryos during spring months and newborns during the summer months suggests a late spring or summer pupping period. Sixgill and sevengill sharks give birth in areas of high primary productivity. Energetically, this is advantageous for the newborns to be placed in an area with an abundant food source. The rapid growth rates of sixgill and sevengill sharks over the first year would enhance their survivorship since neither species has many predators. The number of female sevengills entering the breeding population is regulated to ensure that some portion of the population is reproductively active at any one time. The "staggering" of females which enter into the breeding population in any given year indicates a two year reproductive cycle. Fecundity estimates for 19 specimens with a largest egg diameter of at least 40 mm indicates a litter size of 67 to 104. The recapture of an adult female sevengill in approximately the same location in which it was tagged suggests that the same individual sharks may return to the same breeding grounds. As with any predators, sharks tend to exploit advantages over their prey. The hexanchoids, especially the sevengill, have evolved complex foraging strategies including social facilitation whereby they actively hunt in packs for large prey species. Sharks of the order Hexanchiformes, although lacking the diversity of the major shark orders, nonetheless play an integral role in the marine environment. The group's success can be attributed to their apical trophic position. In most habitats in which they occur, hexanchoids have no comparable competitors since equivalent sized sympatric squaloids and carcharhinoids feed at a lower trophic level.

As the requirements for vitamin “A” increased during World War II, the livers from the Pacific coast dog-fish (Squalua suckleyi) and the soup-fin shark (Galeorhinus galeua) became one of the principal sources of vitamin "A". Under the pressure of a high and increasing fishing intensity, the catch of these two sharks in British Columbia has dropped greatly during the years following 1944. Changes in the availability or relative abundance of the dog-fish and soup-fin shark caught in Hecate strait and the dog-fish caught off Barkley sound on the west coast of Vancouver island were determined from the analysis of the-individual tally slips or fish receipts of each fishermen's landing of the livers from these two sharks caught by sunken gill-nets. Methods employed in the analysis of the data to determine the availability, included the analysis of the total landings of the livers from each area under investigation; the average boat catches per month; and average boat catches per trip per month. The method of link relatives is used in the analysis and the catch per unit of effort off Barkley sound is determined. The availability or relative abundance of the dog-fish in Hecate strait was found to decline from 1943 to 1945 with a slight increase during 1946. The availability of the soup-fin shark was found to decline greatly from 1944 to 1946. In the year 1946, the soup-fin shark fishery in Hecate strait was almost a failure. The decline in the availability of the dog-fish and the drop in the average vitamin “A” per gram of liver oil is closely related to the removal or possible depletion of the older age classes from the population. On the west coast of Vancouver island, off Barkley sound the index of return per unit of effort (one sunken gill-net 75 fathoms long fishing over a period of 24 hours) indicated that the availability of the dog-fish has increased in each year since 1944. The sunken gill-nets (7 inch stretched mesh) were found to select; dog-fish greater than 76 cm. in length. Small dog-fish of no commercial value (less than 76 cm.) tend to pass through the meshes. / Science, Faculty of / Zoology, Department of / Graduate

No description available.

published_or_final_version / Biological Sciences / Master / Master of Philosophy

Thesis (M.S.)--University of West Florida, 2009. / Submitted to the Dept. of Biology. Title from title page of source document. Document formatted into pages; contains 49 pages. Includes bibliographical references.

Thesis (Ph. D.)--University of Hong Kong, 1994. / Includes bibliographical references (leaves 128-140).

Thesis (Ph.D.) - University of Queensland, 2004. / Includes bibliography.

Orientador: Otto Bismarck Fazzano Gadig / Banca: Fabio dos Santos Motta / Banca: Patricia Charvet de Almeida / Resumo: Uma revisão taxonômica dos tubarões do gênero Mustelus, família Triakidae, que ocorrem na costa brasileira foi realizada, baseando-se em consulta as coleções ictiológicas brasileiras e três localizadas nos Estados Unidos. As características morfométricas, morfológicas e meristicas foram analisadas, sendo encontradas cinco espécies M. canis (Mitchell,1815); M. fasciatus Garman,1913; M. higmani Springer & Lowe,1963; M. norrisi Springer,1940 e M. schmitti Springer,1940. Uma nova chave para identificação das espécies brasileiras foi proposta. Novos dados de anatomia, morfometria e meristicos foram observados, bem como comparados com os dos espécimens que ocorrem no Atlântico Norte ocidental. Nove espécimes adicionais de M. norrisi foram encontrados e analisados. Diferenças substanciais para os exemplares brasileiros foram descritas. / Abstract: The taxonomy of sharks of the genus Mustelus from Brazil was reviewed. Five species were identified M. norrisi Sringer,1940; M. canis Mitchell,1815; M. higmani Springer & Lowe,1963; M. schmitti Springer,1940 and M. fasciatus Garman,1913. A new identification key for species found in the Brazilian cost was proposed. New data on the distribution, anatomy, morfometry and meristic characteristics were noted, and compared to the ones of specimens found in North American waters. Strong differences between M. norrisi from North America and Brazilian one is described, and nine new specimens catalogued. / Mestre