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Age determination of the sixgill shark from hard parts using a series of traditional and novel approaches

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Title	Age determination of the sixgill shark from hard parts using a series of traditional and novel approaches
Author	Campbell, S. Jeffrey (Steven Jeffrey)
College affiliation	Huxley College of the Environment
Department or program affilliation	Department of Environmental Sciences
Abstract	Necessary to the management of any species of fish is the ability to determine age in individuals. Age information is used to establish growth rates, longevity, age at maturity, and population age structure, and to predict how population demographics will change over time. For most species of fish, reliable aging techniques have been in use since the early 20th century. Most boney fish are aged by counting bands of calcium phosphate hydroxyapatite that form over time in skeletal hard parts such as otoliths, fin-spines, and scales, which can be used as proxies for age in years. Fishes in the Class Elasmobranchii lack otoliths and have skeletons composed of cartilage, which often do not incorporate enough calcium to enable enumeration by traditional aging methods that rely on light microscopy, in some cases aided by enhancement techniques such as histological staining. For these fishes, alternative methods and aging structures are used to identify and enumerate annual patterns in calcium deposition. The aging structure of choice for most elasmobranches is the vertebral centrum, where bands of calcium are deposited that can be used as proxies for age in years. A few deep-dwelling species of Elasmobranchii, such as the sixgill shark (Hexanchus griseus,) have as yet defied efforts at age determination, inhibiting efforts to implement science-based management plans. This study has attempted to identify alternative aging structures that may incorporate seasonally-mediated concentrations of elements or isotopes into cartilage. Once identified, these structures were subjected to two recently developed methods of elemental microanalysis, energy dispersive X-ray spectroscopy (EDAX), and laser ablation, inductively-coupled, plasma mass spectrometry (LA-ICP-MS), in an effort to develop an aging method for H. griseus, and potentially other poorly calcified elasmobranchs. In addition, it has also used two traditional, histological staining methods, Von Kossa's AgNO3, and Alizarin Red-S and applied them to these non-traditional aging structures. This study identified regions within the cartilaginous skeleton of H. griseus that lay down systematic banding patterns. These patterns were visually detected using AgNO3 staining enhanced light microscopy, as well as by periodic oscillations in isotopic concentrations for 24Mg, 88Sr, 107Ag, and 109Ag that were detected through the use of LA-ICP-MS. Future research in this field will need to verify if these bands are deposited on an annual basis. Methodologies must be developed for verification, and validation of these procedures to determine if the band patterns identified by either of these methods have utility for age determination in this and other poorly calcified species of elasmobranchs.
Subject - LCSH	Hexanchiformes--Age determination
Subject - Local	Masters thesis--Western Washington University--Marine and estuarine science
Publisher	Western Washington University
Date	2010
Collection title	Huxley College Collection
Rights	Copying of this document in whole or in part is allowable only for scholarly purposes. It is understood, however, that any copying or publication of this document for commercial purposes, or for financial gain, shall not be allowed without the author's written permission.
Format	application/pdf
Faculty Advisors	Bodensteiner, Leo R. Helfield, James M. Bargmann, Greg

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