This thesis deals with in situ estimates of fish target strength distribution which are important in acoustic stock assessment. The data were gathered on Newfoundland's Grand Banks in 1992 using a dual-beam sonar system. In situ measures of target strength distribution are biased unless a correction is made for nonignorable missing data because high target strength fish can be detected more readily than low target strength ones. / Two methods of correcting for the bias are described and implemented. Both methods use measured off-axis angle and rely on the accuracy of these angle measurements since they compare the distributions of measured and true off-axis angles. The first method involves varying the beam pattern threshold with the observed target strength of the fish. The second method uses a logistic model for the probability of detecting a fish given its target strength. / The analysis in this thesis found several previously undocumented results. Firstly, it was demonstrated that off-axis angles measured with a dual-beam system do not correspond well with true ones, which makes the results of both methods dubious; secondly, measured off-axis angles are shown to be dependent on target strength, which suggests that the process of measuring off-axis angles could be improved by taking this into account, and finally, target strength measurements below about -34 dB are observed to be strongly dependent on characteristics of the dual-beam system.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.69664 |
| Date | January 1993 |
| Creators | Hammond, Tim |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Master of Science (Department of Mathematics and Statistics.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001358324, proquestno: AAIMM91759, Theses scanned by UMI/ProQuest. |
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