{"id":{"repo_id":"cape-town","oai_identifier":"oai:open.uct.ac.za:11427/12613"},"canonical_url":"https://search.dev.ndltd.org/etd/cape-town/oai:open.uct.ac.za:11427/12613","repository":{"repo_id":"cape-town","name":"University of Cape Town","base_url":"https://open.uct.ac.za/oai/request"},"display":{"title":"A computer simulation of the population dynamics of the Cape hakes (Merluccius capensis and M. paradoxus)","abstract":"Catch and effort statistics for the Cape hakes (Merluccius capensis and M. paradoxus) have indicated a substantial decrease in the stock size over the period 1955-74; consequently, a catch projection model was designed to investigate the hake population. Where appropriate, available data have been included in the model; however, some further research was required: 1. The monthly pattern of availability for 1974-76 was examined using South African data; it was found to be similar to that reported for earlier years, and the later figures were used. 2. Assuming that selection curves for different mesh sizes are identical except for their position on the X-axis, a method to calculate selection values for combinations of mesh size and fish length has been outlined, and used with data presented by Bohl et al. (1971). 3. An investigation was made of two methods of estimating natural mortality (M), utilizing the results of Virtual Population Analysis (V.P.A.). In both cases the criteria used to judge M were found to be insensitive, and therefore neither can be used. 4. The stock estimates obtained using V.P.A. were applied to two stock/recruit curves. The goodness of fit in both cases was poor, and nearly identical.","abstract_html":"Catch and effort statistics for the Cape hakes (Merluccius capensis and M. paradoxus) have indicated a substantial decrease in the stock size over the period 1955-74; consequently, a catch projection model was designed to investigate the hake population. Where appropriate, available data have been included in the model; however, some further research was required: 1. The monthly pattern of availability for 1974-76 was examined using South African data; it was found to be similar to that reported for earlier years, and the later figures were used. 2. Assuming that selection curves for different mesh sizes are identical except for their position on the X-axis, a method to calculate selection values for combinations of mesh size and fish length has been outlined, and used with data presented by Bohl et al. (1971). 3. An investigation was made of two methods of estimating natural mortality (M), utilizing the results of Virtual Population Analysis (V.P.A.). In both cases the criteria used to judge M were found to be insensitive, and therefore neither can be used. 4. The stock estimates obtained using V.P.A. were applied to two stock/recruit curves. The goodness of fit in both cases was poor, and nearly identical.","abstract_has_math":false,"creators":["Mertens, Robert George Stephen"],"institution":"Department of Biological Sciences","degree_name":null,"degree_level":null,"degree_discipline":null,"degree_department":null,"school":null,"contributors":[],"advisors":["Field, John G","Newman , G G"],"committee_chairs":[],"committee_members":[],"year":1978,"date_issued":"1978","date_published":"1978","updated_at":"2026-07-22T22:22:49Z","subjects":[],"languages":["eng"],"rights":[],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"http://hdl.handle.net/11427/12613","outbound_label":"Handle","outbound_source":"dc:identifier.uri"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor.advisor","label":"Advisor","values":["Field, John G","Newman , G G"]},{"key":"dc:creator","label":"Author","values":["Mertens, Robert George Stephen"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.accessioned","label":"Dc Date Accessioned","values":["2015-03-16T10:30:35Z"]},{"key":"dc:date.available","label":"Dc Date Available","values":["2015-03-16T10:30:35Z"]},{"key":"dc:date.issued","label":"Date","values":["1978"]},{"key":"dc:publisher.department","label":"Dc Publisher Department","values":["Department of Biological Sciences"]},{"key":"dc:publisher.institution","label":"Dc Publisher Institution","values":["University of Cape Town"]},{"key":"dc:type","label":"Dc Type","values":["Master Thesis"]},{"key":"dc:type.qualificationlevel","label":"Dc Type Qualificationlevel","values":["Masters"]},{"key":"dc:type.qualificationname","label":"Dc Type Qualificationname","values":["MSc"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language.iso","label":"Language (ISO)","values":["eng"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier.uri","label":"Identifier URI","values":["http://hdl.handle.net/11427/12613"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description","label":"Description","values":["Includes bibliographical references (leaves 63-68)."]},{"key":"dc:description.abstract","label":"Abstract","values":["Catch and effort statistics for the Cape hakes (Merluccius capensis and M. paradoxus) have indicated a substantial decrease in the stock size over the period 1955-74; consequently, a catch projection model was designed to investigate the hake population. Where appropriate, available data have been included in the model; however, some further research was required: 1. The monthly pattern of availability for 1974-76 was examined using South African data; it was found to be similar to that reported for earlier years, and the later figures were used. 2. Assuming that selection curves for different mesh sizes are identical except for their position on the X-axis, a method to calculate selection values for combinations of mesh size and fish length has been outlined, and used with data presented by Bohl et al. (1971). 3. An investigation was made of two methods of estimating natural mortality (M), utilizing the results of Virtual Population Analysis (V.P.A.). In both cases the criteria used to judge M were found to be insensitive, and therefore neither can be used. 4. The stock estimates obtained using V.P.A. were applied to two stock/recruit curves. The goodness of fit in both cases was poor, and nearly identical."]},{"key":"dc:title","label":"Title","values":["A computer simulation of the population dynamics of the Cape hakes (Merluccius capensis and M. paradoxus)"]}]}],"canonical_facts":{"dc:contributor.advisor":["Field, John G","Newman , G G"],"dc:creator":["Mertens, Robert George Stephen"],"dc:date.accessioned":["2015-03-16T10:30:35Z"],"dc:date.available":["2015-03-16T10:30:35Z"],"dc:date.issued":["1978"],"dc:description":["Includes bibliographical references (leaves 63-68)."],"dc:description.abstract":["Catch and effort statistics for the Cape hakes (Merluccius capensis and M. paradoxus) have indicated a substantial decrease in the stock size over the period 1955-74; consequently, a catch projection model was designed to investigate the hake population. Where appropriate, available data have been included in the model; however, some further research was required: 1. The monthly pattern of availability for 1974-76 was examined using South African data; it was found to be similar to that reported for earlier years, and the later figures were used. 2. Assuming that selection curves for different mesh sizes are identical except for their position on the X-axis, a method to calculate selection values for combinations of mesh size and fish length has been outlined, and used with data presented by Bohl et al. (1971). 3. An investigation was made of two methods of estimating natural mortality (M), utilizing the results of Virtual Population Analysis (V.P.A.). In both cases the criteria used to judge M were found to be insensitive, and therefore neither can be used. 4. The stock estimates obtained using V.P.A. were applied to two stock/recruit curves. The goodness of fit in both cases was poor, and nearly identical."],"dc:identifier.uri":["http://hdl.handle.net/11427/12613"],"dc:language.iso":["eng"],"dc:publisher.department":["Department of Biological Sciences"],"dc:publisher.institution":["University of Cape Town"],"dc:title":["A computer simulation of the population dynamics of the Cape hakes (Merluccius capensis and M. paradoxus)"],"dc:type":["Master Thesis"],"dc:type.qualificationlevel":["Masters"],"dc:type.qualificationname":["MSc"]},"updated_at":"2026-07-22T22:22:49Z"}