Optimization of trawlnet codend mesh size to allow for maximal undersized fish release and a model consideration of towing time to the effects of the selection curve

Ma, Liangzhuang (2005) Optimization of trawlnet codend mesh size to allow for maximal undersized fish release and a model consideration of towing time to the effects of the selection curve. Masters thesis, Memorial University of Newfoundland.

[English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (2MB)

Abstract

This dissertation consists of two research topics related to the fishing industry. -- First, the problem of comparing several gears occurs frequently in the fishing industry. There is a desire to determine whether the response to one or more experimental gear(s) differs from the response of a traditional gear, and, if so, to further identify which experimental gear(s) is better than the traditional gear and which is the best under certain criteria. In many fishing experiments, one often has prior knowledge that the experimental gears are at least as effective as the traditional gear, and their responses are monotonically increasing or decreasing. It is well known that utilization of this ordering information increases the efficiency of statistical inference procedures. The aim of the first part of this thesis is to give a useful statistical inference procedure for the problems met in the fishing industry by utilizing this prior information. -- Secondly, we introduce the towing time concept into the framework of gear selectivity studies. In the past, scientists have generally not considered the effects of the towing time. It is only considered since prolonged towing time may destroy the fish. Hardly any research had been done on the effects of gear selectivity and total catch by varying the towing time. In this dissertation, a new model is proposed, with its corresponding selection curve, considering the effect of towing time. This new model also generates a Sigmoid-shaped selection curve, which is different from the one generated by the traditional selection model. Based on this new model, some adjustments can be proposed in towing time, the fishing process, and gear design. These changes may be of benefit to both fishing industry and fishery management.

Actions (login required)

View Item