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UBC Theses and Dissertations

Consistent harvesting strategy in salmon aquaculture Dubreuil, Michel


The goal of this study was to design a consistent harvest strategy using various types of salmon smolts differentiated by species, weight and timing of introduction into seawater. Consistent harvesting is a production strategy leading to the continuous harvest of fresh salmon at a predictable size 52 weeks of the year. The economic and production characteristics of six chinook salmon (Oncorhynchus tschawytscha) and six Atlantic salmon (Salmo salar) cohorts were first analyzed to establish the economic and production factors leading to their respective optimal harvest time and to compare the performance of each cohort. The study was developed with reference to the British Columbia salmon farming industry. To achieve these objectives, a discrete and deterministic bioeconomic model was developed following the theoretical framework proposed by Bjorndal (1988, 1990). A series of sub-models were incorporated to simulate three major components of the biological system. First, fish growth was simulated using a modified Iwama-Tautz growth model to which was added a dampening factor to embody a size/growth relationship. Second, feed requirements was computed using a bioenergetic feeding model based on a formulation empirically derived by Cho (1992) and the work published by Maroni et al (1994) on differential feed conversion efficiencies. Finally, two mortality rate scenarios were specified on the basis of the underlying causes of mortality and the effect of sexual maturation on fish quality and survival. In scenario 1, a fixed mortality rate was relaxed by the convergence of two conditions beyond which the mortality rate began to increase. These conditions were specified as a lower fish weight threshold and a spring to fall timeframe during the year. In scenario 2, the mortality rate was assumed fixed through the production cycle. The results showed that most fish cohort had a comparative advantage in terms of maximizing returns over a specific market window during the year. The major factors determining the comparative advantage of each cohort were life expectancy and growth performance in relation to water temperature. As a result, the optimal harvest timeframe for a cohort selected within a production portfolio could differ from its own optimal harvest time as a single production unit.

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