Graduate Thesis Or Dissertation
 

A model for understanding the influence of selective and nonselective harvest on fish populations

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/g158bm63w

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  • To understand the influence of selective harvesting on the adaptive capacity of fish populations in changing environments, a computer simulation model was developed. In the model, hypothetical populations were composed of five different life histories, which were genetically determined. Each life history type had its own rate of survival and reproduction that varied with changing environment and population density. In nonselective harvesting, life history types were equally vulnerable to harvest. In selective harvesting some life history types, were more intensively harvested than others. Population life history composition changed continuously in response to both changing environmental conditions and harvesting. Changes in life history composition were closely related to changes in numerical population performances such as density and yield. In general, selective harvesting of the simulated populations reduced mean and terminal abundance, total catch, and life history diversity. Nonselective harvesting tended to eliminate individuals evenly from the life history distribution so that the life history diversity was not greatly influenced. Selective harvesting tended to severely reduce or eliminate the life history types that were more intensively harvested. This generally resulted in extreme reduction of life history diversity. Variation in abundance, as measured by the absolute value of the residuals, was consistently larger in selectively harvested populations. Increased variation was probably related to reduction in life history diversity. Perhaps the most potentially alarming impact was the dramatic increase in incidences of extinction of selectively harvested populations at the highest exploitation rate. High selective harvest rate led to severe reduction in life history diversity which diminished the population's ability to persist in a changing environment. Furthermore, the extreme reduction of life history diversity made it difficult for populations that were able to persist to recover in abundance after termination of harvest. It is important to note, however, that the above conclusions are general outcomes based on 20 different environmental regimes. The results from a few individual regimes were not in accordance with some of the general outcomes, illustrating simply that particular results are highly contingent on the particular environmental pattern.
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file details HiraiTakayuki1988.pdf 2017-08-16 Público Descargar