L26_fisheryHO11

L26_fisheryHO11 - Fisheries 1 EEMB 106...

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Fisheries - 1 EEMB 106 Fisheries/Conservation I. Background: - Most fishing concentrated in upwelling areas, where nutrient-rich water is brought up into the epipelagic zone. - Current yield is about 100 million tons/year. Maximum yield is estimated to be about 120 million tons/year. So no inexhaustible supply, virtually no underexploited stocks left. - Fished stocks tend to be either very low on the food chain (e.g., anchovies; go to fish meal) or high on the food chain (e.g. tuna; go to direct consumption). II. Goal of Fisheries Management: To determine and predict harvest rates that maximize a predictable and sustainable yield, and minimize detrimental affects on the structure (including genetic) and persistence of populations. In effect, fishing causes a second kind of mortality: Natural mortality + Fishing mortality = Total mortality Idea is to substitute much of the natural mortality with fishing mortality. But fishing and natural mortality are not equivalent. A. Some negative consequences of fishing mortality: - Selection for earlier reproductive size and age, therefore - Shorter generation times - Slower growth to large size - Loss of genetic diversity within species (e.g., salmon) - Reduction in numbers increases vulnerability to environmental disturbances -
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