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  • 學位論文

溫度變化和漁業壓力如何對魚群的體長結構造成影響?

How do temperature and fishing affect the size structure of fish populations?

指導教授 : 謝志豪

摘要


體長結構 (size structure)是代表魚群狀態的重要指標,因為它可以反應魚群的穩定度、對環境的抵抗力、以及族群的生產力。過去研究顯示體長結構主要受到 (1) 漁業捕撈以及 (2) 溫度變化 兩者的影響。然而,漁撈及溫度變化哪一者對體長結構有較大的影響並不清楚。另一方面,以往研究多使用體長結構指標 (size-based indicator)將體長結構簡化為單一指標來表示體長結構的變化,然而許多研究顯示這些指標僅能反應體長結構部分的變化,不一定能反應體長結構整體的改變,所以本篇的目的是使用多元回歸分析中的變異分配,來分析完整的體長結構變化,藉以了解23個經濟魚種的體長結構如何受到溫度變化和捕撈影響,以及去探討他們是否有一個交互作用。 研究顯示漁撈和溫度變化都會對體長結構造成影響,但線性的交互影響很小甚至沒有。我進一步去探討哪些因子與影響程度有相關,我發現會影響的因子包括1. 物種本身生長速率、2. 其受捕撈的程度與3. 其環境溫度變化的速率。其中漁撈對體長結構的影響與物種生長速率呈負相關,表示生長較慢的魚群其體長結構受漁撈的影響程度較大;另外,漁撈和溫度對體長結構的影響程度分別與溫度變化還有捕撈強度有關,而進一步使用廣義線性混合的效應模型(GLMM)去驗證單一因子是否有顯著影響,僅溫度在體長結構中影響程度與漁撈強度有顯著正相關;這些結果表示,即使在變異分配分析中線性的交互影響並不顯著,漁撈與溫度變化的交互作用可透由加乘的方式存在,且機制為:當魚群受到較強的捕撈,其族群對環境抵抗力較弱,較容易在其體長結構找到溫度的影響。本研究也將變異分配分析之結果與常用的體長結構指標做比較,我發現變異分配爭對上述漁撈與溫度變化之分析有較低的p值,亦即結果較顯著;因此,相較於傳統指標,使用變異分配分析體長結構受外在因素影響的程度是較有效的方法。

並列摘要


Influenced by growth, maturation, and mortality history, size structure represents a key demographic characteristic of fish populations, and plays an important role in maintaining stability and reproductive output. There are two important external forces that potentially shrink the size structure of a fish population: fishing and warming. Nevertheless, the relative importance of fishing and warming in affecting size structure of fishes has not been quantified. In addition, existing analysis focus on size-based indicators (SBIs) to represent the size structure of fish population, but some of them may not effectively quantify external forces on size structure. To bridge the knowledge gap, we used variation partitioning approach to quantify the relative contribution of temperature, fishing on size structure of exploited stocks, and then test whether these two factors have an interactive effect. We analyze the size structure (length frequency) of 23 exploited stocks in the Northeast Pacific, Northeast Atlantic, Mediterranean Sea, North Sea, Baltic Sea and Arctic Sea. Our results showed that the variance of size structure is affected both by fishing (explaining on average of 9.29%) and temperature (explaining on average of 9.29%). In comparison, the interactive effect on size structure was very subtle (on average of 1.79%). We then examined what determined the relative contribution of fishing and temperature. We found that the relative contribution was related to life history traits, mean fishing mortality, and increasing rate of temperature. Specifically, our result showed that fishing effect on size structure significantly decreased with the growth rate, suggesting the size structure of K-selected species was influenced more by fishing. Furthermore, the temperature effect significantly increased with the intensity of fishing, suggesting that fishing makes the exploited stocks more vulnerable to environmental changes. Finally, by comparing our results of variation partitioning approach versus indicators-based analysis, we found that variation partitioning serving as a size structure-based analysis outperformed analysis using SBIs in terms of the lower p-values, suggesting that the size structure-based analysis featured the adoption of variation partitioning is a more suitable method to investigate the external effects on size structure of fish populations.

參考文獻


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