氣候與漁撈效應對魚群空間分布與體長結構之影響

Climate and fishing effects on the distribution and size structure of exploited fish populations

杜貞儀(Chen-Yi Tu)

指導教授 ： 謝志豪

國立臺灣大學/理學院/海洋研究所/博士(2018年)

https://doi.org/10.6342/NTU201802401

摘要

氣候與漁撈活動對於魚的影響是近年研究的焦點。雖然全球尺度的統合分析顯示，對溫度升高的反應有著分布往極區移動的趨勢，然而不同物種間的反應仍有許多變異。而漁撈族群的體長結構同時受氣候與捕撈行為影響，但兩者究竟各佔多少比例，亦屬未知。更重要的是，魚群分布與體長結構間可能有相互關係，這是由於魚類隨個體發育而有棲地移轉的現象。因此，為了更全面的了解氣候變遷以及捕撈活動對魚群的影響，需要能同時涵蓋分布與體長結構的分析框架。
本研究中，我採用三種研究角度來切入氣候與漁撈活動對魚群分布與體長結構的影響。在第一章中將簡要介紹現象以及研究背景，而第二章則以日本海底拖漁業為例，研究不同生活史特徵魚群的分布與豐度，如何反應年間與年代際間的環境變動，結果顯示暖化對於日本海內體型較大的物種有負面影響。第三章關注魚群體長結構，以變異分離法來拆解氣候與漁撈的協同效應對體長的影響。結果顯示漁撈能解釋絕大多數魚群的體長變異，而受到漁撈壓力波動較大的魚群，其體長結構對溫度的反應也更大。這顯示，漁撈活動可能會讓魚群對環境變動更為敏感。第四章則檢視魚群於不同生活史階段的空間分布變化如何受氣候因素（如溫度）影響。結果發現，成魚階段因溫度變化而分布移動較稚魚階段快，而成魚與稚魚往同方向移動的物種，通常其成魚與稚魚階段的空間分布有較大重疊，可能表示該物種的成魚與稚魚的棲位相近，因此對溫度變化有類似的反應。
總結本研究的結果，空間分布與體長結構確實在魚群對氣候以及捕撈活動的反應有一定關聯，因此必須同時檢視兩者才能對魚群的反應有較全面的了解。這些結果應能對氣候變遷下的生態系漁業管理提供有助益的訊息。

關鍵字

氣候變遷 ； 空間分布 ； 體長結構 ； 漁撈效應 ； 生活史特徵

並列摘要

Climate and fishing effect on the exploited populations is an important research topic. Although the global meta-analysis indicates a general pattern of poleward distributional shifts in response to rising temperatures, the specific responses have varied among species. The size structure of exploited populations is simultaneously affected by both climate and fishing, but what determines the relative contribution of the two remains unknown. More importantly, the dynamics of distribution and size structure of exploited populations may be interwoven because of the ontogenetic habitat shift of fish. Therefore, a framework to incorporate these two demographic aspects is urgently needed to gain the whole picture for understanding exploitation population’s response to climate and fishing effect.
In my thesis, I use three different approaches to investigate climate and fishing effects on the distribution and size structure of the exploited fish populations. The first chapter describes the general phenomenon and set the research scene. The second chapter describes how fish with different life history traits respond differently at interannual and decadal scales of climate change, using the bottom trawl fishery in the Japan Sea as an example. The results indicate that the distributional changes of species in response to decadal climate variability are best explained by asymptotic length, which indicates that warming has greater negative effects on larger fishes in the Japan Sea. The third chapter focuses on the size structure of exploited fish population, with emphasis on applying variation partitioning to disentangle the synergetic effect of climate and fishing. The results show that fishing has the most prominent effect on the size structure of exploited stocks. In addition, the fish stocks experienced higher variability in fishing displayed a greater response to temperature in their size structure, suggesting that fishing may elevate the sensitivity of exploited stocks in responding to environmental effects. The variation partitioning approach provides complementary information to univariate size-based indicators in analyzing size structure. The fourth chapter examines how the change in spatial distribution at different life stages is affected by climate change in exploited fish populations. I found adult stage generally move faster as response to temperature change than juvenile stages. Also, the species whose adults and juveniles move toward the same direction are more likely to have more overlapping in distribution among the two life stages, indicating that adults and juveniles of given species occupying similar niches are more likely to have similar response.
Overall, this study concludes that size structure and distribution are related in the response of the exploited population to climate and fishing effects. It would be necessary to examine both for a better understanding the responses of exploited populations. These results may provide useful information for ecosystem-based fisheries management in light of climate change.

並列關鍵字

climate change ； spatial distribution ； size structure ； fishing effect ； life history traits

參考文獻

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