2012-08-012024-05-18https://scholars.lib.ntu.edu.tw/handle/123456789/698687摘要：魚群數量變化由許多因素影響，包括族群本身的變化、環境影響（包括氣候，種間交互作用等）、及漁業壓力。了解這些因素個別以及其共同的交互影響為漁業科學研究和管理主要目標。目前有越來越多的證據顯示許多魚群中體型大或年紀較老的個體漸漸消失，推測可能是由於漁業過度捕撈造成。魚群的年齡或體長結構窄化可能造成族群加入率的下降。這個影響可透過幾種不同的方式: 較年輕或體長較小的繁殖個體通常產較少及較小的卵，造成較低的成功繁殖率。此外，這些較小的繁殖個體一般產卵的時間較短並且產卵局限於較小的範圍，導致子代存活率依據環境狀況而變，對環境變化的耐受度較低。針對北大西洋的美國鰈魚族群，我們計畫來探討年齡結構與族群動態的關係。我們將會針對美國及加拿大the Gulf of Maine-Georges Bank以及冰島區域的族群。我們會調查北大西洋溫度與漁業壓力(單位努力的年捕撈量、漁業死亡率) 對族群大小的關係，並探討年齡階層結構的變化（成長率，彈性，平均產卵年齡）與這些影響的關聯性。<br> Abstract: The patterns of variations in fisheries time series are known to result from complex combinations of species and fisheries dynamics all coupled with environmental forcing (including climate, trophic interactions, etc.). Disentangling these relative effects as well as their potential synergistic impact has been major goals of fisheries science for conceptual and management reasons. Accumulating evidence shows that the oldest and largest individuals are disappearing from fish stocks, triggered by overexploitation. Such age- or size-truncation for fish stocks may impair subsequent recruitment, through 1) decreasing the reproductive capacity of the spawners, 2) decreasing the number and the size of eggs, and 3) reducing spatial and temporal dispersion of eggs, which may reduce the likelihood of survival for the offspring. A truncated age-class structure may thus decrease population growth rates as well as increase the risk of collapse due to poor environmental events or long-term environmental changes. In this project we will examine this hypothesis that truncation of the age structures increases population sensitivity to environmental variability using data on the American plaice Hippoglossoides platessoides stocks in the North Atlantic Ocean. The history of American plaice fisheries dated back to 1960, and age structures of several stocks are observed to decline. We will investigate the Gulf of Maine-Georges Bank region and Icelandic waters stocks. Specifically, for each stock we will examine the relationships between stock dynamics (indexed by annual abundance, spawning stock biomass) and 1) the North Atlantic temperature variability and 2) fishery pressure (annual catch per unit effort, fishing mortality), respectively. Then, we relate these effects to changes in age structure, taking into account changes in growth rates, elasticity of vital rates to the recruitment, and mean age of spawners. We expect to determine whether pronounced changes in the spawning stock, including a trend towards younger fish, a less diverse distribution across ages, and a declining proportion of repeat spawners can be highlighted for the American plaice from the 1970s to recent years and according to its biogeographical area.族群年齡結構成長率彈性Population demographygrowth rateresilience