魚群體型大小與空間聚集潛能之關係為駝峰分佈

Hump-shaped relationship between aggregation potential and body size in fish population

潘若虞(Ruo-Yu Pan)

指導教授 ： 謝志豪

國立臺灣大學/理學院/海洋研究所/碩士(2019年)

https://doi.org/10.6342/NTU201902889

摘要

空間分布變異程度對於魚群的穩定性扮演重要的角色，舉例來說，在面對區域性環境變動的衝擊時，魚群可藉由分布在不同區域(空間分布變異低)達到分散風險的效果，使其能在環境變動下生存。雖然許多研究指出空間分布變異和物種的體型大小相關，但針對一族群內，空間分布變異和體型的關係仍沒有明確的結論。因此，本研究利用Taylor’s power law（V=a*M^b）探討在單一物種魚群中，不同體長的魚在空間的群聚結構。Taylor’s power law 中的指數數值（b）代表魚群的「群聚潛能」，說明魚群在空間上的變異程度（V）會如何隨著魚群平均數量（M）的增加而改變。b值越高，代表該魚群隨著其數量的增加而越聚集。本研究藉由1991年至2015年間北海的底拖網調查資料，檢驗八種受捕撈物種其b值與體長的關係。結果顯示，b值與體長的關係為駝峰分布，且最高的b值大約落在魚群的成熟體長，此結果指出：體型較大的成魚有較低的群聚潛能，亦即在數量上升時，空間分佈上比體型較小的成魚平均，也因此，體型較大的成魚對魚群保持低的空間變異程度扮演著重要的角色。根據本研究的結果，我們發現族群體型結構對族群空間聚集潛能有重大的影響；因此，在漁業管理上除了監控族群數量的變化外，亦需考量魚群體長結構、空間結構以及兩者之共同作用，以期達到更佳的漁業管理。

關鍵字

空間群聚潛能 ； 體長結構 ； 年齡截斷 ； 分散風險

並列摘要

Overfishing could increase spatial heterogeneity of fish populations, leading to weaker bet-hedging capacity and undermined population sustainability of the fishes. Although previous studies have found that the aggregation pattern of a population is associated with the size across species, few studies have examined the relationship between aggregation and size within a population. In this study, we examined how the “aggregation potential” changes among different size classes of the same population. Aggregation potential was quantified as the exponent b of Taylor’s power law (V=a*Mb), which measures how the spatial variance (V) changes with the mean abundance (M) of a population. We estimated b by size class for each of the eight commercial-important fish species in the North Sea, using the ICES survey data spanning 25 years. We found that the relationship between b and body size is hump-shaped, with the peak around the mature length of the species. This result indicates that the larger adults in a population tend to distribute more homogeneously when abundance increases and they play a critical role in maintaining homogeneous distribution of the population. Our findings highlight the importance of size structure for homogeneous distribution of populations. Both size and spatial structure and their joined effects on population stability should be considered for a sound fishery management.

並列關鍵字

Spatial aggregation potential ； Size structure ； Size-truncation ； bet-hedging capacity

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