生活史、區域、年級共振效應對漁業族群週期性變動之調控

Abstract

透過瞭解驅使族群週期性變動的因子可以降低漁業管理的不確定性。理論研究中指出族群週期性變動可能產生於外在因子 (例：環境變動)和內在因子 (例：生活史特徵)的交互做用，儘管如此，過去很少有研究提供實驗證據來探究相關機制。為填補此知識缺口，我們調查了九種來自單拖漁業重要魚種的捕獲資料 (1970-1999)、並藉由量化其單位努力捕獲量(CPUE)之週期性變動來瞭解外在及內在因子交互作用的過程。這九種物種擁有多樣化的生活史特徵 (以快慢連續階層表示 (fast-slow continuum))，並且是台灣海峽及東海區域的主要目標物種。在此研究中我們有三個假說：1) 物種豐度之週期性變動可以反應其生活史特徵模式（例：和擁有比較快的生活史特徵的物種相比，擁有比較慢的生活史特徵的物種會出現比較長的週期性變動） 2) 地區性環境因子會造成不同地區的同物種擁有不同的週期性變動 3) 年級共振效應 (cohort resonance)（意指族群對於週期相似於其成熟年齡的環境變動特別敏感而產生的現象）會在頻譜上產生短週期的週期性變動。我們發現生活史特徵和物種頻譜的模式並沒有明顯的關係性，且物種間及地點間的頻譜模式差異不大。除此之外，我們在快和慢物種的頻譜中都有觀察到區域性環境及年級群共振效應的跡象，這些跡象可能會影響生活史特徵和頻譜模式間的關係。整體來說，這些結果提供了關於環境變動與物種內在因子交互作如何帶給漁業物種影響的證據。在漁業管理上，我們建議應對於出現短週期週期性變動、特別那些有出現年級共振效應的物種，給予優先的管理。

Understanding the key drivers of population cycles can reduce uncertainty in fisheries management. Theoretical studies suggest that population cycles arise from the interactions between external forcing (e.g. environmental variability) and a population’s internal process (e.g. life-history traits). Nonetheless, few empirical studies have explored these underlying mechanisms. To bridge this knowledge gap, we examined the otter trawler catch-per-unit-effort (CPUE) time series (1970-1999) for nine important fishery species, quantifying their CPUE cycles in relation to external and internal processes. The nine species constitute various life histories (represented as fast-to-slow continuum of life histories) and are the main target species in two regions: East China Sea and Taiwan Strait. We hypothesized that 1) species abundance cycles should reflect life-history patterns; e.g., species with slow life histories show relatively long-period cycles as compared to those with fast life histories, 2) regional environments could induce different cyclic patterns between conspecific populations, and 3) cohort resonance (which involves sensitivity to specific time scales of environmental variability that match species maturation ages)would induce short-period cycles on wavelet spectra. We did not find a clear relationship between the species spectral patterns and the fast-slow continuum in life histories. Instead, the power spectral patterns were similar among all species in both regions. There were signs of regional environments and cohort resonance on power spectra in species with fast and slow life histories, confounding the effects of life histories on power spectra. Overall, these results provide evidence on complex interactions of environmental effects and internal processes on fisheries species. For sustainable management, we suggest setting high priority for management for species that exhibited short-period cycles, especially those with signs of cohort resonance.