西北太平洋秋刀魚生殖動態於漁季間之時空變動及其影響因子

Abstract

本研究透過台灣遠洋棒受網漁船於2018及2019 年7至11月漁季間在西北太平洋公海漁場（40°N–49°N；149°E–168°E）蒐集的秋刀魚樣本來分析其生殖動態在漁季間之時空變動。應用廣義加成混合模型（generalized additive mixed models，GAMMs）分別探討0歲及1歲秋刀魚在漁季間達到成熟或產卵階段之機率（probability of maturing and spawning occurrence，PMOS）與不同因子（月份、體長及海水表面溫度為固定效應；單船作業日期為隨機效應）間之關係。此外，本研究也探討了過去0歲秋刀魚在空間上成長速度（以耳石年輪半徑來量化）之差異是否對於1歲秋刀魚的PMOS造成影響。研究結果顯示，秋刀魚的平均肥滿度（condition factor）在各月份間具有差異，且較高肥滿度個體多出現在45°N以北海域。然而，平均生殖腺指數（gonadosomatic index）並未有明顯的時空差異。另外，根據秋刀魚卵巢成熟狀態之空間分布顯示，秋刀魚產卵場範圍較先前研究結果更為廣泛分布，並與遠洋棒受網漁船作業之公海漁場部分重疊。GAMMs的估計結果指出0歲魚PMOS普遍較低（平均值 19%；標準差10%），且隨著體長增加而上升。相較之下，1歲魚的PMOS較高（平均值37%；標準差10%），並隨著海水表面溫度上升及緯度遞減呈現增加的趨勢。GAMMs估計結果也指出在0歲時具有較高成長速度的秋刀魚，於1歲時PMOS則較高。本研究為少數探討漁季間秋刀魚生殖動態的研究之一，有關當前該類研究限制、未來研究方向及漁業管理意涵均被提出及討論。

This study examined the spatiotemporal variations in reproductive dynamics of Pacific saury collected in the high sea (40°N - 49°N, 149°E - 168°E) of the Northwest Pacific during the fishing season of the Taiwanese stick-held dip net fisheries (July - November) in 2018 and 2019. Generalized additive mixed-effects models (GAMMs) were applied to explore the relationship between the probability of maturing and spawning occurrence (PMOS) and the explanatory variables (month, body length, sea surface temperature as fixed effects and fishing set as random effect) for the age-0 and age-1 fish, respectively. In addition, the impact of the geographical difference in growth rates of age-0 fish, quantified as the radius of the otolith annual ring, on the PMOS of age-1 fish was also explored in the GAMMs. Results showed that the mean values of the condition factor (CF) varied by months and higher mean CFs were observed in north of 45°N. However, the mean values of the gonadosomatic index did not show a clear spatiotemporal pattern. The spatial distribution of the ovarian maturation states revealed that the spawning ground of Pacific saury during July - November was broader than that previously known and had partly overlapped with the high sea fishing ground. The GAMMs showed that the predicted PMOS of the age-0 fish were generally low (mean = 19%; SD = 10%) and tended to increase with increasing body length. In contrast, the predicted PMOS were relatively higher (mean = 37%; SD = 10%) for the age-1 fish, and increased with increasing SST and decreasing latitude. The GAMMs also indicated that higher growth rate of age-0 fish could result in higher reproductive activity in age-1 fish. This is one of few studies focusing on the reproductive dynamics of Pacific saury during the fishing season, current limitations, future directions and management implications were discussed.