台灣東北部海域三種腔吻鳕屬鼠尾鳕的食性及棲所資源分配之研究

Abstract

鼠尾鱈 (macrourid)是台灣東北部海域底棲魚類群聚的優勢物種，因其體型較大及在數量上的優勢，可能使其成為底棲群聚中的主要掠食者。本研究利用網板拖網漁船，採集台灣東北部龜山島附近海域水深100至600公尺間，三種優勢種鼠尾鱈：岸上氏腔吻鱈 (Coelorinchus kishinouyei)，窄吻腔吻鱈 (C. leptorhinus) 及多棘腔吻鱈 (C. multispinulosus)，並分析其食性 (diet) 組成，藉此探討：(一)在同一地區內，共存之同屬不同種間的鼠尾鱈是否會存在深度分佈及食性上的相關性，形成群聚內的資源分配 (resource partitioning) 現象；(二)如果同屬不同種間的鼠尾鱈在同ㄧ深度共共棲時，如何運用有限的資源分配；以及(三)同種鼠尾鱈是否會隨著不同體長，發育階段的不同，而有棲息深度的差異和食性的轉變 (ontogenetic diet shifts)。本研究的深度分布結果顯示：在水深100至200公尺主要為C. multispinulosus；200至400公尺為C. kishinouyei；400至600公尺為C. leptorhinus，此三種鼠尾鱈以深度分布差異做為空間資源上的區隔。食性組成分析結果顯示，此三種魚的食性並不相同。但其中200公尺的C. multispinulosus及C. kishinouyei；以及在400公尺的C. kishinouyei及C. leptorhinus因有在同深度共棲的情況，而出現在食物利用上的資源分配，用以避免種間的相互競爭。而本研究結果之深度區隔範圍甚窄可能與當地鼠尾鱈之物種多樣性甚高有關；且在族群數量上較弱勢的魚種會改變其食性。另由三種鼠尾鱈的體長頻度分佈顯示：C. leptorhinus可分為兩個組別，體型較小 (4-9公分) 的組別主要吃橈腳類及多毛類，體型較大 (10-15公分) 的組別則以蝦類及多毛類為主，顯示此物種之食性有隨體型而改變的現象 (ontogenetic diet shift)。此外，本研究亦發現體型較小的C. leptorhinus組別分佈的深度反而較體型大的組別為深，此有別於前人之研究結果所稱：體長越大棲息深度越深 (bigger-deeper)的現象。

Grenadiers are the most dominant fish species of the demersal fish community in the waters off northeastern Taiwan. Due to their relative large size and high abundance, they are major predators in the local demersal community. Three congeneric species of grenadiers, Coelorinchus kishinouyei, C. leptorhinus and C. multispinulosus were collected by bottom trawler at depths of 100-600 m in the study area. The diets and depth distributions of these fishes were analyzed to investigate: 1) whether resource partitioning exists among these three congeneric grenadier species by water depths or feeding habits; 2) How to used resource partitioning when congengeric species coexists in the same depth; and 3) whether ontogenetic shifts in diet or distribution depth exist for grenadiers with different developmental stages. Results showed that C. multispinulosus mainly occupied depths of 100-200 m, C. kishinouyei 200-400 m and C. leptorhinus 400-600 m. Two grenadier species pairs coexisted at some depths, C. kishinouyei and C. multispinulosus at 200 m, and C. kishinouyei and C. leptorhinus at 400 m. Diet analyses of these pairs reveal apparent resource partitioning resulting from interspecies competition. When species coexistence occurred, the numerically dominant species would retain its preferred diet while the less abundant species made adjustments in its food habits. The distributions of body size for C. leptorhinus suggested separation into two size groups. The smaller size group (4-9 cm PAL) ate mainly copepods and polycheates while the larger size group (10-15 cm PAL) ate shrimp and polycheates, suggesting an ontogenetic diet shift. The previously described “bigger-deeper” phenomenon was not supported because of inconsistent patterns observed between body size and distributional depths of the three grenadier species studied.