马鞍列岛多种生境中鱼类群聚的昼夜变化

为了解岛礁水域鱼类群聚的昼夜变化特征,以便更全面地设计采样方法和掌握采样的时间尺度,于2009年9月对马鞍列岛7种生境进行了共计24网次的刺网昼夜采样,结合排序和聚类方法,从种类组成、相对生物量和丰度、种类丰富度、多样性和相似性等方面对研究海域鱼类群聚特征的昼夜变化作了探讨.在采获的55种鱼类中,昼夜出现的分别为41和46种,数量差别不大,但其昼夜组成却随栖息水层的变化而不同,底层鱼类更趋向于夜间在硬相生境集群活动；近底层鱼类的昼夜集群随生境变化而变化,在同一生境中既有偏向白天也有趋向夜间的；中上层鱼类更多地出现在白天的人工生境(AH).AH白天的丰度渔获率显著大于晚上,而天然生境(NH)昼夜差别不大；生物量渔获率无论NH还是AH皆无显著昼夜差异.具体到种类,仅有小黄鱼Larimichthys polyactis和赤鼻棱鳗Thryssa kammalensis等少数种类的数量在AH有显著的昼夜差别,其他多数种类虽然昼夜的出现率大多有别,但渔获率昼夜差异皆不明显.多样性差异更多的表现在不同生境之间,而同一生境的昼夜差异往往不甚显著.各个生境中鱼类的昼夜种类交替现象非常明显,形成了以褐菖(鲐)Sebastiscus marmoratus和鳗鲇Plotosus anguillaris为代表的夜间优势类群为主的硬相生境群聚格局、以丝背细鳞鲀Stephanolepis cirrhifer和细刺鱼Microcanthus strigatus为代表的白天优势类群为主的硬相生境群聚格局以及缺乏底层优势类群、以石首鱼科鱼类为代表的近底层鱼类为绝对优势类群的软相生境群聚格局.因此,采用被动性渔具在近岸典型生境进行鱼类等相关生物调查时,应使采样时间覆盖昼夜两个时段,且至少保证24h.

Diel variations of fish assemblages in multiple habitats of Ma'an archipelago, Shengsi, China

In order to develop effective methods on fish sampling at different habitats as well as to test the assumption that collection of fishes by passive gear in specific habitat should ensure at least a time coverage of 24h, both day and night surveys on fish assemblages in seven habitats(i.e., rocky reef, sandy bottom, soft-bottom, hard bottom, artificial reef, cage aquaculture and mussel farms) were carried out in Ma'an archipelago, Shengsi, China, from 16th to 27th of September, 2009, using multi-mesh trammel nets. The species composition, relative abundance and biomass, species richness and diversity, species similarity were compared between two sampling period and among different habitats. Multi-variable statistics such as cluster analysis and non-metric multidimensional scaling (nMDS) were used to explain the fish assemblage patterns from our diel fish collections. A total of 55 species, belonging to 2 classes, 8 orders, 37 families and 50 genera, among which, 28 families and 38 genera at daytime, 34 families and 44 genera at night, were collected from our 24 diel samplings in 12 sites. The diel shift patterns of habitat use by fishes varied with their eco-types, especially with their habitation on certain water levels. More ground fishes, such as Sebastiscus marmoratus and Plotosus anguillaris, were collected at night in hard-substrate habitats (i.e. rocky reef and artificial reef habitat) than daytime. The diel variations of near-ground fish assemblages varied at different habitats. Some of them had a much higher occurrence (e.g. Stephanolepis cirrhifer ) during daytime while others(e.g. Pagrus major) appeared frequently at night. Pelagic fishes such as Thryssa kammalensis were mostly collected during daytime in artificial habitats. In general, a much higher abundance catch rate (ACR) was found in artificial habitats (AHs) during daytime than it was at night. However, no significant diel variations were found in natural habitats (NHs) for both ACR and biomass catch rate. Only few species, including Larimichthys polyactis and Thryssa kammalensis, were observed with significant diel variations. No significant differences were found in species richness and diversity between daytime and night both in AHs and NHs. Significant changes of fish species were observed due to low species similarity between day and night. Three patterns of fish assemblages can be described, including the dominance of night-tendency fishes such as Sebastiscus marmoratus and Plotosus anguillaris at hard-bottom habitats, the dominance of day-tendency species such as Stephanolepis cirrhifer and Microcanthus strigatus at hard-bottom habitats, and high abundance of Sciaenidae at soft-bottom habitats. Based on the results of the present study, it is recommended that the time duration of any surveys on fish assemblages in coastal areas shall last more than 24h.