Patterns in the distribution of larval and pelagic juvenile fishes in the central Great Barrier Reef lagoon

The distribution of larval and pelagic juvenile fish was investigated along 2 cross shelf transects in the central Great Barrier Reef (GBR) lagoon, during October to December 1988 and October 1989 to January 1990. One transect originated just north of Cape Cleveland and extended out in the direction of Lodestone Reef (Transect LR), while the second transect originated near Cape Bowling Green and extended in the direction of Davies Reef (Transect CB). During the first survey season, 4 stations were located 8 km apart along each transect. The distance between the 4 stations was extended to 16 km for the second survey season, to span the width of the GBR lagoon. The sampling period was chosen to coincide with peak spawning of most fish species in the region and sampling equipment was deployed within a 10 day period either side of the new moon. Each transect was sampled between 1 and 3 times each month.At each station, 6 light traps were deployed 200-300 m apart, approximately 1 m below the surface and allowed to drift with the water mass. Traps were set up to fish for 1 hour, emptied and redeployed at the next station on the transect. While the traps were fishing, three 10 minute plankton tows were carried out in the immediate vicinity of the light traps. Plankton nets, fitted with a digital flowmeter, were set to fish between 0.5 and 2 m below the surface and towed at between 0.5 and 1.0 m/s. Samples were immediately preserved in 80-90% alcohol.Fish collected in the plankton nets were identified to family level, while fish collected in the light traps were identified to the lowest possible taxa. Fish were also measured under a stereo dissecting microscope with an ocular micrometer.The effect of time of night on catch rate was investigated for 4 nights at the 16 m station on the LR transect during October and November 1990. Four traps were fished within the the same general area for 1 hour at three times during the night (19:30 to 20:30h, 23:30 to 00:30h and 03:30 to 4:30h). Comparisons between anchored and drifting light traps were made on three occasions. On each occasion, 6 traps were set in a line perpendicular to the prevailing current direction. Alternating traps were then either anchored to the bottom or allowed to drift with the water mass and the traps fished for 1 hour. This research was undertaken to:1. describe the spatio-temporal variability in the distribution and abundance of larval and pelagic juvenile fishes across the central Great Barrier Reef lagoon2. compare the catches from light traps with those from plankton nets3. compare the catches from drifting light traps with those from anchored light traps4. compare catches at different times of night

本研究于1988年10月至12月、1989年10月至1990年1月期间，在大堡礁（Great Barrier Reef, GBR）中部泻湖的2条跨陆架断面上，对仔鱼与中上层稚鱼的分布展开调查。第一条断面始于克利夫兰角（Cape Cleveland）北侧，向磁石礁（Lodestone Reef）方向延伸（记为LR断面）；第二条断面始于鲍灵格林角（Cape Bowling Green）附近，向戴维斯礁（Davies Reef）方向延伸（记为CB断面）。首轮调查季中，每条断面上设置4个站位，站位间距为8 km；第二轮调查季为覆盖大堡礁泻湖的完整宽度，将站位间距调整为16 km。

采样时段选取该区域多数鱼类的产卵高峰期，且所有采样作业均安排在新月前后10天的窗口期内。每条断面每月采样1至3次。在每个站位处，布设6台灯光诱捕器，间距200~300 m，布放于水下约1 m处，随水团自然漂流。诱捕器单次作业时长为1小时，完成作业后清空并移动至下一个站位继续布设。在诱捕器作业期间，需在其紧邻水域开展3次10分钟的浮游生物拖网采样。

浮游生物网搭载数字流量计，布设深度为水下0.5~2 m，拖曳速度控制在0.5~1.0 m/s。采集的样本立即以80%~90%的酒精进行固定保存。浮游生物网采集的鱼类样本鉴定至科级分类单元，灯光诱捕器采集的样本则鉴定至尽可能低的分类阶元。所有鱼类样本均通过体视显微镜搭配目镜测微尺进行体长测量。

1990年10月至11月期间，本研究在LR断面水深16 m的站位开展了连续4夜的夜间时段对捕获率影响的调查：在同一大致区域内布设4台诱捕器，分别在夜间三个时段（19:30~20:30、23:30~00:30及03:30~04:30）开展1小时的诱捕作业。此外还开展了3次锚定式与漂流式灯光诱捕器的捕获效果对比实验：每次实验均布设6台诱捕器，呈垂直于主流向的直线排列，交替采用底锚定与随水团漂流两种布设方式，诱捕作业时长均为1小时。

本研究旨在达成以下4项目标：
1. 阐明大堡礁中部泻湖内仔鱼与中上层稚鱼分布及丰度的时空变异特征；
2. 对比灯光诱捕器与浮游生物拖网的鱼类捕获效果；
3. 对比漂流式与锚定式灯光诱捕器的鱼类捕获效果；
4. 分析夜间不同时段对灯光诱捕器捕获率的影响。