Commercial fishes as predators of adult crown-of-thorns starfish, Acanthaster planci, in the southern Great Barrier Reef

Snake Reef and Gannet Cay in the Swain Reefs of the southern Great Barrier Reef, which were experiencing outbreaks of crown-of-thorns starfish, were chosen for this study and surveyed in February 1994. Areas of high starfish density were located within these reefs by systematic manta tows and snorkelling and marked with buoys.Three fishermen targeted Lethrinus miniatus, within 500 m of the starfish concentrations. The time of capture (to the nearest hour) was recorded in the majority of cases and standard length was recorded for all fish caught. The entire digestive tracts of the 98 Lethrinids caught were removed shortly after capture and preserved. In the laboratory, entire gut contents were washed out onto fine plankton mesh (17 µm), drained and weighed. Gut contents were examined under a microscope for any Acanthaster planci remains and large prey items were recorded.At Gannet Cay, starfish were located in two patches, a small one on the west side of the reef, just south of the Cay, and another larger one on the south face. Starfish were counted in a series of dives and each animal was tagged with a temporary tag once counted. Small numbers of starfish were collected for examination of their reproductive state.The outbreak at Snake Reef covered a larger area and the numbers of starfish were estimated from a series of 50 m transects. Two divers counted Acanthaster planci in a 2 m band on one side of a tape laid along the edge of the reef, giving an estimate of the length of the affected portion of reef, as well as the density of starfish. The width of the affected area was estimated by swimming transects 5 m wide and 15 m apart, starting at the sand and running at a normal to the reef edge. The width of the infestation was taken to be the distance from the sand to the starfish that was second furthest from the sand. This was to reduce bias due to outlying starfish.Lethrinids were counted in the vicinity of the starfish outbreak at Snake Reef, in twenty 50x10 m transects. The transects were placed haphazardly along the reef edge at least 20 m apart, starting at a depth of about 3 m and running down the slope. Sixteen similar transects were swum along the west face of the reef at Gannet Cay. It was not possible to count fish in the immediate vicinity of the large aggregation because of rough seas and strong currents. This research was undertaken to: - collect a large sample of possible fish predators of Acanthaster planci close to outbreak populations of adults with developed gonads to look for evidence of predation and to estimate per capita predatory mortality- look for evidence of timing of Lethrinus miniatus feeding because Acanthaster planci, particularly smaller size classes, are active at night and cryptic during the day.

大堡礁南部斯温礁群内正暴发长棘海星（crown-of-thorns starfish, Acanthaster planci）疫情的蛇礁与甘尼特卡伊礁，被选为本次研究对象，并于1994年2月开展野外调查。
研究人员通过系统拖曳帆板调查与浮潜作业，定位两处礁体内的高密海星分布区，并以浮标标记。三名渔民在距海星聚集区500米范围内，定点捕捞小带裸颊鲷（Lethrinus miniatus）；多数捕获个体记录了精确到小时的捕获时间，所有捕获鱼类均测量了标准体长。
研究人员在捕获后即刻取出98尾裸颊鲷的完整消化道并进行固定保存。在实验室中，将全部肠道内容物冲洗至17微米孔径的浮游生物筛绢上，沥干后称重；随后在显微镜下检视肠道内容物，寻找长棘海星残体，并记录大型猎物种类。
在甘尼特卡伊礁，海星分布于两处斑块：一处小型斑块位于礁体西侧、甘尼特卡伊礁以南，另一处大型斑块位于礁体南侧崖面。研究人员通过多组潜水作业统计海星数量，每统计到一只个体便为其加装临时标记标签；同时收集少量海星样本，用于检测其生殖状态。
蛇礁的海星暴发覆盖范围更广，海星种群数量通过一系列50米样带进行估算：两名潜水员沿礁体边缘铺设的测绳一侧的2米宽样带内统计长棘海星数量，以此估算受影响礁体的长度与海星种群密度。受影响区域的宽度则通过游泳样带法估算：以距沙床为起点，沿垂直于礁体边缘的方向设置间距15米、宽度5米的样带；侵染宽度以距沙床第二远的海星位置为准，以规避边缘零散个体带来的统计偏差。
在蛇礁海星暴发区附近，研究人员通过20条50×10米的样带统计裸颊鲷种群数量。样带沿礁体边缘随机布设，间距不小于20米，起点水深约3米，沿礁坡向下延伸。在甘尼特卡伊礁的西侧崖面，研究人员布设了16条相同规格的样带；由于海况恶劣且洋流强劲，无法在大型海星聚集区的紧邻水域开展鱼类计数。
本次研究旨在达成以下目标：一是在性腺发育成熟的成年长棘海星暴发种群附近，采集大量疑似长棘海星鱼类捕食者样本，以搜寻捕食行为证据并估算单位个体捕食死亡率；二是搜寻小带裸颊鲷的摄食时间节律证据——因长棘海星尤其小型个体夜间活跃、日间隐匿。