Fish community composition in Half Moon Creek, a mangrove creek near Cairns, northern Australia

Fish populations in Half Moon Creek, near Cairns, north Queensland were sampled in the wet season (12-16 November 1990) and in the dry season (11-15 April 1991). Replicated sampling with three gear types (multipanel gill nets, pocket seine and fish traps) was carried out.Pelagic and large benthic fishes using the main channels were sampled with static gill nets anchored across the tidal flow, from the bank towards the centre of the creek. Gill nets were set at six locations. With the exception of the most seaward site, each net was located so as to cut off one or more side channels leading from the mangroves as well as intercepting fish moving downstream following the bank of the main channel. Two sites were located in the side branch leading to Reed Canal where most modification would occur and two sites were set in Half Moon Creek below (seaward) of this junction. These sites were selected on the basis that they would experience a different flow regime after development. Two sites were located above (landward) of this junction and were expected to remain relatively unchanged after development. Each of the five day sampling periods was chosen so that a high tide fell during the morning. All six gill nets were deployed during the last hour of the flood tide, fished for approximately five hours on the ebb, and were retrieved during the final hour of the ebb. Four shallow locations were found where it was possible to pull a small pocket seine net to collect benthic fishes. During both of the field trips, each one of the four sites was sampled once, at which time three replicates were taken on the same day. Each replicate consisted of a 10m advance once the net was fully open in which case it should have sampled an area in front of the net of at least 50m².To sample larger roving fishes, baited fish traps were deployed at six locations in the creek. Generally, these sites were adjacent to the gill nets although they had to be placed in microhabitats where predatory fishes might be expected to congregate such as overhanging banks or snags. These traps were deployed on the first day of sampling and thereafter checked at least daily. Baits consisting mostly of frozen Western Australian pilchards (Sardinops neopilchardus), supplemented by fresh mullet, were suspended inside the cage in a permeable canister; they were replaced as required but refreshed at least every second day.Live fish caught in the baited fish traps were identified, measured (Standard Length, mm), tagged and released back into the creek. Later, their individual weights were estimated by extrapolation from dead fish of similar shape and size. All other fish were preserved at the point of collection in 10% formalin. Subsequently, every individual was identified, measured (Standard Length, mm) and weighed on an electronic balance (g). In the case of common species with little size variation, especially juveniles, not all individuals were measured; instead, a size range was established and their aggregate biomass determined for each sample.
This research was undertaken to characterise the fish fauna of Half Moon Creek and to evaluate options for monitoring the impact of a marina development in Reed Canal, which flows into Half Moon Creek. The planned alterations in Reed Canal involve considerable excavation to enlarge the internal space as well as dredging downstream to maintain a navigable channel to the sea.

昆士兰州北部凯恩斯附近的半月溪（Half Moon Creek）鱼类种群分别在湿季（1990年11月12日至16日）与旱季（1991年4月11日至15日）开展了系统采样调查。本次研究采用三类渔具开展重复采样：多片式刺网（multipanel gill nets）、袋形拉网（pocket seine）与鱼笼（fish traps）。
针对利用主河道的洄游性与大型底栖鱼类，研究人员采用横跨潮汐流、从河岸向溪中心布设的固定刺网开展采样，共设置6个采样点位。除最靠海的采样点外，其余每个刺网的布设位置均可阻断一条或多条源自红树林的支河道，同时拦截沿主河道河岸向下游移动的鱼类。其中2个采样点设于连通里德运河（Reed Canal）的支流河段——该区域将受到最为显著的工程改造；2个采样点设于该交汇处下游（向海一侧）的半月溪主河道，这些点位在工程完成后将面临与改造前显著不同的水文情势；另有2个采样点设于该交汇处上游（向陆一侧），预计在工程完工后水文环境将保持相对稳定。
每次五日的采样时段均选定在早间出现高潮位的日期。全部6张刺网均在涨潮最后1小时布设，在落潮期间作业约5小时，并于落潮最后1小时完成收网。
研究人员在4处浅水区布设小型袋形拉网，以采集底栖鱼类。两次野外考察期间，4个采样点均各完成1次采样，单日开展3次重复采样。每次重复采样均为拉网完全展开后前进10米，此时拉网覆盖的有效采样面积不小于50平方米。
为采样活动范围较大的漫游性鱼类，研究人员在溪内6处点位布设了带饵鱼笼。这些点位大多紧邻刺网采样点，但需设于掠食性鱼类易聚集的微生境中，例如悬垂河岸或沉水枯木区域。鱼笼于采样首日布设，此后至少每日检查1次。饵料以冷冻西澳大利亚沙丁鱼（Sardinops neopilchardus）为主，辅以新鲜鲻鱼，放置于透水容器中悬挂于笼内；饵料按需更换，至少每两日更新一次。
带饵鱼笼捕获的活鱼需完成种类鉴定、体长测量（标准体长，Standard Length，mm）、标记后放归溪中。后续通过比对形态与体型相近的死鱼，外推估算这些标记个体的体重。其余捕获鱼类均在采样现场以10%福尔马林溶液固定保存。后续对每尾鱼完成种类鉴定、体长测量（标准体长，Standard Length，mm）与电子天平（electronic balance，g）称重。针对体型变异较小的常见物种（尤其是幼鱼），无需测量每一个体，而是通过划定体长范围，计算每个采样样本的总生物量。
本研究旨在明确半月溪的鱼类区系组成，并评估针对接入半月溪的里德运河游艇码头开发项目的生态影响监测方案。里德运河的规划改造工程包括大规模开挖以拓展内部水域，同时疏浚下游河道以维持通往海洋的通航航道。