航道整治透水框架群对鱼类集群影响的水声学探测

Effect of Tetrapod Clusters on Fish Assemblage in Channel Improvement Projects

四面六边透水框架是一种具有良好防冲促淤功能的生态水工构造物,在航道整治工程中得到广泛应用。为了探究四面六边透水框架群对鱼类的影响,于2014年5-6月,应用EY60回声探测仪和双频识别声呐(ARIS Explorer 1800)对金城洲透水框架工程区水域进行定点水声学监测,并采集工程区附近的渔获物。结果表明,工程区共捕获鱼类114尾,包含3目、4科、12属、14种,体长均值为(27.64±10.06)cm,95%置信区间为25.77~29.50 cm;体重均值(551.84±1 252.02)g,95%置信区间为319.52~784.16 g。EY60回声探测仪对工程区共监测时长9 589 min,测得鱼的数目12 356尾,工程区鱼体的目标强度均值为(-63.24±5.79)d B,95%置信区间为-63.35^-63.15 d B;数据独立性T检验显示,工程区与对照区之间无显著性差异(P>0.05);通过回声探测仪和双频识别声呐对鱼类出现频次监测,工程淹没区是对照区的1.18倍,而工程半淹没区却是对照区的0.85倍;说明处于水下的四面六边透水框架群对鱼类具有一定的诱集作用。

Tetrapod clusters （interlocking concrete tetrahedral frames）are widely used in channel improvement projects to prevent scouring and promote siltation.The tetrahedral shape dissipates flow force and the randomly dis-tributed tetrapods interlock to stabilize the cluster.However,the use of tetrapod clusters changes the riverbed sub-strate and water flow field,directly and indirectly influencing the fish community.In this study,hydroacoustic mo-nitoring was used to investigate the effect of tetrapod clusters on the fish assemblage at Jincheng sandbar of Wazikou waterway,middle reaches of the Yangtze River,where a tetrapod cluster was constructed in 2010.In May and June of 2014,fixed location hydroacoustic monitoring of the fish community was carried out using a SIMRAD EY60 echo-sounder and dual-frequency identification sonar （ARIS Explorer 1800）.Three monitoring areas were selected：fully submerged tetrapods,partially submerged tetrapods and a control area with no tetrapods.The target strength （TS） of the fish community in the three areas was compared to analyze the effect of tetrapod clusters on fish assemblage. The two types of hydroacoustic apparatus were mounted on the left side of the research ship with transducers set 50 cm below the surface,15 meters from the monitoring site and aimed toward the tetrapods with Garmin GPSmap 60CS.Monitoring was conducted daily from 9∶00 to 14 ∶00.Fish samples were also collected by local fishermen using drift-gill nets.Fifteen fish catches were completed and species composition,body length and mass were recor-ded for each fish.A total of 114 fish,belonging to 3 orders,4 families,12 genera and 14 species were obtained, with an average length of （27.64 ±10.06）cm and a 95% confidence interval of 25.77 -29.50 cm.The average body mass was （551.84 ±1 252.02）g,with a 95% confidence interval of 319.52 -784.16 g.Total hydroacous-tic monitoring time was 9 589 minutes and 12 356 fish were detected.The average target strength was （-63.24 ± 5.79）dB and the 95% confidence interval was -63.35 to -63.15 dB,converting to a standard length of （10.55 ± 9.62）cm and a 95% confidence interval of 10.38 -10.72 cm.The average length of the fish caught was longer than that of the hydro-acoustically monitored fish and attributed to the mesh size of the drift-gill net.T-tests indica-ted no significant difference in fish number among the three areas monitored.But the occurrence frequency of fish in the submerged tetrapod area was 118% of that in the control area and 85% of that for the semi-submerged area. While fully submerged tetrapod clusters seem to attract fish,there is also a tendency for fish to avoid partially sub-merged clusters.