Estimation of the Anchovy Resources in the Yellow Sea Based on Acoustic Data Post-processing System
|School||Shanghai Ocean University,|
|Keywords||fishery resources fisheries acoustics acoustic data post-processing system integration threshold anchovy Yellow Sea|
Anchovy (Engraulis japonicus) is a pivotal fish species in the Yellow Sea ecosystem. Accurate estimation is the primary base for the scientific conservation of the anchovy stock, which is also the requirement for the monitoring and researching of the Yellow Sea ecosystem. Developed since the 1960s, acoustic fish abundance estimation is a convenient and efficient method for the survey and estimation of living marine resources, it can offer quasi-continuous, high resolution observation through the water column, and provide rich spatial and temporal data without any additional harm to the nature resources.Data processing and analysis is one of the core-procedure in acoustic fish abundance estimation, where the analysis of echogram and apportion of the integration value to different fish species is the critical step. With the successful development of post-processing system, the main manner of acoustics data processing has transferred from mainly relying on manual work based on paper material to utilizing computerized data post-processing system.The acoustic signals received by echo-sounder can contain ambient noise and non-target echo signals besides echo signals from the target. In order to obtain accurate estimation, the ambient noise and non-target signals should be removed in the post processing of acoustic data. An appropriate integration threshold may effectively remove noise and part of non-target signals while keep the signals from the target species intact.In the first chapter, the development of acoustic fish abundance estimation and its data post-processing system were reviewed briefly. In the second chapter, the methods on the determination and optimization of integration threshold were studied for both scattered target and schooling target using the data collected during the survey of the wintering anchovy in the Yellow Sea in January 2010. Firstly, methods on the determination of integration threshold for scattered target was studied, Based on the derived functional relation between Volume Backscattering Strength (Sv) and Target Strength (TS), two methods, namely the TS–Length method and the in situ TS data method were proposed for the determination of integration threshold. For schooling target distribution, a threshold-tuning method was applied for the study on the determination and optimization of integration threshold through observations on echogram changes and analysis of changes in integration values.In the third chapter, the acoustic data obtained from the survey of the anchovy wintering ground in the Yellow Sea in January 2010 was processed and analyzed using the Echoview acoustic data post-processing system, where the integration threshold was determined based on the results from the second chapter. The stock structure of the wintering anchovy was then estimated using the acoustic and trawl sample data. The main results were as follows:1. The total abundance and total biomass of the wintering anchovy in the survey area were 12.2 billion individuals and 136 thousand tons, respectively.2. The wintering anchovy population mainly distributed in waters deeper than 50 m east of 122°30′E; areas with dense anchovy concentrations were mainly distributed in the southern-eastern part of the Yellow Sea (33°30′-35°00′N; 123°00′-124°00′E), a smaller area with dense anchovy concentrations was also found off the tip of the Shandong peninsular (approximately 37°00′N; 123°50′-124°00′E).3. The total length of the anchovy ranged from 4 cm to 17 cm, with a mean of 12.4 cm. The length distribution was unimodal, the dominant length classes was 10 cm to 13 cm, accounting for 84.5% of the total anchovy individuals. The biomass at length was also unimodal; the dominant biomass-length class was 10 cm to 15 cm, accounting for 96.0% of the total anchovy biomass.4. The wintering anchovy in January 2010 was mainly maintained by recruitment stock and its age structure was still on a low-age state. The proportion of three-year old fish was only 4.2% and no four-year old fish was found. Compared with the survey result from January 2004, the length range, mean length and mean weight of one-year old and two-year old fish increased markedly, implying that the growth rate of the anchovy was accelerated.