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Background. Repetitive species-specific sound enables the identification of the presence and behavior of soniferous species by acoustic means. Passive acoustic monitoring has been widely applied to monitor the spatial and temporal occurrence and behavior of calling species. Methods. Underwater biological sounds in the Pearl River Estuary, China, were collected using passive acoustic monitoring, with special attention paid to fish sounds. A total of 1408 suspected fish calls comprising 18,942 pulses were qualitatively analyzed using a customized acoustic analysis routine. Results. We identified a diversity of 66 types of fish sounds. In addition to single pulse, the sounds tended to have a pulse train structure. The pulses were characterized by an approximate 8 ms duration, with a peak frequency from 500 to 2600 Hz and a majority of the energy below 4000 Hz. The median inter-pulsepeak interval (IPPI) of most call types was 9 or 10 ms. Most call types with median IPPIs of 9 ms and 10 ms were observed at times that were exclusive from each other, suggesting that they might be produced by different species. According to the literature, the two section signal types of 1+1 and 1+N 10 might belong to big-snout croaker (Johnius macrorhynus), and 1+N 19 might be produced by Belanger's croaker (J. belangerii). Discussion. Categorization of the baseline ambient biological sound is an important first step in mapping the spatial and temporal patterns of soniferous fishes. The next step is the identification of the species producing each sound. The distribution pattern of soniferous fishes will be helpful for the protection and management of local fishery resources and in marine environmental impact assessment. Since the local vulnerable Indo-Pacific humpback dolphin (Sousa chinensis) mainly preys on soniferous fishes, the fine-scale distribution pattern of soniferous fishes can aid in the conservation of this species. Additionally, prey and predator relationships can be observed when a database of species-PeerJ Preprints | https://doi.org/10.7287/peerj.preprints.3301v1 | CC BY 4.0 Open Access | rec

Chao, M.; Shi, Y.; Quan, W., and Shen, X., 2015. Distribution of macrocrustaceans in relation to abiotic and biotic variables across the Yangtze River Estuary, China, Journal of Coastal Research, 31(4), 946-956. Coconut Creek (Florida), ISSN 0749-0208.In this article, we report on a study of the spatial and seasonal distribution of macrocrustaceans and reveal the correlation between macrocrustacean community and environmental variables in the Yangtze River Estuary, China. A total of 44 species belonging to 21 families were identified during sample collection in May, August, and November 2010 and February 2011. Species richness of four survey trips showed significant differences among seasons and zones. The most frequent species identified were Neoeriocheir leptognathus (M.individuals/1000 m 2 , respectively. The distribution of macrocrustaceans demonstrated a significant variation among seasons and zones based on PERMANOVA analysis. In terms of the value of species dominance, P. gravieri was the most dominant species throughout the study period, which composed 27.4% of the total specimens obtained. The distribution of macrocrustacean abundance in relation to biotic and abiotic variables was studied by multivariate analysis of macrocrustaceans using cluster and canonical correspondence analyses. These results demonstrated three typical classifications of communities and a significant relationship between macrocrustaceans and environmental variables. Salinity was the determining factor for spatial distribution of species and temperature for species occurrence on the entire estuarine scale. Additionally, biotic variables such as abundance of Polychaeta, abundance of primary production, and abundance of estuarine resident fishes also found significant variables that correlated with the abundance of macrocrustaceans in the Yangtze River Estuary. The study on relationship between macrocrustaceans and environmental variables provided baseline information for future ecological risk assessment in the Yangtze River estuary.

Summary This study aimed to test the hypothesis that biotic influences play a role in determining estuarine fish assemblages. Thus the mechanisms that regulate the observed spatial niche segregation between fish species with morphological and ecological similarities within estuaries were investigated. Fishes were sampled seasonally at 30 stations along an entire salinity gradient of the Yangtze River estuary from spring 2010 to winter 2011, using bottom trawling (10 mm mesh size in the cod end). A total of 62 species belonging to 28 families were collected. Marine migrants (21) and estuarine species (19) dominated the assemblage and accounted for the highest abundances (marine migrants = 42.5%, estuarine species = 38.3%), with the marine migrants having the highest biomass (57.2%). Canonical correspondence analyses indicated that chlorophyll a, salinity, temperature, and geographic distance were the four main variables influencing the occurrence of fishes within the system. A stable fish assemblage in the upper zone during the wet season (spring and summer) was more obvious than in the dry season. The Pianka index showed a clear spatial segregation in four pairs of tonguesoles species (Cygonobius), and in most pairs of gobiids (Gobiidae), and a high degree of overlapping (>0.60) in only four pairs of gobiid species during the wet season. However, according to the results of the null model the observed segregating or pattern sharing was not caused by interspecific competition.

To fully understand the water quality status of the Yuyao section in the Yaojiang River Basin, we utilized the single factor and comprehensive water quality identification index methods, as well as factor analysis in this study. The single factor water quality assessment results showed that the common parameters exceeding the standard in both the wet and dry seasons included dissolved oxygen and total nitrogen, which were inferior to the target water quality grade III by 1–6 grades. The comprehensive water quality order reaching the target grade III was Hutang River (87.5%), Changling River (50.0%), Yaojiang River (43.8%), and Linzhou River (37.5%). The comprehensive water quality in the dry season (90.0% standard-achieving rate) was better than that in the wet season (25.0% standard-achieving rate). These results suggested that the surface runoff might considerably impact water quality. The factor analysis results showed that the basin surveyed in 2018 was mainly polluted by urban sewage and agricultural sources, while the primary pollution source in 2019 was agricultural pollution. Integrated with comprehensive water quality assessment results, in this study, we demonstrated that series of water treatment projects carried out in Yuyao City positively impacted municipal sewage treatment.