ABSTRACT
Yangtze River Estuary is the biggest estuarine ecosystem in the western Pacific Ocean. Evaluating fish community in this ecosystem can provide scientific basis for its restoration and mana-gement. Generalized additive model (GAM) and boosted regression tree (BRT) were built to examine the relationship between fish community diversity and environmental and spatio-temporal variables based on data collected during 2012-2014. Combined with linear regression analysis, a cross validation was used to evaluate the fitness and predictive performance of both models. We plotted the spatial distribution of fish community diversity and richness in each station of the Yangtze River Estuary in 2014. The results showed that salinity, pH and chlorophyll-a had the most contribution on diversity, while pH, dissolved oxygen and chlorophyll-a were the most contributive variables on richness. BRT models showed better fitness and lower prediction error than GAM models. In contrast to GAM models, BRT models could distinguish the fish community index in each station area with respect to the spatial prediction. The diversity index in external water was obviously greater than that in internal water. Meanwhile, the station at higher latitude had a higher diversity index in both external and internal water.
Subject(s)
Rivers , Animals , China , Estuaries , Fishes , Pacific OceanABSTRACT
Based on data collected from four trips of trawl surveys in offshore water of southern Zhejiang in 2015-2016, a generalized additive model was used to analyze the distribution of small yellow croaker (Larimichthys polyactis) and its relationship with environmental factors. The results showed that the highest resource abundance occurred in the summer trip, primarily in Yushan fishing ground with an average density of 500.74 kg·h-1·km-2. Environmental factors influencing the density and distribution of small yellow croaker changed with season. The effect of environmental factors on the resource density of small yellow croaker was not significant in autumn. In spring, the small yellow croaker mainly distributed in waters with high salinity, while both sea bottom temperature and salinity had negative correlation with resource density of small yellow croaker in summer, and the fish habited in Yushan waters with middle temperature and high salinity. In winter, water temperature had a positive relationship with resource density of small yellow croaker which primarily distributed in waters of outside stations with suitable temperature. Generally, the distribution characteristic of small yellow croaker accorded to its migration habit. It was hard to explain the relations between environmental factors and resource density of small yellow croaker, which needed to further study. The results are helpful for understanding the living behavior and the conservation and management of the small yellow croaker stock in offshore water of southern Zhejiang.