The Non-stationary Environmental Effects on Spawning Habitat of Fish in Estuaries: A Case Study of Coilia mystus in the Yangtze Estuary

Dong Wang,Pengbo Song,Lu Zhai,Zengguang Li,Junbo Zhang,Rong Wan,Shuo Zhang,Xiangyu Long

doi:10.3389/fmars.2021.766616

Dong Wang, Pengbo Song + Show 6 more

Open Access

https://doi.org/10.3389/fmars.2021.766616

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Abstract

The estuarine areas provide necessary spawning habitat, nursing habitat, and migratory for a variety of fishes and the environmental conditions are of significant heterogeneity. Coilia mystus is the key commercial fish that spawns in the Yangtze Estuary and the yield has declined sharply in the past 30 years. In order to understand the spawning habitat selection mechanism of C. mystus, the geographically weighted regression (GWR) model was applied to explore the non-stationary effect of environmental variables [e.g., the sea surface temperature (SST) and the sea surface salinity (SSS)] and geographical variables [e.g., the distance to the coast (DTC) and the depth (DEP) of water] on the egg density distribution of C. mystus. The data were derived from the spring and summer ichthyoplankton surveys carried out from 2019 to 2020 in the Yangtze Estuary, China. The GWR model results showed that the key variables in different seasons had spatial non-stationary effects on the distribution of spawning habitat of C. mystus, which were mainly caused by regional rise in temperature and saltwater intrusion of the South Branch. In the spring, the SSS, the DTC, and the DEP were the main impact factors and saltwater intrusion in the South Branch might lead to the trend that the spawning habitat moved further upstream to the Changxing Island. The SST was most important in the summer and the relatively lower SST was more crucial in the spawning habitat selection than the DTC and the DEP. The GWR model performed well in the study of C. mystus potential spawning habitat in the Yangtze Estuary. We recommend that more attention should be paid in regional variation of environmental factors to explore fish potential spawning habitat in the estuarine areas.

Highlights

The distribution of fish spawning habitat is usually determined by the adaptation of reproductive physiology and species response to the surrounding environmental conditions (Gallego et al, 2007; Zorica et al, 2013; Gonzalez-Irusta and Wright, 2016; Reglero et al, 2017)
The geographically weighted regression (GWR) models had good performance according to r2 (0.53–0.69)
The observed C. mystus eggs were confined in the South Branch, near the Chongming, Changxing, and Hengsha Islands (Figure 3)

Summary

Introduction

The distribution of fish spawning habitat is usually determined by the adaptation of reproductive physiology and species response to the surrounding environmental conditions (Gallego et al, 2007; Zorica et al, 2013; Gonzalez-Irusta and Wright, 2016; Reglero et al, 2017). The estuaries, as important fish spawning and nursery habitats, are usually characterized by complex hydrological systems and spatially varying environmental conditions (Andrew et al, 2009). Examining fish spawning activity and its response to the spatial nonstationary environment is important for gaining a comprehensive understanding of spawning habitat selection mechanism, which helps to understand fish stock fluctuations and, establish appropriate protection strategies for estuarine fish

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