Patterns of larval fish assemblages along the direction of freshwater input within the southern branch of the Yangtze Estuary, China: implications for conservation

Abstract

The Yangtze Estuary is the largest estuary in the western Pacific Ocean, and harbors a high diversity of fish fauna. In this study, larval fish were surveyed monthly across three sections within the southern branch of the Yangtze Estuary (SBYE). A total of 49 taxa were collected, with 51.4% of the identified species being freshwater fishes. The collected numbers of larval taxa in the upper, middle, and lower sections were 22, 28, and 43, respectively. Species with differing salinity adaptations displayed different patterns along the direction of freshwater input. The collected numbers of larval taxa were 47 and 29 in the near-shore and mid-stream areas, respectively; and the abundances of larval fish in the near-shore areas tended to be higher than in the mid-stream areas in all the three sections. Larval fish occurred year-round with two peaks of abundance. Our results suggest that the freshwater input was the dominant factor shaping larval fish assemblage structure and dynamics within the SBYE. Influences of the Three Gorges Dam and South-to-North Water Transfer Project on larval fish assemblages within the SBYE should be considered with regard to conservation practices.

Spatial distribution patterns of fish egg and larval assemblages in the lower reach of the Yangtze River: Potential implications for conservation and management

“…The high abundance of larval fish collected in this sampling location most probably accumulated from both Poyang Lake and the main channel of the Yangtze River. The number of species and the abundance of fish eggs and larvae observed at HK and AQ are also higher than any such previous result observed in the middle reach and the estuary of the Yangtze River (Li et al, 2010;Gao et al, 2018). Given these results, the connected river-lake system (regions directly above and below the HK region) together with the river sections from HK to AQ in the main channel should be designated as priority conservation areas in the lower reach of the Yangtze River to maximize fish recruitment.…”

“…The contents of each sample were counted and identified in the laboratory. Larval fish were identified by a combined morphological and molecular approach (Gao et al, 2018;Song et al, 2019). Whenever possible, specimens were first identified using morphological descriptions in Cao et al (2007).…”

“…In addition, some studies have reported adverse effects of the Three Gorges Dam on populations of these four species (Li et al, 2011;Song et al, 2017). Other studies have focused on the distribution and assemblage structure of larval fish, although these surveys have mainly been conducted in the estuary (Jiang, Zhong & Zhou, 2010;Gao et al, 2018) and tributaries of the upper reaches of the Yangtze River (Liu et al, 2014;Wang H. et al, 2017). However, research on the early life stages of fishes is rare in the lower reach of the Yangtze River, with the exception of our previous study, which investigated monthly occurrences of larval fish, described the annual composition of larval assemblages, identified the prevailing fish spawning season (mid-April to mid-August), and implied potential influences of landscape patterns in the lower reaches (Ren et al, 2016).…”

Reviewing Research About the Early Life History of Freshwater Fish in China

“…Otolith microstructure records early life events and stage durations of fishes, such as, the first feeding, the metamorphosis, settlement, and so on [14,19] Using otolith microstructure, the variations on growth and mortality rate among cohorts hatched in different dates, months and years and come from discrete spawning grounds can be compared in relation with environmental conditions. The relationship between growth rate, environmental variables and recruitment can be erected to reveal population dynamics [1,2] The development and characteristics of otolith in the early life history have been largely described for many fish species. And daily increments have been verified in the otoliths of diverse fish species, the first daily increment are deposited at hatching, or one day after hatching or the first feeding [7,12] However, in China, growth and mortality rates have rarely analyzed for larvae in the natural rivers.…”

“…mortality rate and its relationship with environmental variables in the larval and juvenile stages [2] Early life history studies have been highly developed since 1914, when Hjort first proposed that variation in larval survival could generate recruitment variability [3] Research contents of early life history can be categorized into three aspects: ontogenetic development and identification, distribution and abundance, and growth and survival. Larval species can be identified by morphological characters and molecular analysis [4] Spatial and temporal changes on larval occurrence and abundance in relation with environmental factors have been widely documented [5,6] Larval dispersal is an important component of understanding distribution and recruitment [7] Spatial and temporal variations on growth and mortality rates and its relationship abiotic and biotic factors are essential for revealing recruitment mechanism [8] In addition, the 'growth-mortality' hypothesis has been verified and implemented in many studies [9,10].…”