Progress in Fishery Sciences (Dec 2023)
Habitat History of Coilia nasus in Fujian Waters Based on Otolith Microchemical Analysis
Abstract
The Japanese grenadier anchovy Coilia nasus Temminck & Schlegel, 1846 belongs to the family Engraulidae of the order Clupeiformes. This species is widely distributed in China, Japan, and Korea and in Northwest Pacific Ocean. In China, C. nasus is found in the Bohai Sea, the Yellow Sea, the East China Sea, and the middle and lower reaches and the estuaries of some main rivers, such as the Liao River, the Yellow River, and the Yangtze River. The life history of C. nasus is diverse and it is found to have three main ecological types (i.e., anadromous migratory, freshwater resident, and freshwater landlocked), indicating its strong adaptability to different habitats. Because of its commercial importance in China, C. nasus has been heavily exploited for years. Due to the significant decline of the wild stocks and the degeneration of freshwater spawning grounds in its distribution region, C. nasus was listed in the IUCN Red List of Threatened Species as "Endangered" category in 2018.Currently, the exact distribution boundary of C. nasus to the southern limit of China is unclear. Based on the fishery surveys in the southern Zhejiang Province for the past 15 years, the adjacent waters of Ou River estuary in Wenzhou are the known southernmost distribution area for C. nasus. The distribution of C. nasus in Fujian waters, both freshwater and seawater was documented from 1960—2008; however, the sampled individuals were very rare. It is impossible to understand the habitat history and life history pattern of C. nasus using traditional fishery survey methods. In this study, three C. nasus individuals were collected by trawl net, set net, and gill net in Fuzhou and Ningde waters in 2017—2019 during various fishery surveys along the coastline of Fujian. To reconstruct the life history of C. nasus in Fujian waters, the X-ray electron probe micro-analysis (EPMA) approach was used to analyze otolith (sagitta) microchemistry patterns of the fish for the first time. Otolith microchemistry is an effective tool for revealing the anadromous pattern and the spatial and temporal distribution of fishes. The otolith Sr/Ca ratios are powerful indicators for identifying freshwater, brackish water, and seawater habitats throughout the life history of fish.The results of this study showed that the Sr/Ca ratios of the otolith core areas of all three C. nasus individuals were less than 3, and the core areas exhibited a blue pattern in the X-ray intensity maps of Sr content. Both results indicated that the three individuals originated from freshwater and hatched in freshwater habitat. Among the three individuals, the individual collected in Fuzhou waters was more dependent on freshwater at its early life stage and did not enter brackish water until it was almost 1-year-old. Combined with the sampling site and the adjacent water of Min River, it is deduced that it might have originated from the pure freshwater habitat of Min River. Two individuals collected in Ningde waters were less dependent on freshwater habitat at their early life stage. Combined with the sampling sites, i.e., the outer water of Sansha Bay, it is deduced that the two individuals from Ningde might have originated from the pure freshwater habitat of Jiao Brook in Ningde, Ou River in Wenzhou, or Min River in Fuzhou. According to the fluctuations of the Sr/Ca ratio from the core to the edge of the otoliths and X-ray intensity maps of Sr content through the otolith core, all three C. nasus individuals were confirmed to be typically anadromous ecological types. The habitat history of the only one C. nasus individual in Fuzhou was a freshwater-brackish type; its hatching and early life stage were also associated with freshwater habitat, and then it entered the brackish water habitat and traveled back and forth between brackish water and freshwater habitats to grow out until it was captured. The habitat history of the other two C. nasus individuals in Ningde was freshwater-brackish-seawater type; their hatching and early life stage were associated with freshwater habitat, and then they entered high salinity habitat and traveled back and forth between brackish water and seawater habitats for growth until captured. Moreover, we found that the higher salinity in the capture waters of the three C. nasus individuals did not correspond to the Sr/Ca ratio at the edge of the otoliths, indicating a certain time delay in otolith responding to the salinity of their most present living habitats.This study not only revealed the diversity of C. nasus life history patterns and habitat histories but also confirmed the current distribution of anadromous C. nasus in Fujian waters. Since February 2019, the Yangtze River, the most important habitat for C. nasus and many endangered fishes and mammals has initiated a new management measure, i.e., a 10-year fishing ban plan. However, there is still a lack of sufficient understanding of the distribution, the locations of spawning grounds and the population size of C. nasus in Fujian waters. Further studies on the key habitats of C. nasus such as spawning ground and ecological type are needed to formulate effective management measures for its natural resource conservation in Fujian waters.
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