Abstract
To evaluate the importance of the northern Satsunan area in southern Japan as a spawning and nursery ground for chub mackerel (Scomber japonicus), we investigated the early life history characteristics (e.g., larval distribution, feeding habits, and growth) ofS. japonicusover five successive years. This area is considered the main habitat and spawning ground of the congeneric species,S. australasicus. Using polymerase chain reaction-restriction fragment length polymorphism analysis, we first confirmed thatS. japonicuslarvae were abundant in the northern Satsunan area, potentially representing a major spawning and nursery ground in the Japanese Pacific coastal area. The number of recorded larvae started to increase in 2016, corresponding to the population dynamics of the Pacific stock of the species, which has shown increasing trends in recent years. Morphological and DNA metabarcoding analyses of gut contents and stable isotope analysis showed that, in addition to copepods, the larvae fed substantially on appendicularians. The trophic pathway involving appendicularians might support the feeding habits ofS. japonicus, promoting its coexistence with other dominant species. Both the instantaneous growth rate and daily specific growth rate were comparable to those in the southern East China Sea, which is the main spawning and nursery ground of the species. Our data strongly suggest that the northern Satsunan area has favorable conditions for sustaining high larval population densities, even during phases with high population numbers. Our results provide insights for the fisheries management forS. japonicusin the Japanese Pacific coastal area, especially during high-stock periods.
Highlights
IntroductionIt is essential to ensure successful feeding for the survival of fish larvae (Hirai et al, 2017)
In fish population dynamics, it is essential to ensure successful feeding for the survival of fish larvae (Hirai et al, 2017)
The mean larval density tended to be higher in the mouth of the Kagoshima Bay than in the Osumi Strait, suggesting that the increased lower-trophic productivity following upwellings could result in favorable conditions for S. japonicus larvae
Summary
It is essential to ensure successful feeding for the survival of fish larvae (Hirai et al, 2017). At the critical larval stage, fish that have completed yolk absorption start exogenous feeding. Both the quality and quantity of prey are important for the growth of fish (Hjort, 1914). The growth rate of fish is determined by multiple environmental factors, such as water temperature and prey availability (Heath, 1992; Takasuka et al, 2016), along with the key factors regulating the survival potential during the early life stages and the recruitment success of the fish (Shoji et al, 2005; Robert et al, 2007; Kamimura et al, 2015; Takasuka et al, 2016). The population of the Pacific stock of S. japonicus has shown an increasing trend in recent years
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