Spawning strategy of Japanese anchovy Engraulis japonicus in the coastal Yellow Sea: Choice and dynamics

Abstract

Understanding the relationships between hydrodynamics and the spawning activities of small pelagic fishes is crucial for understanding their recruitment dynamics and for fisheries management. Here, we clarify the effects of marine environmental factors and the associated hydrodynamic processes on the spawning activities of the Japanese anchovy Engraulis japonicus in the coastal Yellow Sea using data from in situ ichthyoplankton surveys (7 recent years), a hydrodynamic model and satellite remote sensing. We confirmed the peak spawning period (May and June) and primary spawning location (Haizhou Bay). We defined the ‘spawning temperature optima’ hypothesis to identify the optimal spawning temperature (13.0–18.0°C) for the Japanese anchovy based on egg occurrence and abundance. We detected fortnightly variation in spawning behaviour, which peaked after the spring tide. Anchovy eggs showed evident aggregation in the nearshore upwelling area during May and June, while strong upwelling in July may cause a negative spawning‐site choice in upwelling zone. These findings clarify the effects of hydrodynamics on the spawning behaviour of the Japanese anchovy in the coastal Yellow Sea.

Spawning overlap of Japanese anchovy Engraulis japonicus and Japanese Spanish mackerel Scomberomorus niphonius in the coastal Yellow Sea: A prey–predator interaction

“…The “spawning temperature optima” hypothesis was tested by calculating the occurrence (presence/absence) of eggs, which was assumed to reflect the spawning preference and has been used as an index to characterize the physical and biological aspects of spawning habitats of SPF (Takasuka, Oozeki, & Kubota, 2008; Takasuka, Oozeki, Kubota, & Lluch‐Cota, 2008; Twatwa et al, 2005; van der Lingen et al, 2005; Zhang et al, 2020). This hypothesis was proven to be useful for anchovy, and 13.0–18.0°C was identified as the optimal spawning temperature for anchovy in the coastal Yellow Sea (Zhang et al, 2020). Here, we further applied the hypothesis for mackerel to test whether the hypothesis was appropriate for large epipelagic predators.…”

“…Then a quotient curve was constructed and used to assess the temperature optima for anchovy and mackerel spawning. A similar quotient for egg abundance (hereafter referred to as the abundance temperature index [ATI]; Equation 2) representing the percentage egg abundance (%) versus the relative frequency of positive samples in each temperature interval, which combined with the STI would better assess the optimum temperature for spawning (Zhang et al, 2020). The egg abundance (number of eggs per 100 m 3 of seawater; ind./100 m 3 ) for each station was determined based on the number of eggs caught divided by the volume of filtered water (m 3 ).…”

“…The stations surveyed in different years are distinguished with colors and symbols. Samples were divided into three groups according to their locations (Subei Bank, Haizhou Bay, northern coast) useful for anchovy, and 13.0-18.0 C was identified as the optimal spawning temperature for anchovy in the coastal Yellow Sea (Zhang et al, 2020). Here, we further applied the hypothesis for mackerel to test whether the hypothesis was appropriate for large epipelagic predators.…”

“…Anchovy is the mackerel's dominant prey, particularly during the spawning migration of mackerel (Huh et al, 2006;Jin et al, 2010;Kishida, 1986), and larval anchovy is the important prey items for larval mackerel from the first feeding stage (Nakajima et al, 2013;Shoji et al, 1997Shoji et al, , 1999, which is why anchovy is commonly known as the "food of Japanese Spanish mackerel". Both mackerel and anchovy are among the most important fishery resources in the China Sea (Pan et al, 2020;Zhang et al, 2020;Zhao et al, 2003). Despite the overexploitation of many commercially important species in the China Sea under warming and intensive fishing, the catches of both mackerel and anchovy maintained a high yield (i.e., the fifth and second in China's marine fishery, respectively) in F I G U R E 1 Migration routes of (a) Japanese anchovy and (b) Japanese Spanish mackerel in the coastal China seas (these were redrawn from Zhang, 1965 andWei, 1980, respectively) recent years (Pang et al, 2018;Yu et al, 2020).…”

“…But the early recruitment success of mackerel might be related to the degree of spatiotemporal match between mackerel larvae and their food anchovy larvae. Nevertheless, the prey-predator interaction between mackerel and anchovy during early life stages is not well understood because previous studies tended to analyze the two species separately (Wan et al, 2008(Wan et al, , 2020Zhang et al, 2020). Therefore, determining whether mackerel in the China Sea have a unique spawning strategy in response to anchovy spawning dynamics, and exploring their interspecific relationships during the early stages, is essential, as it may be a determinant of mackerel recruitment and could be used to explain population fluctuations under conditions of overexploitation and climate variability (Li et al, 2015;Oozeki et al, 2007;Yu et al, 2020).…”