Investigating the population structure of small yellow croaker (Larimichthys polyactis) using internal and external features of otoliths
Introduction
The small yellow croaker, Larimichthys polyactis of the family Sciaenidae, is a bentho-pelagic species that is widely distributed throughout the Bohai Sea, the Yellow Sea, and the East China Sea of the Northwest Pacific Ocean, and this species supports important demersal fisheries in China, Korea and Japan with annual landing of more than 300,000 tonnes (Guo et al., 2006, Kim et al., 2010, Liu and Cui, 2010).
The population structure of the small yellow croaker was originally established by Kasahara (1948) and Ikeda (1964) based on geographical differences in catch rates of the CPUE and morphological characteristics. Liu (1962) and Lin et al. (1964) carried out detailed morphometric studies on this species in the Chinese coastal waters and suggested the existence of two groups: the Southern Yellow Sea and the East China Sea groups, however, they differed in the definition of the Bohai and the Northern Yellow Sea groups. Conventional tag-recapture and molecular variance analysis also have not provided firm evidence for the existence of geographic groups (Kim et al., 2010, Liu, 1990, Xiao et al., 2009).
Variations between putative stocks may be directly measurable based on variable life history characteristics but may also indirectly act as phenotypic characteristics, such as meristic and morphological characteristics (Bergenius et al., 2006). Otolith shape has been shown to be an ideal natural marker of fish populations; furthermore, incremental patterns formed in otoliths could provide a permanent record of growth and other life history and habitat features (Begg et al., 2001, Campana and Casselman, 1993, Dawson, 1991, Petursdottir et al., 2006). Castonguay et al. (1991) first introduced Fourier analysis of otolith shape into stock identification, and the method has been widely used in stock identification in marine fishes, such horse mackerel (Trachurus trachurus) (Stransky et al., 2008), Japanese Spanish mackerel (Scomberomorus niphonius) (Zhang et al., 2012), common dolphinfish (Coryphaena hippurus) (Duarte-Neto et al., 2008), and Icelandic cod (Gadus morhua L.) (Petursdottir et al., 2006). To our knowledge, no studies on otolith morphology or incremental growth have been conducted in the small yellow croaker.
Metapopulation is defined as a group of subpopulations within a larger area that can be relatively discrete and self-replenishing but maintain sufficient exchange to preserve genetic homogeneity through the dispersal of individuals, these subpopulations function as basic unit and management object (Hanski, 1999, Hanski and Simberloff, 1997). Since the theory was introduced into marine ecology, an increasing number of traditionally managed marine fish stocks were deemed to have a metapopulation structure (Kritzer and Sale, 2004). Ying et al. (2011) first hypothesized the presence of a metapopulation structure in the small yellow croaker and further confirmed its importance in fishery management of this species.
In the current study, we investigated the population structure of the small yellow croaker from the main spawning grounds along the Chinese coastal waters and attempted to do the following: (1) define the relevant spatial scale of the population processes, and (2) re-divide the subpopulations using internal and external features of otoliths.
Section snippets
Sample collection
Small yellow croaker specimens were collected from local trawlers and research vessels during the spawning season (March–July) of 2011 from nine main spawning grounds (as described in Liu (1962)) off the coast of China (Fig. 1 and Table 1). All of the samples were stored frozen and brought to the laboratory for further analysis. The sex of each individual was determined, and standard length (SL mm) and weight (0.1 g) determined. Sagittal otoliths were dissected, cleaned in fresh water,
Otolith growth
Incremental growth differed between the regions (ANOVA, p < 0.0001). The mean incremental growth of the small yellow croaker populations sampled at Lvsi and Haizhou Bay were larger than fish sampled from the other regions, while the incremental growth of the samples from Qingdao, Qinhuangdao and Haiyang Island were the smallest (Fig. 3). Tukey HSD comparisons gave a detailed measure of the similarity among the nine spawning grounds (Table 2).
Otolith morphology and discriminant analysis
The gross morphology of the otolith was demonstrated in
Discussion
Great distinction was observed in the otolith increment growth. The variance in R1, or the juvenile growth years, indicate that the juveniles from the different spawning stocks may have inhabited different nursery areas. According to this difference, the total nine stocks could be divided into three groups, namely, the Northern Yellow Sea and Bohai Sea group that was represented by the Qingdao, Haiyang Island and Qinhuangdao stocks, the Central and Southern Yellow Sea group that was represented
Acknowledgements
This study was supported by the Fundamental Research Funds for the Central Universities (Grant No. 201022001). We would like to thank Lecturer J. Li and B.J. Zhu for their great assistance in sample collection and Professor D.G. Chen for his guidance in age determination and manuscript writing.
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