Estimation of life history traits and stock status for Scomber japonicus based on data-limited method.

The age-structure data is usually unavailable for most traditional fishery species in the East China Sea. The data-limited method is thus particularly important to understand life history and population dynamics of commercial fishes. At the offshore waters of southern Zhejiang, Chub mackerel (Scomber japonicus) is one of the dominant economic species. Based on fork length data from 2016 to 2020, we estimated its life history traits with the data-limited method, including the growth parameters and mortality coefficients. We further evaluated the status of Chub mackerel by the yield per recruitment (YPR) model. The results showed that the relationship between fork length (L) and body weight (W) based on 1606 samples was estimated to be W=4.18×10-3L3.28(R2=0.96). The asymptotic fork length L∞ of Chub mackerel was 28.34 cm, the growth rate was 0.36 a-1, and the initial theoretical age was -0.40 a. The total mortality was estimated as 1.67 a-1, and the estimated natural mortality (M) was 0.85 a-1. The fishing mortality (F) was 0.82 a-1, and the development rate was 0.49. The current capture age was estimated to be 1.78 a, while the capture fork length was 15.44 cm. The YPR model results showed YPR value showed a trend of increasing and then decreasing with the increases of F. The values of biological reference points F0.1 and Fmax were 0.97 a-1 and 4.55 a-1, respectively, which were higher than the value of current F. The sensitivity analysis showed that the uncertainty of M greatly influenced the estimation results of YPR and biological reference points. A decrease in M significantly increased the YPR value, but F0.1 and Fmax decreased. The status of Chub mackerel stock at the offshore waters of southern Zhejiang is in good condition. However, the miniaturization of catch is intensifying. It is recommended to extend the capture fork length to 20 cm (the impact point age) to improve the quality of the catch, which would sustainably use the Chub mackerel resources.

[Heterogeneity of growth and maturity of Larimichthys polyactis in the offshore waters of southern Zhejiang, China]. / 浙江南部近海小黄鱼生长和性成熟特征的异质性.

The variations of life history traits have been observed for many fish species, which gains much concerns in the study of aquatic biology and ecology. In this study, the biological characteristics were explored for yellow croaker (Larimichthys polyactis) in the offshore waters of southern Zhejiang, based on 4920 individuals collected from 13 fishery-independent seasonal surveys from autumn 2015 to autumn 2018. Linear mixed effects models were used to estimate the growth, maturity characteristics, and their heterogeneity. The body length of yellow croaker samples ranged from 13 to 215 mm with the dominant body of 110 to 154 mm. The body weight ranged from 0.5 to 182.2 g, with the dominant body weight from 20 to 55 g. The results showed that the linear mixed effects models with random effects from season, gender, and year performed best for length-weight relationship, with the lowest AIC and RMSE values. The effects of season were much larger than those of genders and years. When the length exceeded 160 mm, the weight gain rate of yellow croaker was faster in spring and summer, lower in autumn and winter, while the male individuals gained more weight than the females with the same body length. Among 4841 individuals of specimens with gonadal data, the individuals at maturity Ⅱ stage occupied 50.4%, and the individuals at maturity stage contributed to 19.6%. The results from the best linear mixed effects model showed that season had the most significant influence on the maturity of yellow croaker. The 50% maturity length (L50%) was much lower in winter (124.6 mm) with no much difference between other seasons, indicating that yellow croaker matures earlier in winter. Our results indicated that linear mixed effect model could reflect the biological heterogeneity of yellow croaker conveniently and that the growth and maturity of yellow croaker had significantly sexual and temporal variations, which should be considered in the stock assessment and fishery management for yellow croaker.

[Feeding habits of Rhinogobius pflaumi in Jiaozhou Bay, China based on carbon and nitrogen stable isotope analysis]. / åŸºäºŽç¢³ã€æ°®ç¨³å®šåŒä½ç´ ç ”ç©¶èƒ¶å·žæ¹¾æ™®æ°æ ‰è™¾è™Žé±¼çš„æ‘„é£Ÿä¹ æ€§.

Rhinogobius pflaumi is a small-sized, warm-temperate demersal fish species. It is one of the dominant species in fish community, and plays an important role in Jiaozhou Bay ecosystem. The trophic level and feeding habits of R. pflaumi were investigated by carbon and nitrogen stable isotope analysis, based on the data collected from the bottom trawl surveys during May 2011 in Jiaozhou Bay, China in this study. The results showed that the δ15N and δ13C values of R. pflaumi ranged from 11.24‰ to 13.99‰ and -20.67‰ to -18.46‰, respectively. The mean values of δ15N and δ13C were (12.70±0.70)‰ and (-19.08±0.36)‰, respectively. The mean trophic level of R. pflaumi was (3.62±0.21) for all size classes, ranging from 3.49 to 3.76 for different size classes. There was a significant negative correlation between the δ15N values and standard length, while no significant correlation was observed between δ13C values and standard length. The main prey groups of R. pflaumi were polychaeta, decapoda and mollusca. The trophic contributions of zooplankton and particle organic matter (POM) were relatively low. The similarities of prey species composition among different size classes were more than 92%, indicating that there was no significant difference in feeding habits with different standard lengths. R. pflaumi was an intermediate consumer in Jiaozhou Bay ecosystem. The significant negative correlation between trophic level and standard length might be due to variation in the proportion of different prey groups.

[Feeding ecology of Amblychaeturichthys hexanema in Jiaozhou Bay, China].

From February to November 2011, four seasonal bottom trawl surveys were conducted in the Jiaozhou Bay of China. A total of 624 Amblychaeturichthys hexanema individuals were collected to analyze their stomach contents, with the feeding ecology of A. hexanema studied. The prey items of A. hexanema included more than 40 species, among which, Alpheus japonicas, Philine kinglippini, and Leptochela gracilis were the dominant prey species. The diet composition of A. hexanema had an obvious seasonal variation, with the gastropods, fish, decapods, and microcrustacean being the most important prey items in spring, summer, autumn, and winter, respectively. This phenomenon could be mainly related to the seasonal variations in the species and biomass of the preys in Jiaozhou Bay. With the increase of predator size, the prey species of A. hexanema varied from small size copepod to larger sizes P. kinglippini, Raphidopus ciliates, and A. japonicas. The canonical correspondence analysis (CCA) showed that water temperature and salinity were the most important factors affecting the feeding of A. hexanema, followed by predator size and water pH.