World fisheries, including freshwater, marine, and capture fisheries, as well as aquaculture, provide approximately 17% of the total animal protein consumed by humans, and around 56.6 million people are directly engaged in fisheries (Kang et al., 2018). After decades of rapid development, China has become the largest contributor to global marine fishing (FAO, 2019). At present, China’s marine catch exceeds 15 million tons (Wang Y. et al., 2020). However, since the 1970s, many of China’s marine fishery resources have been over exploited and the structure of the fish community has greatly changed (Kang et al., 2018; Zhang et al., 2020); the catches of some traditionally important economic fish have decreased significantly (Jin et al., 2015; Zhang et al., 2020). Only approximately 12% of the global fisheries are properly managed through stock assessments results (Kindong et al., 2020). Therefore, stock assessment is essential for the management of fisheries resources.

The South China Sea is located at the center of the Indo Western Pacific region and is the third largest marginal sea in the world (Li et al., 2019). It is rich in marine biodiversity, with more than 8,600 species of animals and plants (Ng and Tan, 2000). Perciformes play an important role in the structure of fish resources in the South China Sea, which have complex feeding habits, feeding on phytoplankton and zooplankton as well as other Marine animals such as invertebrates and fish. There are 979 species of Perciformes in the whole South China Sea, accounting for 42.2% of the total species (2321) (Ma et al., 2006). There are more than 300 species of Perciformes in the Beibu Gulf in the South China Sea, accounting for more than 50% of the total fish species, and most of them are economically important fish (Sun et al., 2010).

In China, only a small number of commercially developed fish resources have been specifically assessed, owing to limited data and expertise (Liang et al., 2020). Recently, two methods have been applied to the assessment of fishery resources in China. One is the maximum sustainable yield (MSY) model, which uses a time series of catch and auxiliary data to estimate the MSY (Ju et al., 2020b; Liang et al., 2020; Zhai et al., 2020); The other is the length-based Bayesian biomass (LBB) model, which uses length frequency (LF) data to estimate asymptotic length, length at first capture, relative natural mortality and relative fishing mortality (Ju et al., 2020a; Kindong et al., 2020; Liang et al., 2020; Wang Y. et al., 2020, 2021; Zhang et al., 2020, 2021; Wang X. et al., 2021). Size measurement is the basic requirement for marine fishery resource surveys in China (Jin et al., 2012), and LF data are usually easier to obtain and cheaper than other data types (Liang et al., 2020). This allows the LBB method to be used to evaluate the commercial fishery resources in China’s marine waters where there is little knowledge of other parameters (Zhang et al., 2020). LBB is a newly developed Bayesian biomass estimation method based on length, which needs no data except LF (Froese et al., 2018). The growth and mortality parameters and the relative stock size are estimated using a Bayesian Monte Carlo Markov chain (MCMC). Furthermore, LBB results can be informative for other data poor stock assessment models that use priors for the status of the biomass [e.g., AMSY or Catch-MSY (CMSY)], regarding the relative biomass (B/B₀) in a certain year.

In this study, we applied the LBB method to 19 Perciform fish populations in the Beibu Gulf to explore the extent of biomass depletion caused by fisheries, and to provide evidence for potential alternative harvest policies.

In this study, the stock resources of 19 Perciformes living in the Beibu Gulf were evaluated using the LBB method. The parameters L_mean/L_opt, L_c/L_{c_opt}, L_95th/L_inf, B/B₀, B/B_MSY, F/M, F/K, and Z/K were obtained (Table 3). The ratios L_mean/L_opt and L_c/L_{c_opt} were below one in 14 out of the 19 stocks, suggesting a truncated length structure and fishing of undersized individuals. The ratio of the 95th percentile length to asymptotic length L_95th/L_inf was close to one (>0.9) in 10 out of 19 stocks, suggesting that at least some large fish were still present. The ratio B/B₀ was smaller than B_MSY/B₀ in 19 stocks, suggesting these fish species included in this study are being low biomass. Furthermore, the relative biomass (B/B₀) for nineteen of the species in the Beibu Gulf evaluated here was 0.25 on average, which indicated a depletion rate of 75%.

Figures 2–5 are the specific evaluation results of LBB method. The blue line in the figures represents the fit of the data and the LBB estimation, and the red line is the evaluation from the LBB method of population resources. Figure 2 shows similar results for five species. The LBB model gives a good fit. The parameter B/B_MSY ranges from 0.12 to 0.17, and the estimated value of F/M is far greater than one. Therefore, the status of the stock of these five species (Branchiostegus argentatus, Parastromateus niger, Nemipterus virgatus, Evynnis cardinalis, and Trichiurus japonicus) is “collapsed.” The results for four similar species are shown in Figure 3. The estimated value of B/B_MSY ranges from 0.25 to 0.49, and the estimated value of F/M is greater than 1. It is considered that the resource status of these four species (Nemipterus japonicus, Siganus fuscescens, Terapon theraps, Upeneus moluccensis) is “grossly overfished.” The results of six similar species are shown in Figure 4. The estimated values of the parameter B/B_MSY range from 0.53 to 0.94, and the estimated value of F/M is close to 1. It is considered that the resource states of Acropoma japonicum and Pennahia pawak are “slightly overfished,” while Pennahia microcephalus, Ariomma indica, Decapterus maruadsi, and Pennahia anea are “overfished.” Finally, Figure 5 shows the results of four similar species where the parameter B/B_MSY ranges from 1 to 2.3. Our assessment considers that the resource status of these species (Johnius belangerii, Nemipterus peronii, Trachurus japonicus, and Upeneus bensasi) is “healthy.”

Most coastal fish populations in China cannot be evaluated comprehensively because of a lack of data (Liang et al., 2020). However, the LBB method can effectively evaluate the population with limited LF data (Ju et al., 2020a; Liang et al., 2020; Wang Y. et al., 2020, 2021; Zhang et al., 2020, 2021; Wang X. et al., 2021). The stock status was given in the LBB model based on the parameter B/B_MSY, which had been described in detail in previous studies (Froese et al., 2018; Wang Y. et al., 2021).

In this study, the LBB method was used to evaluate the resource status of 19 Perciformes in the Beibu Gulf. The results showed that only 21% of the evaluated stocks were healthy and 79% were overfished. In particular, 26 and 21% of the assessed species were exhausted and severely overfished, respectively, while only 11 and 21% of the assessed species were slightly overfished and overfished, respectively. Zhang et al. (2021) assessed the resources of 10 species around the Nansha Islands, South China Sea. It was considered that the resources of 80% of the species assessed were overfished. According to Ju et al. (2020a), 80% of the five shark stocks living around Taiwan, South China Sea, were overfished; Zhang et al. (2020) evaluated 20 stock resources in Min River Estuary and found that 65% of the stock was overfished. The results of this study are consistent with these reports indicate most fish living in the South China Sea are facing overfishing pressures (Table 4). The ratio B/B₀ was smaller than B_MSY/B₀ in all 19 stocks, suggesting the fish species included in this study are being low biomass. The relative biomass (B/B₀) for the 19 species in the Beibu Gulf evaluated here was 0.25 on average, which indicated a depletion rate of 75%. This result was consistent with the 84% average depletion reported by Zhai and Pauly (2019). The ratios L_mean/L_opt and L_c/L_{c_opt} were below one in 14 out of the 19 stocks, suggesting a truncated length structure and fishing of undersized individuals. However, the ratio of the 95th percentile length to asymptotic length L_95th/L_inf was close to one (>0.9) in 10 out of 19 stocks, suggesting that at least some large fish were still present.

In this study, five stocks (Branchiostegus argentatus, Parastromateus niger, Nemipterus virgatus, Evynnis cardinalis, and Trichiurus japonicus) had collapsed. Branchiostegus argentatus belongs to the warm-temperate fish, living in the middle and lower layers, and its maximum body length is 27.3 (see text footnote 1). In the 1990s, the resource status was healthy (Lin et al., 1996; Wang, 2002). However, because the mesh size used is less than 5 cm, its larvae are also caught in large quantities (Lin et al., 1996). With the increase in fishing intensity, the stocks of Branchiostegus argentatus are almost exhausted. Parastromateus niger is a pelagic fish that migrates in warm water in the open sea. It is one of the fish species with high economic value in the South China Sea. Its stock resources were rich from 1972 to 1984, but with the increasing catch (Lu et al., 1986), the resources by 2011 were overburdened, and the biomass was at a very low level. Nemipterus virgatus is one of the five major economic fishes in the northern South China Sea. Overfishing occurred in the 5 years from 2008 to 2017, especially in 2012, which was consistent with our assessment results (Wu et al., 2021). Evynnis cardinalis is mainly distributed in the South China Sea and the South East China Sea and is one of the important species for the bottom trawl fishery. Wang X. et al. (2020) evaluated the stock resources in Beibu Gulf from 2006 to 2018 by the LBB method, and the results showed that the resources were overfished, especially in 2010 and 2011, which is consistent with our evaluation. Trichiurus japonicus is a warm water pelagic fish, which is one of the most valuable fish species in the northern South China Sea.

Four stocks (Nemipterus japonicus, Siganus fuscescens, Terapon theraps, and Upeneus moluccensis) are grossly overfished. Nemipterus japonicus is widely distributed through the Indian Ocean and West Pacific. Ali et al. (2014) analyzed the population resources in the Indian Ocean from 1986 to 2014, but not in the South China Sea. Similarly, although Siganus fuscescens, Terapon theraps, and Upeneus moluccensis occupy an important economic position in China’s fisheries (Ma and Liu, 2006), the specific assessment of their resources has not been reported before.

The resource status of four stocks (Pennahia microcephalus, Ariomma indica, Decapterus maruadsi, and Pennahia anea) is overfished. Pennahia microcephalus is widely distributed in the Indo-West Pacific tropical regions, including the East China Sea and the South China Sea. It is one of the dominant commercial fish species throughout the coastal area of Southeast China (Yan et al., 2009). Wang M. D. et al. (2021) used the LBB method to evaluate its resource status in the Beibu Gulf. The results showed that the white croaker was overfished from 2006 to 2014, especially after 2009, which was consistent with the results of this study. Ariomma indica is a bottom fish, living in warm water. It is one of the most common economic fish in the South China Sea and also the main fishing target of bottom trawlers in the South China Sea (Lin, 2003). Decapterus maruadsi is one of the most common croakers currently on retail sale in Hong Kong, and its resources were overfished in 2008–2009 (Tuuli et al., 2011).

In this study, two stocks (Acropoma japonicum and Pennahia pawak) were slightly overfished, and four stocks (Johnius belangerii, Nemipterus peronii, Trachurus japonicus, and Upeneus bensasi) were healthy. Acropoma japonicum is one of the dominant species in the Beibu Gulf (Zhang et al., 2016; Cai et al., 2018), but there are few reports on its stocks. Pennahia pawak is a relatively stable resource species in the Beibu Gulf, which has important ecological status and economic benefits. On the basis of the analysis of fishery biology, Yi et al. (2021) thought that the resources of Pennahia pawak were lightly exploited. Johnius belangerii is one of the main economic species of fishing in China. With the overfishing of offshore waters, its resources have begun to decline (Guo et al., 2017). Nemipterus peronii is widely distributed in the Indo Western Pacific, from the Red Sea to Taiwan and northern Australia, and its maximum body length is 29 cm (see text footnote 1). Trachurus japonicus is one of the main upper middle economic species in the northern South China Sea, and its resource status was healthy from 1997 to 1999 (Chen and Qiu, 2004). Upeneus bensasi is one of the main economic fishes in Beibu Gulf of China. Its resources were in a healthy state in 2008 (Zhu et al., 2008).

The Bayesian estimation model based on body length (LBB) is a new method to analyze the LF data of economic fishery catches (Froese et al., 2018). The advantages of the LBB model are as follows: (1) the results of relative biomass or stock state have been verified by simulation and actual stocks; (2) there is no significant difference between the predicted LBB and the simulated B/B₀; (3) the prediction of stock status by LBB is similar to that of other models; (4) LBB makes a preliminary estimation of the status of the fish group according to the LF data of the fishery; and (5) the results of LBB provide objective B/B₀ priors for other evaluation methods such as CMSY and AMSY (Froese et al., 2017, 2018). The LBB method only needs body length and frequency to evaluate the fish resources in a certain region, which solves the problem that some regions cannot evaluate the fishery germplasm resources owing to the lack of available data. However, the LBB model is not always accurate because it only inputs length and frequency data. If the LBB method is combined with other models, the results will be more reliable (Wang Y. et al., 2020, 2021).

The stock status of 19 species of Perciformes living in the Beibu Gulf was evaluated by the LBB method. Among the 19 fish stocks assessed, 15 were overfished and only 4 were healthy. The resources of Branchiostegus argentatus, Parastromateus niger, Nemipterus virgatus, Evynnis cardinalis, and Trichiurus japonicus have collapsed because of long-term overfishing, and the existing biomass is at a low level. Fishery managers need to take specific measures, such as limiting the size of fishing nets and reducing the operation time of fishing vessels, to restore fishery resources. However, the resource status of Johnius belangerii, Nemipterus peronii, Trachurus japonicus, and Upeneus bensasi is relatively healthy, and the population development rate is relatively low. There is still room for development of these fisheries. Therefore, we can appropriately increase the catch of these populations, so as to reduce the fishing pressure on depleted fish species in the South China Sea. Although LBB can easily and quickly evaluate the status of fishery resources, the assessment results may not be accurate because only the frequency of fish body length is used. It needs to be combined with other models or methods to obtain more accurate resource assessment results.

The original contributions presented in the study are included in the article/Supplementary Material, further inquiries can be directed to the corresponding author.

The animal study was reviewed and approved by Guangdong Ocean University.

GH and HZ analyzed the LF data and completed the first draft. HZ provided guidance on data analysis and structure of the manuscript. JW, YC, and JL provided suggestions on the revision of the manuscript. JW, YC, and JL helped to collect the original length data. All authors are contributed to revise the manuscript.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.