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Catches have remained relatively high in the Gulf of Thailand and the Bohai Sea, China, despite severe biomass declines (around 95%) evidenced by fishery-independent surveys. Such high production at very low stock sizes is not predicted by simple-surplus production theory, but can be explained by age-structured models that predict high recruitment rates even when biomass per recruit (BPR) has been drastically reduced. Recruitment rates can be reconstructed by estimating changes over time in biomass and BPR, for alternative assumptions about survey catchability, growth, and mortality rates. These reconstructions indicate that likely severe decreases in BPR, due to high fishing mortality rates, imply that total recruitment rates have likely been relatively stable over time, with catch consisting largely of new recruits making up most of the low biomass. These considerations may apply to numerous areas in east and southeast Asia where most of the catch of coastal trawlers is used to produce animal feeds, notably for aquaculture.

Among fishery biologists and even ichthyologists, maturation and spawning of fish are viewed as processes that use “energy” that would otherwise be applied to somatic growth, which is supposed to explain why post-maturity growth in length tends to decline. This widespread conceptualization may be called the “reproductive drain hypothesis” (RDH). However, when growth is correctly viewed as involving body mass, and is thus expressed in weight, post-maturity turns out (in iteroparous bony fish whose maximum length exceeds 10 cm) to accelerate after first maturity, despite its energy cost. This, and other common observations flatly contradict the RDH, and the time has come to withdraw this hypothesis. As a contribution towards this task, we propose an alternative reconceptualization of fish spawning consistent with what is known about fish biology.&nbsp, Los biólogos pesqueros e incluso los ictiólogos tienden a ver la maduración y el desove de los peces como procesos que usan “energía” que, de otro modo, sería aplicada al crecimiento somático, lo cual se supone que explica por qué el crecimiento post-maduración, en lo que se refiere a longitud, tiende a declinar. Esta popular conceptualización puede ser denominada “Hipótesis del Drenaje Reproductivo” (RDH). Sin embargo, cuando el crecimiento es visto de manera correcta como un proceso que involucra el volumen o masa corporal y, por lo tanto, se expresa en peso, la post-maduración (en peces óseos iteróparos cuya longitud máxima supera los 10 cm) se acelera luego de la primera maduración, a pesar de su costo energético. Esta, y otras observaciones comunes, contradicen la RDH y, por lo tanto, ha llegado el momento de jubilar esta hipótesis. Para contribuir con esta tarea, se propone una reconceptualización alternativa del desove en peces, la cual es consistente con el conocimiento existente sobre la biología de los peces.&nbsp

Estuaries are nutrient-rich environments with a gradient of fresh to salt water. They support high primary productivity and an abundance of zooplankton. Estuaries are used by many fish as nursery grounds because their environmental conditions provide abundant food for larval and adult fish. Ichthyoplankton, which comprise fish eggs and larvae, are important for the recruitment of fish species. At present, there are no systematic reviews on ichthyoplankton in estuaries from a global perspective. Here, research on ichthyoplankton over the last 60 years (1951–2022) was reviewed, focusing on three aspects: evaluation of ichthyoplankton published studies, community structure, and factors affecting community structure. The results show that research on estuarine ichthyoplankton has increased, from less than 1 article per year in the 1950s to more than 30 articles per year in the 2020s. The keyword used most commonly was ‘community structure’ and ‘dynamics’ and the word used most recently was ‘climate change’. Regarding the geographical distribution of the studies carried out on estuarine ichthyoplankton, USA had the most (32.9% of all studies), followed by Australia (8.1%), South Africa (6.1%), Brazil (5.6%), Japan (5.1%), China (4.9%), Canada (4.8%), and Portugal (4.8%). Salinity and turbidity were the main factors affecting the ichthyoplankton community structure in estuaries. Climate change indirectly affected the community structure of estuarine ichthyoplankton by changing the spawning time, spawning location, and hatching time of species. The movement of spawning sites poleward and the advance of spawning time showed a consistent trend. In addition, the development of DNA barcoding techniques will be a useful supplement to traditional taxonomic methods for identifying ichthyoplankton and will provide new opportunities for the development of systematic taxonomy in this field. Our review contributes to a broader understanding of estuarine ichthyoplankton and provides theoretical support for estuarine environmental protection and the sustainable use of estuarine fishery resources.

In recent years, the proportion and economic value of Lophius litulon (family Lophiidae) in the coastal fishery off Shandong Province, China has increased. In this study, we mapped the distribution of L. litulon abundance [catch per unit effort (CPUE)] and applied a generalized additive model (GAM) to explore the relationship between CPUE and environmental factors. Two data-limited methods (the BSM related to the CMSY method and the AMSY method) were used to evaluate the stock status and relevant fishery reference points of L. litulon. The results showed that the L. litulon stock was concentrated in the central Yellow Sea, at 34.0°–37.0° N and 121.0°–124.0° E, and the highest average CPUE of L. litulon in this area occurred in winter. The three most significant environmental factors affecting species abundance were bottom temperature, bottom salinity, and depth. L. litulon was most abundant when bottom temperature ranged from 5.8 to 10.6°C, depth was > 18 m, and bottom salinity varied from 31.0 to 33.2‰. The BSM and AMSY models indicated that the L. litulon stock was unhealthy and had been overfished in recent years, as its biomass remained below the level that can support maximum sustainable yield. The relative exploitation ratios were also high. These results provide the basic data for improving sustainability of the exploitation of L. litulon in the Yellow and Bohai Seas.

River-ocean continuums are rich environments key to the transformations of organic matter and nutrients from many sources. Human impacts on these ecosystems can be local, upstream, or global. Particulate organic matter provides one tool for exploring these processes; inventories and carbon and nitrogen stable isotopes are useful indicators. This study conducted comprehensive field investigations from the upper reaches of the Yangtze River to the coastal waters to explore the distribution and spatial-temporal variation of particulate organic carbon (POC) and nitrogen (PON), and dissolved organic carbon (DOC) in surface waters from April–May (Spring) and October–November (Autumn) 2014. Carbon and nitrogen isotopes (δ13C and δ15 N) were used to assess organic matter sources. Numerous environmental factors were also measured. PON and POC exhibited similar spatial and temporal variations along the river mainstream. POC increased from the upper to lower reaches, similarly in both seasons; POC declined seaward from the river mouth. In contrast, PON showed greater seasonal and spatial variations along the continuum, with greater primary production in offshore areas. DOC along the continuum was higher in autumn, likely related to greater river discharge and warmer waters. The DOC/POC ratios by weight were >1 in most samples except for the ones collected from the turbidity maximum zone, suggesting that DOC contributed to a larger fraction of the total organic matter inventories. End-member mixing models revealed that the proportion of organic matter from upstream (allochthonous) sources was >70% in the mainstream during both seasons. In coastal waters, the proportion of allochthonous sources was only >57%. Compared with other major world rivers, DOC and allochthonous POC are especially high in the Yangtze River-ocean continuum. Human activities causing variations in terrestrial inputs are likely an important driving factor. In addition, the contribution of soil erosion caused by urbanization to riverine organic carbon cannot be ignored.

Estuaries, where fresh and salty water converge, provide abundant nutrients for ichthyoplankton. Ichthyoplankton, including fish eggs, larvae, and juveniles, are important fishery recruitment resources. The Yangtze Estuary and its adjacent waters comprise a typical large-scale estuary and supply many important fish spawning, feeding, and breeding areas. In this study, 1,291 ichthyoplankton individuals were collected in the Yangtze Estuary in spring, from 2013 to 2020. The aims of the study were to provide detailed information on characteristics of the ichthyoplankton assemblage, explore interannual variation, and evaluate the effects of environmental variables on the temporal variation in assemblage structure. Twenty-six species in seventeen families were identified. The dominant species were Coilia mystus, Chelidonichthys spinosus, Engraulis japonicus, Hypoatherina valenciennei, Larimichthys polyactis, Salanx ariakensis, Stolephorus commersonnii, and Trachidermus fasciatus. The ichthyoplankton assemblage changed significantly over time, and Chelidonichthys spinosus became one of the dominant species. Canonical correspondence analysis showed that temperature and chlorophyll a were the key factors affecting the assemblage structure in the Yangtze Estuary in spring.

The status of fishery resources in the Yangtze estuary and its adjacent waters is still unclear for the effective implementation of fishery management strategies. To help address this gap, a new method especially for data-limited fish stocks (LBB) was applied to assess seven commercially and ecotrophically important fish stocks. Fish specimens were collected in the estuary by bottom trawling quarterly from May 2018 to February 2019. Two historical datasets were collected with the same method in the same area for Indian perch (Jaydia lineata) and sickle pomfret (Pampus echinogaster). To explore the growth features and resilience of fish stocks, auximetric plots and growth performance indices (Φ′) were used. Results showed that common hairfin anchovy (Setipinna tenuifilis) in 2018 and Indian perch in 2018 showed a healthy stock biomass status with complete length structures under a sustainable fishing pressure. The others were outside of safe biological limits or overfished. The Lmean/Lopt < 0.9 in six (67%) of nine LBB models for seven fish stocks suggested that most of the stocks were truncated in length structures. This contribution provides the main fishery reference points regarding stock status that can inform managers and form the basis for various management strategies.

The catch-maximum sustainable yield (CMSY) method and a closely-related Bayesian state-space Schaefer surplus production model (BSM) were combined with published catch-per-unit-effort (CPUE) time series or spawning stock biomass (SSB) data to evaluate fisheries reference points for exploited resources of the Japan Sea. Eleven fish and invertebrate stocks were assessed; outcomes obtained through this analysis were the carrying capacity, biomass trajectory, maximum sustainable yield, and related parameters of each stock. Results showed that the stock of Japanese sandfish (Arctoscopus japonicus) was slightly overfished; the stocks of sohachi (Cleisthenes pinetorum), flathead flounder (Hippoglossoides dubius), bastard halibut (Paralichthys olivaceus) and snow crab (Chionoecetes opilio) were overfished; and the stocks of shotted halibut (Eopsetta grigorjewi), yellow striped flounder (Pseudopleuronectes herzensteini), red seabream (Pagrus major), Alaska pollock (Gadus chalcogrammus) and deep-sea smelt (Glossanodon semifasciatus) were grossly overfished; only Alaskan pink shrimp (Pandalus eous) was in a good condition. These results are consistent with the few previous studies on the status of fish species around Japan, where overfishing is becoming increasingly apparent. These assessments provide a basis for guiding the use of fishery resources in the Japan Sea.

Sixteen marine fish species (populations) exploited by Chinese fisheries were assessed, using published time series of catch and the CMSY and BSM methods. Given the catch times series as inputs, some ancillary information and reasonable constraints, carrying capacity, maximum sustainable yield, and likely time series of biomass and exploitation rate were estimated. The results show that one (7%) of the assessed species was severely depleted, four species (27%) were fully/overfished, six (40%) were outside of safe biological limits, one species (7%) was recovering and three species (20%) were in a healthy state at the end year of their assessment. However, one species, Pacific sardine (Sardinops sagax), could not be assessed using CMSY, as the exceedingly large fluctuations of its biomass were mainly environmentally driven. These results correspond with previous knowledge on the status of fish populations along the coast of China, where overfishing is rampant. Based on these assessments, some of the benefits that would result from a reduction of the excessive fishing effort are outlined.

This contribution presents stock assessments for ten fish and two squid populations exploited by Chinese, South Korean and Japanese fishing fleets in the Tsushima Warm Current region, i.e., West of Japan and East of China. The methods used are a Monte Carlo method (CMSY) and a Bayesian state-space implementation of the Schaefer model (BSM), based on published time series of catch and abundance data (SSB and CPUE). Results show that two fish stocks, Japanese jack mackerel (Trachurus japonicus) and yellowback sea-bream (Dentex hypselosomus) are in a healthy status, while daggertooth pike conger (Muraenesox cinereus) appears to have collapsed. The other nine stocks show varying degrees of overfishing. The cooperation of several countries will be required to recovery the fishery resources in the Tsushima Warm Current region.

We assessed 12 marine fish species in the Northwestern Pacific exploited by Japanese fisheries, using published catch time series, CPUE data and the CMSY and BSM methods. The results showed that one stock was severely depleted, three stocks were outside of safe biological limits, three stocks were fully/overfished, three stocks were recovering, while the other two stocks were in good condition. These results match those of previous research on the status of fish species in the Northwestern Pacific, where overfishing is becoming increasingly apparent. We used the CMSY/BSM assessments as a basis for suggestions to assist in the management and rebuilding of fishery resources in this area.

The status of fifteen marine fish and invertebrate populations exploited by Chinese, South Korean or Japanese fishing fleets were assessed, using two newly developed computer-intensive methods, CMSY and BSM. The results show that among these fifteen populations in question, 2 have collapsed, 3 are grossly over-fished and 9 are overfished. Also, we compared results of the CMSY and BSM methods, and it shows that, while the CPUE data for use with the BSM method lead to narrower confidence intervals and may modify the shape of the biomass trajectory, they do not lead to over- or underestimates of terminal B/BMSY values. These results, although still tentative because the methods used to generate them are relatively new, generally match what is known of the status and exploitation of the populations in question, which makes CMSY and BSM to be promising stock assessment approaches in data-sparse situations. Based on our results, a consistent signal is obtained, thus suggesting that a reduction in fishing pressure would be necessary to restore the abundance status of these fifteen populations.

Due to lLimited by data availability, only a small subset of the exploited fish and invertebrate populations have been assessed along Chinese coastsal waters, which precludes comprehensive management of the fisheries. Here, we applied a length-based Bayesian biomass estimator (LBB) to 14 fish and invertebrate stocks in China’s coastal waters to estimate their growth, length at first capture and current relative biomass (B/B0, B/BMSY) from length-frequency (LF) data. Of the 14 populations assessed, 1 have collapsed, 9 are grossly over-exploited, and 3 are overfished. Moreover, 13 populations have smaller mean lengths at first capture (Lc) than the optimal length at first capture (Lc_opt), indicating that they are suffering from growth overfishing. Thus, larger mesh sizes in commercial fishery would increase both the catch and biomass for these species, given current levels of fishing mortality. Our results confirm that fishery resources in China’s coastal waters are strongly depleted, and that stricter management measures are needed to restore the abundance of China’s marine fisheries resources.

Eight common and commercially important marine fishes from coastal and offshore areas of Shandong Province, China, were assessed using the “Length-based Bayesian Biomass” estimator (LBB) method. These species were Scomber japonicus (chub mackerel), Sebastiscus marmoratus (false kelpfish), Hexagrammos otakii (fat greenling), Thryssa kammalensis (kammal thryssa), Gadus macrocephalus (Pacific cod), Setipinna taty (scaly hairfin anchovy), Sillago sihama (silver sillago), and Lophius litulon (yellow goosefish). LBB is a new and powerful, yet simple, approach to evaluate a fisheries’ status using length and frequency data. Shandong Province’s coastal areas, adjacent to the Yellow and Bohai Seas, are an important fishing ground of China, where the 2018 catch of three of these species, yellow goosefish, chub mackerel, and Pacific cod, yielded up to 57,200, 21,100, and 1330 tons, respectively. The ratios of current relative to unexploited biomass (B/B0) is smaller than the relative biomass that can produce MSY (BMSY/B0) in eight stocks save for silver sillago, indicating overfishing. Also, the sizes at first capture were well below the optimal, suggesting that larger mesh sizes would be beneficial. Our study provides evidence that LBB is an efficient method to evaluate the fishery resources in the Yellow and Bohai Seas, especially when length frequencies are the only available data. Also, LBB provided evidence useful for the management of the costal fishery resources of Shandong Province.

Two investigations of the Changjiang River mainstream and forty-two cruise surveys of the estuary were conducted to determine the distribution of the dissolved inorganic nitrogen (DIN), phosphorus (DIP), and silicon (DSi) contents in the Changjiang, as well as the long-term nutrient transportation trends and impacts on the estuary. The N and P contents in the Changjiang were low in the Jinshajiang section, and then dramatically increased because of intensive anthropogenic activities and convergence of high nutrients tributaries. The DSi was distributed evenly along the Changjiang River, except that low values were observed in the Three Gorges Dam (TGD) section. Since the 1980s, the transportation of nitrate (NO3-N) and DIP nutrients by the Changjiang has exhibited increasing trends. However, DSi transportation did not change significantly, although a decreasing trend in DSi was observed from 2004 to 2010. The nutrients transported by the Changjiang were significantly correlated with the nutrients observed in the estuary, and increased amounts of NO3-N and DIP and ratios of NO3-N:DIP and NO3-N:DSi have been observed in the estuary since the 1980s. The nutrients enrichment and altered ratios have had important impacts on the estuary ecosystem.

Limacina helicina is the dominant pelagic gastropod mollusc species in temperate and polar ecosystems, where it contributes significantly to food webs and vertical flux. Currently, considerable uncertainty exists in the interpretation of L. helicina’s life cycle, hindering our understanding of its potential responses to environmental change. Here, we present size-frequency data on L. helicina collected from three consecutive years (2008–2010) in a North Pacific temperate fjord. Two methods of length-frequency analysis were used to infer the growth of L. helicina, i.e. linking successive means extracted from finite-mixture distributions, and using the ELEFAN software to fit seasonally oscillating versions of the von Bertalanffy growth equation to the available length-frequency data. Against a background of continuous low level spawning between spring and autumn, both approaches identified two sets of major cohorts, i.e. (i) spring cohorts (G1) spawned in March/April by (ii) overwintering cohorts (G). G overwintered with minimal to low growth, before undergoing rapid growth the following spring and completing the cycle by spawning the G1 generation and disappearing from the population by May/June. Our findings are discussed in the context of L. helicina response to climate change.

Riverine supply of largely terrestrial carbon is important to the carbon cycle chemistry of the oceans. Along a river-ocean continuum, sedimentary organic matter composition and distribution can provide insights to the balance of terrestrial input and in situ production of an estuary. In the Yangtze River estuary (YRE), this balance is especially important to understand as human impacts and climate change continue to modify processes along the continuum. Here we discuss the sources and spatio-temporal distributions of organic matter in the coastal ocean surface sediments and how environmental factors have affected changes there. The isotopic compositions (δ13C and δ15N), total organic carbon (TOC), and total nitrogen (TN) of surface sediments were investigated along with sediment grain size and bottom water temperature, salinity, and total suspended matter. Evidence suggests that fine sedimentary grain size, bottom water temperature, and the circulation dynamics of water masses such as Changjiang Diluted Water (CDW) and Taiwan Warm Current (TWC) were the main factors affecting spatial and temporal distributions, with organic matter concentrations in autumn showing higher than that in spring and nearshore areas higher than offshore. An isotopic-based two end-member mixing model suggests that terrigenous inputs were the main source (about 53%) of organic matter in the YRE, followed by autochthonous marine organic matter, in both seasons. Terrestrial organic matter distribution, controlled by the CDW, decreased seaward from the mouth, as expected, and the proportion of terrestrial organic carbon increased in autumn compared to spring. Intrusions of the TWC water likely contributed to the increase of marine components in a tongue-shaped area during both seasons.

The Bohai Sea, in Northeastern China, which has been severely overexploited since the 1950s, is not only an exemplary case of the ‘fishing down’ phenomenon (where large, high-trophic level fish are replaced by smaller fish and invertebrates as the overall biomass is reduced), but also can be used to illustrate one of the masking effects for fishing down. Thus, the decadal decline in the mean trophic level of the biomass in the Bohai Sea is more pronounced than the decline of the mean trophic level of the catch extracted from that sea. This effect is similar to what occurred in the Celtic Sea, where previous authors called this difference ‘skipper effect’ (because skippers try to maintain catches of larger fish), and in the Gulf of Thailand. The skipper effect appears to be a powerful masking factor for the fishing down phenomenon, i.e., biomass tend to be more affected than suggested by time series of the mean trophic of catches.

Ocean warming can strongly impact marine fisheries; notably, it can cause the “mean temperature of the catch” (MTC) to increase, an indicator of the tropicalization of fisheries catches. In this contribution, we explore MTC changes in three large marine ecosystems (LMEs) along China’s coasts, i.e., the Yellow Sea, East China Sea, and South China Sea LMEs, and their relationships to shifts of the sea surface temperature (SST). The results show that, while the MTCs began to increase in 1962 in the East China Sea and in 1968 in the Yellow Sea, there was no detectable increase in the South China Sea. There also was a strong relationship between MTC and SST in the Yellow and East China Seas from 1950 to 2010, especially when taking a 3-year time-lag into account. The lack of change of the MTC in the South China Sea is attributed to the relatively small increase in SST over the time period considered, and the fact that the MTC of tropical ecosystems such as the South China Sea is not predicted to increase in the first place, given that their fauna cannot be replaced by another, adapted to higher temperature. Overall, these results suggest that ocean warming is already having an impact on China’s marine fisheries, and that policies to curtail greenhouse gas emissions are urgently needed to minimize the increase of these impacts on fisheries.