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Climate change has led to significant fluctuations in marine ecosystems. As a component of the food web, the trophic diversity and spatiotemporal changes of fish communities are crucial for understanding ecosystems. In recent years, stable isotope analysis has been increasingly used as a comprehensive tool for quantitative assessment of trophic diversity to explore spatiotemporal variations in fish community diversity. This study is based on carbon (δ 13C) and nitrogen (δ 15N) stable isotope analysis using different biomass-weighted isotope diversity indices, including isotopic divergence index (IDiv), isotopic dispersion index (IDis), isotopic evenness index (IEve), and isotopic uniqueness index (IUni). The overall results indicate that IDis, IEve, and IUni values of fish communities were relatively low, while IDiv was relatively high in the Haizhou Bay ecosystem. IDiv, IDis, IEve, and IUni were lower in autumn than in spring; IDiv and IDis were relatively higher in offshore waters, while IEve and IUni were relatively higher in inshore waters. The changes in species composition and intensive pelagic–benthic coupling in Haizhou Bay may lead to significant spatiotemporal variations in the trophic diversity of fish communities in the area. These findings highlight the importance of incorporating trophic relationships into ecosystem models, which will help to enhance our understanding of the complexity of the trophic structure of fish communities. [ABSTRACT FROM AUTHOR]

Research about feeding ecology of fish is important to understand individual behavior and population development, which is also the basic to analyze trophic structure and function of aquatic ecosystems. Chaetrichthys stigmatias is one of the key species in the Haizhou Bay fisheries ecosystem, which has critical ecological niche within the food web. In this study, we collected samples through bottom trawl surveys during the fall of 2018 in the Haizhou Bay, and analyzed the feeding ecology of C. stigmatias based on both stomach content analysis and stable isotope technology. The results showed that the primary diet groups for C. stigmatias were Ophiuroidea and Shrimp, including Ophiothrix marenzelleri, Ophiopholis mirabilis, Ophiura sarsii, Penaeidae, and Alpheus japonicus. The range of δ13C values of C. stigmatias was from -19.39% to -15.74%, with an average value of (-18.07± 0.87)%, which had no significant correlation with body length. The range of δ15N values was from 8.16%c to 12.86%, with an average value of (10.14± 1.51)%, which was positively correlated with body length. The trophic level of C. stigmatias showed a positive relationship with body length, with an average value of (3.74±0.34) and a range value of 3.32 to 4.20 among different size groups. The contribution rates of different prey groups varied significantly. Based on the structural equation modeling, we found that the feeding intensity of C. stigmatias was primally influenced by body length, sea bottom salinity, sea bottom temperature, and water depth, with a particularly significant positive correlation with body length. The combination of stable isotope technology and stomach content analysis methods could contribute to comprehensive understanding on the feeding ecology of C. stigmatias, providing essential data and foundation for research on trophic structures and resource conservation in the Haizhou Bay ecosystem. [ABSTRACT FROM AUTHOR]

Extensive applications of fishery stock enhancement worldwide bring up broad concerns about its negative effects, creating a pivotal need for science‐based assessment and planning of enhancement strategies. However, the lack of mechanistic understanding of enhanced population dynamics, particularly the density‐dependent processes, leads to compromise in model development and limits the capacity in predicting enhancement effects. Here, we developed an individual‐based model based on dynamic energy budget theory and full life‐history processes, to understand the mechanism of density dependence in population dynamics that emerge from individual‐level processes. We demonstrated the utility of the model framework by applying it to an extensively enhanced species, Chinese prawn (Fenneropenaeus chinensis, Penaeidae). The model could yield projections reflecting the observed trajectory of population biomass and yields. The model also delineated the key effects of density dependence on the vital rates of growth, fecundity and starvation mortality. Regarding the manifold effects of stock enhancement, we demonstrated a dampened shape in population biomass and yields with increasing magnitude of enhancement, and trade‐offs between the ecological and economic objectives, that is, pursuing high benefit might compromise the wild population without proper management. Furthermore, we illustrated the possibility of combining stock enhancement and harvest regulation in promoting population recovery while maintaining fisheries yields. We highlight the potential of the proposed model for understanding density dependence in enhancement programme, and for designing integrated management strategies. The approach developed herein may serve as a general approach to assess the population dynamics in stock enhancement and inform enhancement management. [ABSTRACT FROM AUTHOR]

Data-limited methods (DLMs) in stock assessment may provide potential critical information for data-limited stock management. However, the sensitivity of those methods to life-history parameters is largely unknown, resulting in extra uncertainty and consequent risks. In the present study, we designed six parallel workflows (WFs) to incorporate classic and state-of-the-art methods of estimating life-history parameters and examined their influences on the assessment of small yellow croaker (Larimichthys polyactis) in Haizhou Bay, China. The sensitivity was evaluated with three objectives: (i) the evaluation of stock status with the spawning potential ratio following different assumptions; (ii) the length-based harvest control rules derived from three management procedures; and (iii) the management performance of these harvest control rules with simulation of management strategy evaluation. The results showed considerable sensitivity regarding the three objectives to the estimations with different WFs, indicating the previous practice of credulously accepting empirical values and indiscriminately selecting references are inadvisable. We also identified the most appropriate WFs used for different purposes with limited data, aiming to provide more reliable inputs for effective fisheries management. Les methodes de traitement de donnees limitees (MDL) utilisees dans revaluation de stocks peuvent fournir de l'information potentiellement cle pour la gestion de stocks pour lesquels les donnees sont limitees. La sensibilite de ces methodes aux parametres du cycle biologique est generalement inconnue, ce qui se traduit par une incertitude accrue et les risques qui en decoulent. Nous avons concu six flux de travail (FT) paralleles pour incorporer des methodes classiques et de pointe d'estimation de parametres du cycle biologique et examine leur influence sur l'evaluation de la courbine jaune (Larimichthys polyactis) dans la baie de Haizhou (Chine). L'evaluation de la sensibilite avait trois objectifs, soit (i) revaluation de l'etat du stock par l'estimation du rapport du potentiel de frai pour differentes hypotheses; (ii) les regles de controle des prises basees sur la longueur decoulant de trois procedures de gestion; et (iii) le rendement de la gestion de ces regles de controle des prisesavec simulation de l'evaluation de strategies de gestion. Les resultats revelent une sensibilite considerable concernant ces trois objectifs aux estimations avec differents flux de travail, qui indique que la pratique passee de tenir pour acquises les valeurs empiriques et de choisir des references sans discrimination n'est pas recommandable. Nous avons egalement cerne les flux de travail les mieux adaptes pour differentes fins en presence de donnees limitees, dans le but de fournir des donnees d'entree plus fiables pour une gestion efficace des peches. [Traduit par la Redaction], Introduction Over 90% of the fish stocks in the world are managed without formal stock assessment, including the majority of fisheries in the developing countries (Costello et al. 2012). The [...]

Effective ecological indicators (EI) should reflect changes to ecosystem status in a timely manner to guide fisheries management; however, the robustness of EIs in the face of sampling uncertainty is not well understood and sampling errors may result in delayed or even unhelpful actions for management. In this study, we use a size-spectrum model to evaluate the effectiveness of EIs in detecting fishery-induced ecosystem changes given various levels of sampling uncertainty. We demonstrate that there is a time-lag that exists between changes in fishing pressure and EI response. The selectivity of survey gears can strongly determine the level of EI responses within certain size ranges. EIs may lose statistical power once sampling errors exceed a certain level, implying that several decades of monitoring data may be needed to be sure of detecting even a large change. Multivariate methods can strengthen the statistical powers of EIs, but only when the level of sampling noises is low. This study suggests the need for considering the impact of sampling uncertainty on the use of EIs in fisheries management. Les indicateurs ecologiques (IE) efficaces devraient refleter en temps opportun les modifications de l'etat des ecosystemes pour guider la gestion des peches. La robustesse des IE en presence d'incertitude associee a l'echantillonnage n'est toutefois pas bien comprise, et des erreurs d'echantillonnage peuvent se traduire par des mesures de gestion tardives, voire inutiles. Nous avons utilise un modele de spectre de tailles pour evaluer l'efficacite d'IE pour la detection de modifications d'ecosystemes induites par la peche pour differents degres d'incertitude associee a l'echantillonnage. Nous demontrons qu'il y a un decalage temporel entre les variations de la pression de peche et les reactions des IE. La selectivite des engins utilises pour revaluation peut etre un determinant important du degre de reaction des IE dans certaines fourchettes de tailles. Les IE peuvent perdre de leur efficacite statistique si les erreurs d'echantillonnage depassent un certain seuil, de sorte que des donnees de surveillance sur plusieurs decennies pourraient etre necessaries pour deceler des changements meme importants. Des methodes multivariees peuvent rehausser l'efficacite statistique des IE, mais seulement quand le bruit d'echantillonnage est faible. L'etude fait ressortir la necessite de tenir compte de l'incidence de l'incertitude associee a l'echantillonnage sur l'utilisation des IE en gestion des peches. [Traduit par la Redaction], Introduction The concept of 'ecosystem-based fisheries management' (EBFM) has been widely accepted in fisheries management with an increased recognition of fishing impacts on marine ecosystems (Hall and Mainprize 2004; Pikitch [...]

Trophic dynamics is one of the major regulators of fishery production in marine ecosystems, which is important for the implementation of ecosystem-based fisheries management. Based on data collected form bottom trawl surveys in Haizhou Bay and adjacent waters during autumn of 2011 and 2018, Delta-GAMMs (Delta-generalized additive mixed models) were constructed to evaluate the effects of biotic and abiotic factors on the predation of five key prey species (including Leptochela gracilis, Alpheus japonicus, Loligo spp., Larimichthys polyactis, and Oratos- quilla oratoria) in the Haizhou Bay. Percent frequency of occurrence and predation pressure index were used to identify their major predators. Variance inflation factor and full subsets regression were analyzed to quantiiy the degree of multicollinearity between these factors. The results showed that the occurrence frequency of keystone prey species in the stomach of predators ranged from 8.5% to 42.2%, and the weight percentage ranged from 4.2% to 40.9%. The average deviance explanation rate of' the "binomial" model was 16.1%, and the average deviance explanation rate of the "positive" model was 23.8%. Body length of predator, predator population density, and sea bottom temperature were important factors influencing prey-predator trophic interactions. Predator length was the most important factor, with feeding probability and weight percentage of keystone prey species all increasing with body length of predator. Feeding probability and weight percentage of key prey species decreased with predator population density. The effects of environmental factors such as sea bottom temperature, depth of water, latitude, and sea bottom salinity showed different trends, depending on the prey-predator assemblage. This study showed that the Delta-GAMMs was an effective method to explore the trophic interactions between prey and predators in marine ecosystems, and could provide a theoretical basis for the conservation and sustainable use of fisheries resources. [ABSTRACT FROM AUTHOR]

Occasional species are often neglected in community ecology studies due to low abundance and frequence. However, they are closely related to biodiversity maintenance and marine conservation. We used index of relative importance (IRI), distribution center of gravity and Mann-Kendall trend test to elucidate the spatial and temporal distributions and changing trends of occasional fishes in Haizhou Bay based on the fishery resources survey data collected from 2013 to 2019. The occasional fishes in Haizhou Bay was identified based on IRI. Nine of the occasional species were selected to analyze the spatial distribution and interannual trends of relative biomass and occurrence frequency. The results showed that a total of 93 fish species were recorded in the multi-year survey in Haizhou Bay. Among which, 61 species had IRI<10, indicating the existence of a large number of occasional fishes in Haizhou Bay. The nine selected occasional species had distinctive spatial distribution characteristics. Erisphex pottii, Azuma emmnion, and Raja porosa were mainly distributed in the eastern part of Haizhou Bay, with a wide habitat range. Sphyraena pinguis, Coilia nasus, and Zebrias zebra were distributed in the western and southern parts, respectively. The rest species were mainly distributed in the southwestern part. In terms of interannual variation, the biomass and occurrence frequency of Coilia mystus, R. porosa, A. emmnion, and S. pinguis showed fluctuating changes, while Odontamblyopus rubicundus and Ctenotrypauchen microcephalus showed an increasing trend. The biomass and occurrence of Z. zebra, C. nasus and E. pottii gradually decreased with no catch in recent years. This study would contribute to the understanding of the spatial and temporal distribution of occasional species, and provide guidance for the conservation of occasional biological resources and species diversity, especially for the establishment of marine protected areas. [ABSTRACT FROM AUTHOR]