Recruitment success of commercially important marine resources, such as the Peruvian anchovy Engraulis ringens, is based on continuous assessment and fisheries management. Potential egg production (PEP) is a valuable tool that, unlike the reproductive indices, quantifies spawning activity and increases the likelihood of a better prediction of recruitment. From 2000 to 2008, spawning females >14.0 cm total length contributed largely to the annual PEP (more than 60%), while females ranging from 12.0 to 14.0 cm TL had a significant participation during peak spawning periods. During the main spawning periods, 68% of the total PEP was obtained, with each length group contributing 50% of this production, whereas during the period of low activity, females >14.0 cm were those that kept spawning, contributing 81% of PEP. The breeding-related closed fishing seasons protected 57% of PEP, 22% in summer and 35% in winter-spring; fishery closure is an effective management measure to protect the main reproductive activity. This protection and quantitative knowledge of the spawning of E. ringens, such as that provided by PEP, will help us to better understand the recruitment process and predict recruitment.
The principal objective of this work is to present a new model for the assessment of recruitment of the northern-central stock of Peruvian anchovy (Engraulis ringens), and use it to estimate monthly time series of recruits and pre-recruits between 1961 and 2009. The model is length-based and has monthly temporal resolution, allowing the variability in abundance and seasonality of recruitment to be modeled based on fishery and scientific survey information. The anchovy population is modeled with two recruitments per year, parameterizing recruitment using abundance, mean length, and dispersion of the mean length at recruitment. This way of modeling recruitment enables a better representation of the temporal continuity of the recruitment process in comparison to an approach that only considers the abundance of recruits. The monthly time series of pre-recruits (4.0–7.5 cm) and recruits (8.0–11.5 cm) obtained were analyzed, and two regime shifts in recruitment dynamics (1971 and 1991) were identified. Seasonal patterns given by the model are consistent with those obtained by independent direct studies. We discuss the advantages and limitations of this approach within the framework of the study of the recruitment process and the integration of reproductive data in stock assessment models.
Whereas fisheries acoustics data processing mainly focused on the detection, characterization, and recognition of individual fish schools, here we addressed the characterization and discrimination of fish school clusters. The proposed scheme relied on the application of the Bags-of-Features (BoF) approach to acoustic echograms. This approach is widely exploited for pattern recognition issues and naturally applies here, considering fish schools as the relevant elementary objects. It relies on the extraction and categorization of fish schools in fisheries acoustic data. Echogram descriptors were computed per unit echogram length as the numbers of schools in different school categories. We applied this approach to the discrimination of juvenile and adult anchovy (Engraulis ringens) off Peru. Whereas the discrimination of individual schools is low (below 70%), the proposed BoF scheme achieved between 89% and 92% of correct classification of juvenile and adult echograms for different survey data sets and significantly outperformed classical school-based echogram characteristics (about 10% of improvement of the correct classification rate). We further illustrate the potential of the proposed scheme for the estimation of the spatial distribution of juvenile and adult anchovy populations.Résumé : Alors que le traitement de données acoustiques sur les ressources halieutiques est principalement axé sur la détec-tion, la caractérisation et la reconnaissance de bancs individuels de poissons, nous nous penchons sur la caractérisation et la discrimination de groupes de bancs de poissons. Le schéma proposé repose sur l'application de l'approche des sacs de mots visuels (« Bags-of-Features » ou BoF) au traitement d'échogrammes acoustiques. Cette approche est fréquemment appliquée aux problèmes de reconnaissance de formes et s'applique donc tout naturellement à l'étude de bancs de poissons en tant qu'objets élémentaires. Elle repose sur l'extraction et la catégorisation de bancs de poissons à partir de données acoustiques sur les ressources halieutiques. Des descripteurs d'échogramme ont été calculés par unité de longueur d'échogramme, correspondant aux nombres de bancs, dans différentes catégories de bancs. Nous avons appliqué cette approche à la discrimination d'anchois (Engraulis ringens) juvéniles et adultes au large des côtes du Pérou. Si la discrimination de bancs individuels est faible (inférieure à 70 %), la classification des échogrammes de juvéniles et d'adultes reposant sur l'approche des BoF s'est avérée exacte dans de 89 % à 92 % des cas pour différents ensembles de données de levés, ce qui correspond à une augmentation significative de l'exactitude par rapport aux approches classiques reposant sur les caractéristiques d'échogram-mes basées sur le banc (augmentation d'environ 10 % du taux de classification exacte). Nous poussons plus loin la démons-tration du potentiel du schéma proposé pour l'estimation de la distribution spatiale des populations d'anchois juvéniles et adultes.[Traduit par la Rédaction]
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