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Modeling population dynamics and assessing the stock status of the blackspot seabream (Pagellus bogaraveo) in the Azores.
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Abstract(s)
O goraz (Pagellus bogaraveo) é o principal recurso de pesca explorado pela frota demersal açoriana devido à sua abundância e preço médio, que define a dinâmica do regime de exploração multiespecífico da frota. Atualmente, este recurso é considerado intensivamente explorado. Várias avaliações analíticas têm sido implementadas para este stock na Região Autónoma dos Açores, mas as restrições dos modelos são a principal limitação para a sua gestão e exploração sustentável. Esta situação decorre da incerteza dos resultados das atuais avaliações de stocks que não explicam a dinâmica observada nos dados, indicando que os modelos disponíveis não ajudam a prever as características do stock e da pescaria. Por conseguinte, o Grupo de Trabalho sobre Biologia e Avaliação de Recursos Pesqueiros de Profundidade (WGDEEP) do Conselho Internacional de Exploração do Mar (CIEM) classifica este recurso como "limitado em termos de dados" e recomenda a exploração de metodologias de avaliação mais flexíveis, adaptadas à dinâmica dos recursos e à natureza incerta dos dados de entrada. No entanto, os objetivos de gestão do recurso ainda não foram definidos.
Neste estudo, todos os dados biológicos, ecológicos e pesqueiros disponíveis (dependentes e independentes da pesca) foram recolhidos, analisados e resumidos sob a forma de dados de entrada para a avaliação do stock de Pagellus bogaraveo, organizados em camadas ou submódulos de informação. Foram exploradas duas abordagens de modelação estruturadas por idade para a avaliação das unidades populacionais: uma convencional, a eXtended survivor analysis, e uma nova, uma abordagem de modelação estatística de análise integrada – Stock Synthesis. O recurso foi avaliado, combinando todas as informações disponíveis.
Os resultados mostram uma melhoria significativa do volume de dados disponíveis, mas uma incerteza considerável nas estimativas dos parâmetros de reprodução (maturação e proporção entre os sexos) e de crescimento, incluindo as chaves idade-comprimento, provavelmente devido a questões metodológicas na recolha de dados. Os desembarques registam uma tendência crescente até 1992 e uma diminuição acentuada a partir de 2005. Os índices de abundância relativa registam uma tendência decrescente ao longo de toda a série histórica. Nos últimos anos, foi observada uma tendência contraditória nos índices de abundância relativa. Enquanto se regista um aumento do índice de abundância do estudo, verifica-se uma diminuição do índice de abundância da pesca comercial. Este conflito nos índices é explorado através de hipóteses de um aumento real da abundância ou de efeitos de capturabilidade formulados para explicar as tendências observadas. A estrutura etária da população parece manter a sua distribuição geral com uma moda entre 24-34cm LF. No entanto, parecem existir variações interanuais na disponibilidade do goraz para a pesca.
Os métodos de avaliação utilizadas revelam muitas diferenças na caraterização dos dados. A abordagem convencional não apresentou melhorias na estimativa das características do stock. Em contrapartida, o modelo de análise integrada mostrou uma maior flexibilidade na análise e compreensão dos dados, permitindo a exploração de hipóteses para resolver conflitos observados nos dados, como a tendência oposta observada nos índices de abundância ou potenciais alterações observadas nos dados de crescimento. Da análise
exploratória SS3, que explorou um total de 54 modelos de referência, 35 convergiram, sugerindo, em geral, que a interpretação do estado do stock de Pagellus bogaraveo nos Açores é altamente dependente dos pressupostos do modelo.
Considerando todas as conclusões obtidas durante este estudo, os resultados demonstram uma melhoria no conhecimento e uma melhor compreensão da dinâmica populacional de Pagellus bogaraveo no Arquipélago dos Açores.
ABSTRACT: The blackspot seabream (Pagellus bogaraveo) is the primary fishery resource exploited by the Azorean demersal fleet due to its abundance and average price, which defines the dynamics of the fleet's multispecific operating regime. Presently, this resource is considered intensively exploited. Several analytical assessments have been implemented for this stock in the Azores Area, but the restrictions of the models are currently the main limitation for its management and sustainable exploitation. This arises from the uncertainty of the current stock assessment results that do not explain the observed dynamics in the data, indicating that the available models do not help predict the stock and fishery characteristics. Therefore, the Working Group on Biology and Assessment of Deep-sea Fisheries Resources (WGDEEP) of the International Council for the Exploration of the Sea (ICES) classifies this resource as “data limited” and recommends exploring more flexible assessment methodologies adapted to the resource dynamics and the uncertain nature of the input data. Nonetheless, the management objectives for the resource have not yet been defined. In this study, all available biological, ecological, and fisheries data (fishery-dependent and fisheries-independent data) were collected, analyzed, and summarized in the form of input data for the assessment of the Pagellus bogaraveo stock, organized into layers or sub modules of information. Two age-structured modeling approaches for the stock assessment were explored: one conventional, the eXtended survivor analysis, and one novel, an integrated analysis statistical modeling approach - Stock Synthesis. The resource was assessed, combining all available information. The results show a significant improvement in the volume of data available but considerable uncertainty in the estimations of the reproduction parameters (maturation and sex ratio) and growth, including the age-length keys, probably because of methodological issues in the data collection. Landings show an increasing trend until 1992 and a sharp decrease from 2005. Relative abundance indices show a decreasing trend throughout the historical series. In recent years, a contradictory trend has been observed in relative abundance indices. Whereas there is an increase in the abundance index of the survey, there is a decrease in the abundance index of the commercial fishery. This conflict in indices is explored through hypotheses of a real increase in abundance or catchability effects formulated to explain the observed trends. The population's age structure seems to maintain its general distribution with a mode between 24-34cm LF. Still, there appear to be inter-annual variations in the availability of blackspot seabream to fishing. The assessment methods used show many differences in the characterization of the data. The conventional approach did not show improvement in the estimation of stock characteristics. In contrast, the integrated analysis model showed greater flexibility in the analysis and understanding of the data, allowing the exploration of hypotheses to resolve conflicts observed in the data, such as the opposite trend observed in the abundance indices or potential changes observed in growth data. From the SS3 exploratory analysis, which explored a total of 54 reference models, 35 converged, suggesting, in general, that the interpretation of the stock status of Pagellus bogaraveo in the Azores is highly dependent on model assumptions. Considering all the insights obtained during this study, the results demonstrate an improvement in knowledge and a better understanding of the population dynamics of Pagellus bogaraveo in the Azores Archipelago.
ABSTRACT: The blackspot seabream (Pagellus bogaraveo) is the primary fishery resource exploited by the Azorean demersal fleet due to its abundance and average price, which defines the dynamics of the fleet's multispecific operating regime. Presently, this resource is considered intensively exploited. Several analytical assessments have been implemented for this stock in the Azores Area, but the restrictions of the models are currently the main limitation for its management and sustainable exploitation. This arises from the uncertainty of the current stock assessment results that do not explain the observed dynamics in the data, indicating that the available models do not help predict the stock and fishery characteristics. Therefore, the Working Group on Biology and Assessment of Deep-sea Fisheries Resources (WGDEEP) of the International Council for the Exploration of the Sea (ICES) classifies this resource as “data limited” and recommends exploring more flexible assessment methodologies adapted to the resource dynamics and the uncertain nature of the input data. Nonetheless, the management objectives for the resource have not yet been defined. In this study, all available biological, ecological, and fisheries data (fishery-dependent and fisheries-independent data) were collected, analyzed, and summarized in the form of input data for the assessment of the Pagellus bogaraveo stock, organized into layers or sub modules of information. Two age-structured modeling approaches for the stock assessment were explored: one conventional, the eXtended survivor analysis, and one novel, an integrated analysis statistical modeling approach - Stock Synthesis. The resource was assessed, combining all available information. The results show a significant improvement in the volume of data available but considerable uncertainty in the estimations of the reproduction parameters (maturation and sex ratio) and growth, including the age-length keys, probably because of methodological issues in the data collection. Landings show an increasing trend until 1992 and a sharp decrease from 2005. Relative abundance indices show a decreasing trend throughout the historical series. In recent years, a contradictory trend has been observed in relative abundance indices. Whereas there is an increase in the abundance index of the survey, there is a decrease in the abundance index of the commercial fishery. This conflict in indices is explored through hypotheses of a real increase in abundance or catchability effects formulated to explain the observed trends. The population's age structure seems to maintain its general distribution with a mode between 24-34cm LF. Still, there appear to be inter-annual variations in the availability of blackspot seabream to fishing. The assessment methods used show many differences in the characterization of the data. The conventional approach did not show improvement in the estimation of stock characteristics. In contrast, the integrated analysis model showed greater flexibility in the analysis and understanding of the data, allowing the exploration of hypotheses to resolve conflicts observed in the data, such as the opposite trend observed in the abundance indices or potential changes observed in growth data. From the SS3 exploratory analysis, which explored a total of 54 reference models, 35 converged, suggesting, in general, that the interpretation of the stock status of Pagellus bogaraveo in the Azores is highly dependent on model assumptions. Considering all the insights obtained during this study, the results demonstrate an improvement in knowledge and a better understanding of the population dynamics of Pagellus bogaraveo in the Azores Archipelago.
Description
Tese de Doutoramento, Ciências do Mar, 30 de novembro de 2023, Universidade dos Açores.
Keywords
Modeling Population dynamics Stock Assessment Management Pagellus Bogaraveo Azores
Citation
Pabon, Ana Maria Novoa. (2022). "Modeling population dynamics and assessing the stock status of the blackspot seabream (Pagellus bogaraveo) in the Azores.". 182 p. (Tese de Doutoramento em Ciências do Mar). Horta: Universidade dos Açores, 2022. Disponível em http://hdl.handle.net/10400.3/7110