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Caracterização da população de Carcinus maenas na Lagoa de Santo André e potencial de exploração
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As lagoas costeiras são sistemas muito produtivos e que suportam importantes pescarias. A Lagoa de Santo André (LSA) é uma área muito importante sob o ponto de vista da conservação da natureza e da exploração dos recursos haliêuticos. Ela está isolada do mar por um cordão dunar, sendo, em geral, estabelecida uma ligação artificial ao mar durante o mês de março, através de um canal que, de realçar que no presente ano a mesma esteve aberto apenas 1 dia o que dificulta a renovação da água da lagoa bem como o escoamento das larvas e a continuação do ciclo de desenvolvimento de algumas espécies. O caranguejo-verde, Carcinus maenas, é uma espécie muito abundante neste ecossistema e, apesar do seu potencial como recurso, não é alvo de pesca dirigida. Para além disso, o conhecimento sobre a sua população no local era muito reduzido. A recente inclusão da espécie C. maenas no Edital que regulamentou a pesca profissional na Lagoa de Santo André para 2019, como uma das espécies aquícolas que podem ser capturadas, levantou questões relativas à sustentabilidade da sua exploração, O presente estudo surgiu neste contexto, e teve como objetivo principal caracterizar a população do caranguejo-verde na Lagoa de Santo André, nomeadamente em termos de abundância, estrutura dimensional e sexual e avaliar a sua variabilidade espácio-temporal. A recolha dos exemplares bem com a dos parâmetros biológicos sobre a espécie no local foi efetuada através de amostragens mensais, que foram realizadas recorrendo à utilização de artes de pesca passivas (nassas). No total, foram capturados 15 063 exemplares de C. maenas, com uma média mensal de capturas igual a 1255. Os meses de dezembro, com 2116 indivíduos e janeiro. com 2819. apresentaram as maiores capturas mensais. A análise da estrutura sexual da população revelou que esta é maioritariamente constituída por machos. Dos 3898 caranguejos analisados no laboratório: 2288 foram machos, equivalendo a 58,70% do total e 1610, fêmeas, correspondendo a 41,30%. Das 1610 fêmeas que foram analisadas no laboratório, 180 foram consideradas ovadas e 1430 não ovadas, indicando uma superioridade de fêmeas não ovadas em relação as ovadas. A estação A apresentou o indivíduo com menor largura 25,46 mm enquanto que a estação C teve o indivíduo com maior largura 70,12 mm. Relativamente a variabilidade espácio-temporal, a espécie esta bem representada na lagoa, com uma maior incidência na estação A, que está próxima do mar e que apresenta maior salinidade, em contrapartida a estação C revelou menor número de caranguejos capturados. O mês de abril sobressai, uma vez que se destaca com a maior variação temporal em relação aos demais, apresentando valores entre o 1 e 224 indivíduos capturados. Na LSA, 50% das fêmeas de C. maenas atingem a maturidade sexual aos 45,11 mm (largura da carapaça). Ao longo do período de estudo, a menor fêmea que foi encontrada ovada tinha 26,68 mm e a maior fêmea nestas circunstâncias tinha 61,57 mm (média: 42,70 mm). A menor fêmea não ovada tinha 21,24 mm e a maior 73,60 mm (média: 42,87 mm).
Coastal lagoons are very productive systems that support important fisheries. Santo André Lagoon (LSA) is a very important area for nature conservation and the exploitation of fish resources. It is isolated from the sea by a sand dune, and the connection to the sea is established artificially during March, by digging a channel which, sometimes remains open for a short period, which hinders the renewal of the lagoon water as well as the flow of larvae and the completion of the life cycle of some species. The green crab, Carcinus maenas, is a very abundant species in this ecosystem and, despite its potential as a resource, it is not the target of fishing. Moreover, there was very little knowledge about its population on the area. The recent inclusion of the species C. maenas in the fishing byelaw regulating professional fishing in Santo André Lagoon for 2019, as a species that can be caught, raised concerns about the sustainability of its exploitation. The present study was developed in this context, and its main objective was to characterize the green crab population in Santo André Lagoon, namely its abundance, size and sexual structure, and to evaluate its spatio-temporal variability. The collection of specimens as well as the biological parameters about the species was carried out monthly sampling, which was done using passive fishing gear (fyke nets). In total, 15063 specimens of C. maenas were caught, with a monthly average catch equal to 1255. The months of December, with 2116 individuals and January, with 2819. showed the highest monthly catches. Analysis of the sexual structure of the population revealed that it is mostly males. Of the 3898 crabs analyzed in the laboratory: 2288 were male, equivalent to 58.70% of the total and 1610 were female, corresponding to 41.30%. Of the 1610 females analysed in the laboratory, 180 were considered ovated and 1430 were non-ovated, indicating a superiority of non-ovate females over ovate ones. Station A presented the individual with the smallest width 25.46 mm while station C had the individual with the largest width 70.12 mm. In relation to the space-time variability, the species is well represented in the lagoon, with a higher incidence in station A, which is close to the sea and presents greater salinity, while station C showed a lower number of crabs caught. The month of April stands out, because it has the highest temporal variation in relation to the others, with values between 1 and 224 individuals caught. In LSA, 50% of C. maenas females reach sexual maturity at 45.11 mm (carapace width). Throughout the study period, the smallest ovated female was 26.68 mm and the largest female in these circumstances was 61.57 mm (mean: 42.70 mm). The smallest non ovated female was 21.24 mm and the largest 73.60 mm (mean: 42.87 mm).
Coastal lagoons are very productive systems that support important fisheries. Santo André Lagoon (LSA) is a very important area for nature conservation and the exploitation of fish resources. It is isolated from the sea by a sand dune, and the connection to the sea is established artificially during March, by digging a channel which, sometimes remains open for a short period, which hinders the renewal of the lagoon water as well as the flow of larvae and the completion of the life cycle of some species. The green crab, Carcinus maenas, is a very abundant species in this ecosystem and, despite its potential as a resource, it is not the target of fishing. Moreover, there was very little knowledge about its population on the area. The recent inclusion of the species C. maenas in the fishing byelaw regulating professional fishing in Santo André Lagoon for 2019, as a species that can be caught, raised concerns about the sustainability of its exploitation. The present study was developed in this context, and its main objective was to characterize the green crab population in Santo André Lagoon, namely its abundance, size and sexual structure, and to evaluate its spatio-temporal variability. The collection of specimens as well as the biological parameters about the species was carried out monthly sampling, which was done using passive fishing gear (fyke nets). In total, 15063 specimens of C. maenas were caught, with a monthly average catch equal to 1255. The months of December, with 2116 individuals and January, with 2819. showed the highest monthly catches. Analysis of the sexual structure of the population revealed that it is mostly males. Of the 3898 crabs analyzed in the laboratory: 2288 were male, equivalent to 58.70% of the total and 1610 were female, corresponding to 41.30%. Of the 1610 females analysed in the laboratory, 180 were considered ovated and 1430 were non-ovated, indicating a superiority of non-ovate females over ovate ones. Station A presented the individual with the smallest width 25.46 mm while station C had the individual with the largest width 70.12 mm. In relation to the space-time variability, the species is well represented in the lagoon, with a higher incidence in station A, which is close to the sea and presents greater salinity, while station C showed a lower number of crabs caught. The month of April stands out, because it has the highest temporal variation in relation to the others, with values between 1 and 224 individuals caught. In LSA, 50% of C. maenas females reach sexual maturity at 45.11 mm (carapace width). Throughout the study period, the smallest ovated female was 26.68 mm and the largest female in these circumstances was 61.57 mm (mean: 42.70 mm). The smallest non ovated female was 21.24 mm and the largest 73.60 mm (mean: 42.87 mm).
Descrição
Tese de mestrado em Ciências do Mar, Universidade de Lisboa, Faculdade de Ciências, 2021
Palavras-chave
Caranguejo-verde Lagoa costeira Abundância Fatores ambientais Estrutura dimensional Teses de mestrado - 2021