Density of Limnoperna fortunei larval stages in a cascade of subtropical reservoirs: spatiotemporal variation and environmental influences.

The golden mussel (Limnoperna fortunei) is an invasive bivalve that has established itself in several South American river systems, impacting ecosystem functioning. Reservoir cascades provide their larvae with the means of rapid dispersal, but the relationship between environmental variables and larval stage structure remains unclear. In this study, the density of three L. fortunei larval stages and quantitative detection using DNA are analyzed in a cascade of five reservoirs in the upper Uruguay River Basin and associated with spatiotemporal variation in environmental parameters. The analysis of L. fortunei eDNA presence and absence in freshwater systems appears to be a valuable mapping tool; however, no significant link was found between the eDNA magnitude and the overall larval density. The increase in larval density was related to the fluctuation of environmental parameters over a year, with the highest average larval densities observed in the CN and ITA reservoirs, though no significant difference was observed between the five reservoirs, where D-shaped larvae predominated. During winter, larval density decreased significantly, however, other variables also contribute to species activity and development in the upper Uruguay River Basin reservoirs and may be considered limiting factors. The relationships between environmental parameters were evaluated using a multivariate model. The interaction between reservoir area and precipitation, water temperature, electrical conductivity, and dissolved oxygen had a significant effect on larval density but showed specific influences on each larval stage. Any increase in density was regulated by dissolved oxygen and electrical conductivity content at all larval stages. Furthermore, total phosphorus affected the density of F1 and F3 larvae. The interaction between reservoir area and precipitation, nitrate content, phosphate concentrations, and water temperature had the most influence on the density of F2 and F3 larval stages; the F1 stage was mainly affected by calcium concentrations. The isolated effect of precipitation also contributed to the density of F2 and F3 larvae. Our findings shed light on the interaction between different phases of golden mussel larvae and the main nutrients found in reservoirs, which may be a determining factor in the rise in density of the non-native species in these systems.

Long-term monitoring reveals a consistent female-biased sex ratio in Pimelodus maculatus from the Upper Uruguay River Basin / Monitoramento de longo prazo revela desvio sexual em fêmeas de Pimelodus maculatus da bacia do Alto Rio Uruguai

Sex ratio is a crucial demographic parameter for the viability of natural populations, and it is commonly balanced in Neotropical freshwater fish species. This study investigated the sexual proportion of yellow-mandi Pimelodus maculatusin the Upper Uruguay River basin, southern Brazil, between 2000 and 2019. Fish were captured at different sites in a proportion of 2,018 females and 995 males. The total length ranged from 14 to 60 cm for females (31.8 ± 6.8 cm) and 13 to 45 cm for males (26.7 ± 13.6 cm). The frequency of females was higher from class 27 to 51 cm (P < 0.05), with a mean female:male sex ratio of 2.05:1, whereas a 1:1 sex ratio was found in fish shorter than 27 cm. The most important predictor explaining the dominance of females was the length, followed by year, site, and environment. Females are larger and live five years longer than males and they can become more abundant. This disparity in lifespan between females and males, the life history, and social and environmental factors may be associated with the female-biased sex ratio in P. maculatuspopulation of the Uruguay River Basin.(AU)

A proporção sexual é um parâmetro demográfico crucial para a viabilidade das populações naturais e normalmente é equilibrada nas espécies de peixes de água doce neotropicais. Este estudo investigou a proporção sexual do mandi amarelo Pimelodus maculatus na bacia do Alto Rio Uruguai, sul do Brasil, entre 2000 e 2019. Os peixes foram capturados em diferentes locais numa proporção de 2.018 fêmeas e 995 machos. O comprimento total variou de 14 a 60 cm para as fêmeas (31,8 ± 6,8 cm) e de 13 a 45 cm para os machos (26,7 ± 13,6 cm). A frequência de fêmeas foi maior da classe 27 para 51 cm (P < 0,05), com relação média de sexo feminino:sexo masculino de 2,05:1, enquanto a relação de sexo 1:1 foi encontrada em peixes com menos de 27 cm. O preditor mais importante que explica a dominância das fêmeas foi o comprimento, seguido pelo ano, local e ambiente. As fêmeas são maiores e vivem cinco anos a mais do que os machos, podendo tornar-se mais abundantes. Essa disparidade na expectativa de vida entre fêmeas e machos, a história de vida e os fatores sociais e ambientais podem estar associados ao desvio sexual feminino na população de P. maculatus da bacia do Rio Uruguai.(AU)

Using stock assessment to investigate the sustainable fisheries of the yellow mandi Pimelodus maculatus in the upper Uruguay River, southern Brazil / Uso da avaliação de estoque para investigar a sustentabilidade da pesca do pintado-amarelo Pimelodus maculatus no alto Rio Uruguai, sul do Brasil

The yellow mandi Pimelodus maculatus is a medium-sized species with a wide geographical distribution. The species is very common in the Neotropical region, representing an important share of fishing activity in several Brazilian reservoirs. Therefore, the objective of this study was to evaluate the current situation of the yellow mandi fish stock in the Itá reservoir, located in the Upper Uruguay River. Data collected from January 2004 to December 2016 were used to estimate growth, mortality, and fish recruitment rates. In addition, a stock assessment was performed, and the results were used to verify the status of the fishery. The mean of the population parameters were: total length (L) = 55.65 cm; length at which 50% of fish are vulnerable to capture (Lc) = 23.08 cm, growth rate (k) = 0.260 year-1, growth performance index (Ø) = 3.047, natural mortality rate (M) = 0.537, fishing mortality rate (F) = 0.413, total mortality rate (Z) = 0.95, exploitation rate (E) = 0.434, maximum age (Tmax) = 6.68 years. The growth curve obtained via ELEFAN I revealed that fishing operates on eight of the eleven cohorts of the population. Yellow mandi stock assessment did not show signs of fish overexploitation or any risk of depletion.(AU)

O pintado-amarelo Pimelodus maculatus é uma espécie de médio porte com ampla distribuição geográfica. Na região Neotropical é muito comum, apresentando importante participação na pesca em diversos reservatórios brasileiros. Nesse sentido, o objetivo desse estudo foi avaliar a situação atual do estoque pesqueiro do pintado-amarelo no reservatório de Itá, situado no alto rio Uruguai. Dados coletados no período de janeiro de 2004 a dezembro de 2016 foram utilizados para estimar as taxas de crescimento, mortalidade e recrutamento para a pesca. Adicionalmente foi realizada a avaliação do estoque e os resultados foram utilizados para verificar o estado da pescaria. A média dos parâmetros populacionais foram: comprimento total = 55,65cm (L), comprimento no qual 50% da população está vulnerável à captura = 23,08cm (Lc), taxa de crescimento = 0,260 ano-1 (k), índice de performance de crescimento = 3,047 (Ø), taxa de mortalidade natural = 0,537 (M), taxa de mortalidade por pesca = 0,413 (F), taxa de mortalidade total = 0,95 (Z), taxa de explotação = 0,434 (E), longevidade máxima = 6,68 anos (Tmax). Através da curva de crescimento obtida pelo ELEFAN I foi possível observar que a pesca atua sobre oito das onze coortes da população. O estoque do pintado-amarelo não apresentou sinais de sobreexplotação nem risco de depleção da espécie durante o período estudado.(AU)

Using stock assessment to investigate the sustainable fisheries of the yellow mandi Pimelodus maculatus in the upper Uruguay River, southern Brazil / Uso da avaliação de estoque para investigar a sustentabilidade da pesca do pintado-amarelo Pimelodus maculatus no alto Rio Uruguai, sul do Brasil

The yellow mandi Pimelodus maculatus is a medium-sized species with a wide geographical distribution. The species is very common in the Neotropical region, representing an important share of fishing activity in several Brazilian reservoirs. Therefore, the objective of this study was to evaluate the current situation of the yellow mandi fish stock in the Itá reservoir, located in the Upper Uruguay River. Data collected from January 2004 to December 2016 were used to estimate growth, mortality, and fish recruitment rates. In addition, a stock assessment was performed, and the results were used to verify the status of the fishery. The mean of the population parameters were: total length (L) = 55.65 cm; length at which 50% of fish are vulnerable to capture (Lc) = 23.08 cm, growth rate (k) = 0.260 year-1, growth performance index (Ø) = 3.047, natural mortality rate (M) = 0.537, fishing mortality rate (F) = 0.413, total mortality rate (Z) = 0.95, exploitation rate (E) = 0.434, maximum age (Tmax) = 6.68 years. The growth curve obtained via ELEFAN I revealed that fishing operates on eight of the eleven cohorts of the population. Yellow mandi stock assessment did not show signs of fish overexploitation or any risk of depletion.

O pintado-amarelo Pimelodus maculatus é uma espécie de médio porte com ampla distribuição geográfica. Na região Neotropical é muito comum, apresentando importante participação na pesca em diversos reservatórios brasileiros. Nesse sentido, o objetivo desse estudo foi avaliar a situação atual do estoque pesqueiro do pintado-amarelo no reservatório de Itá, situado no alto rio Uruguai. Dados coletados no período de janeiro de 2004 a dezembro de 2016 foram utilizados para estimar as taxas de crescimento, mortalidade e recrutamento para a pesca. Adicionalmente foi realizada a avaliação do estoque e os resultados foram utilizados para verificar o estado da pescaria. A média dos parâmetros populacionais foram: comprimento total = 55,65cm (L), comprimento no qual 50% da população está vulnerável à captura = 23,08cm (Lc), taxa de crescimento = 0,260 ano-1 (k), índice de performance de crescimento = 3,047 (Ø), taxa de mortalidade natural = 0,537 (M), taxa de mortalidade por pesca = 0,413 (F), taxa de mortalidade total = 0,95 (Z), taxa de explotação = 0,434 (E), longevidade máxima = 6,68 anos (Tmax). Através da curva de crescimento obtida pelo ELEFAN I foi possível observar que a pesca atua sobre oito das onze coortes da população. O estoque do pintado-amarelo não apresentou sinais de sobreexplotação nem risco de depleção da espécie durante o período estudado.