Browsing by Author "Maia, Francisco"
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- Assessment of habitat suitability for common cockles in the Ria the Aveiro Lagoon under average and projected environmental conditionsPublication . Matos, Fábio L.; Vaz, Nuno; Picado, Ana; Dias, João M.; Maia, Francisco; Gaspar, Miguel; Magalhães, LuísaThe common cockle Cerastoderma edule is a widespread bivalve species inhabiting estuarine systems across the North East Atlantic, where it provides several ecosystem services, and represents a valuable fishery resource for local economies. However, anthropogenic pressure and more frequent extreme weather events threaten the resilience of the species. Spatially explicit information on species distribution is critical for the implementation of management and conservation practices. This study assessed the potential distribution of C. edule in the Ria de Aveiro by estimating the habitat suitability using an ensemble approach based on ecological niche modeling and recently developed hydrodynamic and water quality models to forecast both average and projected estuarine conditions. The models were developed for the summer of 2013 and spring of 2019 and potential range shifts in the species distribution were forecasted under projected environmental conditions: high and low estimates of freshwater discharge, a 2 degrees C increase in water temperature, and the combined effect of low freshwater discharge and increased water temperature. The results suggest that salinity, time of submersion, and current velocity play an important role in the distribution of cockles, and large areas were consistently classified with high habitat suitability. Increased freshwater discharge (both seasons) and low discharge coupled to increased temperature (spring) resulted in large decreases in suitable habitat. Conversely, low freshwater discharges and average (unchanged) temperatures increased the suitable habitat in the outermost regions of the Ria. The spatially explicit information provided contributes to a better understanding of the vulnerability of C. edule in the Ria de Aveiro to extreme weather events (e.g., droughts, river floods) and may support adaptive management strategies of the cockle fishery during these conditions. Moreover, this approach can be transferred to other estuarine ecosystems for which data describing the environmental conditions (e.g., derived from numerical models), and information about species presence are available (including data-poor species).
- Biological traits and population dynamics for sustainable harvesting of Carcinus maenasPublication . Monteiro, João Nuno; Ovelheiro, Andreia; Maia, Francisco; Teodosio, Maria; Leitão, FranciscoResearch focusing on the biological patterns and population dynamics of Carcinus maenas has not been conducted for the purpose of fishery management along the European coastal systems. This has led to the implementation of fisheries management policies without scientific considerations, adversely affecting fishery profitability. To addrees this gap, we studied the crab species' population dynamics, reproductive biology, and growth patterns across different Portuguese lagoons and estuaries on a monthly basis from 2019 to 2021. Surveys were performed in the Southern (Ria Formosa lagoon and Ria Alvor estuary), Central (Sado river/estuary) and Northern regions (Ria Aveiro estuary) of Portugal. Monthly biological data was used to analyse size-frequency distributions, sex ratios, spawning seasons, recruitment pulses, estimate carapace width at first maturaty and biological growth parameters. It was observed that spawning occurs almost year-round in all systems, with a peak in the colder months, between September and March. In the southern regions of the Portuguese coast, the spawning period starts earlier than in the central and northern systems, with a higher sex ratio recorded for females in all systems. The carapace width at which 50 % (CW50) of individuals reach maturity is similar for both sexes, around 30 mm, a value below to the minimum landing size enforced in Portugal. The analysis of von Bertalanffy growth curves revealed a continuous recruitment with a peak during the colder months, with individuals reaching the size at maturation after six months. The fast growth and continuous recruitment leds to the existence of between four and six growth cohorts for both sexes across all system. The findings of this study can contribute to more effective fisheries management policies for C. maenas in Portugal, such as a reduction of the minimum landing size.
- Biology of the common cockle Cerastoderma edule (Linnaeus, 1758) in Ria de Aveiro (NW Portugal): Implications for fisheries managementPublication . Maia, Francisco; Barroso, Carlos M.; Gaspar, MiguelThis study reports the reproductive cycle, condition index, size at first maturity, growth and the morphometric relationships of the common cockle Cerastoderma edule in Ria de Aveiro (NW Portugal), fundamental knowledge in fisheries management planning and ecosystem conservation. The reproductive cycle was monitored for a period of two years, from January 2013 to December 2014. Spawning extended from June to October, with a peak in the summer months (July to September). The condition index showed a seasonal pattern which appear related to food availability and gametogenic cycle. Sexual maturity was attained at a shell length of 18.6 mm during the first year of life, which stands below the minimum landing size currently in force (25 mm). The von Bertalanffy growth equation was based on size-at-age data obtained from the microscopic analysis of growth rings in sectioned shells: Lt = 40.7[1-e -0.74(t-0.30)]. The morphometric relationships between shell dimensions (length, height and width) were studied in order to understand the effects of ontogenetic changes in cockles` shell morphology, an information that is useful to improve the selectivity of the fishing gears and the size-sorting devices. Some management strategies for the Ria de Aveiro cockle fishery were proposed.
- Growth, reproduction, and size at first maturity of the peppery furrow shell Scrobicularia plana in the Ria de Aveiro, Portugal: implications for sustainable fisheries managementPublication . Maia, Francisco; Gaspar, Miguel; Barroso, Carlos M.The peppery furrow shell Scrobicularia plana is a commercial valuable bivalve in the east Atlantic and Mediterranean Sea. To ensure the sustainability of this resource and implement efficient management strategies, it is essential to understand the life history traits of the species, such as growth, reproduction, and size at first maturity. These features were investigated in the southern range of the species' European distribution, specifically in Ria de Aveiro (Portugal), and compared to other geographical areas. At Ria de Aveiro S. plana spawns from June to October, with a peak in August/September, aligning with the typical reproductive pattern of mid latitude European populations. The condition index is lowest in March and highest in May just before spawning. Sexual maturity (L50 = 27 mm SL) is attained at approximately 1 year of age, enabling offspring to reproduce in the subsequent spawning season. In this study, the overall sex ratio did not differ significantly from 1:1. Hermaphroditism (ovotestis) was detected in one specimen, representing 0.3% of the total examined males. Shell rings are formed annually during growth cessation in fall/winter and become conspicuous when growth resumes in March. The growth equation parameters, estimated from surface shell ring analysis and internal shell microgrowth bands, were: Lt = 58.1[1 - e-0.46(t -0.09)]; Lt = 54.7[1 - e-0.53(t - 0.30)], respectively. Values for K and L infinity are among the highest recorded for the species, highlighting the growth performance of S. plana in the Ria de Aveiro and its potential for commercial exploitation. An analysis of morphometric relationships between shell length, height, and width was performed to optimize the harvesting process of S. plana. Management measures are proposed for the fishery of S. plana in Ria de Aveiro, based on the species' biological traits.
- Macro and microscopic maturation stage key of green crab (Carcinus maenas, Linnaeus 1758): reproductive cycle and differences among estuarine systemsPublication . Ovelheiro, Andreia; N. Monteiro, J.; Gonçalves, Patrícia; Campinho, Marco António; Maia, Francisco; Teodosio, Maria; Leitão, FranciscoGonadal histology is a helpful tool to validate species' macroscopic maturity stages in fisheries biology. Regardless of the many studies on Carcinus maenas, there are still few concerning gonads tissue histology and description of maturity stages. In Portugal, information regarding this species' biology to help support the regulation of crab fisheries, including the minimum landing size, has not yet been defined. In this work, the macro and microscopic characteristics of the reproductive cycle of C. maenas, oogenesis, and spermatogenesis development stages along the Portuguese coast are described, and a new macroscopic scale based on the histological analyses is suggested. During 2019 and 2020, adult C. maenas (both males and females) were collected from the Ria de Aveiro estuary, Rio Sado estuary, and Ria Formosa lagoon, respectively, North, Center, and South Portugal. No-significant differences (P > 0.05) were observed in carapace width and individual weight between all systems. Significant differences (P < 0.05) were observed in gonad weight, gonadosomatic index, and Fulton's condition index between the Rio Sado estuary and Ria Formosa lagoon. Furthermore, significant differences (P < 0.05) in the oocyte diameter between the northern and southernmost locations suggest a geographic variation related to the local environmental conditions of each system. Principal component analysis (PCA) revealed maturity stage and carapace width an association, and a similar morphometry between Ria de Aveiro and Ria Formosa. Temperature was correlated to both maturity stage and carapace width in Ria de Aveiro and Ria Formosa. From the histological analysis and based on microscopic criteria, it was observed that females previously classified within the late macroscopic development stage 2 should be considered mature, so a classification change in the current ovary's developmental stage is proposed. These findings can allow fisheries researchers to reclassify the estimations of maturity ogives and help support the regulation of this species' fishery. The proposed macroscopic scale was validated by histological analyses and can be used elsewhere.