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- 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.
- 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.
- Comparative study of Ruditapes philippinarum and Ruditapes decussatus in Ria de Aveiro, Portugal: Invasive species management and marine resource conservationPublication . Manuel da Silva Rodrigues Maia, Francisco; Gaspar, Miguel; Barroso, Carlos M.Research on the biological traits of commercial bivalves is essential for developing effective management strategies and ensuring their sustainable exploitation. This study offers a comparative analysis of the invasive Manila clam R. philippinarum and the native grooved carpet clam R. decussatus in the Ria de Aveiro, Portugal, focusing on shell morphometry, growth, reproductive cycle, condition index, and length at 50% maturity (L50). Analysis of internal shell microgrowth bands revealed that R. philippinarum exhibits a higher growth coefficient (K) than R. decussatus, with von Bertalanffy growth equations of Lt = 59.49 [1 - e -0.78 (t-0.55)1 and Lt = 75.09 [1 - e -0.33 (t0.10)1, respectively. Notably, the K value for R. philippinarum is among the highest recorded for this species, indicating exceptional growth performance in the Ria de Aveiro. The reproductive cycle analysis showed that R. philippinarum has a longer and more intense spawning period, extending from April to October 2013 and from April to September 2014, with peaks in August and September. In contrast, R. decussatus exhibited a shorter spawning season, from May to October 2013 and from June to September 2014, peaking in August. Seasonal variations in the condition index, likely linked to food availability and reproductive cycle, showed R. philippinarum in better condition during the early stages of gonadal development, indicating more efficient energy allocation towards reproduction. Rapid growth and fast sexual maturity during the first year of benthic life enable recruits of both species to spawn during the following year's spawning season. R. philippinarum reaches sexual maturity slightly faster than R. decussatus (L50 = 20.0 mm SL vs. L50 = 22.1 mm SL), maturing at around 1.08 years compared to 1.15 years. Although this difference is minor, it enables R. philippinarum recruits to begin reproduction approximately one month earlier in the year. Improved growth rates of R. philippinarum during its second and third years likely enhance reproductive capacity, as larger individuals typically produce more offspring. These results suggest that R. philippinarum has a competitive advantage over R. decussatus due to its faster growth and greater reproductive potential. However, these factors do not conclusively explain the rapid proliferation and establishment of R. philippinarum in the Ria de Aveiro, nor the sudden decline in R. decussatus populations following the introduction of the invasive species. Fishery management strategies are proposed based on two distinct scenarios.