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Abstract: The aim of the study was to analyse the size, growth and size at maturity of Nephrops norvegicus in two areas off the Portuguese coast. Samples were collected between September 2006 and January 2007. A total of 2081 individuals ranging between 25 and 88mm carapace length were collected, measured and sexed. The estimated growth parameters were L ∞ =88.33mm CL, k =0.38years−1 for males and L ∞ =64.45mm CL, k =0.38years−1 for females in the northern area, and L ∞ =94.86mm CL, k =0.41years−1 for males and L ∞ =69.20mm CL, k =0.44years−1 for females in the central area. Size at maturity was 50.7mm CL in the northern area and 46.9mm CL in the central area. [Copyright &y& Elsevier]

The utility of oblique separator panels combined with square mesh windows for reducing by-catch (mainly boarfish (Capros aper), blue whiting (Micromesistius poutassou) and horse mackerel (Trachurus trachurus)) was examined in the Algarve crustacean trawl fishery.Three different panel/window mesh size combinations and the window alone were tested. The results suggest that the amount of blue whiting excluded was independent of the use of the separator panel, as well as the mesh sizes of the panel and the square mesh window. Between 67 and 71% of the total catch of this species was excluded. The window mesh size however, significantly affected the escape of boarfish, with the average escape percentage released rising from 10 to 44% as the mesh size increased from 70 to 100mm.The highest exclusion rates were obtained with the use of a 120mm separator panel together with a 100mm square mesh window. Under these conditions, the exclusion of by-catch was maximised while maintaining the catch for the target species(rose shrimp Parapenaeus longirostris, and Norway lobster, Nephrops norvegicus). In hauls where the square mesh window was used alone, only the escape rate of blue whiting was significant (67%), while boarfish escaped in much lower proportions and shrimp above the minimum landing size were lost. Despite the efficiency of these panels as by-catch excluders, their complex design is a major drawback to commercial adoption. [Copyright &y& Elsevier]

The increment at molt for Nephrops norvegicus was studied with the objective of obtaining a model for prediction of post-molt size based on pre-molt size for the population from the south coast of Portugal. Wild animals were maintained in a specially prepared laboratory facility until they molted. Individual values of increment at molt were obtained and used to evaluate alternative models and estimate their parameters. Six alternative models, used previously by several authors to relate pre- and post-molt size, were modified so that increment at molt was the dependent variable and pre-molt size the independent variable. These included the linear relationship of the growth factor (GF) on pre-molt size, the Hiatt equation, post-molt size a power function of pre-molt size, the hyperbolic function, GF exponential function of pre-molt size and the Misra equation.The analysis of the data showed that none of the models could be used to predict increment at molt for either sex. The distribution of the increment at molt was a random normal variable, with mean values not significantly different between sexes, 2.78 mm for males and 2.26 mm for females, variances 0.47 and 0.59, respectively.An analysis of the models suggests that using post-molt size or the GF as dependent variables may lead to a misinterpretation of the dependency of these variables on pre-molt size. It is suggested that the increment at molt should be the variable of interest for predicting post-molt size. The choice of a mathematical formulation should, besides having biological meaning, have the capacity of expressing a true relationship between increment at molt and pre-molt carapace length, namely, be able to model several options for the increment at molt after maturity, including a steady increase of the increment through life, the stabilization of the increment after maturity or the decrease of the increment for larger sizes. [Copyright &y& Elsevier]

Bottom-trawl fishing for crustaceans off the Portuguese south and southwest coasts is a very important segment of the Portuguese fishing fleet, where annual rates of discarding have ranged from approximately 38% to as much as 70% of the total catch. Past experiments to address this problem encompassed the testing of different codend mesh sizes and configurations, square mesh windows and rigid grids to enhance species and size-selectivity. While the use of a Nordmøre grid has proved quite efficient in separating out blue whiting (Micromesistius poutassou), it also led to some losses of the two main crustacean target species, Norway lobster (Nephrops norvegicus) and rose shrimp (Parapenaeus longirostris). The present study addresses that limitation by using a modified grid with 20 mm bar spacing and two open sections, designed with the purpose of separating fish and crustacean species into upper and lower codends. Good separation was achieved, with about 80% of the blue whiting (in number) directed towards the upper trawl section and caught in the upper codend, while a similar percentage of Norway lobster was caught in the lower codend. The grid bars had 50% retention for Norway lobster at 34.1 mm carapace length. The results herein will enable this gear configuration to be fine-tuned with regard to codend mesh sizes and bar spacing, so as to optimize both retention of Norway lobster and exclusion of blue whiting. For example, compared to using the minimum 70 mm diamond mesh size, using an 80 mm diamond mesh upper codend would reduce Norway lobster catch weight by just 1.6% but reduce the number of blue whiting caught by 42%. [ABSTRACT FROM AUTHOR]