Escape, discard and landing probability of Nephrops norvegicus in the Mediterranean Sea creel fishery

Size selection in creel fishery consists of two processes: the first taking place in the creel on the seabed and the second made by the fisher on the vessel. However, no study has ever considered both processes when assessing the size selection in creel fisheries. This study presents a framework for including both and demonstrates it to predict the effect of mesh size and shape on the creel fishery targeting the Norway lobster (Nephrops norvegicus) in the Mediterranean Sea. For this specific fishery, we demonstrate that both processes play a role in the overall size selection. Furthermore, we predict an optimal creel mesh size, which potentially eliminates the second process taking place on the vessel, while maintaining high efficiency for the first process on the seabed for the targeted sizes of Nephrops. The approach here presented can be also applied to other creel fisheries

Influence of soak time on catch performance of commercial creels targeting Norway lobster (Nephrops norvegicus) in the Mediterranean Sea

Source at https://doi.org/10.1051/alr/2017035 .Creel catch performance is known to be affected by the soak time in many fisheries. If creels maintained their efficiency over longer periods, increase in soak time should lead to proportional increase in catch quantity. However, the exact shape of this relationship is unknown for creel fisheries targeting Norway lobster (Nephrops norvegicus). If it was known fishermen could adjust their fishing strategy accordingly and maximize their net earnings. We compared catch performance of creels targeting Norway lobster soaked for one and two days in the Adriatic Sea. Results were obtained for three crustacean species, Norway lobster (N. norvegicus), mantis shrimp (Squilla mantis), and blue-leg swimming crab (Liocarcinus depurator) and two fish species, poor cod (Trisopterus minutus) and blotched picarel (Spicara flexuosa). Doubling the soak time from one to two days did not double the catches and for Norway lobster no increase was found. For the other crustaceans, a slight but not significant increase was estimated. Catches of blotched picarel were significantly lower for the longer soak time, while the results were inconclusive for the poor cod

Mesh sticking probability in fishing gear selectivity: Methodology and case study on Norway lobster (Nephrops norvegicus) and mantis shrimp (Squilla mantis) in the Mediterranean Sea creel fishery

Fish or crustaceans stuck in the fishing gear meshes can lead to operational problems in some fisheries and thereby affect theeconomic gain. However, mesh sticking probability has never been formally quantified as a part of the estimation of fishing gearsize selectivity. Therefore, this study developed a size selection model and estimation procedure that, besides the size dependentretention and escape probabilities, includes the size dependent mesh sticking probability. The new method was applied to quantify the size dependent retention, sticking and escape probabilities for mantis shrimp (Squilla mantis) and Norway lobster (Nephrops norvegicus) in creels with 41 mm square mesh netting. The mesh sticking probability was found to display a bell-shaped curvature with a maximum value for a specific carapace length and decreasing probabilities for both smaller and bigger individuals. For mantis shrimp the maximum sticking probability was found for 32.5 mm carapace length with a value at 13.5%, while 63.1% and 23.4% of that size were respectively retained inside the creels and escaped. For Norway lobster the maximum sticking probabilitywas 2% and occurred for 34.0 mm carapace length. The method and estimation procedure presented in this study might be applicable for quantifying mesh sticking probability as an integral part of future fishing gear size selectivity studies on other speciesand fisheries

Escape, discard and landing probability of Nephrops norvegicus in the Mediterranean Sea creel fishery

Size selection in creel fishery consists of two processes: the first taking place in the creel on the seabed and the second made by the fisher on the vessel. However, no study has ever considered both processes when assessing the size selection in creel fisheries. This study presents a framework for including both and demonstrates it to predict the effect of mesh size and shape on the creel fishery targeting the Norway lobster (Nephrops norvegicus) in the Mediterranean Sea. For this specific fishery, we demonstrate that both processes play a role in the overall size selection. Furthermore, we predict an optimal creel mesh size, which potentially eliminates the second process taking place on the vessel, while maintaining high efficiency for the first process on the seabed for the targeted sizes of Nephrops. The approach here presented can be also applied to other creel fisheries.acceptedVersio

Influence of soak time on catch performance of commercial creels targeting Norway lobster (Nephrops norvegicus) in the Mediterranean Sea

Mass transfer between bubbles and seawater is an important mechanism when determining how much gas reaches the atmosphere from gas sources at the seabed. The mass transfer coefficient is a governing parameter for the phenomenon. Experiments on small bubbles in seawater have been performed where the bubble size has been monitored. The observed evolution of the bubble size has been compared with theoretical predictions of the bubble size. Based on this comparison, it is shown that mass transfer correlations for contaminated conditions is more consistent with experiments than correlations for clean conditions. It is also learned that simultaneous desorption of gases dissolved in the liquid must be accounted for.publishedVersio

CREELSELECT—A method for determining the optimal creel mesh: Case study on Norway lobster (Nephrops norvegicus) fishery in the Mediterranean Sea

In the laboratory, we investigated which sizes of Nephrops (Nephrops norvegicus) could pass through the meshes of different size and shape to establish a predictive model for the creels size selectivity. Predictions agreed well with the results from experimental fishing, demonstrating the reliability of this simple method. Nephrops minimum target size is 20 mm carapace length in the Mediterranean creel fishery, with some areas having restrictions on the mesh size, minimum being 36 or 40 mm. The model predicts that Nephrops below 28 and 32 mm carapace length would escape from creels with respectively 36 and 40 mm mesh size, implying a suboptimal exploitation pattern. Our method provides easy and quick identification of optimal mesh size and shape without the exhaustive sea trials with various creel designs. It was predicted that a square mesh of 30 mm would better match the desired exploitation pattern. The method could easily be adopted to other species and different creel fisheries, helping to determine optimal mesh matching a prescribed exploitation pattern

Size selection of Nephrops norvegicus (L.) in commercial creel fishery in the Mediterranean Sea

In the Mediterranean Sea Nephrops (Nephrops norvegicus) is predominantly caught with bottom trawls, but it is also harvested with creels. While the size selection of Nephrops in bottom trawls is well documented, there is no previous information on creel size selection for this species. Therefore, sea trials were carried out to assess the selective properties of commercial creels with 41 mm mesh size netting mounted as a square mesh netting as prescribed by the legislation. Creel size selection was assessed for Nephrops and two main crustacean bycatch species: mantis shrimp (Squilla mantis) and blue-leg swimming crab (Liocarcinus depurator). The influence of the soak time on creel selectivity was also investigated, and no significant difference was detected between one and two day soak times. The average carapace length of a crustacean with 50% probability of being retained (L50) was 31.69 mm for Nephrops, which is 59% larger than the minimum landing size (MLS) set by the fishery regulation, therefore demonstrating a mismatch between MLS and gear selectivity in this fishery. Comparison of creel selectivity obtained in our study with the historical results obtained from commercial bottom trawl selectivity studies for Nephrops in the Mediterranean Sea demonstrated that the creel L50 was significantly higher than in the trawl fishery, this implies that creel fishery is targeting larger Nephrops than trawl fishery