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.

Asymptotic methods for stochastic dynamical systems with small non-Gaussian Lévy noise

The goal of the paper is to analytically examine escape probabilities for dynamical systems driven by symmetric α-stable Lévy motions. Since escape probabilities are solutions of a type of integro-differential equations (i.e. differential equations with nonlocal interactions), asymptotic methods are offered to solve these equations to obtain escape probabilities when noises are sufficiently small. Three examples are presented to illustrate the asymptotic methods, and asymptotic escape probability is compared with numerical simulations.

THE ESCAPE PROBABILITIES FOR SLAB AND SPHERICAL GEOMETRIES IN PLASMA SPECTROSCOPY

In this paper, the concepts of the photon escape probability and the transmission factor are reviewed and the photon escape probabilities for infinite plane-parallel slab and spherical geometries are discussed. The photon escape probabilities using the transmission factor, for Lorentzian profile and Holtsmarkian profile, are discussed. Finally, the photon escape probabilities we calculated are compared with that calculated using before method for Lorentzian profile and Holtsmarkian profile, and some useful conclusions are drawn.

THE PHOTON ESCAPE PROBABILITY OF Na 330.3 nm RESONANCE LINE

In this paper, the photon escape probability of Na 330.3 nm resonance line is calculated, both for slab and cylindrical geometries. The dependence of the photon escape probability on the optical depth in the line center is considered. The oscillator strength, the number density of the absorbing atoms in the ground state, and the optical depth in the line center are discussed in this calculation. The changes of the photon escape probabilities with different concentrations are calculated. This calculation will provide a method to calculate the photon escape probability for different lines.