Chapter 19. The Blackspot seabream fishery in the Strait of Gibraltar: lessons and future perspectives of shared marine resource

The Blackspot seabream (Pagellus bogaraveo) is one of the most important commercially-exploited fish species for the Spanish and Moroccan fleets which operate in the Strait of Gibraltar. In recent years, landings of Blackspot seabream in the main ports have decreased significantly respect previous periods of maximum catches, which makes it necessary to properly assess the abundance before establishing a management plan to make the fishery sustainable over time. In this chapter, we describe three different approaches to assess the abundance of this species in the Strait of Gibraltar. The results of three approaches tested (LCA/VPA, Gadget model and SimFish model) point out that from the 2010 the stock is kept at very low levels that oscillate between 900 and 1600 t, which supposes that the total biomass is between a 16% and 29% of the potential biomass. Additionally, the reference point values estimated by LCA/VPA and Gadget (F0.1 = 0.12-0.17) imply a clear overexploitation of the resource what is reinforced by the SimFish model results indicating that at least the 64% of abundance variation is a consequence of the fishery component.En prens

Theory of modulational instability in Bragg gratings with quadratic nonlinearity

Modulational instability in optical Bragg gratings with a quadratic nonlinearity is studied. The electric field in such structures consists of forward and backward propagating components at the fundamental frequency and its second harmonic. Analytic continuous wave (CW) solutions are obtained, and the intricate complexity of their stability, due to the large number of equations and number of free parameters, is revealed. The stability boundaries are rich in structures and often cannot be described by a simple relationship. In most cases, the CW solutions are unstable. However, stable regions are found in the nonlinear Schrodinger equation limit, and also when the grating strength for the second harmonic is stronger than that of the first harmonic. Stable CW solutions usually require a low intensity. The analysis is confirmed by directly simulating the governing equations. The stable regions found have possible applications in second-harmonic generation and dark solitons, while the unstable regions maybe useful in the generation of ultrafast pulse trains at relatively low intensities. [S1063-651X(99)03005-6]