Contribución al conocimiento de la biología del surel (Trachurus picturatus australis) del área de Mar del Plata (Pisces, Carangidae)

The individuals studied came from commercial catches on the coastal area off Mar del Plata. The monthly distribution of sizes shows that the juvenile stay in coastal waters, while the adult individuals leave those waters during winter season to return there in the spring during the season of sexual maturation and spawning, when the water reaches temperature of 10-11°C. The jack mackerel is a relatively small fish, compared with other species of its genus, and has a total length of scarcely 25 cm. The comparison of indexes and mesurements does not reveal any marked difference between sexes, except for the total length, which is greater in the females. Sexually nature individuals at a lenth of 13 cm have been found. Spawning takes place in coastal waters. A great part of the population spawns from December to January. There are oscillations ranging from November to March. On this latter month mature individuals of smaller size have veen found. The jack mackerel feeds usually on copepods and other planktonic organims, but it can feed also on juveniles of other fishes. This fish is caught throghout the whole year. The catches show their greater peak during winter; one other non-constant peak occurs during the spring (October-November) and declines shoraply during the summer months. It follows from this that the time of greates catch does not coincide with spawning season, or with the appearence of the greatest mean sizes. This happens because the interests of the fishermen are attracted during those months by others species of greater commercial value.

Marquages de Penaeus duorarum notialis en Côte d'Ivoire. 2 - Migrations et mortalités

Petersen disc tag marking experiments confirm the influence of animal size and marking time on the recapture rate. Westward migrations occur, probably following the Ivorian undercurrent. Catchability coefficients have been evaluated for the Grand-Bassam fishing ground and tentatively extrapolated to the other fishing areas. The extrapolated non weighted coefficient for the entire fishing areas is q=0.00069/fishing day for an area of 390 miles. The instantaneous coefficient of residual mortality X taken as a first and possibly slightly overestimated value of M the natural mortality, has been estimated at 0.155/month, strongly corroborating Berry's results (1967). This value is however much smaller than that given by earlier authors. It is suggested that q could have a higher value during the very first weeks of exploitation at sea, when the juveniles are concentrated near the lagoon outlets.

On the use of combined compact scheme for numerical solution of the two-layer oceanic shallow water equations

Many types of oceanic physical phenomena have a wide range in both space and time. In general, simplified models, such as shallow water model, are used to describe these oceanic motions. The shallow water equations are widely applied in various oceanic and atmospheric extents. By using the two-layer shallow water equations, the stratification effects can be considered too. In this research, the sixth-order combined compact method is investigated and numerically implemented as a high-order method to solve the two-layer shallow water equations. The second-order centered, fourth-order compact and sixth-order super compact finite difference methods are also used to spatial differencing of the equations. The first part of the present work is devoted to accuracy assessment of the sixth-order super compact finite difference method (SCFDM) and the sixth-order combined compact finite difference method (CCFDM) for spatial differencing of the linearized two-layer shallow water equations on the Arakawa's A-E and Randall's Z numerical grids. Two general discrete dispersion relations on different numerical grids, for inertia-gravity and Rossby waves, are derived. These general relations can be used for evaluation of the performance of any desired numerical scheme. For both inertia-gravity and Rossby waves, minimum error generally occurs on Z grid using either the sixth-order SCFDM or CCFDM methods. For the Randall's Z grid, the sixth-order CCFDM exhibits a substantial improvement , for the frequency of the barotropic and baroclinic modes of the linear inertia-gravity waves of the two layer shallow water model, over the sixth-order SCFDM. For the Rossby waves, the sixth-order SCFDM shows improvement, for the barotropic and baroclinic modes, over the sixth-order CCFDM method except on Arakawa's C grid. In the second part of the present work, the sixth-order CCFDM method is used to solve the one-layer and two-layer shallow water equations in their nonlinear form. In one-layer model with periodic boundaries, the performance of the methods for mass conservation is compared. The results show high accuracy of the sixth-order CCFDM method to simulate a complex flow field. Furthermore, to evaluate the performance of the method in a non-periodic domain the sixth-order CCFDM is applied to spatial differencing of vorticity-divergence-mass representation of one-layer shallow water equations to solve a wind-driven current problem with no-slip boundary conditions. The results show good agreement with published works. Finally, the performance of different schemes for spatial differencing of two-layer shallow water equations on Z grid with periodic boundaries is investigated. Results illustrate the high accuracy of combined compact method.