Modeling and control of antarctic marine fisheries with density dependent recruitment

BARRERA ORO, ESTEBAN; BERGALLO, M.; ALESCIO, NADIA S.; MARSCHOFF, ENRIQUE RICARDO; NAGEL, C.; NEUMAN, CARLOS

Trujillo

Seminario; VI Seminario Internacional de Bioinformática; 2010

 We study the problem of modeling fish populations (Notothenia coriiceps, Notothenia rossii, Gobionotothen gibberifrons) with emphasis on the changes of their levels (dependent on biomass) and their spatial localization along several stages of the process. The models are based on recruitment equations and control and surveillance modules and are aimed to the sustainable management of fisheries based on these populations. The diffusion-advection-reaction equations are the basic framework of the model. The "reaction" part of the model, i.e. the recruitment and growth parts as well as the boundary conditions are highly non linear, so the problem is mathematically difficult and sensible to the model specification. Further non linearities appear in the form of age (length) thresholds. We consider the case of a single isolated species and that of two interacting species by means of a model able to be generalized as new data becomes available, specially on species interactions. The age distributions and a complex density dependence are considered using an ecological brake and an age dependent reproductive capacity. The captures in the case of one or two species and the surveillance and control strategies were studied based on prediction and bilinear-quadratic models that have proved to be adequate in other contexts and very useful here. Model results were compared with fish samples collected through an overall period of 25 years at Potter Cove, South Shetland Islands, Antarctica, after the impact of the fishery in the area in 1978-80. The sharp decline in abundance of N. rossii reported for the period 1983–1992 is consistent with the increase in mean size observed between 1983 and 1987 and the duration of the inshore phase of the species, which is known to last for 6–7 years. In the following years, until 1992, the decreasing abundance is consistent with the entrance of low strength cohorts with the consequent reduction of mean size. This interpretation is supported by the length distributions observed between 1982/3 and 1985/6 where the modal age changes from 2/3 to 6/7 years. After 1991/2 the densities, mean sizes and abundances do not depend on a single forcing event but on several interacting factors. The length data of the others species are studied as well and used for the validation of the model. Fisheries in the Antarctic are currently managed by the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) Which has prohibited fishing in the area under study since 1991.