A multi-agent ecosystem model for studying changes in a tropical estuarine fish assemblage within a marine protected area

2012

Article référencé dans le Web of Science WOS:000322290200004

Brochier Timothée, Ecoutin Jean-Marc, Tito de Morais Luis, Kaplan David, Lae Raymond

Aquating Living Resources, 2012, 12 p. ISSN 0090-7440

As marine protected areas (MPAs) are increasingly being utilised as a tool for fishery management, theirimpact on the food web needs to be fully understood. However, little is known about the effect of MPAs on fishassemblages, especially in the presence of different life history and ecological traits. Modelling the observed changes infish population structures may provide a mechanistic understanding of fish assemblage dynamics. In addition, modellingallows a quantitative estimate of MPA spill-over. To achieve this purpose, we adapted an existing ecosystem model,OSMOSE (Object-oriented simulator of marine biodiversity exploitation), to the specific case of the presence of fishwith multiple life histories. The adapted model can manage 4 main categories of life history identified in an estuaryMPA: fish that (1) spend their entire life cycle locally, (2) are present only as juveniles, (3) enter the area as juveniles andstay permanently except during reproduction periods, which occur outside the estuary, and (4) are present occasionallyand for a short time for foraging purposes. To take into account these specific life-history traits, the OSMOSE code wasmodified. This modelling approach was developed in the context of the Bamboung Bolong MPA, located in a mangrovearea in the Sine-Saloum Delta, Senegal. This was the idealcase to develop our approach as there has been scientificmonitoring of the fish population structure inside the MPA before fishery closure, providing a reference state, andcontinuous monitoring since the closure. Ecologically similar species were pooled by trophic traits into 15 groups thatrepresented 97% of the total biomass. Lower trophic levels (LTL) were represented by 6 compartments. The biomass ofthe model species was calibrated to reproduce the reference situation before fishery closure. Model predictions of fishassemblage changes after fishery closure corresponding to the Bamboung MPA creation scenario were compared to fieldobservations; in most cases the model reproduces observed changes in biomass (at least in direction). We suggest theexistence of a 'sanctuary effect', that was not taken into account in the model, this could explain the observed increasein biomass of top predators not reproduced by the model. Finally, the annual MPA fish spill-over was estimated at 11 tons (approx. 33% of the fish biomass) from the model output, mainly due to diffusive effects.

Synécologie [036MILSAU02] ; Ecosystèmes [082ECOSYS]

MILIEU ESTUARIEN ; POISSON ; BIOMASSE ; NIVEAU TROPHIQUE ; FONCTIONNEMENT DE L'ECOSYSTEME ; MODELE ; ANALYSE SYSTEMIQUE ; AIRE MARINE PROTEGEE

SENEGAL

Fonds IRD [F B010058516]

fdi:010058516