Symposium Abstract: Fishing and Environmental Disturbance Indicators in a Shrimp Fishing Ground at the Mexican Central Pacific
E. Godinez-Dominguez, J. Freire, and G. Gonzalez-Sanson
This paper examines the concurrent effects induced by trawl shrimp fisheries, natural seasonal dynamics and interannual processes as ENSO events on a soft bottom macroinvertebrate community. Short-term effects were evaluated during an initial period of two years when five trawl cruises were carried out in successive closed and open fishing seasons coinciding with the main hydroclimatic periods. In each cruise seven sites along 100 km of coastline were selected and four depths were sampled (20, 40, 60 and 80 m). A series of community structural descriptors used frequently to determine the ecological effects of fishing disturbances were employed: ABC curves, W-statistic, normalized species size distribution as biomass spectra, spatial segregation index, Shannon diversity index, species richness and biomass. Inter-annual effects were analysed with data from semimonthly cruises in 2 sites and the same four depths from 1995 to 1998. Theoretical predictions of the effects of fishing in the behaviour of the statistical indices used were tested. Results show a strong evidence that fishing has produced a state of chronic disturbance in the macroinvertebrate community. Short-term fishing effects could be masked by natural seasonal and interannual environmental changes. Results of short-term effects are not in agreement with the fishing disturbance theories. The trends found could evidence interannual effects associated to El Ni-o and La Ni-a events. The complexity of the sources of variability in a exploited community forces managers to adopt a more widely adaptive approach which should be focused on understanding the community structural process through temporal and spatial gradients, and to use several structural indices to evaluate critically their performance as indicators of fishing disturbance.