Quantifying Species Abundance Trends in the Northern Gulf of California Using Local Ecological Knowledge

Ecosystem-based fisheries management requires data on all parts of the ecosystem, and this can be a barrier in data-poor systems. Marine ecologists need a means of drawing together diverse information to reconstruct species abundance trends for a variety of purposes. This article uses a fuzzy logic approach to integrate information from multiple data sources and describe biomass trends for marine species groups in the northern Gulf of California, Mexico. Forty-two species groups were analyzed, comprising fish, invertebrates, birds, mammals, turtles, and algae. The most important new data series comes from recent interviews with fishers in the northern part of the gulf. Respondents were asked to classify the abundance of various targeted and untargeted marine species groups from 1950 to the present. The fuzzy logic method integrates their responses with catch-per-unit-effort series, intrinsic vulnerability to fishing determined from life history parameters, biomass predicted by a Schaefer harvest model, and other simple indices. The output of the fuzzy logic routine is a time series of abundance for each species group that can be compared with known trends. The results suggest a general decline in species abundance across fished and unfished taxa, with a few exceptions. Information gathered from interviews indicated that older fishers tended to recognize a greater relative decrease in species abundance since 1970 than did younger fishers, providing another example of Pauly's (1995) shifting cognitive baselines.