Abalone reef productivity and the problem of scale in the management of the mexican abalone fishery

Fishing regulations are frequently set on a scale of hundreds to thousands of kilometers, assuming that exploited stocks respond uniformly to fishing. However, some marine resources, such as the abalone, are not amenable to such a large-scale approach, for they occur as mosaics of relatively independent populations. In this fishery, the challenge is to reduce the scale at which management and assessment are performed down to the scale of the comprising populations. The objective of this study was to discriminate abalone (Haliotis fulgens) reefs along central Baja California according to their productivity and identify common trends in catch amongst reefs. Annual abalone production of 69 abalone reefs (2005-2013) distributed along Bahia Tortugas was analyzed; data came from daily catches recorded by local fishermen. Statistical treatment of catch time series consisted in applying a cluster analysis for reef grouping, followed by a principal components analysis and linear regressions to explore common variations of reef groups over time and long term trends in production among groups. Analyses revealed four different groups of reefs, unevenly distributed along the study area, all showing a decline in abundance over time: (1) high and continuous productivity, (2) intermediate and continuous productivity, (3) low and continuous productivity, and (4) low and discontinuous productivity. The different levels of productivity may be associated to the complexity of the bottom topography, however hydrodynamics and ecological features may also influence. Our proposal is that current management by zone could be complemented by management at the level of groups of reefs, according to their natural abundance, in order to maintain the productivity of the different reefs at sustainable levels and avoiding concentrating fishing effort solely on the more productive ones, as it presently occurs.