A proposal to define vulnerability of cetacean areas to human development: variables and analysis procedures applied to the Gulf of California

1. Understanding spatial interactions between specific sources of anthropogenic impact on cetaceans and the ecological conditions intrinsic to these mammals, has several applications for conservation and management. Here cetacean habitats are classified into vulnerability levels by combining human development metrics and cetacean characteristics, allowing areas identified as more vulnerable to be given management priority. 2. Ten bio-physical and anthropogenic factors were identified as key shapers of cetacean habitats and, using the Gulf of California as a case study, 18 variables were defined to measure those factors. Principal component analysis (PCA) and GIS were used to distill the relationships across all variables, in order to obtain a vulnerability index. Aggregates of variables were also investigated to map the spatial distribution of anthropogenic impacts and cetacean characteristics (species richness, relative abundance of encounter, residence condition, diet specificity and threat status). For this latter purpose, separate indices representing five 'categories' (pollution from land sources, urban development, potential for accidents, resource depletion and fragility of cetacean areas) and three 'vulnerability components' (risk of hazards, intrinsic resilience and damage) were calculated. 3. The methodology clearly differentiated the study area according to levels for each 'category' and 'vulnerability component', as well as to levels of vulnerability of cetacean areas in relation to human activities; and identified those variables with the greatest contributions, without recourse to the subjective criteria common in other approaches. The analyses were conducted using environmental units generated by the Marine Ecological Zoning Plan for the Gulf of California (OEMGC, by its Spanish acronym) which tied model outputs to this planning framework. The variables selected were easily obtainable through governmental and research institutions which make them suitable for adaptive management purposes. Copyright (C) 2011 John Wiley & Sons, Ltd.