Reconstructing Historical Fisheries Baselines Using Ethnobiological Methods in the Lake Chad Basin: Implications for Shifting Baselines in Conservation

The shifting baselines syndrome describes the systematic erosion of ecological reference points across generations, leading to progressive downgrading of conservation targets and management expectations. This research employs rigorous ethnobiological methods to reconstruct historical fisheries baselines for the Lake Chad Basin in Borno and Yobe States, North East Nigeria, and evaluates the magnitude of the shifting baselines effect on current management targets. A multi-generational interview framework was developed and administered to 340 respondents stratified by age cohort (18 to 35, 36 to 55, and over 55 years old) and fishing role across 12 communities. Semi-structured narratives documented historical catch volumes, species compositions, fish sizes, and habitat characteristics. Historical photograph analysis, fisheries department archival records, and a systematic literature review of documents dating from 1935 to 2024 were triangulated with oral data. A quantitative historical ecology index was constructed to integrate multiple evidence streams into relative abundance estimates for 22 focal species over time. The study documented a mean 71 percent reduction in reported fish size for iconic species since the 1970s. Three large-bodied species including Labeo senegalensis were reported by respondents over 55 as historically abundant but are now functionally absent from catches. Younger respondents systematically rated current abundance as acceptable for species that elder respondents identified as severely depleted, confirming strong generational baseline shifting. Historical ecology index estimates suggest that current total basin fish biomass represents approximately 14 percent of estimated 1960s levels. This research makes a methodological contribution by developing the first quantitative ethnobiological historical ecology index. Keywords: shifting baselines, ethnobiology, Lake Chad, historical ecology, North East Nigeria.