Relative abundance of Osteolaemus tetraspis in Uwa, Edumanom and Ogbe-Ijaw bushmeat markets in the Niger Delta region, Nigeria

Abstract

The dwarf crocodile Osteolaemus tetraspis is globally listed as Vulnerable, yet remains heavily harvested across West and Central Africa particularly in the Niger Delta, Nigeria. This study assessed the spatio-temporal variation in the relative abundance of O. tetraspis across three major bushmeat markets: Uwa (Edo State), Edumanon (Bayelsa State), and Ogbe-Ijaw (Delta State) to inform conservation and management interventions. Bushmeat market surveys were conducted fortnightly between October 2021 and April 2022. All crocodiles encountered were counted and measured across three size classes (60, 90, and ≥ 120 cm). A negative-binomial generalized linear mixed model (GLMM) was fitted to monthly counts of Osteolaemus tetraspis to account for overdispersion in the abundance data. Temporal (Month) and spatial (Market location) effects, as well as their interaction, were treated as fixed effects. A total of 158 O. tetraspis individuals were recorded, dominated by medium-sized (39.24%) and large-sized (39.24%) individuals. Uwa accounted for the highest proportion of individuals (60.76%), followed by Edumanon (25.32%) and Ogbe-Ijaw (13.92%). The negative-binomial GLMM model indicated significant effects of Month (χ²₆ = 19.82, p < 0.01) and Market Location (χ²₂ = 10.46, p = 0.005), as well as a significant Month × Market interaction (χ²₁₂ = 23.17, p = 0.018), demonstrating that temporal patterns in abundance differed among markets. The marginal R² value (R²ₘ = 0.48) indicated that fixed effects accounted for a substantial variation in monthly abundance. Temporal declines were pronounced in April across all markets. Trade pressure on O. tetraspis is greatest during the dry-season months of October-February, with Uwa and Edumanon emerged as the principal markets contributing to the observed trade. The dominance of medium- and large-bodied crocodiles in the trade raises concerns about depletion of reproductive adults and long-term population collapse. These findings highlight the need for market-specific regulatory strategies, dry-season harvest restrictions, enhanced monitoring in high-pressure markets, and livelihood support programs. Integrating these actions with community-based conservation are critical for sustaining remaining O. tetraspis populations in the Niger Delta.