Difference in sale strategies drive spatial heterogeneity in collection pressure through online auctions: the role of body colour variation in the Japanese freshwater crabs, Geothelphusa dehaani species complex

The increase in online sales of living organisms has raised considerable concerns about its impact on wildlife. High demand for specific biological traits can intensify collection pressure via wildlife trades, yet the effects of colour variations and their geographical distribution on regional collection pressure remain poorly understood. This study analysed 11 years of transaction data — including, number, volume, price, date, colour types (DB: dark brown; RD: red; SB: sky blue; OT: other colours; and Mix) and collection locality — for the Geothelphusa dehaani species complex, renowned for its regional colour variations and aquarium popularity. Contrary to expectations that rarer colouration types (SB and OT types) are collected in higher numbers, the wild G. dehaani species complex collection pressure via online auctions (i.e. selling volume of wild-caught individuals) was higher for the common DB type (15,493 individuals) than for the rarer SB and OT types (2,073 and 173 individuals, respectively). This difference arose from a mechanism based on two distinct strategies linked to the colour traits and geographical distribution: the DB type followed a low-profit, high-sales (LPHS) strategy, selling large quantities at low unit prices, while the SB and OT types employed a high-profit, low-sales (HPLS) strategy, selling fewer individuals at higher unit prices. These findings highlight how colour variations influence online auction sales strategies and may negatively impact wildlife populations due to heterogeneous collection pressure at regional or local levels. Given the potential for rapid shifts of such mechanism driven by the appearance of mass sellers or the taxonomic revisions (i.e. additional value by a new species), our study suggests that implementing nuanced regulatory measures — for example, annual limits on the number of living animal auctions per taxon per year — could mitigate the risks associated with the diverse collection pressures through online auctions.