Gastropods shell utilization among hermit crabs targeted by bait fishers along a tropical mangrove fringed creek, Mida, Kenya

Abstract

Mangrove gastropods and hermit crabs are frequently harvested for use as bait by artisanal trap and hook fishers, along the Kenyan coastline and elsewhere. In addition to mangrove degradation, the harvesting of shelled invertebrates, can alter shell availability and hence survival of these interdependent fauna. This study compares shell morphometric characteristics such as shell availability, adequacy and bait yield, among sites with different patterns of bait harvesting and other human disturbances. Shell morphometrics are also related to mangrove forest stand characteristics such as forest complexity, dominance, cutting intensity and sapling regeneration. Results indicate that the sampling regime, hermit crab taxa and mangrove zone influence morphometric characters of the gastropod and hermit crab. Significantly higher (P < 0.001) shell availability, adequacy and bait yield of the predominant hermit crab, Clibanarius danai, are recorded at upper and mid forested zones of sites with robust forest. This was attributed to shell selectivity of the crab, coupled with constancy of the environment at closed canopy sites. Apparently, forest structure is an important determinant of shell utilization patterns compared to prevailing bait harvesting activity. Protection of robust upper mangrove forest zones may therefore enhance sustainability of shelled bait harvesting and consequently the livelihoods support emanating from bait fishery.