Ecological Impact of Introduced Crayfish on Benthic Fish in Strawberry Creek

The introduction of the non-native crayfish Pacifastacus Ieniusculus in Strawberry Creek may be expected to have negative impacts on the stream ecosystem. Recent studies have shown that the declining fish population in Strawberry Creek may be due to the presence and estabishment of a large crayfish population. The purpose of this experiment is to investigate the interactions between the cray fish and the prickly sculpin (Cottus asper), a native benthic fish in Strawberry Creek. The hypothesis that crayfish prey on benthic fish was tested using eight isolation cages placed within the creek: four served as controls and four were experimental. Two fish were placed in every cage and the experimental cages each harbored two crayfish in addition to the sculpins. After ten days the remaining fish and crayfish were counted. All of the fish within the control cages survived whule only two survivors were found in the experimental cages. Two of the experimental cages only had one survivor each, while the rest of the experimental cages resulted in zero fish. The results of the experiment showed that fish mortalities were significantly higher when crayfish were present. The loss of fish could be partly due to predation, which was directly observed in the laboratory observation tank. The crayfish aggressively attacked the fish, yet did not actively pursue them. The results of this experiment may show the potential for crayfish to reduce fish abundance if not local extinctions in Strawberry Creek.