Factors influencing the abundance of the common bully, Gobiomorphus cotidianus McDowall, in small, North Island, New Zealand, lakes

Adult common bullies, Gobiomorphus cotidianus McDowall, are small (total le ngth = 30-120 mm), benthic fish commonly found in the littoral zones of New Zealand lakes where they are a major prey species for trout and eels. Diff erences in their relative abundance (CPUE) were determined between 21 shall ow North Island lakes. Mean CPUE ranged from 2 to > 1000 fish net(-1) night (-1) and was inversely related to water transparency. The abundance of bull ies was not reduced in lakes containing rainbow trout, Oncorhynchus mykiss (Walbaum), but was reduced in all lakes containing self-recruiting populati ons of eels, Anguilla spp. Mean densities of planktonic larval bullies in t he limnetic zone were also inversely related to water transparency. Since l ow water transparency is related to increased trophic status for these lake s, the abundance of bullies is likely to be related to lake productivity, r ather than turbidity.