Nocturnal patch use by redfinned bullies (Gobimorphus huttoni) in a temperate stream of southern New Zealand

Abstract

Understanding how benthic feeding fish track and use patchy resources such as food, is beneficial for conservation and management providing insights into how they perceive and assess their environment. The benthic feeding fish of New Zealand provide ideal study organisms to determine whether fish are selecting patches based on food resources, habitat structure or a combination of both (McDowall, 2010). This thesis aimed to investigate what factors drive nocturnal patch selection by the redfinned bully, in a small temperate stream (Catlins, New Zealand). The descriptive component of this study compared the microhabitat and invertebrate community of nocturnal patches occupied by redfinned bullies to patches sampled at random. It was found that redfinned bullies displayed non-random patch selection, with a preference for patches with cobble substrates and high abundances of invertebrates (particularly chironomids). However, distinguishing whether patch selection by redfinned bullies was driven by the invertebrate community or the substrate was not possible based on the results from the descriptive component of the study. To elucidate what was driving nocturnal patch selection by redfinned bullies an experiment was designed. The experimental component of this study involved a group of twenty stream pools half of which were treated using a cleaning procedure (experimental disturbance) to reduce the abundance of invertebrates and the other half were undisturbed control pools. Pools were monitored over five weeks to observe the response of redfinned bullies to the experimental disturbance (reduced invertebrate abundance), but no distinct response was observed. A lack of response by redfinned bullies suggests a strong affinity to their pool of residence, at least in the short term, despite a low abundance of prey. Home range affinity may have been related to spawning, including activities such as nest guarding, egg laying and fertilisation. If the same experiment were to be repeated outside of the redfinned bully spawning period different patterns of response may have been observed. This study has assisted in understanding aspects of redfinned bully ecology, however further studies, on multiple scales will be required to elucidate the many unknown aspects of redfinned bullies.