Investigating ecosystem processes using targeted fisheries closures: can small-bodied invertivore fish be used as indicators for the effects of western rock lobster fishing?

Abstract

Ecosystem modelling has predicted that fishing for western rock lobster Panulirus cygnus in deep water (50–80m) habitats will result in increased abundance of their macroinvertebrate prey, which would, in turn, support greater production of small-bodied invertivore fish species. To investigate the potential ecosystem effects of rock lobster fishing, a targeted fisheries closure was proposed in deep water habitats along the coast of Western Australia. Data on small-bodied invertivore fish abundance, from baited video, were used to investigate differences across habitats and simulate the likely power of any study to detect change. In general, small-bodied invertivore fish were more abundant at shallower macroalgae-dominated sites, whereas the most abundant single species, the western king wrasse Coris auricularis, was abundant across all habitats and sites. Power simulation of a mixed-model before–after–control–impact (BACI) design found that a 40–50% decrease in either Coris auricularis or small-bodied invertivore fish in general would be very likely to be detected (power ~0.8). Based on the power simulation, we suggest a general sampling design to investigate change before and after the establishment of the fishery closure and make suggestions for further ecological studies to investigate the predicted ecosystem effects of rock lobster fishing.