Diurnal and tidal movements of snapper (Pagrus auratus, Sparidae) in an estuarine environment

Abstract

Using individually coded acoustic transponders and an array of 15 moored receivers (detection range ~300 m), the temporal and spatial movements of the temperate snapper Pagrus auratus (Sparidae) were studied within an estuary. Of the 28 fish initially tagged, 20 were subsequently detected within the study area for up to 70 days. The spatial scale of daily movements was in the order of hundreds of metres for most fish, suggesting relatively restricted home ranges over the period monitored (November–January). The detectability of fish remaining in the estuary was lower at night, probably because of fish moving out of the main channel and onto surrounding shallow banks during darkness. Temporal movement patterns detected using spectral analyses (Fast Fourier Transforms) were predominantly diurnal, with subordinate tidal behaviour also evident in some fish. These results demonstrate that in this system, snapper occupy relatively small (hundreds of metres) and discrete areas of soft sediment seafloor, within which repeated, predictable movements are made. Variability among fish has highlighted the need for a better understanding of the relationship between fish behaviour and fine-scale habitat features (metres).