G. A. Hyndes á M. E. Platell I. C. Potter á R. C. J. Lenanton Does the composition of the demersal ®sh assemblages in temperate coastal waters change with depth and undergo consistent seasonal changes? Received: 21 August 1998 / Accepted: 9 February 1999 Abstract The aim of this study was to determine whether the composition of the demersal ®sh fauna in coastal marine waters in temperate Australia changes markedly with increasing water depth and distance from the shore and whether the composition of the ®sh fauna in water depths of 5 to 35 m undergoes cyclic, seasonal changes. Samples of demersal ®shes were therefore col- lected by trawling over the predominantly sandy sub- strate at nine sites located in water depths of 5 to 15 m or 20 to 35 m and within 20 km of the shore in four regions along 200 km on the lower west coast of Australia. The sampling regime involved trawling for ®shes at each site at night in seven consecutive seasons between the summer of 1990/1991 and winter of 1992. A total of 72 435 ®shes, representing 77 families, 143 genera and 172 species was caught. The compositions of the ®sh faunas in oshore waters with depths of 5 to 35 m were shown to dier markedly from those previ- ously recorded for nearshore marine waters in the same regions. However, as some species, such as Sillago burrus, S. vittata, S. bassensis and Rhabdosargus sarba, increase in size, they move out from their nursery areas in nearshore waters into deeper and more oshore wa- ters, where spawning occurs. Ordination showed that, in each of the four regions, the composition of the ®sh fauna in depths of 5 to 15 m diers from that in depths of 20 to 35 m. This dierence is attributable to the fact that some species, such as S. burrus, S. vittata and Upeneichthys lineatus, are far more abundant in depths of 5 to 15 m, whereas other species, such as S. robusta, U. stotti and Lepidotrigla modesta, occur predominantly in depths of 20 to 35 m. However, the samples collected from the single site that was inshore but in deeper water demonstrate that the composition of the ®sh fauna is in¯uenced by distance from shore as well as by water depth. The compositions of the ®sh faunas diered with latitude, largely due to the fact that some subtropical species, such as Polyspina piosae, S. burrus and S. ro- busta, did not extend down into the more southern re- gions. Ordination also showed that the composition of the ®sh faunas at all but one of the nine sites underwent pronounced and consistent cyclic, seasonal changes. This seasonal cyclicity at the dierent sites was attrib- utable to sequential patterns of immigrations and emi- grations by a number of ®sh species during the course of the year. These seasonal migrations involved, inter alia (1) movements of certain species from their nursery ar- eas into these deeper waters, e.g. S. bassensis and Scobinichthys granulatus; (2) migrations into and o the sandy areas of the inner continental shelf, e.g. Arnoglossus muelleri; (3) migrations to spawning areas, e.g. Sillago robusta; and (4) movements into areas where detached macrophytes accumulate in winter, e.g. Cnidoglanis macrocephalus and Apogon rueppellii. Introduction Some small species of teleosts, such as certain atherinids and gobies, remain permanently in nearshore marine waters (Prince and Potter 1983; Brown and MacLachlan 1990; Ayvazian and Hyndes 1995), whereas some other ®sh species spend the whole of their life cycles in rather deeper and more oshore waters (Ross 1977; Blaber et al. 1989; Hyndes et al. 1996b). It thus follows that the compositions of the ®sh faunas in nearshore coastal Marine Biology (1999) 134: 335±352 Ó Springer-Verlag 1999 Communicated by G.F. Humphrey, Sydney G.A. Hyndes (&) á M.E. Platell á I.C. Potter School of Biological Sciences and Biotechnology, Division of Science and Engineering, Murdoch University, Murdoch, Western Australia 6150, Australia Fax: 0061 (0)8 9360 6303 e-mail: hyndes@central.murdoch.edu.au R.C.J. Lenanton Western Australian Marine Research Laboratories, P.O. Box 20, North Beach, Western Australia 6020, Australia