Influence of latitude, water depth, dayv.night and wetv.dry periods on the species composition of reef fish communities in tropical Western Australia

Abstract

Trap sampling over reefs in deep (mean = 20 m) and shallow (mean = 10 m) waters alongc. 1500 km of coastline in tropical north‐western Australia during both day and night and in wet and dry periods yielded 23 377 fishes, representing 32 families, 58 genera and 119 species. Individuals of the Serranidae, Lutjanidae, Lethrinidae and Carangidae contributed 88·9% to the total catch. The ichthyofaunal compositions of the Kimberley, Canning and Pilbara bioregions were relatively discrete. Species composition was influenced far more by location (latitude) than by water depth, period and time of day, and underwent a gradational change southwards. The latter change reflected differences in the trends exhibited by the relative abundances of certain species with increasing latitude and the confinement of other species largely to particular regions. The three most abundant species,i.e.Lethrinussp. 3,Lutjanus carponotatusandLethrinus laticaudiscontributed 34·8, 20·8 and 11·6% to the total catch, respectively. The first species was rarely recorded in the two most northern locations and was abundant in the four most southern locations, whereas the last two species were relatively more abundant in northern than in southern locations.Lutjanus bitaeniatusandLutjanus johniiwere found exclusively at the two locations in the Kimberley region, whereasAbalistes stellatus,Pentapodus emeryiiandLethrinus nebulosuswere not caught in this region but were found in both locations of the Canning and Pilbara regions. The species composition in deep and shallow waters at each location almost invariably differed significantly between day and night and between dry and wet periods, with species such asL. bitaeniatus,L. johnii,Lutjanus sebaeandA. stellatusbeing more abundant over deep reefs, whereasL. carponotatus,L. laticaudis,Siganus fuscescensandLethrinus lentjanwere more numerous over shallow reefs. Species such asL. johniiandLethrinus atkinsoniwere relatively more important in night‐time than daytime catches, whereas the reverse applied toLethrinus lentjan,L. laticaudisandChoerodon cyanodus.Lethrinussp. 3 andL. laticaudiswere relatively more important in catches during the dry than wet period.