DISTRIBUTIONS, SIZE COMPOSITIONS AND DIETS OF 2 ABUNDANT BENTHIC AMBUSH-FEEDING TELEOSTS IN COASTAL WATERS OF SOUTH-WESTERN AUSTRALIA

The scorpaenid Maxillicosta scabriceps (Teleostei) and the platycephal id Platycephalus longispinis (Teleostei) were trawled seasonally for a year from shallow (5-15 m) and deeper (20-35 m) waters in four distan tly-located regions of the inner continental shelf of south-western Au stralia. The former species was more abundant in southern regions, whi ch is consistent with its temperate distribution, while the latter spe cies was more abundant in deep than shallow waters. Unlike M. scabrice ps, P. longispinis with total lengths <110 mm were rarely caught, indi cating that this latter species only moves on to the sandy substrate o f the inner shelf when it reaches a certain size. As M. scabriceps inc reased in size, the contributions of mysids, amphipods and oxyrhyncan crabs to the diet declined, while those of carid decapods and brachyrh yncan crabs increased. The invertebrate fauna ingested by the smallest length-class of P. longispinis, 110-139 mm, was similar to that of th e same and largest length-class of M. scabriceps. However, unlike M. s cabriceps, this length-class of P. longispinis consumed teleosts, desp ite having a relatively smaller mouth. The contribution of teleosts su bsequently increased as P. longispinis increased in size, a feature re flected by the relatively low dietary breadth of large fish. The marke d shift in the types of prey ingested by P. longispinis as it increase d in size accounted for the fact that, in contrast to M. scabriceps, t here was limited dietary overlap between the larger and smaller member s of this platycephalid. The ability of P. longispinis to ingest other fish is presumably related to the fact that platycephalids lie just u nder the substrate surface and are thus concealed from their potential prey, and that they are able to emerge rapidly and pursue their prey. Unlike several other local demersal fish species, M. scabriceps and P . longispinis ingested only a small amount of sediment, implying that these ambush predators target their prey very precisely, a foraging mo de that would be facilitated by the epibenthic and conspicuous nature of their prey. The absence of marked differences in the dietary compos itions of these two species in different regions, water depths and sea sons is consistent with a specific mode of foraging by these species.