Partitioning of habitat and prey by abundant and similar-sized species of the Triglidae and Pempherididae (Teleostei) in coastal waters

The aim of this study was to determine whether certain co-occurring and abu ndant species of the teleost families Triglidae and Pempherididae are segre gated spatially and/or by diet, and are thus less likely to be susceptible to competition for resources. Nocturnal otter trawling in shallow (5-15 m) and deeper (20-35 m) waters in four regions along similar to 200 km of the south-western Australian coastline collected large numbers of a wide size r ange of the triglids Lepidotrigla modesta and Lepidotrigla papilio and the pempheridids Pempheris klunzingeri and Parapriacanthus elongatus. Although these four species frequently co-occurred at several sites, each species at tained its highest density at different sites, thereby representing a parti al segregation of these species by habitat. This even occurred with the con generic triglid species, with L. modesta being most abundant in the four de ep, offshore sites, while L. papilio was most numerous at three sites which varied in depth and distance from shore. Although triglids and pempheridid s both consumed substantial amounts of amphipods and mysids, only the membe rs of the latter family ingested a large amount of errant polychaetes. The latter difference is assumed to reflect the fact that, in comparison with t riglids, pempheridids can swim faster, have a mouth adapted for feeding upw ards in the water column and feed at night when errant polychaetes emerge f rom the substratum. Although the dietary compositions of L. modesta and L. papilio did not differ significantly when analyses were based on dietary da ta for all sires, they did differ significantly when analyses were restrict ed to dietary data obtained when both species were abundant and co-occurred . The likelihood of competition for food is thus reduced in the latter circ umstances. In comparison with P, klunzingeri, P. elongatus consumed a relat ively larger volume of amphipods and a relatively smaller volume of mysids, which are more mobile, implying that P. elongatus feeds to a greater exten t: on rather than above the substratum surface. The diets of all species un derwent ontogenetic changes, which were particularly marked in P. klunzinge ri where an increase in body size was accompanied by a reduced consumption of mysids and an increased ingestion of errant polychaetes and amphipods. T he fact that L. modesta, L. papilio, P. khunzingeri and P. elongatus are pa rtially segregated by habitat and feed on suites of prey which differ in co mposition, allied with an interfamilial difference in the time of feeding, would reduce the likelihood of competition for resources amongst these four species, when they co-occur and are abundant. Furthermore, ontogenetic cha nges in diet would reduce the potential for intraspecific competition for f ood. (C) 1999 Academic Press.