Dietary compositions of the sparid Acanthopagrus butcheri in three normally closed and variably hypersaline estuaries differ markedly

Abstract

We have compared the species composition and diversity of the diets of black bream, Acanthopagrus butcheri, in three normally closed estuaries on the central south coast of Western Australia, which vary markedly in the extents to which they become hypersaline during dry periods. Although black bream was caught seasonally in Stokes Inlet during this 3-year study, it was obtained from the Hamersley and Culham inlets only during the earlier seasons because salinities in those two estuaries subsequently rose to levels that caused massive mortalities of this sparid. Although a wide range of taxa, including macrophytes, polychaetes, molluscs, crustaceans, insects and teleosts, were ingested by A. butcheri in each estuary, the frequencies of ingestion and volumetric dietary contributions of these taxa varied greatly among the fish in these three estuaries. Thus, for example, in comparison with other estuaries, relatively greater contributions were made to the diet by polychaetes and crustaceans in Stokes Inlet, by macrophytes in Hamersley Inlet, and by insects (mainly chironomid larvae) in Culham Inlet. The relatively greater contribution of teleosts to the diets of black bream in the Hamersley and Culham inlets than in Stokes Inlet, and also differences in the main teleost species ingested in the first two estuaries, are consistent with differences in the densities of fish overall and of the main fish species in those estuaries. The diversity of the diet was far greater in Stokes Inlet than in the other two far more variably saline estuaries, presumably reflecting a greater diversity of food. The dietary compositions of black bream in upstream pools in the tributary of Culham Inlet, which offer refuge when salinities increase markedly in the main body of the estuary, differ from those in those downstream regions, further emphasising the opportunistic nature of the feeding behaviour of black bream. The dietary compositions of black bream underwent size-related changes, but the taxa contributing most to those changes varied greatly among estuaries. Size-related changes would be particularly beneficial in reducing intraspecific competition for food in the two estuaries that vary greatly in salinity and would thus be likely to contain a less diverse range of prey.

Comparisons of the Growth and Gonadal Development of Otolith-Stained, Cultured Black Bream,Acanthopagrus butcheri, in an Estuary with Those of Its Wild Stock

“…In southwestern Australia, this sparid can attain total lengths and weights of at least 475 mm and 2 kg and live for over 20 years , which broadly parallels the situation in eastern Australia (Morrison et al, 1998). However, the growth, age and size at maturity, and dietary composition of A. butcheri vary among estuaries, reflecting, at least in part, marked differences in the environmental characteristics of those estuaries Potter, 1999, 2000;Partridge et al, 2004;Chuwen et al, 2007).…”

Dietary composition of black drum Pogonias cromis in a hypersaline estuary reflects water quality and prey availability

“…Similarly, food resource availability in three hypersaline estuaries in Western Australia has been attributed to the degree of salinity variability for Acanthopagrus butcheri (Chuwen et al . , ). The degree of salinity variability in Florida Bay is related to the quality of food resources ingested by tidewater mojarra Eucinostomus harengulus Goode & Bean 1879 and goldspotted killifish Floridichthys carpio (Günther 1866) (Ley et al .…”

Marked deleterious changes in the condition, growth and maturity schedules of Acanthopagrus butcheri (Sparidae) in an estuary reflect environmental degradation

“…declined and was thus considered to be one of the factors that led to reductions in the growth (Eby et al, 2005). Unfortunately, there are no quantitative data to facilitate comparisons between the quantity and quality of the benthic macroinvertebrates and macroalgae of A. butcheri in offshore and nearshore waters in the two periods and which are known to constitute the diet of this species Chuwen et al, 2007).…”