Gavin A. Sarre

Comparisons between the reproductive biology of black bream Acanthopagrus butcheri (Teleostei: Sparidae) in four estuaries with widely differing characteristics

The reproductive biology ofAcanthopagrus butcheri has been studied in the permanently open Swan River and intermittently open Moore River estuaries on the lower west coast of Australia (31–32°S) and in the permanently open Nornalup Walpole and normally closed Wellstead estuaries on the southern coast of Western Australia (34–35°S). Trends exhibited by gonadosomatic indices, gonadal maturity stages and the sizes and developmental stages of the oocytes demonstrate thatA. butcheri typically spawns in spring and early summer. However, spawning occurred in salinities ranging from as low as 3.5–8 gL−1 in the Moore River Estuary to as high as 41–45 g L−1 in the Wellstead Estuary. Furthermore, water temperatures during spawning were greater in the two northern estuaries (19.7–28.5°C) than in the two southern and cooler estuaries (17.5–23.4°C). Histological studies strongly indicate thatA. butcheri spawn more than once in a breeding season and demonstrate that the development of its oocytes exhibits group synchronysensu de Vlaming (1983). The ages and total lengths at which, on average, female and maleA. butcheri both first attain maturity in the Swan River Estuary were ca 2 years and ca 215 mm. However, the age at which individual fish in that system reach maturity was influenced by body size. This suggests that the attainment of first maturity at an older age but smaller length in the Moore River and Nornalup Walpole estuaries than is the case in the Swan River Estuary is a consequence of the slower growth rates ofA. butcheri in those estuaries. The combination of the young age (ca 2 years) but small length (ca 145 mm) at which maturity is first attained in the Wellstead Estuary could have resulted from selection pressures brought about by high mortality rates and/or heavy fishing pressure in this estuary. The mean fecundity ofA. butcheri, based on the combined number of yolk vesicle and yolk granule oocytes found in ovaries just prior to the onset of spawning, was 1580×103. The significance of the sizes at first maturity, minimum legal length for capture, mesh selectivity data and closure of certain regions of estuaries to fishing for the management of the recreational and commercial fishery forA. butcheri is discussed.

The diets of two co-occurring marine teleosts, Parequula melbournensis and Pseudocaranx wrighti, and their relationships to body size and mouth morphology, and the season and location of capture

The dietary compositions of the co-occurring gerreid Parequula melbournensis and the carangid Pseudocaranx wrighti have been determined, using samples collected seasonally from a 200 km stretch of coastal water in temperate Australia, in which these species are very abundant. Although the small representatives of P. melbournensis and P. wrighti both fed to a large extent on copepods, the latter ingested a wider variety of prey and thus had a greater dietary breadth. The diets of both species changed markedly as body size increased. The larger representatives of P. melbournensis fed mainly on onuphid and other polychaetes, whereas those of P. wrighti consumed a considerable volume of crustaceans, molluscs, polychaetes other than onuphids, and echinoderms. The above differences account for the dietary breadth being far greater in large P. wrighti than large P. melbournensis. Schoeners index and classification showed that dietary overlap between P. melbournensis and P. wrighti was low, suggesting that food resources were partitioned between these two demersal species. Intraspecific overlap was less amongst the length classes of small fish than among those of larger fish, indicating that any competition for food would be less among small fish, when growth would have been most rapid. The larger P. melbournensis fed mainly on prey types which were relatively sessile and can protrude from the substrate, such as tube-dwelling onuphid polychaetes, whereas the larger P. wrighti fed on a variety of epibenthic and/or more mobile species, such as mysids, amphipods, bivalves, gastropods, nereid polychaetes and echinoderms. Although P. melbournensis foraged to a far greater extent on a sessile fauna that occurs on or in the substrate, it ingested a far smaller amount of sand than P. wrighti, even though this latter species fed on a more epibenthic fauna. The presence of smaller amounts of sand in the stomach contents of P. melbournensis than of P. wrighti, presumably reflects the possession of a smaller and far more protrusible mouth, which enabled its sessile prey to be targetted more precisely. The dietary composition of P. melbournensis and P. wrighti underwent some seasonal changes, presumably reflecting seasonal fluctuations in the densities of prey species, and that of P. melbournensis differed slightly between some sites.

The interaction between soil pH and phosphorus for wheat yield and the impact of lime-induced changes to soil aluminium and potassium

Interactions between soil pH and phosphorus (P) for plant growth have been widely reported; however, most studies have been based on pasture species, and the agronomic importance of this interaction for acid-tolerant wheat in soils with near-sufficient levels of fertility is unclear. We conducted field experiments with wheat at two sites with acid soils where lime treatments that had been applied in the 6 years preceding the experiments caused significant changes to soil pH, extractable aluminium (Al), soil nutrients and exchangeable cations. Soil pH(CaCl2) at 0–10cm was 4.7 without lime and 6.2 with lime at Merredin, and 4.7 without lime and 6.5 with lime at Wongan Hills. A significant lime×P interaction (P<0.05) for grain yield was observed at both sites. At Merredin, this interaction was negative, i.e. the combined effect of soil pH and P was less than their additive effect; the difference between the dose–response curves without lime and with lime was greatest at 0kgPha–1 and the curves converged at 32kgPha–1. At Wongan Hills, the interaction was positive (combined effect greater than the additive effect), and lime application reduced grain yield. The lime×P interactions observed are agronomically important because different fertiliser P levels were required to maximise grain yield. A lime-induced reduction in Al phytotoxicity was the dominant mechanism for this interaction at Merredin. The negative grain yield response to lime at Wongan Hills was attributed to a combination of marginal soil potassium (K) supply and lime-induced reduction in soil K availability.

Growth and yield responses in wheat and barley to potassium supply under drought or moderately saline conditions in the south-west of Western Australia

Abstract. This study assessed whether more potassium (K) was required for optimal growth and grain yield of cereal crops under drought and salinity than under non-stressed conditions. In 2011, three experiments on wheat (Triticum aestivum L.) with four K rates (0, 20, 40, 80 kg K/ha), four application times (0, 5, 10, 15 weeks after sowing, WAS) and two sources (KCl, K2SO4) were conducted in the central and southern grainbelts of Western Australia. The lack of plant response to K supply at the sites of Bolgart (36 mg K/kg at 0–30 cm) and Borden (25 mg K/kg at 0–30 cm), compared with significant gain in K uptake, dry matter and grain yield at Dowerin (29 mg K/kg at 0–30 cm), was not explained by differences in soil K levels. However, rain fell regularly through the growing season at Bolgart and Borden, whereas a dry spell occurred from stem elongation to grain development at Dowerin. The effectiveness of K application time followed the trend of 0, 5 > 10 > 15 WAS. In 2012, barley (Hordeum vulgare L.) was grown on a moderately saline (saturation extract electrical conductivity ∼4 dS/m) and low K (20 mg K/kg) farm in the central grainbelt and treated with 0, 20, 40 and 120 kg K/ha. Applying K increased K uptake but decreased Na uptake, especially at 120 kg K/ha. Plant growth and grain yield increased with K supply, but the difference between the K rates was relatively small, indicating possible partial K substitution by Na. Higher than normal fertiliser K supply on low K soils would enhance the adaptation by cereals to water-limited environments, but K-fertiliser management on moderately saline soils may need to account for both K and Na uptake and use by the crops.