Ascending the Avon: fishes of the Northam Pool, and the Swan-Avon catchment

The fish fauna in the vicinity of the Northam Pool Weir was sampled seasonally between winter 2008 and autumn 2009. The results indicate that the fish community was characterised by species that are halotolerant including two estuarine species, the Western Hardyhead and Swan River Goby that are likely to have undergone large upstream expansions in the Swan‐Avon catchment due to secondary salinisation. However, two freshwater endemic species, the Western Minnow and Nightfish were also recorded in the vicinity of the weir. These, and other freshwater endemic species, have undergone large range reductions in this catchment as a result of salinisation. The study found evidence that the weir may be impeding the upstream movements of native fishes as found elsewhere in south‐western Australia and that construction of a well‐designed fishway would enhance population connectivity and increase their sustainability. It is recommended that additional sampling occurs during the major spawning periods of the freshwater species immediately below the weir to determine precisely when a future fishway would need to operate to allow maximum usage by resident native species. It is also recommended that fresh refuge habitats for freshwater fishes be identified to allow effective management measures to be implemented in those systems to halt their decline and reduce the risk of complete loss of these species from the Swan‐Avon catchment

Factors required for the successful aquaculture of black bream (Acanthopagrus butcheri) in inland water bodies

The results of this project will contribute to the on-going development and success of inland black bream recreational fisheries and the inland saline aquaculture industry in general. Several commercial black bream fish-out ventures are now operational in inland Western Australia, one of which utilises saline groundwater. It has been proposed that a pilot project to stock the saline pools of the upper Avon River, which is located in the heart of the W.A. Wheatbelt, should be undertaken to provide recreational fishing opportunities for the inhabitants of a number of rural towns. The continued development of the W.A. inland saline aquaculture industry will result in social and economic benefits to rural areas through increased tourism and opportunities for farm diversification

The tropical South American cichlid, Geophagus brasiliensis in Mediterranean climatic south-western Australia

The highly endemic (82%) freshwater fishes of south-western Australia are imperiled due to severe habitat and water quality declines and impacts of introduced species. As a case study of the recent tropical aquarium fish introductions, the biology and ecology of the pearl cichlid Geophagus brasiliensis was determined in the Swan River catchment south-western Australia. Unlike endemic freshwater fish species of this Mediterranean climatic region, Geophagus brasiliensis underwent a protracted spawning period during the warmer period from December to May. It appeared that recruitment only occurred in lentic habitats; however the species also persists in downstream lotic habitats. Growth rate and maximum size (245 mm TL) of the species exceed all but one of the region's native freshwater fishes. Whilst minimum water temperature may help limit its establishment in many aquatic ecosystems, its salinity tolerance and omnivorous diet would facilitate its colonisation in this region, including freshwaters and estuaries. Past and future habitat and climatic change is predicted to continue to favour species from sub-tropical and tropical regions

Habitat, reproductive biology and size composition of Parequula melbournensis, a gerreid with a temperate distribution

Trawling was carried out over sandy substrates in the shallow (5 15 m) and deeper (20 35 m) waters of four regions along 250 km of the lower west coast of Australia, during seven consecutive seasons. This yielded 32 752 individuals of the gerreid Parequula melbournensis, which constituted c. 42% of the total number of fish. Densities of P. melbournensis were greatest in the most southern region, reaching a seasonal maximum of 835 fish ha-1 at one site in that region. Since P. melbournensis is restricted largely to the southern coastline of Australia, it hits a temperate rather than subtropical or tropical distribution and thus is not a typical gerreid. Furthermore, unlike most other gerreids, it does not spend part of its life cycle in either estuaries or nearshore marine waters. The maximum total length of P. melbournensis was 175 mm, with the length at maturity (L50) being 115 mm in females and 121 mm in males. No clear monthly trends were exhibited by gonadosomatic indices, the prevalence of mature ovaries and the oocyte size frequency distributions of female P. melbournensis, and no clear and consistent modes were observed in length frequency data for this species. These strong indications that spawning occurs throughout the year were substantiated by the occurrence of post-ovulatory follicles in the ovaries of large fish in all months but August, and by the presence in that month of advanced yolk granule oocytes in some ovaries, which implies that spawning was imminent. The spawning of P. melbournensis throughout the year contrasts with the far more restricted spawning periods recorded for other teleosts in the same temperate Australian waters. In this respect, P melbournensis exhibits the characteristics of the essentially tropical family to which it belongs. Annuli, which could be detected on the otoliths of c. 40% of fish, suggest that the majority of P. melbournensis were <3 years old

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

The reproductive biology of Acanthopagrus 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 that A. butcheri typically spawns in spring and early summer. However, spawning occurred in salinities ranging from as low as 3.5-8 g L-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 that A. butcheri spawn more than once in a breeding season and demonstrate that the development of its oocytes exhibits group synchrony sensu de Vlaming (1983). The ages and total lengths at which, on average, female and male A. 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 of A. 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 of A. 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 x 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 for A. butcheri is discussed

Variation in age compositions and growth rates of Acanthopagrus butcheri (Sparidae) among estuaries: Some possible contributing factors

Age compositions and growth rates have been determined for populations of Acanthopagrus butcheri in four estuaries and a saline, coastal lake, all of which differ markedly in their morphological, physicochemical, and biotic characteristics. Because the opaque zones in otoliths were shown to form annually, the number of these zones could be used to age individual fi sh. However, the otoliths of fish that were more than six years old had to be sectioned in order to consistently reveal all opaque zones. The number of annuli on scales did not provide reliable estimates of age. Acanthopagrus butcheri, which typically completes its life cycle in estuaries, was represented in each of the fi ve water bodies by fi sh ≥15 years old and lengths and weights >365 mm and >860 g, respectively. The maximum length and weight of A. butcheri recorded in any of the fi ve water bodies were 485 mm and 2196 g, respectively. The values for L∞ in von Bertalanffy growth equations differed significantly between females and males in three of the four estuarine populations (P<0.001 or <0.01), whereas those for both k and t0 differed significantly between the sexes in only one population and then only at P < 0.05. The values for k and L∞ in the von Bertalanffy growth equations differed significantly among both females and males in the four estuaries at either P < 0.001 or P < 0.05. These parameters also differed significantly between the males in Lake Clifton and the males in each estuary, except the Swan River Estuary. Growth rates in two of the more northern water bodies were greater than those in the two southern and cooler estuaries. The pattern of growth in the Moore River Estuary, as reflected by changes in length with time, differed from that in the other four water bodies in that it was initially slower and subsequently did not show such a marked tendency to form an asymptote. The slow initial rate of increase in length in the Moore River Estuary may be related to particularly high densities of juvenile A. butcheri in nearshore, shallow water, as well as to a relatively lower abundance of appropriate food or very low salinities, or to both of the latter. The percentage contribution made by fish ≥5 years was the lowest by far in the Swan River Estuary, which was subjected to the greatest fishing pressure

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. Schoener's 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

Do the dietary compositions of Acanthopagrus butcheri in four estuaries and a coastal lake vary with body size and season and within and amongst these water bodies?

The dietary compositions were determined for Acanthopagrus butcheri in four estuaries and a saline, coastal lake, which vary in the extent, if any, of their connection to the sea and amongst which, in spring and summer, their salinities ranged from 2 to 7‰ in an intermittently open estuary to >40‰ in a normally closed estuary. The dietary compositions of A. butcheri in each of the five water bodies were significantly different, which reflected differences in the abundance of different components of the biota in those systems. Biotic differences amongst water bodies thus accounted for the far larger contributions made to the volume of the stomach contents by the macroalgae Cladophora sp. in the Moore River Estuary on the lower west coast of Australia, by amphipods and decapods in the Swan River Estuary 85 km further south and by polychaetes in the landlocked Lake Clifton a further 85 km further south. The diet of A. butcheri in the Nornalup/Walpole Estuary on the south coast of Western Australia contained atypically large volumes of the seagrass Ruppia megacarpa and teleosts, whereas that in the normally closed Wellstead Estuary, 260 km to the east was characterised by large volumes of the macroalgae Chaetomorpha sp. and a tube-dwelling amphipod. However, there is evidence that A. butcheri selects certain prey, when two or more of the typical prey of A. butcheri are present in the environment, and that it prefers to feed on or above the substratum, rather than within the substratum. The dietary composition of A. butcheri underwent pronounced ontogenetic changes in each water body, these being progressive in estuaries on the lower west coast and abrupt in those on the south coast. Within the upper Swan Estuary, the dietary composition changed in an upstream direction, reflecting changes in the relative abundance of certain benthic macroinvertebrate prey, but did not undergo conspicuous seasonal changes, which is consistent with the lack of any clear cut seasonal changes in the abundance of their major prey

Restocking the Blackwood River Estuary with the Black Bream Acanthopagrus butcheri

The results of this study show that hatchery-reared Black Bream can be used to enhance the stock of the population of this commercially and recreationally important species in the Blackwood River Estuary in which it has become depleted. An initial trial of different stains demonstrated that alizarin complexone was particularly effective for staining the otoliths (ear bones) of Black Bream. The mark on the otoliths, produced by this stain following immersion of hatchery-reared juveniles, was still visible to the naked eye 3.5 years later. Substantial numbers of the stocked Black Bream, which were introduced into the Blackwood River Estuary, were still living at the end of 3.5 years. On average, these individuals did not grow as rapidly as those in the wild population, and unlike the wild fish, not all stocked Black Bream attained maturity by 4 years of age. However, they still grew at a rate that was greater than that in some other estuaries and many did reach maturity by 4 years of age. The Black Bream is thus a particularly good candidate for restocking an estuary as it completes its life cycle within these systems in south-western Australia and consequently any stocked fish are unlikely to move into other estuaries in this region. The ease and relatively low cost of culture of Black Bream and its hardiness and restriction to its natal estuary make the restocking of Black Bream a feasible and economically-viable proposition. This study shows that restocking provides managers with a further and viable option for countering the effects of a decline in a stock of Black Bream in an estuary