Distribution, identification and biology of freshwater fishes in south-western Australia

A total of 410 sites in the major watersheds in the south-western corner of Australia, bounded by Bunbury in the north-west and just east of Albany in the south-east, were sampled for fish. Sampling of the different sites was carried out using one or more of the following methods, namely seine netting, scoop netting, trapping and electrofishing to catch juvenile and adult fish, and light trapping, scoop netting and haul netting to collect larval fish. The fish caught at each site were identified and the number of each species recorded. These data were then collated, both with those derived from the studies of Christensen (1982) and Jaensch (1992) and with the records of the Western Australian Museum (WAM), to elucidate the distributions of each of the fish species found in freshwater in south-western Australia. The eight species endemic to south-western Australia are Tandanus bostocki, Lepidogalaxias salamandroides, Galaxias occidentalis, Galaxiella nigrostriata, Galaxiella munda, Bostockia porosa, Edelia vittata and Nannatherina baIstoni. The other species found in this region include Galaxias truttaceus and Galaxias maculatus, which are also represented in south-eastern mainland Australia and Tasmania, the anadromous lamprey Geotria australis, and those teleosts which are commonly found in freshwater, but belong to predominantly marine families, i.e. Leptatherina wallacei, Pseudogobius olonum and Afurcagobius suppositus. Finally, there are those species that have been introduced into the region, i.e. Oncorhynchus mykiss, Salmo trutta, Gambusia holbrooki and Perca fluviatilis

Distribution of freshwater fish in the south-western corner of Australia

This study investigates the distribution of freshwater fishes in the Busselton to Walpole Region. A total of 311 sites in 19 major catchments along the south-west coast from Capel to Walpole, were sampled using a variety of methods. New data was collated with that from previous studies to generate 15 species distribution maps. Habitat and life history notes and recommendations for conservation are made for each species. Changes in fish distribution are also commented upon. This study contributes to series of documents published for the purposes of water allocation planning in the Busselton to Walpole Region

Oxygen consumption in ammocoetes of the lamprey Ichthyomyzon hubbsi Raney

1. A continuous flow respirometer suitable for measuring oxygen consumption in some small burrowing aquatic animals is described. 2. Rates of oxygen consumption in ammocoetes of the lamprey Ichthyomyzon hubbsi are low, with mean values at 15.5 °C ranging from 38.8 to 97.1 µl/g/h for large (3.44 g) and small (0.14 g) animals respectively. 3. A Q10 of 3.6 was found for medium-size animals (1.18 g) between 3.5 and 22.5 °C. 4. The slope of the logarithmic linear regression relating weight and oxygen consumption was 0.718 at 15.5°C. 5. The rates of oxygen consumption are discussed with respect to the ecology of ammocoetes and compared with those obtained for other lower vertebrates

Variations in biological characteristics of temperate gonochoristic species of Platycephalidae and their implications: A review

This review provides a composite account of the biological characteristics of the temperate gonochoristic species of the Platycephalidae. Initially, data were obtained for the five abundant platycephalid species in south-western Australia, which each came from either over bare substrata or seagrass and from either estuaries, marine coastal waters or marine embayments. The von Bertalanffy growth curves for females and males of each species differed significantly, with females having a greater TL∞ and lower growth coefficient k. From tests using their upper deciles, the total length (TL) attained by the largest females of each species was significantly greater than that of their males, whereas such a trend did not occur with age. The ratio of females to males in each abundant age class, and overall, exceeded parity for four of the five species (typically P < 0.001) and increased with increasing TL. Mortality estimates, which were similar for each sex of each species, suggest that Platycephalus speculator has been substantially exploited in a seasonally-closed estuary in which it completes its whole life cycle. The above and other biological data for the five species were collated with those published previously for two of those species and five other platycephalid species in south-eastern Australia and one in Japan and another in the Suez Canal, yielding the following conclusions for gonochoristic species of the Platycephalidae. Females attain a larger size than males, the extent varying markedly among species, whereas the longevities of the two sexes of each platycephalid species are similar. The maximum TLs and ages of the various species range widely, with values for females, for example, extending from 221 mm for Ambiserrula jugosa to 985 mm for Platycephalus fuscus and from four years for A. jugosa to 26 years for Platycephalus conatus. The overall ratio of females to males is positively related to the extent to which both the maximum TLs and TL∞s of the females exceed those of males. The above trends imply that growth, rather than differences in longevity and/or mortality, is the main factor contributing to the marked differences in sex ratios, which ranged widely from parity to 3.2:1. As the length at maturity, but not typically age at maturity, was greater for females than males, maturity is also related mainly to growth. The spawning periods of the various species overlapped, commencing as early as late winter/early spring, as temperatures started rising with four species and later in late spring/early summer with the three species found in estuaries, which would be advantageous as spawning in estuaries would occur when environmental conditions are most favourable for spawning success and larval retention

Can biotic indicators distinguish between natural and anthropogenic environmental stress in estuaries?

Because estuaries are naturally stressed, due to variations in salinity, organic loadings, sediment stability and oxygen concentrations over both spatial and temporal scales, it is difficult both to set baseline reference conditions and to distinguish between natural and anthropogenic environmental stresses. This contrasts with the situation in marine coastal and offshore locations. A very large benthic macroinvertebrate dataset and matching concentrations for seven toxic heavy metals (i.e. Cr, Ni, Cu, Zn, Cd, Hg and Pb), compiled over three years as part of the UK's National Marine Monitoring Programme (NMMP) for 27 subtidal sites in 16 estuaries and 34 coastal marine sites in the United Kingdom, have been analysed. The results demonstrate that species composition and most benthic biotic indicators (number of taxa, overall density, Shannon–Wiener diversity, Simpson's index and AZTI's Marine Biotic Index [AMBI]) for sites in estuarine and coastal areas were significantly different, reflecting natural differences between these two environments. Shannon–Wiener diversity and AMBI were not significantly correlated either with overall heavy metal contaminant loadings or with individual heavy metal concentrations (‘normalized’ as heavy metal/aluminium ratios) in estuaries. In contrast, average taxonomic distinctness (Δ+) and variation in taxonomic distinctness (Λ+) did not differ significantly between estuarine and coastal environments, i.e. they were unaffected by natural differences between these two environments, but both were significantly correlated with overall heavy metal concentrations. Furthermore, Δ+ was correlated significantly with the Cu, Zn, Cd, Hg and Pb concentrations and Λ+ was correlated significantly with the Cr, Ni, Cu, Cd and Hg concentrations. Thus, one or both of these two taxonomic distinctness indices are significantly correlated with the concentrations for each of these seven heavy metals. These taxonomic distinctness indices are therefore considered appropriate indicators of anthropogenic disturbance in estuaries, as they allow a regional reference condition to be set from which significant departures can then be determined

The Contrasting Ecology of Temperate Macrotidal and Microtidal Estuaries

Tidal range is a master factor governing the differences in physico-chemical and biological characteristics between microtidal (2 m) estuaries, which, for convenience, thus include mesotidal estuaries (2–4 m). Microtidal estuaries differ from macrotidal estuaries in geomorphology, tidal water movements, salinity regimes, residence times, turbidity, sedimentology and intertidal area. Consequently, their phytoplankton, microphytobenthos and macrophytes communities differ in biomass and production, areal extent, distribution patterns and composition. Mesozooplankton comprise predominantly autochthonous species in microtidal estuaries and allochthonous species in macrotidal estuaries. Meiobenthos in microtidal estuaries have greater densities in subtidal than intertidal areas and species persist along the estuary. Macrobenthos is dominated by small deposit-feeding species in microtidal estuaries, whereas macrotidal estuaries contain some larger species and suspension feeders. Species richness and abundance of estuarine-resident fish species and the contributions of diving piscivorous birds and wading invertebrate-feeding birds are greater in microtidal estuaries. As paradigms regarding estuarine ecology have been based mainly on northern hemisphere macrotidal systems, this review has redressed this imbalance by detailing the extent of differences between microtidal and macrotidal estuaries. In particular, it uses data and case studies for southern hemisphere microtidal systems to demonstrate that the physico-chemical characteristics and ecology of the main flora and fauna of microtidal estuaries are frequently not consistent with those paradigms

Performance and contribution to commercial catches and egg production by restocked Acanthopagrus butcheri (Sparidae) in an estuary

This study has explored whether the restocked fish of a species, which is confined to an estuary, perform as well as its wild stock, and has estimated their contribution to the commercial fishery and egg production. The biological characteristics of the 2001 and 2002 year classes of Acanthopagrus butcheri, which had been cultured and introduced into the Blackwood River in south-western Australia at seven and four months old, respectively, were thus determined from samples collected regularly between 2002 and 2014. The restocked fish could always be distinguished from the wild stock because their otoliths retained the pink colouration of the alizarin complexone with which they had been stained prior to release. Detailed analyses demonstrated the growth and maturity schedules of restocked fish were only slightly inferior to those of the wild stock and the mean gonad weights of the females of these two groups did not differ significantly in any month. As increasing numbers of restocked A. butcheri attained the MLL of 250 mm for retention, their contribution to the commercial fishery increased from 6% in 2005 to 74% in 2010. That contribution subsequently declined to 39% in 2012 and 10% in 2014, due predominantly to the introduction of the very strong 2008 year class in the commercial catches, the first substantial recruitment into the population since 1999. Restocked fish were estimated as contributing ~55% to the eggs produced in 2008, suggesting that substantial numbers of the 2008 year class were derived from spawning by restocked fish. The results of this and a previous genetic study imply that restocking is an effective and appropriate way for replenishing stocks of an estuarine species such as A. butcheri, especially as its recruitment is highly episodic

Factors influencing the timing and frequency of spawning and fecundity of the goldlined seabream (Rhabdosargus sarba) (Sparidae) in the lower reaches of an estuary

We have studied the reproductive biology of the goldlined seabream (Rhabdosargus sarba) in the lower Swan River Estuary in Western Australia, focusing particularly on elucidating the factors influencing the duration, timing, and frequency of spawning and on determining potential annual fecundity. Our results demonstrate that 1) Rhabdosargus sarba has indeterminate fecundity, 2) oocyte hydration commences soon after dusk (ca. 18:30 h) and is complete by ca. 01:30-04:30 h and 3) fish with ovaries containing migratory nucleus oocytes, hydrated oocytes, or postovulatory follicles were caught between July and November. However, in July and August, their prevalence was low, whereas that of fish with ovaries containing substantial numbers of atretic yolk granule oocytes was high. Thus, spawning activity did not start to peak until September (early spring), when salinities were rising markedly from their winter minima. The prevalence of spawning was positively correlated with tidal height and was greatest on days when the tide changed from flood to ebb at ca. 06:00 h, i.e., just after spawning had ceased. Because our estimate of the average daily prevalence of spawning by females during the spawning season (July to November) was 36.5%, individual females were estimated to spawn, on average, at intervals of about 2.7 days and thus about 45 times during that period. Therefore, because female R. sarba with total lengths of 180, 220, and 260 mm were estimated to have batch fecundities of about 4500, 7700, and 12,400 eggs, respectively, they had potential annual fecundities of about 204,300, 346,100 and 557,500 eggs, respectively. Because spawning occurs just prior to strong ebb tides, the eggs of R. sarba are likely to be transported out of the estuary into coastal waters where salinities remain at ca. 35‰. Such down-stream transport would account for the fact that, although R. sarba exhibits substantial spawning activity in the lower Swan River Estuary, few of its early juveniles are recruited into the nearshore shallow waters of this estuary

Factors influencing marked variations in the frequency and timing of bar breaching and salinity and oxygen regimes among normally-closed estuaries

The aim of this study was to determine the factors that influence the breaching of the bar at the mouth of estuaries that are normally-closed to the ocean and the trends exhibited by salinity and oxygen concentration in those systems during protracted periods of closure. Collated data for 1972 to 2016 demonstrate that the frequency and timing of bar breaching of three normally-closed estuaries, located along 100 km of coastline in a low rainfall region of temperate south-western Australia, differ markedly. Breaching occurred in 12 years in Stokes Inlet, ≥ eight in Hamersley Inlet and only three in Culham Inlet. Breaching in each estuary was related to relatively very high volumes of fluvial discharge. Although breaching typically occurred following exceptional winter rainfall in Stokes Inlet, whose catchment received by far the greatest winter rainfall, it usually took place in Hamersley and Culham inlets following atypically high summer and autumn rainfall, often associated with cyclonic activity. Salinity, oxygen concentration and water temperature were measured seasonally between summer 2002 and spring 2004, during which period each of these estuaries was closed to the ocean following major natural breaches of each system and the influx of substantial volumes of oceanic water. Mean salinities in the estuary basins rose by markedly different extents during the three years of closure. They thus increased from 30 in Stokes Inlet, 35 in Hamersley Inlet and 52 in Culham Inlet, to maxima of 64, 143 and 293, respectively, with the highest individual salinity of 313 in the latter estuary the greatest yet recorded for any estuary worldwide. In contrast, oxygen concentrations declined to minima of 5.5, 2.5 and 0.6 mg L−1, respectively, and were inversely related to salinity in the basin of each estuary (r = −0.7 to −0.8). Although salinities in the main river of each estuary did not become as highly elevated as in its basin, they still reached 221 in that of Culham Inlet. The very different extents to which salinity increased and oxygen concentration declined among the three estuaries reflect variations in amount of rainfall and thus fluvial discharge, the area and depth of basin relative to discharge and resilience of the bar at the estuary mouth. Thus, while a suite of factors contribute to bar breaching and physico-chemical trends in normally-closed estuaries, variations in their importance as ‘drivers’ among estuaries should be considered when studying the ecology of a given system

Differential changes in production measures for an estuarine-resident sparid in deep and shallow waters following increases in hypoxia

This study determined how productivity measures for a fish species in different water depths of an estuary changed in response to the increase in hypoxia in deep waters, which had previously been shown to occur between 1993–95 and 2007–11. Annual data on length and age compositions, body mass, growth, abundance, biomass, production and production to biomass ratio (P/B) were thus determined for the estuarine-resident Acanthopagrus butcheri in nearshore shallow (<2 m) and offshore deep waters (2–6 m) of the upper Swan River Estuary in those two periods. Length and age compositions imply that the increase in hypoxia was accompanied by the distribution of the majority of the older and larger A. butcheri changing from deep to shallow waters, where the small fish typically reside. Annual densities, biomass and production in shallow waters of <0.02 fish m−2, 2–4 g m−2 and ∼2 g m−2 y−1 in the earlier period were far lower than the 0.1–0.2 fish m−2, 8–15 g m−2 and 5–10 g m−2 y−1 in the later period, whereas the reverse trend occurred in deep waters, with values of 6–9 fish net−1, 2000–3900 g net−1, 900–1700 g net−1 y−1 in the earlier period vs < 1.5 fish net−1, ∼110 g net−1 and 27–45 g net−1 y−1 in the later period. Within the later period, and in contrast to the trends with annual abundance and biomass, the production in shallow waters was least during 2008/09, rather than greatest, reflecting the slow growth in that particularly cool year. The presence of substantial aggregations of both small and large fish in shallow waters accounts for the abundance, biomass and production in those waters increasing between those periods and thus, through a density-dependent effect, provide a basis for the overall reduction in growth. In marked contrast to the trends with the other three production measures, annual production to biomass ratios (P/B) in shallow waters in the two years in the earlier period, and in three of the four years of the later period, fell within the same range, i.e. 0.6–0.9 y−1, but was only 0.2 y−1 in 2008/09, reflecting the poor growth in that year. This emphasises the need to obtain data on P/B for a number of years when considering the implications of the typical P/B for a species in an estuary, in which environmental conditions and the growth of a species can fluctuate markedly between years