D.L. Morgan

Distribution and impacts of introduced freshwater fishes in Western Australia

Abstract This paper presents comprehensive distributional data, from over 1300 sites, on introduced freshwater fishes in Western Australia. Currently, there are 10 species of introduced freshwater fish established in the inland waters of Western Australia. Most of the introduced fishes found here are those that have formed feral populations elsewhere in the world, and include members of the Salmonidae, i.e., rainbow trout (Oncorhynchus mykiss) and brown trout (Salmo trutta); Cyprinidae, i.e., goldfish (Carassius auratus) and carp (Cyprinus carpio); Poeciliidae, i.e., mosquitofish (Gambusia holbrooki), one‐spot livebearer (Phalloceros caudi‐maculatus), guppy (Poecilia reticulata), and swordtail (Xiphophorus hellerii); Percidae, i.e., redfin perch (Perca fluviatilis), and Cichlidae, i.e., Mozambique mouthbrooder or tilapia (Oreochromis mossambicus). More recently, the eastern Australian silver perch (Bidyanus bidyanus) (Terapontidae), which was introduced for aquaculture, has been captured in the Swan River near Perth. It is not known whether this population is self‐maintaining. The majority of introduced species are confined to the south‐west, although four and one species have been recorded from the Pilbara and Kimberley, respectively. Some species are extremely common and widespread, e.g., G. holbrooki and P. fluviatilis, whereas others are far more restricted and may be confined to between one and three catchments, e.g., C. carpio, P. caudimaculatus, P. reticulata, X. hellerii, O. mossambicus, and B. bidyanus. The impact of these introduced fishes on native species varies, but ranges from predation, e.g., O. mykiss, S. trutta, G. holbrooki, and P. fluviatilis, to aggressiveness, e.g., G. holbrooki, X. hellerii, and O. mossambicus, and competition for food and habitat.

Co-invaders: The effects of alien parasites on native hosts

Graphical abstract

Distribution, biology and likely impacts of the introduced redfin perch (Perca fluviatilis) (Percidae) in Western Australia

Within Western Australia, Perca fluviatilis is restricted to the south-western corner and is found in the Swan, Murray, Harvey, Collie, Capel, Carbunup, Margaret, Blackwood, Donnelly and Warren river systems. Age data suggest it was released into Big Brook Dam (Warren River) in 1992 or 1993, where it has since played a role in eliminating the native teleosts. Its success here is attributed to a young age at maturity, rapid growth (compared with populations elsewhere), predatory nature, large size (compared with native fish), broad environmental and habitat tolerances, and absence of predators. Gonadal development initiates in late summer, with peak spawning between August and September. Males and females attained maturity in their first and second years, respectively, which is earlier than reported for most Northern Hemisphere populations and can be attributed to their rapid growth here because of the warmer climate. At ages 1, 2, 3, 4 and 5, males, on average, attained 102, 159, 206, 246 and 280 mm total length (TL) and females had attained 104, 166, 228, 290 and 351 mm TL at the respective ages. Diets of fish 50–200 mm TL comprised mainly small aquatic invertebrates, whereas larger fish preyed almost exclusively on decapods, mainly marron (Cherax tenuimanus), and teleosts.

Variation in Life History of Land-Locked Lacustrine and Riverine Populations of Galaxias maculatus (Jenyns 1842) in Western Australia

Galaxias maculatus is one of the most naturally widely distributed species in the world yet there is no published literature on the biology of Western Australian populations. Galaxias maculatus in the rivers of the south coast of Western Australia inhabit an environment that is variable and at times unpredictable. By examining trends in gonadal development, lengths at first maturity, growth and appearance and persistence of larvae of G. maculatus in two saline rivers (Jerdacuttup River and Oldfield River) and one freshwater lake (Moates Lake), the life histories of populations in contrasting environments were determined. The stable conditions that prevail in the low salinity, cool waters of Moates Lake have fostered an extremely protracted breeding and larval recruitment period (year round) in comparison to limited recruitment in the riverine environments which experience less predictable flow events and water quality (salinity). An upstream migration for breeding in the Jerdacuttup and Oldfield rivers is similar to land-locked G. maculatus in south-eastern Australia and is a reversal of the downstream migration in Moates Lake or populations with marine larval dispersal, i.e. diadromous populations. Differences in population demographics existed between these habitats, with smaller maximum sizes and significantly smaller sizes at maturation occurring in the rivers compared to the lake. In Moates Lake approximately 93, 6 and 1% were 0+, 1+ and 2+, respectively; while cohort progression in the rivers suggests that most fish do not live beyond their first year. As an adaptable opportunist, G. maculatus can modify its life history strategy at a local level to persist in varied and sometimes unpredictable environments.

Ontogenetic depth partitioning by juvenile freshwater sawfish (Pristis microdon: Pristidae) in a riverine environment

The freshwater sawfish (Pristis microdon) is a critically endangered elasmobranch. Ontogenetic changes in the habitat use of juvenile P. microdon were studied using acoustic tracking in the Fitzroy River, Western Australia. Habitat partitioning was significant between 0+ (2007 year class) and larger 1+ (2006 year class) P. microdon. Smaller 0+ fish generally occupied shallower water ( 0.6 m. Significant differences in hourly depth use were also revealed. The depth that 1+ P. microdon occupied was significantly influenced by lunar phase with these animals utilising a shallower and narrower depth range during the full moon compared with the new moon. This was not observed in 0+ individuals. Habitat partitioning was likely to be related to predator avoidance, foraging behaviours, and temperature and/or light regimes. The occurrence of 1+ P. microdon in deeper water may also result from a need for greater depths in which to manoeuvre. The present study demonstrates the utility of acoustic telemetry in monitoring P. microdon in a riverine environment. These results demonstrate the need to consider the habitat requirements of different P. microdon cohorts in the strategic planning of natural resources and will aid in the development of management strategies for this species.

A global assessment of freshwater fish introductions in mediterranean-climate regions

Mediterranean-climate regions (med-regions) are global hotspots of endemism facing mounting environmental threats associated with human-related activities, including the ecological impacts associated with non-native species introductions. We review freshwater fish introductions across med-regions to evaluate the influences of non-native fishes on the biogeography of taxonomic and functional diversity. Our synthesis revealed that 136 freshwater fish species (26 families, 13 orders) have been introduced into med-regions globally. These introductions, and local extirpations, have increased taxonomic and functional faunal similarity among regions by an average of 7.5% (4.6–11.4%; Jaccard) and 7.2% (1.4–14.0%; Bray–Curtis), respectively. Faunal homogenisation was highest in Chile and the western Med Basin, whereas sw Cape and the Aegean Sea drainages showed slight differentiation (decrease in faunal similarity) over time. At present, fish faunas of different med-regions have widespread species in common (e.g. Gambusia holbrooki, Cyprinus carpio, Oncorhynchus mykiss, Carassius auratus, and Micropterus salmoides) which are typically large-bodied, non-migratory, have higher physiological tolerance, and display fast population growth rates. Our findings suggest that intentional and accidental introductions of freshwater fish have dissolved dispersal barriers and significantly changed the present-day biogeography of med-regions across the globe. Conservation challenges in med-regions include understanding the ecosystem consequences of non-native species introductions at macro-ecological scales.

Distribution and biology of Galaxias truttaceus (Galaxiidae) in south-western Australia, including first evidence of parasitism of fishes in Western Australia by Ligula intestinalis (Cestoda)

The freshwater trout minnow, Galaxias truttaceus, is restricted to the small catchments of the Goodga and Kalgan Rivers in Western Australia. Its large geographic separation from populations in south-eastern Australia, and subsequent reproductive isolation and variation in the prevailing environmental conditions, has created marked differences in biology (and morphology) between the eastern and western populations of G. truttaceus. The biology (spawning period, longevity, growth rates, diet and parasitism) of G. truttaceus in the Goodga River is described and then compared with information on the biology of diadromous and landlocked populations in south-eastern Australia (i.e. Tasmania) (see Humphries 1989). In the Goodga River, ca. 34 and 8% of males and females, respectively, attain maturity at the end of their first year, while only four mature males and one mature female 0+ fish were found in the Tasmanian populations. Adults migrate upstream prior to spawning which peaks during April and May. Larvae, which hatch at ca. 6.5 mm (cf. 7.5–9.0 mm in Tasmania), move downstream into Moates Lake for a few months before re-entering the river. Of the 810 G. truttaceus collected, ca. 53, 34, 10, 2, 1, 0.2 and 0.1% belonged to the 0+, 1+, 2+, 3+, 4+, 5+ and 7+ age classes, respectively. In contrast, the Tasmanian populations have a much higher proportion of older fish. At the end of their first, second and third years, the males on average attain 60, 84 and 95 mm total length (TL), respectively, whereas females attain 63, 89 and 103 mm TL, respectively at those ages. Only one fish > 140 mm TL was captured, which contrasts with the Tasmanian fish, where a substantial proportion are > 140 mm TL. The diet of fish > 40 mm TL consisted of between 65 and 96% terrestrial fauna (mainly coleopterans and hymenopterans) in the different seasons. Larval fish diets were largely comprised of copepods.The occurrence of the introduced cestode Ligula intestinalis in ca. 7% of G. truttaceus represents the first record of this parasite in Western Australia. It was found to cause gonadal retardation and gross morphological deformities, the latter of which possibly increases the risk of avian predation.

Salinity tolerances of endemic freshwater fishes of south-western Australia: implications for conservation in a biodiversity hotspot

Secondary salinisation represents an important threat to terrestrial and aquatic habitats throughout the world. In south-western Australia, widespread salinisation of waterways has caused large range reductions in the highly endemic freshwater fish fauna. We hypothesised that differences in the distributions of three fish species within the salinised Blackwood River would be related to their salinity tolerances. Galaxias occidentalis was widespread throughout the catchment, whereas Nannoperca vittata was restricted to the main channel and freshwater tributaries of the lower catchment, and Nannatherina balstoni was restricted to those tributaries and a perennial section of the main channel that received a considerable amount of fresh groundwater. Acute salinity tolerances (Effect Concentrations) of G. occidentalis and N. vittata were similar (EC50 ∼14.6gL-1), but significantly greater than that of N. balstoni (EC50 ∼8.2gL-1). The greater geographical range of G. occidentalis, compared with N. vittata, may be a consequence of the dispersal capability of the former species, and the lower salinity tolerance of N. balstoni contributes to its highly restricted range. The findings demonstrate that secondary salinisation has greatly impacted these freshwater fishes, and fresh groundwater refuges, predicted to decrease due to reduced rainfall, appear crucial in maintaining remnant populations.

Parasites of native and exotic freshwater fishes in south-western Australia

In this study, 1429 fishes of 18 different species (12 native and six exotic) were sampled from 29 localities to compare the levels of parasitism between native and exotic fish species and to examine the relationship between environmental degradation and parasite diversity. Forty-four putative species of parasites were found and most of these appear to be native parasites, which have not previously been described. Two parasite species, Lernaea cyprinacea and Ligula intestinalis, are probably introduced. Both were found on or in a range of native fish species, where they may cause severe disease. Levels of parasitism and parasite diversity were significantly greater in native fishes than in exotic species, and this may contribute to an enhanced demographic performance and competitive ability in invading exotics. Levels of parasitism and parasite diversity in native fishes were negatively related to habitat disturbance, in particular to a suite of factors that indicate increased human use of the river and surrounding environment. This was due principally to the absence in more disturbed habitats of a number of species of endoparasites with complex life cycles, involving transmission between different host species.

Age Composition, Growth and Reproductive Biology of the Salamanderfish Lepidogalaxias salamandroides: A Re-examination

This study has determined the age and size compositions, growth rate and reproductive biology of Lepidogalaxias salamandroides using data for fish of known sex and age and the monthly trends exhibited by various gonadal variables, including the sizes and stages of the oocytes. The results resolve conflicting conclusions drawn by other workers concerning certain aspects of the biology of this freshwater species and expands our knowledge of this teleost. Our results are based on data derived from samples collected from small, ephemeral acidic pools in south-western Australia in 22 consecutive months. Although ca. 78% of the fish caught belonged to the 0+ age class, substantial numbers of the 1+ and 2+ age classes and some 3+ and 4+ fish were caught. Spawning occurs between late May and late August, with peak activity in late July and early August. During the first year of life, growth is initially rapid, but then ceases in the weeks immediately prior to and during the period when the habitat becomes dry and fish aestivate, before recommencing in autumn as the pools again become filled with water. The growth coefficient (K) in the von Bertalanffy growth equation was lower for females (0.63) than males (1.28), reflecting the greater growth undergone by females after the first year of life. Maturity was attained by ca. 28% of the females and ca. 26% of the males that reached the end of their first year of life and by all fish that reached the end of subsequent years of life. The L50s for females and males at first maturity were 43.2 and 38.6 mm TL, respectively. The mean fecundity was only 82.4, reflecting a combination of a small body size and a relatively large egg (diameter=1.8 mm). Lepidogalaxias salamandroides is a multiple spawner, which increases the chances of some eggs and newly-hatched embryos encountering a period of favourable environmental conditions during the spawning period, which is characterised by bouts of heavy rainfall. The ratio of females to males was essentially parity in the 0+ and 1+ age classes and in all age classes collectively. When testes commence maturing for the first time, the anal fin of males starts to become modified to form a structure that facilitates the transfer of sperm to the female, and it remains modified throughout the rest of life.