Alien fish ascendancy and native fish extinction: ecological history and observations on the Lower Goodradigbee River, Australia

Abstract

Context. The Murray-Darling Basin -Australia's largest river systemis heavily dominated by alien fish. Native fish species have suffered numerous localised extinctions and ~47% are listed on federal and/or state threatened species lists. Aims. This paper explores the hypothesis that alien fish and alien fish stockings can be the primary cause of decline and localised extinction of large-bodied native fish species, as opposed to habitat degradation and river regulation. The Lower Goodradigbee River, which is unregulated, in excellent instream health over the great majority of its course, and replete with high quality habitat, is utilised as a case study. Methods. I investigated the hypothesis by synthesising historical records with contemporary scientific research and recent field observations. The role of alien fish species, particularly alien trout species (Oncorhynchus mykiss and Salmo trutta) and constant stockings of them, were closely examined. Results. Data support the hypothesis that domination by alien trout species and their continual stocking have lead to historical declines and localised extinctions of large-bodied native fish species. Continued alien trout stockings, along with more recent invasions of alien carp (Cyprinus carpio) and alien redfin perch (Perca fluviatilis), are inhibiting native fish recovery. A suspected field sighting of the alien fish pathogen atypical Aeromonas salmonicida is reported, and the status of the declining native crayfish Murray cray (Euastacus armatus), and potential alien fish impacts upon them, are examined. Conclusions. The impacts of alien fish and alien fish stocking in Australia require major re-evaluation and dedicated research. Implications. It is strongly recommended that stocking of alien trout into the Lower Goodradigbee River for angling cease in order to conserve surviving native fish and Murray cray populations. Conservation stockings to effect a Murray cod (Maccullochella peelii) recovery in the Lower Goodradigbee River are warranted.

Quantifying the contributions of tributaries to large‐river fish populations through mark‐recapture modeling

“…Trout have negative impacts on native fish abundance and distribution in Bright Angel Creek and other tributaries (Whiting et al 2014;Spurgeon et al 2015a;Healy et al 2020b). Rainbow Trout can have negative population-level effects on native fishes throughout their introduced range (Shelton et al 2015;Hasegawa 2020;Kaminskas 2021), which include negative effects on survival, growth, and recruitment of Humpback Chub in the Grand Canyon (Yackulic et al 2018;Dzul 2021;Healy et al 2022a). Flooding may also have both positive and negative impacts on translocated Humpback Chub populations (Healy et al 2022a).…”

“…Rainbow Trout can have negative population‐level effects on native fishes throughout their introduced range (Shelton et al. 2015; Hasegawa 2020; Kaminskas 2021), which include negative effects on survival, growth, and recruitment of Humpback Chub in the Grand Canyon (Yackulic et al. 2018; Dzul 2021; Healy et al.…”

Freshwater fish as hosts for parasites in Australia: How much do we really know?

“…However, the impacts of climate change on parasitic diseases of freshwater animals have received very little attention (Lymbery et al, 2020). Combined with the impacts of invasive species, leading to severe declines in fish species diversity and abundance (Kaminskas, 2022), levels of parasitism and parasite diversity in native fish species have been found to be negatively related to habitat disturbance (Lymbery et al, 2010). The combination of all of these effects could lead to substantial losses of fish populations and their parasites.…”

Age-Related Changes in Survival Behaviour in Parasite-Free Hatchery-Reared Rainbow Trout (Oncorhynchus mykiss)

“…Ecological research into the impacts of trout on Australian ecology is increasing and is making the impacts of trout on the environment and native fauna more recognised [16]. Trout pose a threat to native fish through direct predation and out-competing native species [14,17] which can lead to population fragmentations and disrupt the ranges occupied and available to native species [15,18]. Trout are a predatory species that feed on aquatic fauna such as small fish and crustaceans, and have been known to eat frogs [12].…”

“…Trout are a predatory species that feed on aquatic fauna such as small fish and crustaceans, and have been known to eat frogs [12]. For example, native Australian species such as the endangered stocky galaxiid (Galaxias tantangara) are highly affected by trout predation to the point of local extinction in some areas of NSW [12,18]. Trout research focuses on either the impacts of their release on the environment or the management strategies of hatchery trout.…”