Galaxiid_ascent

I can jump (and climb) weirs

By Dr Paul Close, Centre of Excellence in Natural Resource Management, UWA, Albany

The peacefulness of a river bank, somewhere, anywhere, interrupted by an exclamation “You little (insert appropriate expletive here)”, followed by rustling in the leaf litter and a ‘plop’ as a researcher struggles to find an escapee before throwing back (or releasing it un-ceremonially) an uncooperative fish – unwilling to lie nicely on the measurement board. Our experiences of measuring fish might suggest that native species have an ability to ‘jump’, however, documented observations are few and far between.

Sitting on the edge of a fishway one evening in southwestern Australia – a few good mates helping out, setting nets to catch upstream migrating juvenile stages of the Spotted trout minnow (Galaxias truttaceus) – one says, “a fish just climbed that weir”. Disbelieving, we all peered closer – thinking to ourselves…fishway….weir….climbing fish..???  Sure enough, we observed numerous fish, shunning the vertical slot fishway and successfully ascending the vertical weir wall (see Fig. 1a). During their ascent, fish maintained connection with the weir wall and used a modified swimming technique or ‘wriggle’ movement. Some fish were also observed to ‘rest’, mid ascent, maintaining a stationary position on the vertical weir wall. Approximately 30-40% of these climbers successfully reached a narrow angled skirt below the metal v-notch baffle (Fig. 1b). Up to 30 fish were observed congregated to the side of the flow and were exposed to the air, presumably for periods of minutes, but were kept moist with regular ‘water splash’. The fact that these individuals were capable of tolerating presumably short periods of exposure to air is interesting, although not unique in the Galaxiidae, which includes species capable of both long-term (e.g. aestivation) and short term exposure. From here, some fish successfully ascended the metal baffle using the same ‘climbing’ technique described above, however, did so with sufficient burst speed to achieve significant separation from the baffle and water surface (i.e. ‘jump’) and re-enter the water in the weir pool approximately 20cm upstream from the metal baffle. Prior to reaching the weir wall, these fish also negotiated turbulent and high velocity water created by the weir skirt (Fig 1a).

The ability of this species to ‘climb’ the vertical weir wall and to ‘jump’ contrasts with most other Australian native species and particularly their juvenile stages; less than 5% of approximately 205 native Australian freshwater species are thought to posses some ability to climb and jump. While the relative swimming ability of some large-bodied Australian freshwater species and their life stages have been documented, similar published information is generally lacking for the majority of small-bodied Australian native freshwater fish species.   Further consideration of the climbing and jumping capabilities is required for freshwater migratory species to improve our ability to prioritise mitigation works on instream barriers and help improve fishway design.

These observations were made as part of a broader study on the threatened freshwater fish of south-western Australia, funded by the Western Australian Government’s State Natural Resource Management Program and carried out in collaboration with David Morgan and Stephen Beatty (Freshwater Fish Group and Fish Health Unit, Murdoch University) Tom Ryan (Centre of Excellence In Natural Resource Management, The University of Western Australia) and Craig Lawrence (Western Australian Fisheries and Marine Research Laboratories). This work has been recently published in the Australian Journal of Zoology (DOI: ZO14004).

 

Paul is from Fish Ecology Research and Monitoring in the Centre of Excellence in Natural Resource Management, University of Western Australia, Albany.

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