Too little but not too late? Biology of a recently discovered and imperilled freshwater fish in a drying temperate region and comparison with sympatric fishes

Abstract

1. Small-bodied freshwater fishes are commonly overlooked in threatened species management despite being highly imperilled. Before this study, the newly described little pygmy perch (Nannoperca pygmaea) was known from only 0.06 km 2 of habitat in a single catchment in south-western Australia and a lack of knowledge prevented an understanding of its conservation status and priority actions.2. The present study determined the distribution, biology, and movement patterns of N. pygmaea and compared these with other small, sympatric percihthyids to assess its conservation status and likely resilience to threatening processes.3. The current 'extent of occurrence' of N. pygmaea was determined to be 3,420 km 2 and the 'area of occupancy' was 10 km 2 . Nannoperca pygmaea inhabited permanent refuge pools in the main stem of an ephemeral, secondarily salinized catchment where salinities remained <6 ppt during summer. 4. During winter N. pygmaea undertook a short upstream migration into a seasonally flowing freshwater tributary to serially spawn. The timing of reproduction was partitioned among three sympatric pygmy perches within the austral winter/spring period.5. The species qualifies as 'Endangered' under the IUCN Red List assessment criteria.Its restriction to freshwater refugia within salinized rivers suggests that N. pygmaea may have a limited salinity tolerance similar to the sympatric, threatened Nannatherina balstoni, and that the species is susceptible to prolonged drought, drying of critical baseflow refuges, increasing salinization, and introductions of alien species.6. The study serves as an example that small-bodied freshwater fishes need greater research attention to understand the biological and environmental mechanisms underpinning their decline.

When and where are catfish fat fish? Hydro‐ecological determinants of energy reserves in the fork‐tailed catfish, Neoarius graeffei, in an intermittent tropical river

“…Lastly, our results have implications for how the scientific and management community assess the health of intermittent streams and rivers in areas of the world that are experiencing greater drying due to anthropogenic climate change (Allen et al, 2020;Kerezsy et al, 2017;Stevenson & Sabater, 2010).…”

Net design for selective control of the “plague minnow” Gambusia holbrooki that minimises impact on native Australian fishes

“…Two sets were conducted a fortnight apart in two separate river pools c . 150 river metres apart in February–March (austral summer‐autumn) 2014 (see Allen et al ., 2020; Morgan et al ., 2013). A conventional fyke net of the same total fishing dimensions but with a single opening and pocket was deployed concurrently with the stacked fyke net to compare catch rates between the two methods.…”

Long-term climatic stability drives accumulation and maintenance of divergent freshwater fish lineages in a temperate biodiversity hotspot

“…Nannoperca vittata is significantly more widespread and occurs throughout the HRP, whereas N. pygmaea has a restricted occurrence within only three rivers and a lake in the south-eastern HRP (Allen et al, 2020). While both species show some similar ecological characteristics such as body plan and reproductive strategy, they show marked differences in body size, morphology, growth rate, salinity tolerance and reproductive timing (Allen et al, 2020). Additionally, clear-cut genetic differentiation in allozymes (Morgan, Beatty, & Adams, 2013), mitochondrial genes (Unmack, Hammer, Adams, & Dowling, 2011) and genome-wide markers (Buckley et al, 2018), and a lack of observed hybridisation with N. vittata (Morgan et al, 2013; Allen et al, 2020), corroborates the identity of the N. pygmaea as a distinct species.…”

“…While both species show some similar ecological characteristics such as body plan and reproductive strategy, they show marked differences in body size, morphology, growth rate, salinity tolerance and reproductive timing (Allen et al, 2020). Additionally, clear-cut genetic differentiation in allozymes (Morgan, Beatty, & Adams, 2013), mitochondrial genes (Unmack, Hammer, Adams, & Dowling, 2011) and genome-wide markers (Buckley et al, 2018), and a lack of observed hybridisation with N. vittata (Morgan et al, 2013; Allen et al, 2020), corroborates the identity of the N. pygmaea as a distinct species. This is reflected by their strong evolutionary distinctiveness, with divergence between the two species estimated at ~4 million years ago (Buckley et al, 2018; Unmack et al, 2011).…”