Increased population size of fish in a lowland river following restoration of structural habitat

Abstract

Most assessments of the effectiveness of river restoration are done at small spatial scales (<10 km) over short time frames (less than three years), potentially failing to capture large‐scale mechanisms such as completion of life‐history processes, changes to system productivity, or time lags of ecosystem responses. To test the hypothesis that populations of two species of large‐bodied, piscivorous, native fishes would increase in response to large‐scale structural habitat restoration (reintroduction of 4,450 pieces of coarse woody habitat into a 110‐km reach of the Murray River, southeastern Australia), we collected annual catch, effort, length, and tagging data over seven years for Murray cod (Maccullochella peelii) and golden perch (Macquaria ambigua) in a restored “intervention” reach and three neighboring “control” reaches. We supplemented mark–recapture data with telemetry and angler phone‐in data to assess the potentially confounding influences of movement among sampled populations, heterogeneous detection rates, and population vital rates. We applied a Bayesian hierarchical model to estimate changes in population parameters including immigration, emigration, and mortality rates. For Murray cod, we observed a threefold increase in abundance in the population within the intervention reach, while populations declined or fluctuated within the control reaches. Golden perch densities also increased twofold in the intervention reach. Our results indicate that restoring habitat heterogeneity by adding coarse woody habitats can increase the abundance of fish at a population scale in a large, lowland river. Successful restoration of poor‐quality “sink” habitats for target species relies on connectivity with high‐quality “source” habitats. We recommend that the analysis of restoration success across appropriately large spatial and temporal scales can help identify mechanisms and success rates of other restoration strategies such as restoring fish passage or delivering water for environmental outcomes.

Differential responses by two closely related native fishes to restoration actions

“…Murray cod responded positively to IWH supplementation, supporting the notion that the species shows high site fidelity and an affinity for IWH (Nicol et al 2007;Koehn 2009). The significant positive response by Murray cod to the addition of IWH was consistent with findings for other Australian (Nicol et al 2004;Howson et al 2012: Lyon et al 2019) and North American fish species (Roni & Quinn 2001). Such a response may be due to increases in reach-scale carrying capacity (Flores et al 2011), in particular, by increasing Murray cod-preferred habitat (Nicol et al 2007;Koehn 2009;Lieschke et al 2016) along with improved structural (Savino & Stein 1982;Angermeier & Karr 1984;McMahon & Hartman 1989), ecological (Rowland 1983;Crook & Robertson 1999), and behavioral (Sundbaum & Naslund 1998) conditions linked to enhanced habitat complexity.…”

A compendium of ecological knowledge for restoration of freshwater fishes in Australia

“…Numbers increase in nearbank areas when hollows are a component of the SWH (Lieschke et al 2016). Reinstatement of SWHs has been shown to increase the population size when a source of recruits is close (Lyon et al 2019) Occur in floodplain channels when they are inundated (Koehn 2009b), but the use of the floodplain proper by adults, juveniles and larvae appears limited (Koehn and Harrington 2005;Leigh and Zampatti 2013;Koehn and Nicol 2014). Inundation of floodplain channels can greatly increase the proportion of preferred channel habitat area (Koehn 2009b).…”

“…Key threats have been also been identified in the national recovery plan (Koehn 2005a; National Murray Cod Recovery Team 2010a, 2010b; ACT Government 2017) and the Murray cod population model (Todd and Koehn 2009;Koehn and Todd 2012). Key threats include: Loss of instream structure Lyon et al 2019) Thermal pollution that limits spawning and egg and larval survival (Todd et al 2005;Sherman et al 2007) and affects juvenile growth rates (Whiterod et al 2018), adult movement behaviour and survival of juvenile fish (Tonkin et al 2020a) in reaches downstream of major impoundments (Lugg and Copeland 2014) Fish kills; blackwater and poor water quality (Koehn 2005b;King et al 2012;Thiem et al 2017) Recreational harvesting, which can affect population structure (Nicol et al 2005;Rogers et al 2010). The estimated annual national recreational harvest is 128 692 fish (Henry and Lyle 2003); estimated annual catch (AEs.d.)…”

From an irrigation system to an ecological asset: adding environmental flows establishes recovery of a threatened fish species

“…Endemic to Australia's MDB, Murray cod is a nationally endangered fish, growing to 1.5 m long and 50 kg, with an estimated maximum life span of 48 years (Anderson et al 1992). Populations tend to remain in riverine environments that preserve lotic conditions and high loadings of large woody debris (Koehn et al 2009;Lyon et al 2019). Movement occurs at a range of spatial scales, for example within river valleys (hundreds of kilometres) and within reaches (tens of kilometres), and some fish move long distances (e.g.…”