A 2 year (2000)(2001) radio-tagging study was undertaken to investigate the movements of 51 golden perch Macquaria ambigua in the Murray River at Nyah in north-western Victoria, Australia. During the winter of both years, golden perch did not undertake movements >5 km and displayed strong home range fidelity. In the first year of the study there was an increase in the distance of golden perch movement during late spring which coincided with increasing water temperature and river discharge. Nineteen golden perch were tracked during this period, of which 10 travelled downstream between 11 and 290 km. Seven of these fish moved to an area below the junction of the Murray and Wakool Rivers. Five golden perch travelled upstream between 13 and 35 km, four of which travelled to an area around the junction of the Murray River and Speewa Creek. The remaining four golden perch undertook localized movements of <5 km. Many of the long distance movements undertaken in spring 2000 were rapid and 53% of these golden perch returned to within 3 km of their release locations, indicating homing behaviour. Given that the rapid movements of golden perch in spring coincided with the known spawning season of this species, these long distance movements may be associated with reproductive strategy. # 2005 The Fisheries Society of the British Isles

To quantify how electrofishing capture probability varies over time and across physiochemical and disturbance gradients in a turbid lowland river, we tagged between 68 and 95 fish·year −1 with radio transmitters and up to 424 fish·year −1 with external and passive integrated transponder (PIT) tags. We surveyed the site noninvasively using radiotelemetry to determine which of the radio-tagged fish were present (effectively closing the radio-tagged population to emigration) and then electrofished to estimate the proportion of available fish that were captured based on both this and standard mark-recapture methods. We replicated the electrofishing surveys three times over a minimum of 12 days each year, for 7 years. Electrofishing capture probability varied between 0.020 and 0.310 over the 7 years and between four different large-bodied species (Murray cod (Maccullochella peelii), trout cod (Maccullochella macquariensis), golden perch (Macquaria ambigua ambigua), and silver perch (Bidyanus bidyanus)). River turbidity associated with increased river discharge negatively influenced capture probability. Increasing fish length increased detection of fish up to 500 mm for Murray cod, after which capture probability decreased. Variation in capture probability in large lowland rivers results in additional uncertainty when estimating population size or relative abundance. Research and monitoring programs using fish as an indicator should incorporate strategies to lessen potential error that might result from changes in capture probabilities.Résumé : Afin de quantifier les variations de la probabilité de prise à la pêche électrique dans le temps et le long de gradients physicochimiques et de perturbation dans une rivière turbide de basse terre, nous avons doté de 68 à 95 poissons·année -1 de radioémetteurs et jusqu'à 424 poissons·année -1 d'étiquettes externes et de transpondeurs passifs intégrés (PIT). Nous avons sondé le site de manière non intrusive par radiotélémétrie afin de déterminer lesquels des poissons radioétiquetés étaient présents (excluant du fait l'émigration pour la population radioétiquetée), puis effectué une pêche électrique pour estimer la proportion de poissons disponibles capturés selon cette méthode et des méthodes de marquage-recapture normales. Nous avons répété les levés par pêche électrique trois fois sur au moins 12 jours chaque année, pendant sept ans. La probabilité de capture par pêche électrique variait dans une fourchette de 0,020 à 0,310 sur les sept ans et pour quatre espèces de gros poissons (la morue de Murray (Maccullochella peelii), la perche Macquarie (Maccullochella macquariensis), la perche dorée (Macquaria ambigua ambigua) et la perche argentée (Bidyanus bidyanus)). La turbidité de la rivière associée à un débit accru avait une incidence négative sur la probabilité de capture. Plus la longueur des poissons était grande, plus la détection était élevée pour les poissons allant jusqu'à 500 mm en ce qui concerne la morue de Murray; au-delà de cette longueur, la probabilité diminuait. Le...

Abstract. Off-channel habitats, such as wetlands and backwaters, are important for the productivity of river systems and for many species of native fish. This study aimed to investigate the fish community, timing and cues that stimulated movement to and from off-channel habitats in the highly regulated Lake Hume to Lake Mulwala reach of the Murray River, south-eastern Australia. In 2004-05, 193 712 fish were collected moving bi-directionally between a 50-km section of the Murray River and several off-channel habitats. Lateral fish movements approximated water level fluctuations. Generally as water levels rose, fish left the main river channel and moved into newly flooded off-channel habitats; there was bidirectional movement as water levels peaked; on falling levels fish moved back to the permanent riverine habitats. Fish previously classified as 'wetland specialists', such as carp gudgeons (Hypseleotris spp.), have a more flexible movement and life-history strategy including riverine habitation. The high degree of lateral movement indicates the importance of habitat connectivity for the small-bodied fish community. Wetlands adjacent to the Murray River are becoming increasingly regulated by small weirs and ensuring lateral fish movement will be important in maintaining riverine-wetland biodiversity.

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.

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