Search

The intrapopulation variability in the size and age structure of the spawning stock and migration of the threatened Macquarie perch Macquaria australasica in Lake Dartmouth was investigated between 2008 and 2016. Sampling centred on the core reproductive period (October-December) when mature fish migrate from the lake into riverine habitat to spawn. Spawning fish were predominantly large, spanning a broad age structure, with a high proportion of fish (25%) aged 15-30 years. The overall median size of spawning fish did not change for males or females during the 9 year study period. The size of the smaller mature male fish did change in some years suggesting a small proportion of male M. australasica matured at age 1+ and 2+. Acoustic telemetry employed over 3 years showed that M. australasica were most likely to be in the spawning reach from October to mid-December, migrated to this reach annually and moved large distances throughout the lake all year, with no evidence for any spatial structuring. Mature fish sometimes occupied the spawning reach for several months after the core reproductive period, which increased their vulnerability to recreational fishing. Males tagged in the lake were seldom recorded in the spawning reach, presumably because a high proportion had not yet entered the spawning stock despite their size suggesting maturity. Maintaining a broad age and size-structure of the spawning stock of long-lived iteroparous fish species is crucial for recruitment stability and population persistence. Overexploitation of the spawning stock has probably contributed to previous population declines in the lake as well as the collapse of other M. australasica populations in south-eastern Australia., (© 2018 The Fisheries Society of the British Isles.)

Fish habitat restoration efforts frequently involve the reintroduction of instream woody habitat (IWH) in areas where large scale removal has taken place over time. Identifying areas of low IWH density for reintroduction requires a 'current state' spatial representation of the IWH densities that is traditionally a labour intensive and costly exercise. We present a meso-macro scale assessment procedure that incorporates a rapid on-ground field survey method with a novel analytical approach to map IWH densities. In situ IWH locations with categorical values for size and complexity were obtained along the lower Ovens River in South Eastern Australia. Despite relatively high densities of IWH and limited access, 120 km of river was able to be investigated. A bound kernel density estimate (BKDE) analysis was performed using the IWH point locations, weighted by an average volume inferred from the point size and complexity values. A fine scale map is obtained providing a continuous representation of IWH densities (m(3) m(-2)) indicating a high degree of IWH density variability along the river. The relative high resolution map is produced for habitat restoration managers to assess river sections generally less than 1 km long for IWH reintroduction., (Crown Copyright © 2013. Published by Elsevier Ltd. All rights reserved.)