Comparison of Day and Night Fyke Netting, Electrofishing and Snorkelling for Monitoring a Population of the Threatened Golden Galaxias (Galaxias auratus)

Abstract

The littoral zone of small off-stream water storage containing a translocated population of Galaxias auratus was sampled fortnightly at day and night with fyke nets, electrofishing and snorkelling over 3 months. Variation in population data provided by each method, including relative abundance indices, size structure, and habitat preferences, were examined. Aspects of behaviour and activity patterns were also investigated. Night sampling using all methods consistently yielded larger catches than day sampling. The size structure of catches varied, with electrofishing at night and fyke netting during the day having higher proportions of juveniles, whilst snorkelling at night and electrofishing during the day had higher proportions of adults. Fyke netting at night yielded by far the largest catches ($3-fold more than other methods) and also captured balanced proportions of juveniles and adults. Galaxias auratus had a strong diel activity pattern and were most active at night. The majority of the population migrated into the littoral zone during the night and back into deeper water during the day. A small number of juveniles remained in the littoral zone and some adults sheltered in the dense cover of species-rich littoral vegetation during the day. Shores with shallow depth profiles appeared to be preferred due to higher catches in these areas using all methods. Based on the results of this study, fyke netting at night in littoral habitats is recommended for monitoring populations of G. auratus. Fyke netting is likely to be an effective method for monitoring other lacustrine galaxiid species; however, further work is required to investigate the effects of habitat variables and fish community structure on activity patterns of galaxiids, and hence their catchability with various methods, in more extensive lentic environments.

Crying wolf, crying foul, or crying shame: alien salmonids and a biodiversity crisis in the southern cool-temperate galaxioid fishes?

“…It is among the largest Australian galaxiids, reaching about 240 mm. Knowledge of this species derives largely from work of Hardie (2003a;Hardie et al 2004Hardie et al , 2005Hardie et al , 2006a. This species is largely lacustrine, and known primarily from two modified upland lakes in central Tasmania (Fig.…”

A shift in the habitat use pattern of a lentic galaxiid fish: an acute behavioural response to an introduced predator

“…Despite being found to feed during both day and nighttime (Stuart-Smith et al 2006), there is some evidence to suggest its activity and habitat use does show a diel pattern. Hardie et al (2006a) reported that in a small ''insurance'' population of G. auratus translocated to a clear-water, trout-free farm dam reservoir, the fish were more likely to be found in open water habitats during the night, while during daylight they appeared to be generally confined to heavily vegetated macrophyte beds. The objective of the present study was to experimentally test whether the increased predation risk associated with the close proximity of brown trout resulted in a short-term shift in this suggested diel pattern in the use of complex habitats by G. auratus, in order to more clearly understand potential impacts of trout on this threatened species.…”

Fish use of artificial dike structures in a navigable river

“…Previous studies have shown that electrofishing (Witt and Campbell, 1959;Dumont and Dennis, 1997), particularly for black basses (Paragamian, 1989) can yield higher catch rates at night than during day so we cannot disregard this as a factor. However, other studies of juvenile fishes using snorkelling, fyke nets, or seines in addition to electrofishing also indicate higher use of shallow nearshore areas in rivers during night (Pierce et al, 2001;Hardie et al, 2006). Whatever the reason, day versus night influences should have been shared across dike and reference sites such that differences in catch or richness across sites within day or night sampling periods should reflect real differences in fish use between dikes and reference areas.…”