Validating variation in radio-signal strength as an index of aquatic fauna activity

Abstract. Studying biological rhythms of activity and determining the external factors that influence behaviour of animals can be challenging in many aquatic habitats. We investigated the validity of using variations in radio-signal strength to quantify changes in activity of radio-tagged aquatic fauna on a small spatial scale under controlled conditions in the field. We monitored short-term activity (<1 min) of two aquatic species, rainbow trout (Oncorhynchus mykiss) and Murray River crayfish (Euastacus armatus), that differ markedly in their primary mode of movement. Simultaneous video monitoring confirmed that active and inactive periods for both species could be accurately determined by radio-telemetry, as were specific behaviours exhibited by trout. We were also able to quantify activity based on different radio-tag (coil and trailing whip antennas) and receiving antenna configurations (yagi and gap-loop antennas); however, we recommend use of control tags to provide reference data. Variation in radio-signal strength represents a valid means of monitoring activity of moderately site-attached aquatic species

Validating variation in radio-signal strength as an index of aquatic fauna activity

Studying biological rhythms of activity and determining the external factors that influence behaviour of animals can be challenging in many aquatic habitats. We investigated the validity of using variations in radio-signal strength to quantify changes in activity of radio-tagged aquatic fauna on a small spatial scale under controlled conditions in the field. We monitored short-term activity (<1 min) of two aquatic species, rainbow trout (Oncorhynchus mykiss) and Murray River crayfish (Euastacus armatus), that differ markedly in their primary mode of movement. Simultaneous video monitoring confirmed that active and inactive periods for both species could be accurately determined by radio-telemetry, as were specific behaviours exhibited by trout. We were also able to quantify activity based on different radio-tag (coil and trailing whip antennas) and receiving antenna configurations (yagi and gap-loop antennas); however, we recommend use of control tags to provide reference data. Variation in radio-signal strength represents a valid means of monitoring activity of moderately site-attached aquatic species

Effects of radio-tagging on two-year-old, endangered Macquarie perch (Macquaria australasica: Percichthyidae)

Radio-telemetry provides an effective means of studying the habitat use of threatened fishes where repeated recapture of individuals is undesirable. In these circumstances, it is especially important to ensure that radio-tagging methods are appropriate for the particular species of interest. An aquaria-based evaluation of three methods for radio-tagging two-year-old Macquaria australasica was conducted until 28 days post-surgery. Successful radio-tagging was determined from three indicators: (1) survival; (2) healing of the surgical incision or tag attachment site; and (3) resumption of feeding. Internal-coil radio-tags proved to be the most suitable radio-tag type, with complete survivorship and tag retention for the duration of the trial and fish commonly resuming normal feeding behaviour within two days post-surgery. In contrast, implanting a radio-tag internally and exiting a whip antenna is unsuitable for M. australasica on the basis of poor survivorship, rejection of radio-tags and prolonged alteration of feeding behaviour. No mortality or radio-tag rejection was observed in association with externally attached whip-antenna radio-tags, and post-surgery resumption of feeding was comparable with that of fish with internal-coil radio-tags. However, external radio-tags caused substantial abrasion of the epidermis and loss of scales. Internal-coil tags should be applied in radio-tracking studies of this species

Radio-tagging flexible-bodied fish: temporary confinement enhances radio-tag retention

Animals that occupy holes or squeeze into interstitial spaces often have particularly flexible bodies and can be difficult to tag effectively. The present study evaluated three methods for radio-tagging the cryptic, eel-like fish Gadopsis bispinosus, a species that inhabits interstitial spaces among cobbles and boulders in streams. The three methods were an externally attached radio-tag with a whip antenna, an internally implanted coil radio-tag (internal coil) and an internally implanted radio-tag with an externally exited whip antenna (internal-external). Successful radio-tagging was determined in aquaria trials based on a combination of four indicators: (1) survival; (2) retention of the radio-tag; (3) healing of the surgical incision; and (4) rapid resumption of feeding. Externally attached radio-tags were shed and proved to be unsuitable (100%). Three of nine individuals with internal-external tagging completed the study with regular feeding, healed incisions and retained radio-tags. Conversely, five of nine individuals with internal coils were successful. This included two of three individuals held in either a simple environment for 3 days or for the duration of the trial and one of three individuals held in a complex environment. Temporary confinement following implantation with coil radio-tags offers a viable means of radio-tagging G. bispinosus. Temporary confinement following radio-tagging may also be useful for reducing radio-tag rejection and mortality for other fish species with similar body morphs and habitat use (e. g. eel species and sculpin)

Seasonal differences in the diel movements of\ud Macquarie perch (Macquaria australasica) in an\ud upland reservoir

Knowledge of the movement patterns of threatened fishes aids their conservation management and informs sustainable development of natural resources including freshwater. Prior to the expansion of a temperate upland reservoir in Australia, we used radio telemetry to compare seasonal differences in the diel movements of adult endangered Macquarie perch (Macquaria australasica) (235–414 mm total length) in Cotter Reservoir, Australian Capital Territory. Macquarie perch exhibited a diel range of 389 ± 46 m, a diel mobility of 769 ± 93 m and diel area use of 24008 ± 5595 m² among four seasons. Diel range was significantly higher in winter compared with other seasons, and diel mobility was negatively correlated with fish size among four seasons. Macquarie perch inhabited deeper water in summer across the diel cycle (7.2 ± 0.5 m) in comparison with other seasons (spring: 3.8 ± 0.3 m, autumn: 3.0 ± 0.2 m, winter: 3.0 ± 0.3 m). Within seasons, both remote and manual telemetry identified that diel activity was predominantly crepuscular. Prey availability and the threat of avian predation represent the most likely explanations for the differences in seasonal movements. In a reservoir where expansion will likely result in a loss of critical habitat (emergent macrophytes) for this endangered species, we use site-specific knowledge of the spatial ecology of Macquarie perch to inform the placement of shelter habitat prior to filling the enlarged reservoir

Spatial ecology and habitat use of two-spined blackfish Gadopsis bispinosus in an upland reservoir

The scale and patterns of movement and habitat use are primary considerations in the conservation and management of threatened species. Movement, activity and habitat use of the threatened two-spined blackfish Gadopsis bispinosus were assessed in a small upland reservoir in south-eastern Australia using manual and remote radio-telemetry. Movements and activity of two-spined blackfish (n = 19) were studied over a 28-day period and exhibited proportionately large directional crepuscular movement and activity with heightened activity continuing throughout the night (although movement was subdued). Two daily movement strategies were observed: movements from diurnal home-shelter habitats (predominantly rock) to macrophytes at night (14 individuals), and occupation of macrophytes during the entire diel period and restricted movement (five individuals). Daily movement strategies were fixed (not plastic) among all individuals, with one exception, for the duration of the study period. Rock, fallen timber and macrophytes were the most commonly used daytime shelter habitat (in order of preference). Although some information exists on movements and habitat use of this species and the congeneric river blackfish G. Marmoratus in lotic environments, we present the first study of movements and habitat use for either species in lentic environments. Given the occupation of lentic environments by this threatened species, the data presented in this study provide insight into the habitat requirements for this species, and offer opportunities for habitat enhancement in existing reservoirs within the species' geographic range