Ben T. Broadhurst

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).

A possible false negative: lack of evidence for trout predation on a remnant population of the endangered Macquarie perch, Macquaria australasica, in Cotter Reservoir, Australia

Abstract To investigate possible predation on a remnant population of the endangered Macquaria australasica in Cotter Reservoir, ACT, Australia, stomach content analysis was conducted on 63 rainbow trout Oncorhynchus mykiss and 24 brown trout Salmo trutta. Both predators were found to be piscivorous, with the frequency of piscivory generally increasing with body size. Goldfish Carassius auratus were the only fish species identified in stomach contents. That gape‐limitan on prevented trout from feeding on juvenile M. australasica was eliminated as a possibility based on: (1) the body depth of prey and the mouth‐size of predators; and (2) evidence that another species of similar dimensions was ingested by trout. Whether or not trout predation on M. australasica is an important process in Cotter Reservoir remains to be clarified. Juvenile M. austalasica do not reside in the parts of the reservoir from which most trout were actually sampled in the current study. Therefore, it is proposed that the lack of evidence for predation on M. australasica is potentially a false‐negative result.

A rock-ramp fishway expands nursery grounds of the endangered Macquarie perch (Macquaria australasica)

Abstract. Prior to installation of a fishway at a road crossing in 2001, a remnant population of endangered Macquarie perch (Macquaria australasica) was confined to a 6-km section of the Cotter River, Australian Capital Territory. The purpose of the fishway was to provide passage past a barrier and to increase the extent of spawning grounds for M. australasica to an additional 22 km of river. The aim of the current study was to quantify the extent of nursery grounds of M. australasica in the Cotter River catchment by developing and applying a rapid, non-destructive technique for surveying juvenile M. australasica. From October to January in 2006–07 and 2007–08, pools were surveyed by snorkelling in the lower Cotter River to detect juvenile and larval M. australasica. The 9-km study reach consisted of the four pools immediately upstream of Cotter Reservoir, seven pools further upstream but still downstream of the rockramp fishway and 14 pools upstream of the fishway. In 2006–07, juvenile M. australasica were detected at 22 of 25 pools, including 13 of 14 pools upstream of the fishway. In spring/summer 2007–08, low visibility conditions frequently occurred throughout the river preventing survey on several occasions. However, recruitment of M. australasica was again detected upstream of the fishway. The increased extent of the nursery grounds of this M. australasica population has proven to be timely as an enlargement of the Cotter Reservoir, due for completion in 2012, will inundate more than 90% of prefishway nursery grounds in the Cotter River. Our study has demonstrated the benefit of installing a fishway in expanding the nursery grounds and the number of recruits of a remnant population of the endangered M. australasica. We also demonstrate the benefits of employing a visual survey technique to quantify the extent of the riverine nursery grounds of a fish population.

Jailbreak: a fishway releases the endangered Macquarie perch from confinement below an anthropogenic barrier

Management interventions are often needed to facilitate the recovery of ecosystems affected as a result of human alteration. Population-level monitoring is often central to evaluating the effectiveness of specific on-ground actions. In the present study, we assessed the response of a remnant population of the endangered Macquarie perch (Macquaria australasica) to the construction of a rock ramp fishway on the Cotter River, Australia, over a 7-year period. Prior to fishway construction, this obligate riverine spawner had been previously confined to Cotter Reservoir and six kilometres of stream by a raised road-crossing. Surveys conducted in the 2 years following fishway completion failed to detect Macquarie perch upstream of the fishway. Subsequent surveys (6–7 years post-fishway completion) detected Macquarie perch up to 12 km upstream of the fishway. The number and distribution of smaller-sized individuals (0+ ( 150-mm TL)) suggests that individuals found upstream of the fishway are resident stream fish and not fish that have migrated from known downstream spawning areas. The success of the fishway has been timely because enlargement of a downstream reservoir will inundate four kilometres of river and destroy the majority of spawning sites of this species downstream of the fishway in the Cotter River.

An Improved Technique for Small-Scale Radio-Tracking of Crayfish and Benthic Fishes in Upland Streams

Abstract This study measured the accuracy of two radio-tracking techniques: (1) triangulation using a Yagi antenna and (2) a form of direct location, the extended-reach technique, which uses a small loop antenna attached to a lightweight 9-m telescopic pole. The study was conducted in the Cotter River, an upland stream in the Australian Capital Territory. Radio tags were positioned instream to determine whether depth, substrate, or local bank profile affected radio-tracking accuracy. The extended-reach technique was more accurate (mean error ± SE = 1.00 ± 0.21 m) than triangulation (2.57 ± 0.21 m). Decreased accuracy resulted from the triangulation of radio tags positioned close to boulders or in water more than 1 m deep. These variables had no effect on the accuracy of the extended-reach technique. The presence or absence of a steep rocky bank did not affect the accuracy of either radio-tracking method. The increased accuracy of the extended-reach technique provides an improvement over traditional method...