Draughtboard Shark (Cephaloscyllium laticeps) acoustic tagging in Southern Tasmania

Brief description

Between January and March 2003, 25 (15 females, 9 males, 1 no sex recorded) draughtboard sharks, sourced from the Crayfish Point Reserve and the east coast of Tasmania (42-43°S, 147-148°E), were fitted with the acoustic transmitters to investigate movement behaviour.

Lineage

Maintenance and Update Frequency: notPlanned

Statement: An array of 82 VR2 automated acoustic receivers (Vemco Ltd., Nova Scotia) were deployed in October 2002 and retrieved in July 2003 in southeast Tasmania, Australia. The sea floor in these areas consisted of sand, silt, seagrass and low profile reef. Each receiver was secured to a vertical steel post on a concrete mooring, approximately 1 m above the sea floor.

An extensive array of receivers was established as a series of acoustic "curtains" separating the main bays and channels in southeast Tasmania. The depth of receiver placement varied from 2 to 55 m. The distance between receivers was chosen to ensure that detection distances had substantial overlap and varied from 720 to 930 m depending on the habitat type. Receivers were positioned at the entrances of bays and channels to ensure that no shark could move into or out of these areas without being detected. Within the extensive array, an intensive array was established at the Crayfish Point Reserve (total area= 800 m2) and the adjacent areas of Alum Cliff and Taroona High. In the Crayfish Point Reserve, the sea floor includes a complex mix of sand, silt, low and high profile reef. The complexity of this habitat resulted in a reduction of the detection range for the acoustic receivers to a minimum of 60 m. Thus, the receivers were placed approximately 100 m apart to provide sufficient overlap for determining position from detection at multiple receivers. The receivers were placed in depths from 2 to 11 m. The receivers that formed a small "curtain" perpendicular to the shore at Alum Cliff and Taroona High were 400-450 m apart.

The transmitters (V8SC-2H: Vemco, Nova Scotia), were cylindrical in shape, 30 mm in length, 9 mm in diameter and weigh 3.1 g in water. The transmitters emit a 69 kHz frequency "ping" code repeated after a random delay of 20 to 60 s. The battery life was set at 180 days.

Between January and March 2003, 25 (15 females, 9 males, 1 no sex recorded) draughtboard sharks were caught in rock lobster traps. Fifteen sharks were sourced from the Crayfish Point Reserve and 10 sharks from the east coast of Tasmania (42-43°S, 147-148°E) (Fig. 2.1). All sharks were released in the Crayfish Point Reserve. Prior to release, total length, total weight, and clasper length (for males) was recorded. Sharks were fitted with the acoustic transmitters and injected with 25mg/kg of the antibiotic tetracycline dissolved to saturation in seawater.

Raw data collected by the receivers, including transmitter number, and time and date of detection was downloaded (in March-April and July 2003) using the VR2 data processing software (Vemco Ltd). Data from both arrays was analysed using ArcView 3.2 (ESRI 1999) with the Animal Movement Analyst Extension (AMAE) tool (Hooge and Eichenlaub, 2000) and Microsoft Excel.

Notes

Credit
University of Tasmania International Research Scheme

Purpose
This study investigated the movement behaviour of the draughtboard shark using acoustic tagging, which evaluated short-term movements (< 6 months) and habitat utilisation.