Research

Tagging juvenile white sharks near Port Stephens, NSW

Seven juvenile white sharks were fitted with electronic tags near Port Stephens, NSW, in late October 2008 as part of research aiming to better understand shark movements and habitats, and devise strategies for monitoring their population status.

One male shark and six female sharks, ranging in size from 1.75 to 2.3 metres, were surgically implanted with acoustic tags, the first time this technique has been applied to white sharks. The previous use of external tags resulted in a high level of tag loss through shedding, with the tags failing to reach their potential life of five to seven years.

Three of the sharks also were fitted with satellite tracking tags, and four were fitted with self-releasing data archiving (PAT) tags.

The tagging program is led by scientists from the CSIRO Wealth from Oceans National Research Flagship. They were assisted during the October field work by colleagues from James Cook University, Tag for Life/White Tag and the NSW Department of Primary Industries.

The white shark is held on a stretcher in the water next to the vessel while the tag is surgically inserted.

Juvenile white sharks are known to seasonally aggregate in certain coastal areas such as Port Stephens. The sharks feed on finfish such as salmon, snapper, mullet, tailor as well as small rays and other sharks. Many of the food species commonly occur in surf beach areas and coastal reefs, so the presence of sharks around these areas is normal.

Ten juvenile white sharks were tagged by the CSIRO-led team in the same area near Port Stephens in 2007 with satellite tracking tags, self-releasing archival tags and external acoustic tags. These sharks spent periods of residency off beaches in the region, followed by coastal and offshore movements as far north as Fraser Island, Queensland, and south to Bass Strait and across the Tasman Sea to New Zealand.

An extended view of their movements was not possible, however, due to the limited lifespan of the tags. It is hoped that this year’s tagging exercise will start building a picture of the long-term movements of juvenile white sharks, including whether individuals return to the Port Stephens area on an annual basis.

Other questions being addressed include:

• what habitats the sharks favour, what brings them there and how long they stay;
• the location of nursery areas;
• whether individual sharks reside in the area or move more widely; and
• whether there are other, similar areas of aggregation.

Smooth tagging

The juvenile white sharks were located from a six-metre vessel in surf zone habitat, caught on a heavy line and gradually tired before being held on a stretcher in the water next to the vessel. They were given an oxygen feed while in the stretcher to facilitate recovery.

The acoustic tags were surgically implanted in the gut cavity using techniques developed for other species such as southern bluefin tuna. A three-centimetre incision was made, the tag carefully inserted, and the incision closed using sutures. The external satellite and data archiving tags were attached to the dorsal fin.

The surgical procedures and the attachment of external tags went smoothly and all sharks were successfully released. Satellite positions transmitted by the tags indicated a rapid recovery from capture and surgery.

The acoustic tags transmit a unique series of pulses that are detected and decoded by listening stations moored to the seabed. Data can be downloaded from listening stations upon their retrieval.

Listening station arrays have been deployed by various research institutions in Australian coastal waters and gradually are being developed as a tool for monitoring movement patterns of a variety of species world-wide. Many of these deployments are coordinated under The Australian Acoustic Tracking and Monitoring System, a facility of the nationally funded Integrated Marine Observing System.
More information about AATAMS [external link].

An expanding network of listening stations in the Port Stephens area, along the NSW coastline and in other areas of Australia, is providing the opportunity to monitor the presence of tagged sharks. Sharks with internally implanted acoustic tags offer the most reliable opportunity to test whether individuals return to the region on an annual basis.

With improvements in tag retention through the placement of internal acoustic tags, the opportunities for long-term monitoring of juvenile white shark movements via these Australian coastal listening station networks offers an unprecedented opportunity to follow their behaviour and habitat preferences as they move through life history stages towards adulthood.

The satellite tracking tags transmit their approximate positions via the ARGOS satellite network when the sharks come to the surface and are expected to continue operating for the next few months. These tags also collect and archive data on water temperature, swim depth and light level at 10 second intervals.

This information is also transmitted via satellite if the sharks surface for sufficient time. The data archiving tags are set to release from the shark after period ranging from three to six months.

Larger questions

Similar tagging and tracking programs are building a profile of the movements of large white sharks.

Research on white sharks in Australian waters, focused on sub-adult and sharks greater than 3.0 m in length, has shed light on their spatial dynamics, links between populations and habitat preferences. These sharks are commonly seen near of seal colonies, but can make extensive coastal migrations coupled with periods of temporary residency. They may show a propensity for returning to specific sites, sometimes on a seasonal basis, and make excursions into the open ocean.

Last updated 14/11/08