Revealing kingfish science

Many Aussie anglers enjoy nothing more than fishing for yellowtail kingfish (seriola lalandi) in our coastal waters. The kingfish population along eastern Australia is thriving since the banning of fish traps 20 years ago, yet little is known about their habitats and behaviour.

Scientists have spent the past four years monitoring the movements of kingfish in NSW using acoustic technology. This technology was used to tag 70 specimens between Coffs Harbour and Narooma.

Tagged fish were found to be highly resident, spending the majority of their time within 20km of their tagging location. They were also found to be most abundant in 22°C waters, but can be found between 16 and 26 °C in NSW.

Occasionally, individuals were tracked moving long-distances but did not return to their tagging location – one fish was found to swim over 675 km from Sydney to Tweed Heads.

SYDNEY ARTIFICIAL REEF A KING'S CASTLE
The Sydney Offshore Artificial Reef, located just outside Sydney heads, was found to be a popular spot for kingfish.

Nine of the tagged Kingfish were detected at the artificial reef, with most of these individuals returning to the reef multiple times – one fish returned to the reef 14 times in just two months. These fish were also detected on nearby natural reefs, highlighting the connectivity of artificial and natural fish habitats across Sydney.

HARBOUR KINGS
Researchers also tagged kingfish within Sydney Harbour to further understand their use of estuarine environments. Kingfish enter the harbour during summer periods and typically left during winter. However, two Kingfish were found to over-winter in the upper reaches of Middle Harbour despite water temperatures dropping as low as 12 °C.

Kingfish in coastal waters were found to swim faster than those in the harbour, this is likely in response to a different prey type for estuarine resident kingfish.

BIG APPETITE
Researchers found that Kingfish need to eat up to 4.5 per cent of their body weight every day – this is equivalent to an average human adult eating 7 serves of calamari and chips every day. To meet this demand, kingfish spend the day hunting for food deep in the water column and return to shallow waters at night to rest.

This work represents a collaboration between the University of NSW, NSW Department of Primary Industries – Fisheries, and CSIRO, and funded by the NSW Recreational Fishing Saltwater Trust, the Australian Research Council, and CSIRO.

LONG-DISTANCE RECAPTURE
Meantime, a kingfish released by Adelaide Game Fishing Club (AGFC) member Adam Todd at Port August on November 25, 2013 aboard Like a Boss was recently recaptured off the Gold Coast by Dave McKenzie.

The fish spent some 866 days at liberty, swum at least 1600 nautical miles (3087km), and headed around the south and east coast of Australia during which time it grew from 121cm to 127cm (16.25kg).

Interestingly, the second furthest recorded swim north by a tagged SA kingfish was also originally captured aboard Like a Boss. The AGFC president Paul Williams released that fish at Port Augusta on October 21, 2013, and it was recaptured and re-released approximately 387 days later off Coffs Harbour, NSW.

So it appears that what we know about kingfish is that they are resident and long-distance travellers, oceanic but also estuarine and, well, a little erratic in their behaviour. More to come on the mighty king.