Rare fish seen at Busselton Jetty

Unusual visitors were sighted at the Busselton Jetty’s Underwater Observatory this season, including the scissortail sergeant which returned for a second year in a row.

Observatory manager Sophie Teede said they were surprised to see two juveniles of the predominantly tropical fish had joined a school of young stripeys.

“The observation is very exciting to scientists and the range of this species is currently being reexamined,” she said.

The species had not been sighted south of Rottnest Island since monitoring surveys began in since the 1970s.

The fish species first entered the region last year during a “marine heatwave” when the water temperature peaked at 25.6C, which was a 3.7C increase above the recorded February/March average.

The WA coastal water temperature spike was associated an unusually strong La Nina event in 2011.

Western Australian Museum fish collection manager Sue Morrison said the scissortails may have been transported there by the southward-flowing Leeuwin Current which had been stronger in recent years and was “associated with a southern range extension for many marine species”.

The observatory guides also noted other tropical species during the 2011 unprecedented rise in sea temperature including a “massive and rare Queensland groper of approximately 3m length”.

A tiger shark, a western seahorse and record numbers of the tropical roundfaced batfish were also reported.

“Several friendly grey nurse sharks have been sighted around the seafloor over the previous year and indicates that a population of these beautiful sharks resides nearby the jetty,” she said.

Australian tailor numbers increased during the 2011-12 season when sightings of large schools of several hundred individuals became a common occurrence.

The 2011 sea temperature rise may also be reason for the disappearance of the bright orange short tailed nudibranchfrom the area.

Ten nudibranch and sea hare species came back this year when the sea temperature fell.

The observatory team record water temperature and the presence of species twice each day to provide information on the changes to the marine environment.