Rare fish find in SA

A Blue Marlin that washed up on a southern Adelaide beach last week may be the first recorded sighting in South Australia.

Measuring 3.2m from the tip of its bill to its tail and weighing approximately 250kg, the discovery of the typically tropical and subtropical fish was reported to Fishwatch last Wednesday.

Located midway between Carrickalinga South and Normanville, the big fish was transported to researchers at the South Australian Research and Development Institute (SARDI) for investigation.

SARDI researcher, Dr Paul Rogers, said it was extremely rare for billfish to be sighted in South Australian gulf waters, as they are usually found in warm tropical and subtropical oceanic and shelf waters.

"The Blue Marlin is a large, highly migratory pelagic species that is usually found in waters off eastern and western Australia, and can range as far south as Tasmania depending on the current and water temperatures that are broadly influenced by El Niño and La Niña events,” Dr Rogers said.

"Blue Marlin typically spend their time in warm surface water layers that form above cooler bottom water and it’s likely that the Blue Marlin followed the warm Leeuwin Current that originates in the Indian Ocean off Western Australia.

"It’s likely the Marlin became confused by the geographical barriers formed by Eyre Peninsula and/or Kangaroo Island, and subsequently moved north where it succumbed to the colder South Australian gulf waters.

"Routine examinations will be conducted using samples taken at SARDI Aquatic Sciences to rule out the possibility that it died from an infectious disease.”

The rare find, which will be on display at the SARDI Aquatic Sciences Open Day on Sunday 17 November, follows the discovery of a record 4.4m Blue Marlin east of Albany in Western Australia in June. This area is considered to be the southern extremity of the Marlin’s typical migratory range in that region.

PIRSA Community Based Fisheries Program Leader, Keith Rowling, said the appearance of the Blue Marlin in gulf waters may be an example of the impact that changes in the marine environment, such as rising water temperatures, can have on the range distribution of some marine species.

"Late last year, the Range Extension Database and Mapping Project (Redmap) was launched nationally to engage everyday users of the marine environment to help record marine species that may be shifting or extending their range," Mr Rowling said.

"Recreational and commercial fishers, SCUBA divers, boaters and scientists are invited to spot, log and map sightings of uncommon marine species not usually seen in particular coastal areas.

"The sighting of the marlin south of Adelaide highlights the value of contributing to sources such as Redmap to help add to our available knowledge of how our marine ecosystems might be changing.

"Over time, this information will provide an indication of species and regions that are experiencing the most range shifts, so that management and research can be better channelled into these areas."

To register a sighting visit www.redmap.org.au

SARDI scientists will work with SA Museum researchers to conduct further investigations and the find will also be recorded on Redmap.