Finding more than Nemo
The unexpected discovery of the larvae of an important coastal fish species, the pilchard, 300 kilometres off the New South Wales coast may give scientists a new way to predict commercial fish catches and the seasonal wellbeing of the harbour's small colony of little penguins.
"This came as a surprise because pilchards are thought to be a coastal species that spend their lives no more than a few kilometres from shore," says UNSW marine scientist, Iain Suthers, whose research team made the discovery in the East Australian Current (EAC), popularised by the animated film, Finding Nemo.
"We hope this find may let us predict yields of adult fish populations off Australia's eastern coastline."
As the EAC turns east, it cuts a warm trail across the Tasman Sea towards New Zealand. It was here the discovery was made - 34 degrees south, and only 153 degrees east, says Dr Suthers, who led a 12-member research team aboard Australia's National Marine Research Facility, the Southern Surveyor.
Like all fish, larval pilchards possess an ear-bone in their skull - an otolith - that exhibits concentric growth rings, like those used to estimate a tree's age. The growth rings are laid down daily and provide an accurate way to estimate a fish's age. They provide a chronological life history of the fish, from its embryonic stages at the centre to its death in the outside ring.
The discovery is significant for two further reasons, according to Dr Suthers: "First, just as the human birth rate is important for predicting the size of the adult population, larval growth rates strongly predict future adult fish populations.
"Second, pilchards are a benchmark for several fish species that are commercially fished around the world. Having data on this pilchard gives us another tool for estimating what may be happening to other commercial fish species globally. Everything from tuna to fairy penguins eat pilchards, so if pilchards have a bad year, then everything else does, too."
Over the next year, Dr Suthers and his team will analyse their data to see if there is a relationship between zooplankton production rates and larval pilchards in the EAC. This might help explain why Australia ranks 50th in terms of its landed commercial fish weight but has the world's third-largest fishing zone.
