• Image: Jamie Crawford
    Image: Jamie Crawford
  • Jamie Crawford with a school-sized SBT caught in South Australia.
    Jamie Crawford with a school-sized SBT caught in South Australia.
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THERE'S been some pretty unusual activity in South Australian waters so far this summer, which has left a lot of people scratching their heads wondering what’s going on.

It started first with our annual migration of southern bluefin tuna. The schools of fish arrived early and in force, invading a lot of near-shore grounds right along the Eyre Peninsula though to areas further east.

The fish are now holding in areas (and in significant numbers) where they haven’t been seen for years such as close to the coast at Cape Jervis, Victor Harbor, and even out from the Murray Mouth near Goolwa. These are reasonable fish too, with many in the 18 to 25kg size range.

Jamie Crawford with a school-sized SBT caught in South Australia.

Jamie with an example of the typical size of SBTs being caught close to the SA coast. 

The commercial tuna fleet, based in Port Lincoln, have left their traditional grounds in the Great Australian Bight to target fish further east, around Kangaroo Island in particular. But what’s interesting is that these fish usually hold in the Bight at this time of year, but they’ve beelined through the Bight to hold over untraditional eastern grounds. Why would that be so?

There are currently a couple of oil companies doing seismic surveys in the Bight for oil deposits. Coincidence, or is there a correlation?

We’ve also had several whales beach themselves in South Australia so far this summer, over at least four separate incidences. Very unusual. About a fortnight ago we had a pod of killer whales attack and kill a white pointer shark in full view of a dive boat at the Neptune Islands. Would have been an unforgettable sight to see, but again, to see killer whales in waters this close to the SA mainland is unusual. The commercial tuna purse seine boats have recorded killer whales on occasions in the Bight, but never this close to shore.

And lastly, there have been mahi mahi caught south of Adelaide near Victor Harbour. This may not be as unusual as the other points of interest, but still strange nevertheless. Speaking to a tuna-spotter pilot last week, and a couple of old fishing salts here in Port Lincoln, they’re convinced it’s related to the seismic surveys.

The survey boats work by sending a powerful underwater pulse which is said to interfere with the orientation of mammals and, to a lesser extent finfish. One of the whales that beached itself in the Port Lincoln National Park was sent away for a post mortem to try and establish whether the seismic surveys have interfered with the mammals. We’re all awaiting the results.

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