Friday, March 6, 2009

Tag sharks.Then have informed debate

The Australian media are having what amounts to an "orgastic anti shark field day" with a spate of recent high profile shark attacks.

One lone voice, Professor Iain Suthers, has popped up in a local op ed with a novel idea.

Of course no one would consider a tagging program for shark populations at the cost of $2K per tag and an overall $500,000 for the final conclusions - when a shark program like this (see image) would do the immediate job much faster. Or would they? Ideas can be very dangerous things:

A surprising aspect of the recent shark attacks is what we don't know. Certainly the risk of shark attack per swimmer is less than in the past. But we don't know if there are more sharks around Sydney than last summer (although it seems to be so). We don't know if this is a trend. There were many reports last summer, but no attacks.

We don't know if it is due to the fish bait abundance, caused by recent strong upwelling. With the strengthening East Australian Current and warming of the Tasman Sea, perhaps this is a climate-related process we could model. We don't even know the life history of bull sharks - are they just summer tourists, and if so, where do they winter? At present all such speculation needs data, and the only long-term data is the controversial shark-meshing program.

First, data could be sourced from reliable observers of the harbour and beaches: ferry captains, charter fishing operators and experienced observers from high-rise apartments. They could dial in an observed index from 0 to 9 which, with other data (water temperature, rainfall, upwelling), could form the basis of a weekly shark risk, similar to UV risk.

Second, we need more research and communication. The bad reputation of hammerheads and grey nurse sharks has no basis. Many researchers around Australia are tracking sharks with acoustic tags. The presence of tagged sharks will be tracked with 900 receivers distributed around Australia as part of the Federal Government's integrated marine observing system. One part of that array has just been deployed off Tamarama. Science is needed so we can enjoy the harbour without fear.

Professor Iain Suthers, Sydney Institute of Marine Science, University of NSW

Editors Note: Kudos to Professor Iain Suthers for this "idea".

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