Monday, March 21, 2005

Jaws

An email from Katie reminded me to say something about sharks.

The Australian ran an article on February 17th declaring Australia the shark fatality capital of the world based upon 2004 statistics. This now looks to have been in very poor taste after a deck hand on a dive boat was bisected by a 20 foot shark while snorkelling off the coast of West Australia on March 19th. This prompted a three day search for both the body as well as the shark, but neither ever turned up. There was fierce debate in the media over the weekend as to the merits (or lack) of hunting down the shark and killing it. This follows on a couple of shark related deaths back in December, both involving teenagers.

Australia clearly as a reputation for this kind of thing, but I wanted to try and put it into perspective (being interested in risk and all that). Since 1990, Australia has experienced 63 shark attacks with 16 fatalities (actually, now I should probably add 1 to each of those numbers). In contrast, the United States has experienced 490 with 11 fatalities. At first glance, it may seem that one is more likely to get attacked in the United States, although the death rate is clearly much greater in Australia (25% vs. 2%). However, in the United States, the risk is spread over a huge populace. The United States has about 14 times as many people as Australia. If one looks at risk on a per capita basis, one's odds of becoming shark food in Australia are roughly twice what they are in the U.S., and if you are attacked you are 10 times more likely to not live through it.

4 comments:

Anonymous said...

Epidemiologist in the house, here, Ben. The most relevant statistic would be the percent of OCEAN SWIMMERS that get chomped. I surmise that a much larger proportion of Aussies swim in the ocean compared to Americans. Hence, the rate of shark death among ocean swimmers is probably many times larger in Australia than in America.

Anonymous said...

P.S. Logan wrote that comment.

BP said...

Yes, thank you Logan. I knew you would not be able to resist.

However, there are a number of other density-dependent effects here: specifically, the population density of the predators, their feeding behavior, and their response function (how feeding behavior changes with prey density).

Anonymous said...

Although, Ben, your listed variables may be interesting when looking at the cause of shark attacks, I don't believe they help answer the question of where you are more likely to get bitten/killed by a shark -- the U.S. or Australia.

It seems to me that the most relevant statistic would be a scalar somewhere along the lines of total swim hours (total # swimmers * average hours swum) per mile of commonly used beach. The "commonly used beach" variable would only include those miles of beach that have a certain, reasonably chosen minimum visitor density. This variable choice would eliminate those thousands of miles of Australian shoreline (and Alaskan, for that matter) that are probably seldom used for recreational purposes. Such a statistic, when compared with the shark attack statistics mentioned, would give a more accurate "death rate," like total flight-miles versus total drive-miles when comparing plane and car fatalties.

But that's just one layman's opinion.

Tad