Sunday, January 09, 2005
The manatee mortality conundrum
The fury of four hurricanes in Florida may have spared the state's endangered manatee population from further decline.
The annual report by the state Fish and Wildlife Research Institute shows deaths statewide fell to 276 in 2004 from 370 recorded in 2003.
"One theory is the four hurricanes that affected the state this year means we had less boating activity," said Tom Pitchford, a biologist with the research institute. "Fewer boats on the water means fewer manatees struck."
The total manatee death rate spiked in 2003 because of an aquatic phenomenon called a red tide event. It's caused by an unpredictable algae bloom that can sicken and kill sea life when it is ingested.
In 2003, the red tide event killed about 96 manatees. Otherwise, the 2003 death rate would have been closer to the total in 2004.
So let me get this straight: 94 fewer manatees died in 2004 than in 2003. The hypothesis advanced by both the headline writer and the quoted -- or misquoted -- Tom Pitchford is that the manatee population owes its good fortune to interdiction of boaters by hurricanes.
But then the article says that in 2003 an incremental 96 manatees died from a "red tide" bloom. So doesn't that mean that, controlling for the red tide spike in 2003, two more manatees died in 2004? The hurricanes had nothing to do with it.
Indeed, if you go straight to the Fish and Wildlife Institute's report on manatee mortality, you learn that the hurricanes had nothing to do with it.
According to preliminary reports, 69 manatees died this year due to watercraft-related injuries. That number (69) is consistent with past years, with watercraft representing 25% of total manatee mortality.
Why should we care about blowing cause and effect when it comes to the croaking of manatees? Apart from those of us who want to save the manatees (actually, I think they're pretty cool), does not this sort of brainless spew call into question the analytical skills of the typical reporter? It is stories like this -- and headlines that get written for like this -- that make you realize that most of the mainstream media is completely incompetent to examine numbers, be they public opinion polls, monetary policy, tax policy, corporate accounting, civil liability reform, the costs of the healthcare system, Social Security reform, the oil-for-food scandal, the impact of various reforms on the criminal justice system, or any other subject that involves thinking clearly about numbers.
For reading this far, you have earned some manatee blogging:
4 Comments:
By 
, at
Sun Jan 09, 03:18:00 PM:
Aww! That was so cute.
-evariste
By , at
Mon Jan 10, 08:47:00 PM:
I think you need to drill down on that number more. 64 manatees killed by watercraft is a big decrease in absolute terms. Per Fish & Wildlife, the body count has not been that low since '97. The average over the last 5 years (99 to 03) is 82 deaths by watercraft, so 2004 is almost 22% less than the 5-year average. Maybe the hurricane theory--if it is a theory--has merit?
By , at
Mon Jan 10, 11:48:00 PM:
Anonymous, you raise an interesting question. And I would drill down a bit more, but that I've moved beyond manatee blogging. However, taking your data as correct, we might wonder why the Fish and Wildlife Institute characterized the number of 2004 "watercraft-related" manatee deaths as "consistent with" prior years, unless perhaps it meant as a proportion of the whole. Also, if last year's spike was the result of red tide deaths not repeated this year, in order for the decline in boating accidents to be a cause of the decline of total deaths there had to be an increase of deaths from some other cause to make up for the decline in red tide deaths. I think.
Thanks for the close reading!
By , at
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