Does Lightning Kill Marine Animals?

A reader brought to my attention a question that is floating around the internet.
Q: If lightning strikes the ocean, do the marine animals get hurt or killed? (Sault Ste. Marie, Minn.

Honestly, I have never given this question any thought. Given that I am a biologist and not a physicist means I may not even be the best to answer it. The first question is obviously how often lightning strikes the ocean?

The map below assembled by a crack team of NASA scientists shows the number of flashes per km2 per year. You can see that most of the worlds oceans are at less than 2 strikes per year (light blue). Areas near the coast receive more but typically still less than 10 per year. However the Gulf of Mexico especially near the Gulf Coast of the US and Florida appears to be quite a hotspot.

So even though lightning likes land, parts of the ocean receive frequent jolts.

What happens to the charge once the lightning makes contact with water? According to Don MacGorman, a physicist at the National Severe Storms Laboratory in Norman, Oklahoma.

"Basically lightning stays more on the surface of the water rather than penetrating it. That's because water is a reasonably good conductor, and a good conductor keeps most of the current on the surface."

So if I understand this correctly the surface is acting bit like the Gaussian surface of a Faraday cage. How far this charge carries across the surface likely depends on surface topography of the water, total power of the lightning, temperature, salinity, etc. Thus to the original question: what about the animals? If of course this is all true, and I know someone is out there waiting to pounce on this, then unless an organism breaks the surface it will not get electrocuted.

But what about the sound wave? A lightning strike at the surface generates up to 260 decibels at 1m away. That is about twice the decibels of a gun shot or firecracker. There is some evidence (Hasting and Popper 2004) that suggest hearing loss can occur in cod at 180 dB, with some other species closer to 220 dB. How many dB's does it take to rupture a swim bladder or interfere with other organs?

Ultimately I am hoping some of the readers will chime in and provide a more solid answer.

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fish typically don't get killed in large quantities by lightning because, as you guessed once again, they tend to swim deeper than humans do, while according to Florida physics professor Joseph Dwyer "most of the current from the lightning flows over the surface of the water."

The key word there is MOST of the current, not all. It can still kill them near the surface, they don't have to break it.

What about the heat generated by the strike? Does it boil the water at the surface and if so how much and does that matter?

Dunno so much about the acoustics side, but let's try it from another: natural mortality rates. In most bony fishes (things like Coelecanths aside), there's a normally high natural mortality rate (M), especially in the juvenile and young-adult stages that are more likely to be within the upper 1 m. I'd hazard to guess that while a lightning strike at sea might indeed boil, electrocute, or otherwise rupture apart any unfortunate fishes at or near the surface, it ultimately doesn't matter much for most species from a population level.

By FishGuyDave (not verified) on 17 Mar 2008 #permalink

I love the story, but I don't believe lightning is very harmful to marine animals. I've been surfing when the water was hit by lightning and all I felt was a warm tingly feeling. Could have been something besides the lightning, though. :)