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Ocean Watch Susan Scott |
Sharks, marlins are
not afraid to ram boatsI received some good e-mails last week. One reader wrote: "My 34-foot fishing boat will be in dry dock in a couple of weeks. If I paint a school of fish on the hull over the bottom paint, will this attract larger fish? Is there a danger that this may cause predators like marlins and sharks to ram the hull and damage the wood planks?"
This question reminds me of two antelope hunters I met a few months ago who cut a big piece of plywood in the shape of a cow and painted on it the image of a Holstein. The couple carried their cow to a Wyoming hunting site, crouched behind and waited. When an unwary antelope came close, they stood up and shot it.
This didn't seem fair to me, but the hunters didn't see it that way. To them, all is fair in love, war, hunting and fishing.
But my writer didn't ask whether I thought his idea was sporting. He wanted to know if fish can be tricked by pictures.
Well, why not? They're fooled by lures. Here in Hawaii, barracudas have even attacked shiny barrettes in snorkelers' hair. (They needed stitches but survived.)
Given that large, predatory fish spend most of their lives searching for food, it seems reasonable that lifelike fish painted on a hull might attract big fish.
But as my reader suspected, he might not want some of them that close.
As fearless predators, billfish and sharks aren't usually hesitant about checking out possible food sources. In the early 1980s, researchers found a Boston Whaler washed ashore at Kure Atoll with a marlin spike poked through the hull into one of the seats. The operator was never found.
Tiger sharks aren't particularly shy of boats, either. A monk seal biologist told me that a tiger shark once attacked the whirring propeller of his outboard motor as he motored along in a remote atoll. The blow raised the end of his Boston Whaler out of the water. Amazingly, the shark swam off with no obvious injury.
Another e-mail I received this week came from a fellow writer and also mentioned boat bottoms. "I'm researching a book about the Atlantic Intracoastal Waterway ... and am exploring the source of the noise boaters hear under their hulls at night when anchored or docked in the warm waters of the southern waterway.
"The cruisers' folklore is that the noise is caused by 'krill' gnawing on the growth on their hulls. I suspect ... that snapping shrimp are the source of the crackling noise. Can you confirm that?"
I can. I once thought this common snapping sound was something weird that happened to fiberglass in warm water. That snap-crackle-pop, however, comes from 1- to 2-inch-long snapping shrimp, also called pistol shrimp. These shrimp have one enlarged claw that snaps shut loudly to threaten predators or trespassers and to stun passing plankton.
And even though they sound like they're right there, snapping shrimp can't hang onto hulls. They stay well hidden inside mud burrows, sponges or corals. The snapping noise is loud because sound carries so well through water.
And finally, an e-mail from Italy referred to my column on harp seals. "Thank you for helping the planet," wrote Marco. "I hope one day I will be so lucky, too."
I'm not sure what luck Marco was referring to, but if he means my job, I agree. May he also be so lucky.
See the Columnists section for some past articles.
Marine science writer Susan Scott can be reached at http://www.susanscott.net.