Shark Feeding Dives...Yes or No

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rjgiddings

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I'm not a marine biologist. I still would like to see these critters behave in their natural world - without boats buzzing, chumming, and divers feeding and filming them.

All the while - I'm secretly wanting to cage dive w/ great whites off the coast of MX. I just love those sharks that much.

There is a massive line between:
A.) big cattle boats taking hordes out to Molokini crater for a days snorkeling, the area is just totally dove out inside that crater. Maybe 1500 snorkelers a day go out there and back? It's nuts. Like a moonscape now.
B.) Diving while hovering - in Zen bliss - off the bottom on a shore dive while a shark happens to cruise by. Unchartered, unplanned, and really quite rare. The shark is as surprised to see me as I would be to see him.

Not to derail the OP - but I'd argue maybe we focus on saving sharks by outlawing the sales, distribution, harvest of shark fins - of any species. Anywhere in the world. My .02 is that's wayyyy more important.
 

tursiops

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No matter how sharp their senses are, the stimulus has to get to them

the scent trail has gone 10 nautical miles after three hours

before they hear or smell something interesting
You are completely forgetting the electro-receptors of the shark; arguably its best sensing too. The e-m field has no time-lag, and is not swept away by currents.
That might be the electrical field around the strobe during the recycling. The sharks can sense that. One shark expert analogized for me the sensitivity of a shark's electroreceptors as being able to detect the e-field from a D-cell whose terminals were a mile and a half apart.
 

HalcyonDaze

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You are completely forgetting the electro-receptors of the shark; arguably its best sensing too. The e-m field has no time-lag, and is not swept away by currents.
It also has an effective range of a few feet at best when it comes to things like nerve impulses and metallic objects in the water. It's only a long-ranged sensory/navigation system when it comes to large magnetic fields (e.g., potentially things like volcanic islands or seamounts). I have seen a baited operation off Cabo San Lucas deploy an electromagnetic lure ("Mako Magnet"), but given that it generally took at least three hours for anything to show up (and on two out of five days we got nothing) I'd say the chum slick was the primary attractant.


 

tursiops

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It also has an effective range of a few feet at best when it comes to things like nerve impulses and metallic objects in the water. It's only a long-ranged sensory/navigation system when it comes to large magnetic fields (e.g., potentially things like volcanic islands or seamounts). I have seen a baited operation off Cabo San Lucas deploy an electromagnetic lure ("Mako Magnet"), but given that it generally took at least three hours for anything to show up (and on two out of five days we got nothing) I'd say the chum slick was the primary attractant.


Did you actually read the article you linked all the way through? Or just stop when you got to navigation and seamounts?

The article quotes Ad Kalmijn, with whom I worked at Woods Hole Oceanographic Institution. I think Ad would disagree with your conclusions.
 

HalcyonDaze

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I'm not a marine biologist. I still would like to see these critters behave in their natural world - without boats buzzing, chumming, and divers feeding and filming them.

All the while - I'm secretly wanting to cage dive w/ great whites off the coast of MX. I just love those sharks that much.

There is a massive line between:
A.) big cattle boats taking hordes out to Molokini crater for a days snorkeling, the area is just totally dove out inside that crater. Maybe 1500 snorkelers a day go out there and back? It's nuts. Like a moonscape now.
B.) Diving while hovering - in Zen bliss - off the bottom on a shore dive while a shark happens to cruise by. Unchartered, unplanned, and really quite rare. The shark is as surprised to see me as I would be to see him.

Not to derail the OP - but I'd argue maybe we focus on saving sharks by outlawing the sales, distribution, harvest of shark fins - of any species. Anywhere in the world. My .02 is that's wayyyy more important.
I think this is sort of the line for me. I've never done one of the Caribbean reef shark feedings that are common in the Caribbean where you have a fixed site, operator in chain mail goes down with a crate of fish, and everyone sits in a circle on the bottom and keeps their hands tucked in while the buffet is on (we did have one site in FL where that was done before I was certified; years later at least one operator would mimic that setup by having everyone tuck down and then the DM would spear a small fish and stuff it under a rock). It doesn't have much of a lure for me. I hate to admit it, but I even get somewhat bored with our lemon sharks in FL; they're almost always present and unless I see something interesting (mating wounds, recovery from injuries) I generally put the camera down unless I'm getting shots of people with the sharks or otherwise am presented with an interesting photographic composition.

I'm much more interested with the seasonal variations in sharks; this spring is unusual because on the Jupiter Deep Ledge we're not seeing many bulls but the sandbar sharks have moved in about 6-8 weeks ahead of their normal schedule. Great hammerheads and tigers are only around at certain times of the year and you typically have to "work" to get them in.

Did you actually read the article you linked all the way through? Or just stop when you got to navigation and seamounts?

The article quotes Ad Kalmijn, with whom I worked at Woods Hole oceanographic Institution. I think Ad would disagree with your conclusions.
Yes, I have read it all the way through (multiple times; I discovered that site back in high school) and I'm very familiar with the Steinhart Aquarium incident mentioned. As described, "Sandy" only noticed the small 125-microvolt current when passing within a few feet of it on her normal route around the tank. Unfortunately, the tank design meant she had to pass that spot constantly as she swam, and as there was no way to fix the fault without draining the tank she had to be released.

While we're namedropping, I'm also familiar with Steve Kaijura's work; back when I had undergraduate illusions of being a hotshot shark biologist he was kind enough to spend 45 minutes on a phone call to discuss my research interests (another shark researcher at the time just blew me off with "well, go to the American Elasmobranch Society meetings;" from talking to one of his grad students recently he's no more helpful now that he has tenure) and one of Steve's grad school labmates (Chris Lowe) was on my M.S. thesis committee. Just because elasmobranchs have a high sensitivity to electromagnetic fields does not mean they can detect small point sources at long range. If that was the case I'd be very concerned; with all the submerged cables, metal objects, and electronic gizmos we've put all over the ocean they'd go mad.
 
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