On a sample of 17 divers with a combined total of many many many hours of diving we have only 3 encounters with a Great White Shark (GWS) that occurred while the diver was looking at the GWS through water (as opposed to through the air, like from a boat or kayak) giving a rate between 0.00007 and 0.00010 GWS encounters per hour (somewhere around 1 encounter every four years spent continuously in the water). A rough estimate of the attack rate per hour in water gives similar numbers to this encounter rate, so, here in Northern California, its probably just as likely that you'll encounter a GWS as get attacked while you're in the water.
First we count the numerator (number of in-water encounters).
1. Tony Civitell has one encounter whilst scuba spearfishing alone in
Reverse Cove, south of Soberanes Point, south of Carmel.
2. Bob Bachman's buddy has one encounter in Fitzgerald Marine Reserve
two years ago while freedive spearfishing.
3. Seth Hopkins and Joe Jackson in Fitzgerald Marine Reserve for
30-35 seconds (Citizen watch info) during a breathold dive Saturday
August 7 1999, Seth laying, back down, on the bottom at 35 feet
(Casio watch info) and Joe suspended around 18 feet, both of us
making sure It knew we were watching. My rate is 1 per 75 hours total
in Northern California (0.013), but my San Mateo rate is 1 per 4
hours (0.25). Joe's rate is about the same at 1 per 50 hours NorCal
total (0.020) and 7 hours San Mateo (0.14).
Now we count up the (more comforting) denominator (total hours in-water):
1. Dennis Haussler: 0 per 1000 hours.
2. Kurt Bickel: 0 per 2560 hours (16 years X 40 days X 4 hours).
3. Paul Castillou: 0 per 14 years (hours unknown, let's use Kurt's
metric to say 2240).
4. Dave Wittington: 0 per 21 years (hours unknown, Kurt's metric says 3360).
5. Dave Wittington's Friend: 0 per 25 years (Kurt's metric says 4000).
6. Dave Edlund: 0 per 26 years (this Dave says his 1990s totaled
1000-1500 hours, so let's say the total is around 3000 hours).
7. Joe Tobin: 0 per 20 years (Joe says about 10 hours per month X 6
months per year X 20 years = 1200 hours).
8. Terry Maas: 0 (Joe Tobin says) per many years (lets say 5000 hours)..
9. Allan Spehar: 0 per 1000 hours (his shore sighting doesn't count here).
10. Peter Wolfgram: 0 per 30 years (4800 hours).
11. Bob Bachman: 0 (I'm already counting his buddy's encounter while
Bob was on a diveboard) per 3120 hours.
12. One of Bob's buddies: 0 in 3120 hours.
13. Another of Bob's buddies (the one who encountered the GW) also
has a total of around 3120 hours.
14. Dusty Boeger: 0 in 15 years (he estimates hundreds of hours,
let's say 400 hours).
15. Seth Hopkins: 1 in a measly 75 hours.
16. Joe Jackson: the same 1 in a minuscule 50 hours.
17. Tony Civitell: 1 in 2000 hours.
Therefore, our survey shows that in a sample of 17 divers we have 3 encounters per 40045 total hours (0.00007 encounters per hour) (In the numerator, I'm counting Joe Jackson and I as one diver, one encounter since it was the same GWS. We now tend to stick together while diving, since after pulling that 30lb Halibut up together on July 29th by the shooting line and especially after Joe's squaring off to the GWS swooping in on my ass on August 7th our buddy lessons are well-learned. If I dive with any of you in the future you'll know why I am trailing by your fins in full-out symbiosis!)
This number of 0.00007 encounters per hour is confirmed by Alan Spehar's separate, more or less independent, estimate from the CENCAL competitions (Alan's estimate is 25 divers X 5 meet hours X 5 meets per year X 40 years) producing 1 (by Conrad, in Carmel River, this year, not included in the survey's 17) encounter per 25,000 meet hours cumulative of all divers (0.00004 encounters per hour). Our encounter rate is in this range of 0.00001 to 0.00020 even if we discover one or two more of us has had an encounter I haven't heard about yet, considering there are also some heavy-hitting veterans with 1000+ hours that we likewise aren't including.
I am aware from the CENCALFREEDIVER list that Larry Burris SCUBAing in Carmel Bay encountered (two passes) a GWS. I don't know how many hours he's been in the water though, nor do I know how many other vets are out there to contribute their thousands of GWS-less hours to the denominator. You can see that I don't want to prejudice the count towards the numerator!!
Notice that if we back off of Kurt Bickel's eager metric (160 hours per year, is he a fanatic?) and move towards a more sane metric like Joe Tobin's (60 hours per year) for those guys that just have yearly estimates, then our total hours becomes 1 encounter per 31045 hours (0.00010 encounters per hour). Cool, very cool, it all works out to quite rare indeed :-).
But what might be the number of GWS attacks per hour? Boy this is gonna be rough, but change the numbers as you see fit. Starting from 60 attacks in 73 years (1926 to 1999, I know many of these weren't while diving, but...) I would guess 100 (low?) to 500 (high?) full-on scuba/freedivers logging 160 hours (Kurt Bickel's metric) to 60 (Joe Tobin's metric) hours a year. This gives 0.00001 to 0.00014 GWS ATTACKS per hour in the water, remarkably similar to our range of GWS encounters per hour. I conclude that the two are just as improbable, but at least I would be more comfortable if the attacks were MORE improbable than encounters :-(. I'm just glad Joe Jackson and I landed on the encounter side of these two improbabilities, at least for this time :-) . One final number to consider is the 0.10 fatality rate given an attack. That is a tough one to get around and would only increase if we consider the poor souls who were never found again.
It should be noted that Joe Jackson and I believe we may never have even seen the GWS (unless it had attacked, and we may have caused it to abort its attack) if we weren't buddy diving in our (by now) typical style: always in eye contact, one following the other and meeting up on the bottom. It was on our way down that Joe squared off with the GWS heading toward my legs (from the bottom I was watching Joe, wondering why he wasn't coming on down, then I saw the GWS in an "einne-meanie-minny-moe" stalemate wondering who might taste better.
Our suits were identical, did we confuse Whitey with our schooling-fish tactic? Was my lingcod-style defense, holed up on the bottom waiting for danger to pass effective? Was Joe's China Rockfish tactic of raising his spines to make himself appear larger effective? We probably would all agree that the number of times that a GWS encounters us is likely to be more than 0.00010 per hour, and after seeing how that thing moves in the water I'm convinced it doesn't have to let us know that its checking us out for a dinner potential. It is able to sense us from well beyond our visibility range here in Northern California, and it can move in with great stealth, should it like the prospects.
So, given the indistinguishable rates of encounters and attacks, the GWS's stealth, predatory sense, low visibility in the water, and finally its range, I might speculate that they encounter us quite frequently, but should you encounter it, the bugger is really seriously considering an attack, or, the optimist might say, it has just called one off. In any case, you'd best find a cave quick and go in there with your best static breathold!
Some people say that the drive to the dive site is more likely to kill you than a shark. Auto fatalities are probably more remote than shark encounters, given that you are a freediver around here (let's say 3 hours driving per dive per person for 40 dives a year multiplied by the national average (I think) of 50,000 fatalities per year per 250,000,000 person gives 0.000002 fatalities per hour driving, significantly less than encounter rates and, incidentally, less than attack rates too. Sorry that's no comfort either. Sleep tight and D(r)ive Safe!
Whether by shallow-water blackout, entanglement (kelp, fishing line, etc.), knocking yourself out on a rock, or some other means, its drowning that has to be the biggest gotcha. No statistical data on that yet, though.
Thanks to all those named and not named for your participation in this study. You guys have dove a lot, and Kurt, if you keep it up, you're bound to encounter one too. Might I suggest you try at Fitzgerald Marine Reserve?!
-Seth