and on if you are likely to be attacked within the SF Bay itself.
Theme:
Reassuring details about Great White Sharks migration, and that you are safe swimming and doing water sports in San Francisco Bay
I live in San Francisco. I like to try and Kiteboard in the Bay, and I get concerned sometimes about Great White Sharks. I decided to research how dangerous it is to be within the San Francisco Bay. And also in the Red Triangle. What I've found, is it matters where you are, what time of day it is, and also what time of year that you are there.
Where you are:
This is the second biggest driver of a potential incident with humans
The SF Bay is very safe, there has never been a fatal shark attack inside the SF Bay. Also salinity and pollution keeps Great White Sharks away. Less than 1% of Great White Shark detections in one study were found to have been within the Bay. Sharks are very territorial and like their specific feeding areas. They don't wander to feed much.
What time of day it is:
Avoid dawn and dusk. These are prime hunting times for sharks. Don't splash, Great White Sharks first use auditory senses, they then use sight as they get closer to prey within ~150ft. Sharks have excellent vision.
What time of year it is:
This is the biggest driver of a potential incident with humans
March to Early August is OK, Great White Sharks have migrated away from SF.
August to February is when Great White Sharks are in the area. However the population is not that large, it is estimated that there are only 219 in all of the Central and North California coast (2011 study). This estimated was recently found to be low. New estimates believe there may be greater than 2,000 Great White Sharks in the general California area (2014 study). The California government states a wide range between a few hundred and greater than 3,000. The variance is generally because of different statistical methods.
There are great seasonality charts available based on sensor tag data and research of the sharks. You can see the Great White Sharks are gone in May and back in November. I've posted the by month charts below. Here are the sources (*5)
To summarize my findings, if you are looking to go into the water in SF, and are nervous about Great White Sharks. Don't go out from late August to early February when there will be the most Great White Sharks around. You can go out March, April (maybe Late April) until Early August and should have very little chance of running into a Great White Shark (maybe even Mid August). The reason for this is the migratory patterns of Great White Sharks.
Within the SF Bay itself should always be pretty safe. It isn't a favorable environment for Great White Sharks, partly due to salinity and pollution.
(*2) The hotspot for Sharks is outside the Bay itself, but in the Bay Area, the hotspot is the Farallon Islands. I found that Scott Anderson has done quite a bit of research on Shark Attacks off the coast of SF, and in the Red Triangle (Farallon Islands). The above picture is from some experimentation he did. He found that in the Red Triangle, sharks hit once every 1.9 hours when he would leave a surfboard out (Southern Farallon Islands).
From Surfer.com, he then upgraded to a fake seal as 'bait' and did the experiment at the northern tip of Point Reyes.
"In the ’90s, he spent many a glassy fall day trolling for whites off the northern tip of Point Reyes, using a surfboard as bait. On average, it took six hours for a shark to “investigate” the board. Later, Anderson began using a seal silhouette instead of a surfboard. By 2004, his incident rate had increased to every 1.9 hours—on par with the Farallon Islands, where conventional wisdom dictates entering the water is suicide."
For Point Reyes Specifically
"White sharks are observed at PRNS most frequently in the late summer and fall (August, September, October)"
Seasonal timing of when you are in the water is important. (*3)
"It is significantly safer to do those things between January and July, when the sharks live in the deep ocean near Hawaii."
January through July being safe is one of the many time ranges that seems slightly off from the actual sensor tag data below. You'll notice more sources that in some cases are even further off from the actual sensor tag data which I'll present below. Various publications can't seem to agree on the population size either, which makes more sense.
The best information I found came from the Mercury News in 2009 (*4)
"The five sharks that came into San Francisco Bay represent less than 1 percent of the nearly 64,000 detections researchers picked up along the California coast from acoustic tags. Some details are known about the bay visits, however. One shark was detected one time inside the Golden Gate Bridge in December 2008; a second shark was detected one time, in April 2008; a third shark was detected four times, between November 2007 and November 2008; and a fifth shark was detected three times, in August and September 2007. In it, scientists used high-tech acoustic tags to find that white sharks display amazingly precise migration patterns.
The 'amazingly precise' migration patterns are worth noting, sharks like to stay in their areas or territories, so they aren't just roaming the ocean looking for you.
Again, seasonality should be emphasized.
They are most numerous off Northern and Central California between September and November, and almost all gone from April to July.
The only documented white shark fatality in San Francisco came on May 7, 1959, when Albert Kogler Jr., 18, died while swimming in less than 15 feet of water after he was attacked off Baker Beach, about one mile west of the Golden Gate Bridge"
Tragically comic that this was in May. The month with lowest odds of a Great White Shark being in the area. This young man likely lost his life to a Juvenile Great White Shark.
The above data from 2008 indicates that 179 Great White Sharks in the SF Bay Area were tracked. This would mean there are likely close to that number in the total Great White Shark population for the area.
Per wikipedia, SF's Great White Sharks are distinct genetically. (*5)
The movement of sharks and other large marine animals in this region were studied starting in 1999 under the Tagging of Pacific Predators (TOPP) program, an international collaboration. TOPP found that white sharks in the Red Triangle are genetically distinct from others in the Pacific Ocean, such as those found off South Africa and Australia.
Taylor Chapple, post-doc researcher, did extensive studies to estimate the Great White Shark population in the North East Pacific Ocean (2011 study). He found (*17)
Using statistical techniques that are beyond the scope of this summary, scientists estimated that there were between 130 and 275 unique adult and near-adult white sharks off Central California during the study. The likelihood that there were more than 275 individual sharks is less than five percent. The best estimate of the population size was 219. This implies that the total number of adult and near-adult white sharks in the northeast Pacific could be in the range of 300 to 400.
Another number from the California Government gives a wide range of the above study and the below studies (*18)
In 2014, the Fish and Game Commission determined that based on the best available science, listing the northeastern Pacific population of white shark as threatened or endangered under the California Endangered Species Act was not warranted. This was consistent with CDFW's recommendation. There are currently multiple estimates of the northeastern Pacific white shark population ranging from just a few hundred to greater than 3,000 individuals. All current estimates involve some degree of uncertainty, as there are significant gaps in understanding of white shark movements, reproductive biology and mating behaviors. Based on a thorough review of the best available scientific information, the higher estimates are more likely correct.
The Florida Program for Shark Research estimates 2,000 sharks (2014 study). (*19)
The study published by the Florida Program for Shark Research estimates there are 2000 swimming off the coast of central California. Although there are now more great whites swimming in U.S. waters, they are still rarely spotted by humans. There have been only 649 confirmed sightings of the great white between 1800 and 2010.
A number from PLOS that uses the first study of 219 by Taylor Chapple, also estimates greater than 2,000 sharks in all of California (2014 study) (*20)
It is amazing to have seasonality charts available based on sensor tag data and diligent research. Below is by month tracking of Great White Sharks. The intro above highlighted May and November. Sharks are gone in May and back in November. Again, late March to early August look like there are minimal Great White Sharks in the area. (*5)
Image sourced via Google Images from The Royal Society Publishing (*5)
Athletes swim the Escape from Alcatraz triathlon each year in June. If you aren't nervous about sharks at all, go whenever you like! Likely you would be fine, because inside the Bay is not often frequented by sharks.
Image sourced from SF Gate (*24)
Like I've said previously, you will notice how the dates above from various publications are all over the place, I have cited at least 4 different publications on when Great White Sharks are in the Bay Area. I've done this so you get a scope of the mis information on these Great White Sharks. I trust the sensor tag data above. It is the same case with the population data, many different opinions, I'm more okay with there being a range in the population data. One colorful datapoint to add is that of Katherine Roy, author of Neighborhood Sharks. (*22) Her beautifully artistic book is worth buying for your table. She states that the Sharks come back in September, along with the Elephant Seals. This is mostly validated by the sensor tag data above.
Image taken from Google Books database containing the book Neighborhood Sharks (*22)
She also points out some of the distinctions between Male and Female sharks migration, some of which can be seen in the purple (female) & yellow (male) dots of the visuals above. And I won't get into in detail.
I found a great Quora post on additional safety within the SF Bay (*6)
"According to tracking data on some members of the species YES, GREAT WHITES ENTER the San Francisco Bay and this was back in 2009.
The problem for pelagic sharks entering the bay that no one has mentioned is that the SALINITY of the Bay is different than the open ocean. So while white sharks might ENTER the water body they probably do not stay long and are more than likely confined to the immediate Bay around Alcatraz, Angel Island but probably not further south than the Treasure Island because higher levels of freshwater (lower salinity) occur north and south of that area.
There are plenty of potential meals in the San Francisco Bay because of the number of marine mammals that congregate there."
This would imply North Bay, and South at 3rd Avenue and Alameda are very, very safe places to kite. Especially when Great White Sharks have migrated towards Hawaii and the White Shark Café. Pollution also impacts all of the Bay. One study from 2012 indicated 1.36 million gallons of trash enter the Bay each year.(*23)
Looking at the below salinity chart, you can see that wet Winter-Spring, is when there is low salinity, which Great White Sharks would not like.
Commentary on the above chart in this link
A larger time view is here below
The Bay water is not quite the right temperature. Great White Sharks prefer. Large sharks are less affected by temperature, so it's minimal impact on your risk in the water.
You can get the most recent salinity and temperature data in the SF Bay here, it is a great resource.
Great White Sharks prefer shallow water, many attacks happen there, I don't think the depth of the water protects you much. Great White Sharks do actually prefer shallow water. They swim near the surface of the ocean (*7).
Over a million data points analyzed from eight white sharks revealed that all but one stayed in the Cape Cod area for the entire 28-day period the tags remained attached. They swam in water temperatures that ranged from 48-69 degrees Fahrenheit, and spent an average of 47% of their time in water less than 15 feet deep.
Depths in the Bay average an amazing 14ft only. It is not too shallow in many points for Great White Sharks to spend a lot of time. (*8)
Their preferred temperature is consistently in range of the temperatures of the SF Area, but SF waters are a bit cool for Great White Sharks. (*9)
Although Great White Sharks love the coastal areas in all oceans from all over the world, they typically live on the outskirts of shore waters. Sometimes, they stray into the deep Ocean and are even found in depths of 1000 meters (3,280ft) or more! But their preferred water temperature is from 15C to 24C (59F to 75F), so most of the time they stay in shallow waters and near the surface.
Temperatures in the SF Bay Area seem to align pretty well with their migration patterns. However in general temperatures are cooler in the SF area than what Great White Sharks would like. Santa Cruz is above the 59 degree F minimum for Great White Sharks from August to October. Adult sharks can tolerate wider levels of temperature than juvenile sharks, juveniles are very driven by the water temperature, the Bay Area is too cold for them (*10)
“Once bigger, they are now big enough that they are not influenced by temperatures,” Lowe said, explaining the findings only hold true to sharks under 1 year old, according to the Register. “Like a small kid, they get colder in a pool than an adult that has more mass. The bigger they get, the less temperature-sensitive they become.”
Great White Sharks are not here for the weather, they are here for the Seals and Elephant Seals (collectively pinnipeds). They arrive quiet skinny on their trip back to SF from Hawaii and the White Shark Cafe, and bulk up before the next trip back offshore.
There are seals, sharks, and whales in the Bay. Research suggest female Great White Sharks visit the Farallones every other year. Which is tied to a two year reproduction schedule. Some juveniles sharks wander into the SF Bay Area as well, but don't follow a migratory pattern. (*21)
See this incredible video of a Kiteboarder actually getting bumped by a whale near the Golden Gate Bridge. (*12)
Here is a Great White Shark breaching to attack a seal. It's actually the first hunt ever recorded in the Bay. That’s how rare it is. And like the Quora post above, salinity levels, pollution, and better hunting grounds outside the SF Bay keep Great White Sharks away. (*13) There are an average of 1.8 Great White Shark attacks per year off the coast of California. Since 1950, there have been 194 shark incidents in California involving all species of sharks, at least 172 of which involved white sharks. Of those, 14 were fatal and all of the fatalities involved white sharks. Thats 14 fatalities in 70 years, many of them in SoCal.
There are accounts of shark attacks within the Bay Area, they are very rare. SF Gate provides a map of attacks over the last 100 years in the Bay Area. Pretty cool! (*14)
The attacks near Alameda took place at a time when they had a cannery which ran off into the water, that no longer exists. It was basically constantly putting out chum for sharks.
Outside of the Bay, there are some Shark hotspots. A surfer has even been attacked twice near Bodega Bay years apart. (*15)
That is it for my SF specific commentary. Some useful and more general Great White Shark information is below.
I'm thinking about doing a SoCal write up as well, which is totally different because it's a highway for Juvenile Great White Sharks. Most Great White Sharks in the SF Bay area are adults. If you would be interested in additional research consolidated, or have something to add, please do email me.
Various contraptions exists to repel sharks. Either magnetic or electric oriented, or wetsuit camouflage. In general, probably the best way to avoid sharks, is to look like a seal, because they evolved to do so. That means a standard wetsuit.
Here is a youtube video that tells all about shark senses. It's extremely scientific and informative. It's from Ocean Ramsey and she does a great job of summarizing all of the information.
Summary:
Adult sharks are migratory, and then are very local & territorial as well to their specific areas.
Sharks are like dogs, different sense than we have
Sharks best sense is auditory, BEFORE their sense of smell
Tiger sharks can attack a bird from just it flying toward the surface of the water, couldn't find the clip but here is a link that is close.
Sharks avoid getting hit in the head. If they get hurt in the head, it has a huge impact on their ability to hunt. They will die if that part of their body gets hurt Punching it in the nose might work due to this. Push down on the nose
Sharks get full, and won't be likely to attack or hunt if they have been fed
Sharks have electrical sensitivity up to 6 feet. If you are carrying electronics, they might sense that once they get close, and be curious
Don't be in area with limited visibility, they might bite you to test if prey, don’t splash
Avoid areas where people fish (basically chumming for you)
Stay in shallow waters, close to shore (but keep in mind Great White Sharks prefer shallow waters, so water where you can stand is the right level of shallow but just further out is actually where they spend a lot of their time)
I have read and watched that Great White Sharks actually defer to larger animals and sharks in the water. So if there is a 9 ft great white shark and your kayak is 10 ft, it will be afraid to interact with you. This is why you make yourself big in the water if they are near. I'll need to find a source for this.
I am collecting and curating videos of Great White Sharks NOT ATTACKING people, I'll post them here
It's been suggested to me that I cage dive with Great White sharks to get over any fear of them. I might give it a shot.
Some other general Great White Shark trackers and resources are (*16):
Stay away from the men in the grey suits. The Universe is kind to have made April to September the best and most reliable time to Kite in SF. Respect all of the powerful forces of nature.
-iamnotaconsumer
Footnotes:
(1) Red Triangle Map
(2) Scott Anderson and Sharks in the Red Triangle
(3) Timing
(4) Timing great data and charts
(5) Detailed Seasonal Graphics around migration of sharks
(6) Do sharks enter SF Bay
(7) Sharks like shallow waters
(8) Depth of SF Bay
(9) Great White Shark Temperature Preferences
(10) Temperature Preference of Junvinille vs Adult Shark
(11) Temperature Data in the SF Bay Area
(12) Kite surfer gets bumped by whale in SF Bay
(13) Seal eaten by Great White Shark in the SF Bay
(14) Last 100 years of Shark Attacks
(15) Guy is attacked by Great White Sharks on two separate occasions in SF Area
(16) Reddit thread with Great White Shark resources
(17) Estimate of Great White Shark population in the North East Pacific Ocean from 2011
(18) California Government's estimate of Great White Shark population with a wide range
(19) Florida Shark Research estimates California shark population from 2014
(20) Additional validation of the Great White Shark population in California re examines data from the study in (*17) and estimates over 2,000 Great White Sharks from 2014
(21) Female Great White Sharks migrate every other year because of breeding -
(22) Neighborhood Sharks by Katherine Roy a must own piece of art -
(23) On Pollution of the waters in the San Francisco Bay
(24) Great white shark migration maps by month SF Gate
GREAT WHITE SHARKS NOT ATTACKING PEOPLE
Los Angeles - Beautiful footage with paddle boarder - https://www.youtube.com/watch?v=tsTGibQ5dYE
Los Angeles - Cool footage, calm day, another paddle boarder - https://www.youtube.com/watch?v=xym64NUCJTw
Los Angeles - Kayaker and Family and 9 ft shark - https://www.youtube.com/watch?v=2Wm4voruMSY
Hawaii - Ocean Ramsey with a recently fed shark -
San Clemente - Shark swims by surfer - https://www.youtube.com/watch?v=qDp4F1ppfCU
Australia - Surfer jumps off board onto shark - https://www.youtube.com/watch?v=kjYokU7LjcQ
Monterey Bay, CA - Swimmer and great white -
South Africa - Surfers have no idea great white is around - https://www.youtube.com/watch?v=5WhnkoyQjBY
New South Wales, Australia - Shark not interested in surfer - https://www.youtube.com/watch?v=MzqzeKFJmRM
Undisclosed Location - Great white approaches lineup, not interested - https://www.youtube.com/watch?v=adOq_F7SMPQ
Cape Cod, Maine - Shark photo, not interested in surfer - https://www.youtube.com/watch?v=nNDBVGpB8wI
Florida - Shark doesn't care for people -
Other References:
Great White Sharks, Science, and Info from Ocean Ramsey - Shark Behavior for Swimmers in Hawaii. How to avoid and respond to a shark.
Tiger Shark attacks bird -Tiger Shark Attack! | Benedict Cumberbatch Narrates South Pacific | BBC Earth
Live Salinity and Temperature data in the SF Bay- https://sfbay.wr.usgs.gov/cgi-bin/sfbay/dispsys/plotdata4.pl?cdate=120324&cdate2=120352&X=dist&Y=sal&dyn=y&width=600&mindepth=1&maxdepth=20
Great White Shark drags fishing boat in SF Bay -
Killer whales have been killing off the Great White Shark population in Cape Town. There are Killer Whales that come to the SF Bay Dec to May, they have not had the same impact.
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