UPDATE: April 23, 2018
At the end of turtle monitoring season in September 2017, the high count for Western Pond Turtles at Mountain Lake was eleven. Monitoring started earlier this year, at the beginning of April, and the results are better than anyone expected: 22 turtles. The mystery gets more mysterious!
The confirmed number of turtles has doubled in six months. What is going on? I asked Fue Her, the Biological Science Technician with the Presidio Trust.
“We haven’t changed anything, like the number of logs to bask on. The only difference is the time of year when we started counting. The summer fog hasn’t set in yet…”
But that’s a guess. The larger lesson is this: our ability to understand what’s really going on out there is pretty limited. Nature does as she pleases. Where were all these turtles last year? The truth is, we don’t know.
What next? We keep monitoring. We can look at the data we have for patterns. Perhaps the lake is cooler in April than September, and a cooler lake prompts more sunbathing. Wearing my Citizen Scientist hat, I can take a shot at the data myself. Doing a science!*
*apologies to @SarcasticRover
This story was originally a blog series— I’m leaving it in its original format.
Enter the Turtle
I am a Citizen Scientist, a Turtle Monitor. I count turtles.
July 11, 2017
I got the gig.
I’m an official Citizen Scientist. Courtesy of the Presidio Trust in San Francisco, I am now a Turtle Monitor. I count turtles.
Mountain Lake is the only natural freshwater lake inside the city limits of San Francisco. When the US Army pulled out in 1994, the lake water was dirty and dark brown from steeping in decades of eucalyptus debris. Native species had long since disappeared, replaced by carp, crayfish and red-eared slider turtles.
In 2014, the Presdio Trust began a major effort to restore the lake’s ecology. In 2016, some landmark species were reintroduced — Three Spined Stickleback fish, Pacific Chorus Frogs, and Western Pond Turtles.
How are the turtles doing? That’s where I come in. I watch, and I count. Watch this space for breaking turtle news.
How Many Turtles Were You Expecting?
Last summer, we counted dozens of turtles at a time. Today, I saw one.
July 16, 2017
The turtle release in July, 2015 was a big deal. It was the symbolic culmination of the restoration of Mountain Lake. These Western Pond turtles had been reared from eggs at Sonoma State University. At 5–6 inches across, the biologists said that the turtles were big enough to avoid predators. And each turtle was equipped with a radio transmitter, so they could be accurately counted from a distance.
54 turtles were in that initial release. Today, I counted one turtle. Yesterday, I counted three. There’s a problem here.
Fue Her is the Aquatic Ecologist for Mountain Lake. He is an intern with the Presidio Trust, and has been monitoring the turtles since their release. “We’ve found the remains of five turtles in the past year. Which is a lot. We weren’t expecting that many to die.”
When the turtles were first released, it was easy to spot them. Logs line the edges of the lake, making ideal basking areas. Last summer, there were plenty of turtles on view. With a pair of binoculars or a spotting scope, on a sunny afternoon, Fue would count 20, 25, 30 turtles. During cooler weather or cloudy days, Fue and other Presidio staff would count the turtles using a radio receiver.
Although the radio transmitters are still glued to the turtles’ shells, the batteries have been dead for months. The only way to count turtles right now is to peer through the spotting scope, slowly scanning the lakeside. We wait for the hottest part of the day, when the turtles should be basking, raising their body temperature by soaking up sunlight. We should be seeing dozens of turtles, jammed together like San Franciscans at Baker Beach on a (rare) hot July afternoon.
But the turtles aren’t there. The numbers aren’t adding up. I really hope this is a mystery, and not a tragedy.
Number of Public Engaged
“Lady, those were the wrong turtles.”
July 27, 2017
Making scientific observations requires a particular kind of rigor. For instance, when I do my turtle counting, it’s important to note the conditions: cloud cover, wind speed, air and water temperature. And at the bottom of the form, after I’ve taken notes on each turtle I’ve spotted, there’s one more line: “# of Public Engaged.”
If you stare through a spotting scope on a lakeshore long enough, someone will ask you what you’re doing.
“I’m counting turtles.”
“There used to be lots of turtles here.”
“Yes…those turtles are gone. Now there’s just one kind of turtle here, the Western Pond Turtle.”
“Well, I grew up here, and there used to be lots of turtles.”
“Lady, those were the wrong turtles.”
Only in blogs do I get to say “Lady, those were the wrong turtles.” But that’s the truth. The turtles that used to crowd the lake were Red-eared sliders, the most common pet turtle in the United States. Red-eared sliders are everywhere, which is good for red-eared sliders, but bad news for other turtles.
Red-eared sliders (Trachemys scripta elegans) are native to the southern United States. And it turns out that the Southern US is a hotbed of turtle evolution. It’s warm year round, and there’s lots of slow moving or still fresh water (The Mekong Delta in Southeast Asia is another fertile turtle territory). And one reason that red-eared sliders are popular pets is because they are a durable turtle. They evolved in a competitive neighborhood.
If Red-eared sliders are introduced into Western pond turtle territory, the Western pond turtles will lose. Red-eared sliders will grow faster and lay bigger broods of eggs than the Western pond turtles. It’s not the turtles’ fault; people are the ones spreading species around the globe, with unintended and unpredictable consequences.
So we engage the public. Explaining why the Western pond turtle matters, why restoring ecosystems matters, why biodiversity matters.
Absence of Evidence
Absence of evidence of turtles is not evidence of absence of turtles
August 21, 2017
Five. The current record for “most turtles seen at once” this season is five. In the best-case scenario, these five represent a little more than 10% of all the Western Pond Turtles that should still be doing their turtle thing at Mountain Lake.
So, seeing five turtles doesn’t mean that there are only five turtles (of the 54 released) still alive.
I spoke with David Harelson, a Wildlife Biology Technician with the Presidio Trust. As it happens, hs passion is herpetology — all things reptilian. His perspective on the Western Pond Turtles at Mountain Lake is helpful.
“Remember, it’s still ‘fogust’ [fog+August] in San Francisco. When we get longer days of sunny weather, in September and October, I expect that we’ll see more turtles basking at a time.”
Turtles bask for different reasons. The obvious reason is “to get warm.” But turtles don’t need to bask in order to be active. Turtles can spend the day in the water, looking for food, without needing to sunbathe. And basking has other purposes. Like humans, turtles use sunlight to generate their own vitamin D. Turtles bask to kill off algae that grows on their shells. And after a big meal, basking may help speed the digestive process.
On the foggy days typical of July and August in San Francisco (sorry Outside Lands), there’s not much to gain by basking: it’s not much warmer than being in the lake itself. So an absence of evidence of turtles is not evidence of an absence of turtles.
It’s too early to assume that the Mountain Lake turtles aren’t going to make it. Like many animals, once Western Pond Turtles reach maturity, the odds that they’ll live a long time improve. In the case of Western Pond Turtles, 50 years in the wild is a fair estimate. Turtles take the long view.
The turtles at Mountain Lake are still youngsters; at 3–4 years old, they won’t be mature enough to breed for another 6–10 years. Right now, though they’re too big to be prey for most birds, they are still vulnerable. As David said,
“The predation is real. These turtles are still small enough to be carried off by a determined raptor. The real risk, though, is raccoons. Raccoons are smart, and can work at a turtle, scraping out its carapace like a pumpkin.”
As Fue said, five confirmed deaths is more than expected. Last winter’s record rainfall may have done in some of the turtles, and the raccoons still pose a threat. But turtles have been around a lot longer than us, a lot longer than raccoons. The turtle strategy is sound. The turtles should be fine.
Still, we count the turtles we see, not the turtles we assume are out there somewhere. David was able to capture one of the Western Pond turtles — a big male with an dented shell — and attach a new radio transmitter. That’s one more data point; one more turtle we can track without needing to spot it while basking.
I’ve been observing these turtles for a few weeks now. But I’m hooked. I’m rooting for these little guys, hoping I get to see them grow up to be old farts. And as our best “summer” weather approaches, I look forward to spotting more of my turtle neighbors soaking up the sun, while it lasts, like the rest of us San Franciscans.
It’s Turtles All the Way Down
How many is eleven turtles?
November 9, 2017
Turtle monitoring season has come to a close. Our counts were going up — seven turtles, nine turtles, eleven turtles basking at once — enough for a football team! But internships end, and their programs expire with them. Also, CalTrans (California Dept. of Transportation) began some new work along the same shore of the lake where our turtles bask, and turtles prefer a more serene setting. Finally, the winter weather has settled in; cool and rainy.
Eleven. Last year, the biggest survey counted 38 turtles basking at once. This year, eleven turtles. So how many turtles are left?
It’s pretty clear that the attrition is due to raccoons. As David Harelson (Wildlife Biology Technician with the Presidio Trust) said, “You can see raccoon tracks all along the lakeshore. They’re smart, and there are a lot of them.” As the surviving turtles grow bigger, they’ll be less vulnerable to predators. But it does raise a question: if the Western Pond Turtles at Mountain Lake do live long enough to reach sexual maturity, how well will their offspring do? Hatchling turtles are like pot stickers to herons and grebes, not to mention the raccoons.
Estimating the total number of turtles based on our monitoring is like trying to guess the population of a town by watching the number of sunbathers at the local beach. On hot, sunny days, more residents show up on the shore — but never all of them at once. On rainy days, nobody is at the beach*, but that doesn’t mean that the town is empty.
Over beers at the local Irish pub/bluegrass joint, I spoke to David and Jonathan Young, a Wildlife Ecologist with the Presidio Trust about the turtle population. Jonathan hedges his bets. “If we saw eleven, maaaaaybe there are fifteen or sixteen turtles left.”
David is more sanguine. “I think it’s like a dolphin pod. For every dolphin you see at the surface, there are five or six below the surface. So, with the turtles, I’m thinking there are 20 or 25 out there.” He added, “you know, CalTrans has to have a biologist on site, and he says he’s seen turtles in the reeds while the work crews are there.”
And the reeds are where this author pins his turtle hopes. Presidio biologists (and volunteer Citizen Scientists, like me) observe turtles from the far shore of the lake, through a spotting scope. And all we can see are the logs that have been strategically placed for turtle basking. But behind the logs is a wetland nearly the size of a football field, created as part of the restoration effort at Mountain Lake. The reeds are mature now, ten feet tall. The mud is as swampy as you like — as sticky as molasses, and as aromatic as a manure spreader. These reeds are really hard for me and other Presidio workers to travel through; definitely not raccoon-friendly. I think there are turtles back there, playing it cool.
So is this a success story? Mountain Lake is a little lake in a major urban center. No matter how much we work at habitat restoration, we’ll never create a truly wild space. And the habitat we create is going to require ongoing care. But the results are worthwhile — reintroducing native species increases the diversity of the environment. With a diverse set of plant species, something is always in bloom for the pollinators; something is always in seed for the birds and the field mice. More birds stop at Mountain Lake now, where there’s a wider variety of insects to eat, a bigger array of potential nesting sites. Diversity fosters redundancy. Redundancy means resiliency; an ability to compensate when one resource goes sideways.
They call us habitat restoration volunteers “Presidio Park Stewards.” And stewardship is what this is about. We can’t return Mountain Lake to a pristine condition, even if we could agree on what that meant. But we can make it hospitable for as many native plants and critters as possible. And there are some clear success stories. The three-spined sticklebacks are thriving. And the Pacific Chorus Frogs are going gangbusters.
So this will be the last turtle blog for a while. But the Presidio is buzzing with more stories to tell.
*You might assume that turtles don’t bask in the rain, but testing assumptions is what the scientific method is all about. So one afternoon, when the water temperature was 10°F warmer than the air, and a cool mist was falling, I tested this hypothesis and counted turtles. I saw none.