by Eric Ettlinger
When I think of wildlife migrations I think of wildebeest on the Serengeti, gray whales off the California coast, and arctic terns migrating between hemispheres. I definitely don’t think of pond turtles. In fact, having observed the same turtles loafing about in MMWD’s reservoirs year after year, I assumed turtles barely moved from one end of a log to another. But if you observe wildlife long enough, you’ll always gain respect for their abilities.
Checking the smolt trap on Lagunitas Creek
Each spring, MMWD’s Fisheries Department operates a rotary screw trap in Lagunitas Creek near Point Reyes Station, to monitor salmon smolts as they migrate to the ocean. Fish are swept into the trap and funneled into a live box, where they are counted and released each morning. For two months the trap captured migrating coho salmon and steelhead smolts, as well as 13 other species of fish. The trap also captures amphibians, crustaceans, lots of debris and the very occasional turtle. One morning in late April we captured a western pond turtle, which to my great surprise looked familiar. At the edge of its carapace (shell), on the ninth marginal scute (the ninth square on the edge of the carapace, counting clockwise), was a distinctive notch. As far as I know, I’m the only biologist in the watershed marking turtles, so that was likely my mark designating this as Turtle #9. I measured the turtle, took some pictures and sent him on his way.
Western Pond Turtle #9, with arrow showing notch in marginal scute
Back in the office I reviewed the data from six years of turtle monitoring in MMWD’s reservoirs. MMWD began a non-native turtle removal project in 2004 to reduce competition between non-native and smaller, native turtles. In 2004 and 2005 I removed 79 red-eared sliders from Phoenix Lake, outside of Ross. These were provided to a turtle rescue organization that would find new, and hopefully permanent, homes for them. As part of that project, volunteers go out each spring and count native and non-native turtles in district reservoirs to track the ratios of turtle species. Native turtles are once again the majority in two lakes, but non-natives still dominate in another.
Turtle #9 was one of 17 western pond turtles captured and marked in Phoenix Lake while non-natives were being removed. In 2004 his carapace measured 176 millimeters (6.9 inches), and when he was recaptured in 2009, still in Phoenix Lake, he had grown two millimeters. By 2011 he had grown an additional two millimeters and had migrated 16 miles, straight as the crow flies, into another watershed. Of course he didn’t travel straight as the crow flies. His most likely route was to trek one mile west and approximately 500 vertical feet up to Bon Tempe Lake in the Lagunitas Creek watershed, and then down to Alpine Lake. Obstacles from there include Alpine Dam (135 feet high) and Peters Dam (215 feet high), before a turtle can get to the undammed reaches of Lagunitas Creek. By this point Turtle #9 would have traveled over nine miles, with nine more creek miles to go before reaching our rotary screw trap in Point Reyes Station.
Why would a small turtle undertake such a journey? Young males of many species disperse to find open territories, but this was a fully-grown male, from a lake recently cleared of 79 non-native competitors. Maybe he started out looking for new mating opportunities close by and just kept going. Another possibility, although remote, is that he hitchhiked. While that sounds absurd, turtles often get moved around by people. Usually it’s a female, traipsing overland to lay her eggs, that’s picked up by a well-meaning person and put into the closest body of water, which isn’t always where she came from. But someone driving a turtle to Point Reyes Station is an even more implausible theory than a turtle making the journey alone.
Which brings me to the sermon part of this post. Everyone loves turtles, but that love can have consequences for the objects of our affection. When we see a turtle shuffling across dry land, our inclination is often to put it back in the water. This forces the likely heavily pregnant female to start her nesting journey all over again. If you see a turtle on a busy road, help it by moving it in the direction it’s going, but otherwise leave it alone. And if you have a pet turtle that was once cute but is now a large, smelly paperweight, please don’t release it into the wild. Contact the Marin Humane Society instead. You may think you’re sending your turtle on an amazing journey, but along the way it may compete with or spread diseases to our native turtles, which almost always prefer to loaf about in peace.
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