Crawdads

Q. A group of families go out every year, often catching up to 300 crawdads for a big feast, releasing those with eggs. We often wonder if we are depleting the supply. How long do crawdads live? Are they native to the Bay Area? -Sam,

Well, Sam I am here to tell you go right ahead and eat all the crawdads you want, with or without eggs. And you can do so completely guilt free. In fact, your annual feast is likely benefiting some native species, such as the California newt. Depending on where you have been catching the crawdads, they could either be red swamp crayfish (Procambarus clarkii) or signal crayfish (Pacifastacus leniusculus). Neither is native to the Bay Area and both are considered invasive pests. The Bay Area native sooty crawdad (Pacifastacus nigrescens) has actually disappeared due to competition from the signal. California now has only one native crayfish — the Shasta crawdad. Native to Shasta County, it is listed as endangered because of water diversions, predation, and competition from that nasty signal crawdad.

The red swamp crawdad, native to the southeastern US, has been transplanted all over the world from Sweden to Kenya as a food source. It is extremely adaptable to a wide range of conditions and is very common in the Delta and Central Valley. Researchers have found that it preys on native California newts and it has been implicated in the disappearance of these amphibians from streams.

Both of these introduced crawdads eat a wide variety of plant and animal matter and can live from five to ten years in the wild. They have also become an important food item for California river otters, herons, egrets, raccoons, and occasionally Sam and his family.

Michael Ellis – Ask the Naturalist – Bay Nature Magazine

Most Rain in the SF Bay area

Q–Which spot in the nine-county Bay Area gets the most yearly average rainfall (and why) and which spot gets the least (and why)? And, of course, how much in each case?

Nearly all of the precipitation that we receive comes between November and April in the form of rain from moisture-bearing clouds off the Pacific. The San Francisco Bay area is well-known for its many micro-climates. Folks at the beach are freezing as the fog lingers in the Sunset District while others are sweltering in the bright sun in Livermore. The distribution and amount of rain is also all over this proverbial map.

At the Pt. Reyes Lighthouse, sticking way out into the ocean, you might expect rain to be plentiful. Wrong. Average rainfall there is only 15 inches. As storm clouds move inland and begin to rise up over the coastal mountains, the air cools. When air cools it cannot hold as much moisture and rain occurs. This is known as orographic precipitation and results in Kentfield getting 48 inches of rain per year from the same storms. And on the back side of these mountains rain shadows exist. So the city of San Jose may only average 16 to 20 inches of rain.

So the bottom line is that Mt. Tamalpais and the Santa Cruz mountains may get 45+ inches, Petaluma and San Francisco 23 inches and Livermore and Tracy 15 or less inches.

Michael Ellis – Ask the Naturalist – Bay Nature Magazine

Last Volcanic Eruption in the SF Bay area

Q: When was the last volcanic eruption in the Bay Area? Where was it?

A: You can easily visit the 10-million-year-old Sibley Volcano (see Bay Nature, April-June 2005) in the hills above Oakland. And I often see college geology classes stopped at the base of the Nicasio Dam in West Marin looking at pillow basalt lava that erupted from the floor of the Pacific Ocean over 100 million years ago.

But for the most recent local volcano, travel north to the 4,200-foot Mount Konocti near Clear Lake. It ceased erupting just 10,000 years ago-a geologic blink of an eye. Konocti (Pomo for “Mountain Woman”) is in the Clear Lake volcanic field, which has been active for at least 2 million years. The field is part of the larger San Andreas Fault complex, and the magma here fuels the largest geothermal energy production field in the United States-the Geysers Complex, in northeastern Sonoma County.

Michael Ellis – Ask the Naturalist – Bay Nature Magazine

Largest Fish in SF Bay

Q: What is the largest species of fish you could find in San Francisco Bay?

A: Let’s limit ourselves to the true bony fish, which would leave out any great white sharks that might wander into the Bay looking for harbor seals. (Like all sharks and rays, the great white’s skeleton is cartilage rather than bone.) Among the Bay’s bony fish, the white sturgeon (Acipenser transmontanus) takes the prize.

When Stafford Lake near Novato was drained for repairs in 1985, a seven-foot sturgeon was found that weighed 170 lbs and was 75 years old. Rumors of a giant fish lurking the depths of Stafford were rampant for years for once, a monster tale was true. But that fish was not so big by sturgeon standards. The West Coast record was taken long ago from the Frasier River in British Columbia-1,800 pounds and 20 feet long!

Sturgeon are the most primitive of the bony fishes, little changed from the age of dinosaurs. Instead of scales, they have overlapping bony plates called “scutes.” As adults, they are blind and toothless. With a specialized sucking tube and highly sensitive barbels (whiskers), they cruise along the bottom feeding on anything remotely edible [[plant or animal?]]. They are also among the world’s longest-lived fish, sometimes living over 100 years. Not surprisingly, they reproduce late in life-females don’t spawn until age 18.

During their long lives, these fish can build up a high level of contaminants from polluted waters, so San Francisco Bay fishers should eat no more than two meals per month of sturgeon.

Better yet, let those wonderful fish live out their long lives unhooked.

Michael Ellis – Ask the Naturalist – Bay Nature Magazine

Banana Slug Slime

Q – Why are banana slugs so slimy?

A – Back when I used to teach children about nature, I often relied on
a “hook” to keep them focused. Slapping myself with stinging nettle was a great attention grabber but banana slugs worked just as well and didn’t hurt as much. I’d find one and ask the kids “How do you really know it’s a banana slug? It could be a raspberry slug, or even a peach slug. There is only one way to find out for sure.” They would scream as I carefully licked the entire body of the slug. Rolling my eyes upward as if I were tasting a fine wine, I would announce, “Yep, that’s a banana slug.”

If I licked too hard and got some of the slug’s slime on my tongue I
would experience directly one of the many benefits of being
slimy-protection from predators. The slime is not only difficult wipe
off and unpalatable to eat, it also contains an anaesthetic that can
numb the slug nibbler. Not all predators are deterred: shrews love to
eat banana slugs and raccoons will roll slugs around in the dirt to
help get them down the hatch.

The slime of these ancient animals is a truly amazing and useful
substance. It allows the slugs to retain moisture and is especially
important when they aestivate-become dormant-during the dry summer months. They can roll up into a smaller mass with a protective slime shield and wait comfortably for the next fog or rain. The slime also helps slugs get where they need to go, whether that’s squeezing in to a tight space or sliding across the forest floor. They use the slime to adhere to steep surfaces and can even hang upside down from slime threads.

Slime is also an important part of the slugs’ mating process, as the
slow-moving creatures follow mucous trails in order to find each other and consummate their hermaphroditic sexual bliss. They often eat each others’ slime during courtship and then wrap themselves up in a nuptial bed of slime during the actual reproductive act.

Slug slime was originally thought to behave like a bowl of
spaghetti-the more tangled the strands, the thicker the mucus. But
researchers studying the chemistry of slug slime at the University of
Washington (where else?) have found that it is it is a highly-organized
polymeric material which can absorb water extremely rapidly-up to 100 times its initial volume! Once the mechanisms and molecules of slug slime are better understood, researchers foresee numerous potential applications in materials science and bioengineering, such as pollutant traps for sewage treatment plants, effective water-based lubricants, and better surgical implants and wound coverings. Hurray for the slugs!

Michael Ellis – Ask the Naturalist – Bay Nature Magazine