Biology Reference
In-Depth Information
can tolerate some salt in the water. By the time they've doubled their
length—to the size of a dime—they can handle full-strength sea water.
Whatever their size, longfin do require a little time to acclimate as they
move between fresh and salty conditions.
“Longfin Smelt have a broad-based strategy for life and multiple life his-
tory patterns,” says Randy Baxter. “They spread their options out over a
fairly extensive environmental gradient looking for conditions conducive
to feeding and survival. If spawning conditions are good, they can repro-
duce as early as their first birthday. If not, they wait until the second or
third. They take advantage of seasonal flows, positioning themselves up
and down the estuary to exploit open niches. They also position themselves
up and down the water column seeking the most advantageous conditions.”
Like salmon, adult Longfin Smelt move upriver to spawn, but most
only venture a short distance above the limit of saltwater intrusion. As
larvae, they seek out brackish water. Outflows from rivers and tides dis-
perse the hatchling fish downstream, increasing the likelihood they will
find food. As Longfin Smelt age, they move farther downstream, eventu-
ally reaching the Central Bay or the ocean before the end of their first year.
In the San Francisco Bay estuary, Longfin Smelt have a short life span
that averages around two years. That means small changes in conditions—
shifts in freshwater flows, ocean currents, temperature, or food supplies,
for example—can have a dramatic effect on their abundance. If one year-
class doesn't make it, there isn't much wiggle room for recovery in the
years before or after. Though their adaptable estuarine nature has made
them survivors, Longfin Smelt are currently threatened by human changes
to their habitat.
California Halibut
Many flatfish live in the bay, including California Halibut (
Paralichthys
californicus
). But contrary to their name, halibut do not always stay flat.
They may raise their heads up off the bottom to snap up a goby or even
swim into the water column to chase anchovies. Or they may get vertical
to do one other important thing—reproduce. Halibut males and females
release gametes in open water in close proximity to one another. “It's a
surprising sight: adults swimming up off bottom into the water column
and spawning like undulating stack of pancakes,” says Randy Baxter. “Hal-
ibut are pretty big. Imagine a 40-pound fish about three feet long. So to see
them swimming almost attached, and in tandem, head to head, tail to tail,
undulating almost as one, is unexpected to say the least.”
The undulations produce fertilized eggs, which drift, grow into larvae,
and then undergo the transformation that leaves them peering at the
world from only one side of their bodies. At this point juvenile halibut