Biology Reference
In-Depth Information
swimming shoreward over the mudflats during inundation and retreating
to deeper waters as the tide ebbs. In open waters, they swim about in
groups made up of other Leopard and sometimes Smooth-hound Sharks.
Creek Fish
Local streams flowing into the bay are storehouses of aquatic diversity, no
matter how urban their setting or how altered their condition. Fish biolo-
gist Robert Leidy of the U.S. Environmental Protection Agency has con-
ducted several surveys in Bay Area streams over the past 25 years, and he
finds that even dramatically altered urban streams still contain robust, di-
verse native fish assemblages. According to his latest survey, published in
2007, at least 24 of the 33 native fish species historically found within estu-
ary streams still have reproducing populations. These range from Three-
spine Stickleback to Sacramento Suckers and the California Roach. One
reason for the persistence of native fish is that they may be better adapted
to wide seasonal and annual variations in water temperature and flow than
introduced exotics. Species such as Topsmelt and Pacific Staghorn Sculpin
are accustomed to wide swings in salinity at the mouths of streams and in
the delta.
“From the sky it can look like it's all concrete. But it's amazing how
much native life there is in these little corridors weaving through neigh-
borhoods and up into the hills. Creeks are surviving islands of biodiversity
in our urbanized landscapes,” says San Francisco Estuary Institute ecolo-
gist Robin Grossinger.
THE CREEK CONNECTION
Creeks connect the food webs of the uplands to the bay. Their waters carry nu-
trients—decaying vegetation, organisms, insects, and larvae—to the edges of
the bay, where the mixing zone of salt water and fresh water provides a rich
habitat. Creeks also connect regional ecosystems to those of the Pacific as a
whole. Steelhead and salmon are the most obvious link, spawning and rearing
in creek riffles, feeding in the brackish shallows of marshes, and maturing in
the open ocean. But other species roam back and forth between the estuary
and the wider world as well. For example, Yellow Warblers (
Dendroica petechia
)
migrating between nesting grounds in North America and overwintering areas
in Mexico often take a break from their grueling flight at San Jose's Coyote
Creek. The creek is an oasis of available food within the urban sprawl of the
South Bay. The majority of migrating warblers gain weight at this rest stop by
feeding on insects that thrive in the creek's wet greenery. The creek and its
food stores are even more critical to Pacific Flycatchers, which have exhausted
their fat stores and are running on empty by the time they arrive.
