The Northern Threespine Stickleback, pictured below, has a series of lateral scale plates distributed
across each side. The Unarmored Subspecies (G. a. williamsoni)
has few to no such plates (See Figure 1, above: CDFG Field Guide drawing).
The unarmored threespine stickleback is a small, scaleless. freshwater fishoriginally described from the
headwaters of the Santa Clara River in northwestern Los Angeles County. California. Previously found also in low gradient portions of the nearby Los Angeles, San Gabriel and Santa Ana Rivers, and from a few localities in Santa Barbara County, California, it has
been eliminated from most of its original range. It was reported in 1917 to be abundant throughout the Los Angeles basin. By 1942 it was no longer found, and believed to be extinct there. In the Santa Maria River drainage, populations regarded as the unarmored threespine stickleback (Gasterosteus aculeatus
williamsoni) were replaced by another stickleback (G. a. microcephalus) and by intermediate types, through
competition, introgressive hybridization or both, following introduction of the latter in trout plants. So far as.known, it persists only in the area where it was
first found and in one creek in Santa Barbara County.
The upper Soledad Canyon locality from which this fish was originally named in 1854, then known as
Williamson’s Pass, was described in an 1857 Pacific Railroad Survey as similar in some respects to its present condition. A continuous flow of water in the upper canyon was maintained in dry seasons by several feeder springs, but water levels in the lower canyon then as now retreated for much of the year below the surface of the stream bed.
on the biology of California
sticklebacks suggest that a slow continuous flow of water in a headwater stream, isolated, except during rainy periods, from the ocean by stretches of
dry stream bed, is necessary for this particular form to thrive. The intermittent lower watercourse evidently
confers a necessary degree of isolation
from other related sticklebacks found
in most lower stream segments connected
above ground with the ocean.
A similar form of isolation is provided at the mouth of San Antonio Creek by beach sandbars formed by ocean currents
that block the entrance of all fishes,
except during periods of high water
and swift currents that could be expected
to prevent entry of other
Apparently intolerant of turbidity. since it is not found in muddy water. this stickleback also avoids zones of swift current and those without any current. An additional biological requirement suggested by studies on similar fishes elsewhere is relative freedom from predation by larger carnivorous
fish. Although trout are present in
the Santa Clara River system,
they are confined to separate habitats
from the stickleback by a different range
of temperature tolerance.
A document entitled “Recovery Plan
for Unarmored Threespine Stickleback.
Gasterosteus aculeatus williamsoni, an
Endangered Fish” was submitted to the
Fish and Wildlife Service in 1977 by a
recovery team assigned to this species.
The team is headed, by Shoken Sasaki of
the California Department of Fish and
Came, and includes biologists and
wildlife specialists from other State and
Federal agencies. The recovery team
also submitted to the Service in 1977 a
draft proposal of essential habitat
recommendations, which was reviewed
by the Bureau of Land Management,
Office of State Director for California:
by the Director of the California
Department of Fish and Game; and by
the Regional Forester of the U.S. Forest
Service (San Francisco). The present
proposal incorporates recovery team
Research commissioned or conducted
by the Unarmored Threespine
Stickleback Recovery Team indicates that the present status of this fish is precarious. Negative impacts resulting in or contributing to complete elimination
of populations in various river systems are documented from large scale impoundments, stream channelization. increased water turbidity, introduction
of non-native competitors and predators.
and from water pollution of several
kinds. Many of these impacts are
corollary to increased urbanization in
the Los Angeles Basin area. In contrast.
some stickleback populations have
appeared to benefit from certain kinds
of very small scale impoundments. and
from legally mandated, limited but
sustained release of water from storage
Endangered status of the unarmored
threespine stickleback under the
provisions of Section 4(a) of the
Endangered Species Act of 1973. as
amended (18 USC. 1531 et seq.) is not
affected by this proposal to determine
The Act defines “Critical Habitat” to
include [a] areas within the geographical
area occupied by the species at the time
that the species is listed, which are
essential to the conservation of the
species and which may require special
management considerations or
protection: and (b) specific areas outside
the geographic area occupied by the
species at the time of listing, upon a
determination by the Secretary that such
areas are essential for the conservation
of the species.