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2. SANCTUARY RESOURCES
(b) Living Resources
The area was selected and designated
as a national marine sanctuary because of concentrations of these
living resources of exceptional significance: (1) marine mammals
(pinnipeds and cetaceans); (2) seabirds; (3) fish, shellfish, and
kelp; and (4) intertidal organisms (Department of Commerce, 1980).
A review of these resources is helpful in understanding the populations
and ecological linkages being protected, their status, and options
for protection.
Pinnipeds
The dramatic recovery of pinniped
populations in the Channel Islands since the end of the fur trade
has been documented through several systematic studies in recent
decades (Le Boeuf and Bonnell, 1980). Past and on-going research
has also helped establish the status of seals and sea lions in different
parts of the Southern California bight including the Channel Islands
National Marine Sanctuary.
The Channel Islands National
Marine Sanctuary currently provides habitat for breeding populations
of five species of pinnipeds; the California sea lion, the Stellar
sea lion, the northern fur seal, the northern elephant seal, and
the harbor seal. A sixth species, the Guadalupe fur seal, is an
occasional visitor to the area. All six species are found in the
sanctuary at different times of the year, feeding on the abundant
fish and invertebrate resources of the island shelves or hauling
out on rocks and beaches.
Pinniped speciesÖ diversity
and concentration varies across the sanctuary. The greatest numbers
occur around the western tip of San Miguel Island, the only location
in the United States, and one of the very few in the world, where
breeding populations of five species of pinnipeds can be found.
Three species“California sea lions, northern elephant seals, and
harbor seals“breed at Santa Barbara Island. Harbor seals breed on
Santa Rosa, Santa Cruz, and Anacapa Islands. The life history of
each species has been described elsewhere (see Department of Commerce,
1980). The description below focuses on aspects relevant to the
sanctuary resource protection program.
The California sea lion
(Zalophus californianus) is the most abundant and widely distributed
pinniped of the sanctuary with approximately 30,000 individuals
hauling out and breeding in the area (NMFS, 1982). These numbers
represent about 25 percent of the total world population. San Miguel
Island is also considered the northernmost rookery for this species.
Estimates for 1981 set the annual pup production in the sanctuary
at 8,955 with San Miguel accounting for most of these numbers (NMFS,
1982). Some pups are also born at Santa Barbara Island. Growth of
the San Miguel population in the last two decades has been rapid
and is expected to continue (Le Boeuf and Bonnell, 1980).
Premature pupping and aborted
pups have been reported in recent years but it is currently not
known whether human-related factors such as pollution or natural
causes are involved (Le Boeuf and Bonnell, 1980). The northern elephant
seal (Mirounga angustirostris) is the largest and second
most abundant pinniped in the sanctuary. The total population in
1981 was estimated at 24,000 or 38 percent of the worldÖs total
population (NMFS, 1982). Elephant seal rookeries are located on
Santa Barbara and San Miguel Islands“the latter now being the largest
colony in the world (De master, pers. comm.) Total pup production
in 1981 was estimated to be 7,125 and further rapid growth of the
San Miguel Island population is expected (NMFS, 1982). Le Boeuf
and Bonnell (1980) report that elephant seal groups have expanded
their breeding area on the island from 1968 to 1979 to include virtually
the entire southern shore. Colonies may be forming on the northern
shore and establishment on the islands further to the east is also
a possibility.
The small colony of northern
fur seals (Callorhinus ursinus) on San Miguel Island represents
the southern breeding limit for this species. It is also the only
colony along the eastern Pacific south of Alaska. Since about 100
individuals were first discovered at Adams Cove in 1968, the population
has grown exponentially to about 2,195 animals in 1981 of which
1,220 were pups (NMFS, 1982). The species has also expanded its
breeding area to include Castle Rock. The waters within 3 miles
(5 km) of both rookeries are reported areas of concentration (BLM,
1981c).
All five islands (San Miguel,
Santa Rosa, Santa Cruz, Anacapa, and Santa Barbara) are hauling
sites and rookeries for harbor seals (Phoca vitulina). The
total population in 1981 amounted to about 2,100 individuals, with
the largest colonies occurring on Santa Rosa and San Miguel Islands
(NMFS, 1982). Le Boeuf and Bonnell (1980) report that the harbor
seal population has been increasing slowly but consistently in southern
California and throughout their range. This species is much more
wary than any of the other pinnipeds found in the Channel Islands
area, avoiding pupping at beaches used by other species and also
avoiding areas that are chronically disturbed by human activities
(NMFS, 1982).
Since 1968, the Stellar or
northern sea lion (Eumetopias jubatus) has been observed
in the southern California bight only on San Miguel Island (Point
Bennett, Richardson Rock, Castle Rock), and in steadily decreasing
numbers (Le Boeuf and Bonnell, 1980). The island is also the speciesÖ
southernmost rookery. Total numbers breeding on San Miguel Island
are thought to be low, with the total state population estimated
at 1,000, and with no more than 5 pups being born annually (NMFS,
1982). Factors contributing to the decline of the population are
not understood, but may involve a decline in prey availability,
competition with other pinnipeds, fluctuations in habitat parameters,
or some combination of these factors (NMFS, 1982).
The Guadalupe fur seal (Arctocephalus
townsendi) currently breeds only on the Isla de Guadalupe in
Mexico although it was once a resident of the Channel Islands. In
recent years, occasional male Guadalupe fur seals have been sighted
on San Miguel Island but pups have not been observed to date (NMFS,
1982). This species is listed by the State of California as rare.
It is also being considered for listing under the Federal Endangered
Species Act (R. Hofman, pers. comm.).
In summary, the significance
of the pinniped resources of the sanctuary rests on the following
characteristics:
- It is one of the few areas of the world
with an overlap in distribution of species characteristic of warm-temperate
waters (i.e., the California sea lion, the Guadalupe fur seal)
and cold temperate waters (northern fur seal, Stellar sea lion);
- The rookeries for several species have
been expanding in recent years and further growth is expected;
- For some species, the sanctuary population
represents a high percentage of either the southern California
population or the worldÖs total population;
- The indication that sanctuary waters must
be highly productive to support such a large and rapidly growing
mammal population; and
- The populations are relatively accessible
to major urban centers, providing opportunities for research and
interpretation.
While much is now known about
the status of pinnipeds, several key questions remain with respect
to their ecology and behavior that may affect how they can be protected
in the sanctuary. Management concerns which are being jointly addressed
by agencies such as the National Marine Fisheries Service, the CF&G,
and the Sanctuary Programs Division include: (1) the nature and
extent of interactions between pinnipeds and several net fisheries;
(2) the effects of hydrocarbon spills and chronic pollution on individuals
and populations; (3) the potential effects of the Space Shuttle
Program; (4) food requirements of pinniped populations and their
implications for fisheries management; and (5) the need to minimize
existing and future levels of human disturbance.
Cetaceans
At least 27 species of whales
and dolphins have been sighted in the sanctuary. About 18 species
are seen regularly and of these common dolphin, Pacific white-sided
dolphin, bottlenose dolphin, DallÖs porpoise, northern right whale
dolphin, short-finned pilot whale, killer whale, and minke whale
are considered Ñresidentsæ (Leatherwood, pers. comm.). RissoÖs dolphin,
fin whale, humpback whale and gray whale are other species possibly
residing in the sanctuary. Very little is known concerning the areas
of concentration, life history, or behavior of the resident populations
in the sanctuary.
The sanctuary also lies on the
migratory pathway of the California gray whale and other large baleen
and toothed whales. Gray whales with calves have been observed in
the nearshore kelp beds of the sanctuary which are thought to offer
protection from strong seas and resting habitat for calves (Leatherwood,
pers. comm.). The Pacific right whale, one of the rarest of the
great whales, has also been sighted in the area.
Cetaceans are considered a
significant sanctuary resource because of the frequency and diversity
of sightings in the vicinity of the islands, and the fact that the
worldÖs total populations are so small.
Marine Birds
Marine birds constitute another
significant resource because of the large concentrations and high
species diversity observed in the sanctuary. Over 60 species may
be using sanctuary waters to varying degrees as nesting and feeding
habitat, for wintering, and/or as migratory staging areas (Department
of Commerce, 1980).
Of the sixteen resident species
of marine birds in the southern California bight, eleven breed in
the sanctuary. Some of the colonies represent large percentages
of the southern California or statewide total population (Sowls
et al., 1980).
San Miguel Island, together
with its small islets (i.e., Prince Island, Castle Rock, and Richardson
Rock) supports the most abundant and diverse avifauna in the sanctuary.
Nine species have established colonies on the island and form dense
feeding concentrations in nearshore waters during their nesting
season. Santa Barbara Island has several nationally and internationally
significant seabird colonies including the largest XantusÖ murrelet
colony in the United States and the only U.S. colony of black stormpetrels.
The only permanent rookery in
California for the brown pelican“an endangered species“occurs on
Anacapa Island. As with the other marine birds, this species is
critically dependent of the abundant fish resources of the sanctuary.
The island also supports a large western gull colony.
In summary, the significance
of the marine bird resources of the sanctuary is based on the following
characteristics:
- The large concentrations and high species
diversity, particularly in the vicinity of San Miguel, Santa Barbara,
and Anacapa Islands;
- The presence of a unique colony of an
endangered species (the brown pelican) and several other rare
species on Anacapa and Santa Barbara Islands, all of which depend
on the productivity of sanctuary waters; and
- The colonies and nearshore feeding habitats
accommodate major percentages of the StateÖs total populations
that no longer breed on the southern California mainland.
The biology and ecology of
a few species of marine birds such as the California brown pelican
and the western gull have been well documented in the sanctuary
(NPS, 1982b; Ingram et. al., 1983). If the distribution of nesting
colonies are known for most other species, information is lacking
on colony sizes across the sanctuary, reproductive success, foraging
areas and habits. A handbook has recently been [prepared to guide
monitoring of selected seabird species of the national park and
sanctuary (Ingram et. al., 1983). If the distribution of nesting
colonies are known for most other species, information is lacking
on colony sizes across the sanctuary, reproductive success, foraging
areas and habits. A handbook has recently been prepared to guide
monitoring of selected seabird species of the national park and
sanctuary (Ingram et al., 1983). The monitoring program will be
used to detect changes in seabird populations over time.
Other management concerns being
addressed by agencies such as the NPS, the U.S. Fish and Wildlife
Service, the CF&G, and others include: (1) the food habits and biomass
requirements of some species and possible effects on commercial
fishery stocks; (2) interactions with certain types of fishing practices;
and (3) the effects of hydrocarbon spills and other types of pollution
on various species.
Subtidal Invertebrates,
Fish, and Kelp
Descriptions of subtidal environments
and species assemblages are available, albeit not complete, for
some sites within the Channel Islands National Marine Sanctuary
(California State Water Resources Control Board, 1979a, 1979b; NPS,
1982b). The predominant nearshore communities are: (1) the kelp
forest rock bottom community, and (2) the shallow sand bottom community
(CF&G, 1979).
The kelp forest rock bottom
community is by far the better studied nearshore habitat type in
the sanctuary. Luxuriant forest-like growth of giant kelp (Macrocystis
pyrifera) occurs in shallow waters, usually from 26 ft (8
m) to 112 ft (34 m) throughout the sanctuary (CF&G, 1979; Department
of Commerce, 1980). While the kelp canopy will vary from year to
year depending on storms and other factors, the most dense and extensive
formations occur along protected island shores (e.g., the southwest
side of San Miguel Island, southern and western shores of Santa
Rosa, around all of Anacapa Island, the northeast side of Santa
Barbara Island). Several other numerous brown algae (e.g., Agarum
sp., Laminaria farlowii, Pterygophora californica) occur
in association with giant kelp. Other subtidal algal zones reported
in the sanctuary are: (1) a shallow zone from the intertidal to
26 ft (8 m) dominated by other brown algae such as southern palm
kelp (Eisenia arborea), feather boa kelp (Egregia
sp.), and Laminaria farlowii; and (2) a deeper zone below
112 ft (34 m) typified by small red algae (Rhodophyta) and scattered
Agarum fimbriatum (California State Water Resources Control
Board, 1979a; Neushul, 1967; see also CF&G, 1979 for a more complete
list of common algae).
The kelp forest rocky bottom
community occurs in association with an unusually diverse and abundant
invertebrate fauna (CF&G, 1979). However species lists are available
only for a few sites such as the ecological reserves (around Anacapa
and San Miguel Islands) and Areas of Special Biological Significance.
Additional research is required to delineate areas of exceptional
significance. Large conspicuous invertebrates of the rocky bottom
kelp forest include several sponges, kelp crabs, spiny lobster,
abalone, octopus and squid, sea stars, and sea urchins. Common fish
of the kelp forest community include garibaldi, opaleye, kelp bass,
California sheepshead, sea perch, painted greenling and several
species of rockfish.
Shallow sandy bottoms are another
nearshore subtidal habitat prevalent in the sanctuary (CF&G, 1979).
Except in very calm shallow coves, sandy substrates do not support
extensive algal growth. Fish and invertebrate species tend to be
less diverse and abundant than in kelp forest communities. Common
species include sea pansies, polychaetes, sand dollars, several
species of rays, sanddab, and turbot (CF&G, 1979).
Accurate characterizations
of the deeper subtidal habitats of the sanctuary are extremely limited
(CF&G, 1979). Surveys have shown that the benthic fauna of the silt-dominated
canyons is diverse (CF&G, 1979). The walls of such canyons are often
covered by a dense animal Ñturfæ“a thin living mat of encrusting
sponges, bryozoans, and tunicates. Equally high diversities and
concentrations are found in the offshore pelagic environment of
the sanctuary. Common pelagic invertebrates include several copepods
and euphausiids, a pelagic shrimp, squid, and the pelagic red crab.
Over 30 species of fish are also common to the pelagic environment
of the sanctuary. Concentrations of the pelagic schooling species
such as northern anchovy are a critical food source for other sanctuary
inhabitants, such as the brown pelican.
Intertidal Organisms
Intertidal fish and invertebrates
of the Channel Islands have been comparatively well documented (Littler,
1980). Common habitat types include rock shelves, boulder beaches,
tidepools, rubble piles, and sand flats. A diverse and abundant
fauna is reported at the sites that have been surveyed (California
State Water Resources Control Board, 1979a, 1979b, 1981a, 1981b).
Common species include acorn barnacles, periwinkles, limpets, chitons,
sea stars, shore crabs, several species of brown, red, and green
algae, sea lettuce, California mussel, and black and green abalone.
Black abalone concentrations in remote areas of Santa Cruz, Santa
Rosa and San Miguel Islands are particularly significant as these
no longer occur in more accessible areas.
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