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Chapter 6
Conservation Conflicts Between Species
Plants and animals are linked to other organisms in ecosystems in a variety of ways, so it is
inevitable that conflicts will arise when attempts are made to protect individual species of plants or
animals. Part of the charge presented to the Committee on Scientific Issues in the Endangered Species
Act was to consider the severity of conflicting conservation needs when more than one species is listed
in the same geographical area and provide recommendations for resolving these conflicts.
INTERACTIONS OF SPECIES IN NATURE
To evaluate the potential problem of conservation conflicts between listed species, two
fundamental ecological principles must be considered. The first principle is that organisms are
components of networks in which they interact. This principle has significant implications in planning
for survival and recovery of endangered species. If a management strategy does not account for the
important relationships and interactions embodied in networks, then unexpected or untoward results can
be expected (Holt and Talbot, 1978; Walker, 1989; Pickett et al. 1992; Fiedler et al., 1993; Franklin,
1993; Orians, 1993~. For example, management of the New Jersey Pine Lands without consideration
of certain rare herbs in the successions of pitch pine lowland or Atlantic white cedar swamp
communities results in the decline in density of herb populations and their extirpation from many sites
(Little, 1977; 1979~. Likewise, managing Pennsylvania forests for high densities of white-tailed deer to
support sporting interests inhibits tree regeneration in some stands and eliminates many shrub and herb
species from the understory of the majority of forest stands (Marquis et al., 1975), although if hunting
were prohibited, the problem would get worse.
Management or planning for recovery of endangered species in ignorance of the networks in
, ~ ~ ~
which they exist is scientifically untenable. In situations where two or more endangered species are
present, taking account of any network that includes them both (or all) should enhance the chances of
optimizing the persistence and recovery of all species.
The second fundamental principle of ecology that is relevant to potential conflicts among listed
species is that species are parts of spatial and temporal mosaics. The spatial dimension is cast in terms
of mosaics because both natural and human-modified landscapes are conspicuously patchy (Pickett and
White, 1985; Kolasa and Pickett, 1991; McDonnell and Pickett, 19931. This principle implies that the
networks of interaction in which species exist have a spatial component.
The important ecological characteristics of mosaics for conservation of endangered species are
that the resources, interactions, and constraints of endangered species can originate in the mosaic in
components other than the current location of the listed entity (Risser, 19851. Although it is difficult to
learn about the important ecological fluxes between patches that affect listed species, neglecting such
fluxes can result in failures to preserve targeted species (Saunders et al., 1991; Tyser and Whoriey9
1992~.
Taken together, the two fundamental principles described above suggest improvement in
iNot all the species discussed in this chapter are listed under the ESA, but the cases illustrate the kinds of
conservation conflicts that could occur between listed species.
89
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Science and the Endangered Species Act
endangered species management. Management that views each species as an entity by itself, with no or
little attention to the network of interactions, is likely to produce faulty protection strategies. Likewise,
neglecting the larger spatial context in which species exist may well miss key forces that are needed to
maintain the species. Taking these two principles into account in planning for management of listecl
species can provide a basis for assessing the potential for species conflicts and mitigating them
effectively. Without considering networks and spatial contexts, species conflicts are relegated to ad hoc
solutions on a crisis footing.
The committee has found few well-documented cases in which management practices focusing
on particular species protected! under the Endangerec! Species Act have resulted in direct conflict
between conservation needs for the species. Such situations likely will increase, however, as more
species are listed and as species and their networks become better understood. A sample of a few
specific cases demonstrates how management practices clirecte(1 solely at single species might present
such problems.
NORTHERN GOSHAWK AND MEXICAN SPOTTED OWL
Potential conflicts arise between the northern goshawk ant! the Mexican spotted owl, two
species of avian predators, when the U.S. Forest Service attempts to manage habitat for one or the
other in areas where both species occur. In the case of the Mexican spotted owl, current management
favors comparatively large, dense stands of closed canopy forest. However, guidelines for the northern
goshawk require a much more varied forest condition, with major areas of low stand density, open
canopies, and numerous forest openings. In addition, the Fish and Wildlife Service postulates that with
more openings in the forest (i.e., forest fragmentation), the Mexican spotted owl will be increasingly
susceptible to avian predation (Fed[. Reg. 58:14269~. Thus, such habitat manipulation might increase
direct loss to the listed species through predation by the northern goshawk (see Box 6-1~.
WINTER-RUN CHINOOK SALMON AND DELTA SMELT
Another example involves the enciangerect winter-run chinook salmon and the threatened delta
smelt, two species of fish that occur where the Sacramento and San Joaquin rivers meet in the Central
Valley region of California (see Box 6-2~. The 1992 Central Valley Improvement Act (Title 34 of P.
L. 102-575) contains a series of provisions that dictate water use and contracting for the Central Valley
Project, as well as mitigation and restoration activities that will benefit the threatened fish species in the
area. Revenues from water users and other direct beneficiaries of the water project are to pay for the
restoration costs.
Some of the provisions call for measures that will benefit both the winter-run salmon and the
delta smelt. For example, Provision 4 calls for the improvement of screens and fish-recovery facilities
at the Tracy pumping plant. Benefits to the delta smelt will accrue because of reduced entrainment
(destruction of fish or larvae at the intake mechanisms of diversion facilities such as those in the delta
[Fed. Reg. 59: 81611. These measures will also protect the stronger-swimming salmon. Likewise,
Provision 7 states that the Central Valley Project must comply with all applicable flow standards that
apply to it, including any new regulations that might be imposed. Such regulations shouic] benefit both
species. Furthermore, the recent federal listing of water-quality standards for the Sacramento and San
Joaquin rivers, the San Francisco Bay and the delta region (Fed[. Reg. 59: 810-852) and the recent
critical habitat listing for the delta smelt (Fed[. Reg. 59: 852-861) attempt to restore the important areas
of the drainage system to historic salinity levels.
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91
The northern goshawk, the largest member of the genus Accipiter, is a forest habitat
generalist that uses a variety of forest types, forest ages, structural conditions, and successional
stages (Reynolds et al., 19921. The northern goshawk is listed as a "sensitive species" by the
Southwest Region of the Forest Service because of concerns that its populations and
reproduction may be cleclining in this region clue in part to forest changes caused by historic
timber harvest patterns.
In response to concern for this species, the Forest Service has developed and adopted a set
of management recommendations for the northern goshawk in the southwestern United States
(Reynolds et al., 19921. However, rather than focusing solely on the goshawk, these
recommendations are designed to provide habitat for many of the goshawk's prey species such
as the American robin (Turdfus migratorius), bancl-tailecl pigeon (Columba fasciatay, mourning
clove (Zenaida macroura), blue grouse (Dendragapus obscures), hairy woodpecker (Picoides
villosus), northern flicker (Colaptes auratus), red-raped sapsucker (Sphyrapicus nucha1lis),
Williamson's sapsucker (Sphyrapicus thyroideus), Steller's jay (Cyanocitta stelleri), chipmunks
(Tamias spp.), golden-mantlec! grounc} squirrel (Citellus 1lateralis), rec! squirrel (Tamiasciurus
hud~sonicus), tassel-earecl squirrel (Sciurus aberti), and cottontails (Sylvilagus spp.~.
Management for these species will result in a quite varied forest condition with openings and
low density forest occurring fairly commonly.
The Mexican Spotted owl (Strix occidlentalis Zucida) was listen! as a threatened species on
March 16, 1993 (Fed. Reg. 58: 14248-142711. This medium-sized owl is found in central
Colorado and Utah south through Arizona, New Mexico, and western Texas, primarily in
canyons and areas with steep slopes. It is believed to be threatened due to loss and
mollification of its forest habitat due to timber harvest and fire, and increased predation clue to
habitat fragmentation. When fount} in forested habitats, the Mexican spotted owl is believed to
prefer areas with high canopy closure, high stand density, and a multilayered canopy for its
nesting, roosting, and foraging sites (Fletcher, 1990; Ganey et al., 1988; Ganey and Balda,
1989~. Great horned owls (Bubo virginianus) and red-tailed hawks (Buteo jamaicensis) have
been identified as possible predators, and goshawks as probable predators, of the Mexican
spotted owl (Skaggs, 1990~.
BOX 6-! Northern goshawk and Mexican spotted owl.
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Four races of chinook salmon (Oncorhynchus tshawytschaQ inhabit the Sacramento River system.
The winter-run race migrates upstream in the winter. Although it was previously abundant in this
drainage system, population sizes have cleclinec! drastically (from an estimated 1 17,808 individuals in
1969 to 341 in 1992/93; FWS 1992~. This race is now listed as endangered on the Fecleral
EndangerecI Species List (Feet. Reg. 59:138364. Adults migrate as far up the Sacramento River as
possible in the winter with spawning as early as micl-April, reaching a peak in June, and then
(reclining through the summer until August. Eggs are incubated for 40-60 (lays followed by an
additional 2-4 weeks for the newly hatched fry on grave! substrate. Incubation must occur in coo!
water temperatures (43-58°F) although incubation occurs during the hottest time of the year.
Migration of the juveniles begins after a short period of growth with juveniles migrating to the lower
river up to a year after the beginning of spawning of their cohort.
The delta smelt (Hypomesus transpacificus) is endemic to the Sacramento-San Joaquin River
estuary. The entire species is listed as threatened on the Fecleral Endangerec! Species List (FecI. Reg.
58: 12863~. Comparecl with salmon, the smelt has a short life span. Spawning occurs primarily from
December to March. Eggs hatch ~ 0-12 clays after fertilization into larvae that drift downstream with
the river current. By one year of age the fish are sexually mature with mating of a cohort continuing
into the summer of the year after hatching. While the biology of this species is not known in cletail, it
appears that adults die soon after spawning. The delta sanest is associated with welI-oxygenatecl, very
cold water. It also appears that hard substrates ant! submerged rocks are needed for successful
spawning
Two major water projects, the Central Valley Project (CVP) and the State Water Project (SWP)
and many smaller diversions affect these species both in the Sacramento-San Joaquin delta and the
Sacramento River (for the winter run chinook salmon). These water diversions can entrain fish along
the diverted flows as well as reduce flows downstream. Flow diversions and impoundment storage
behind dams can greatly alter flows, flow pattern, and seasonality. Flows also affect movement of
fish, particularly larvae of delta smelt and striped bass. In addition, flows play a major role in the
location of highly productive areas for phytoplankton and zooplankton. An "entrapment" or "null"
zone that provides important nursery habitat for delta sanest and striped bass is typically formed in
Suisun Bay downstream of the delta. During drought years, this zone occurs in the channel of the
delta much closer to the CVP and SWP water intakes than in normal years. During such periods,
entrainment is expected to be increased. In addition, production of prey organisms are expected to
decrease clue to the smaller size of the delta channels.
An additional problem associated with the major water projects is increased predation by fish-
eating predators, including adult striped bass, which use features of the major intakes to prey on
smaller fish. Such predation is considered to be one of the major sources of loss associated with the
SW1P.
BOX 6-2 Chinook salmon and delta smelt.
In one case, however, a provision of the Central Valley Improvement Act might benefit one of
the threatened species and have an adverse effect on the other. Provision 14 calls for modification of
the flow and control structures at the Delta Cross Channel; it is primarily for the benefit of striped bass,
a popular nonnative sport fish. This provision might benefit the winter-run salmon, because it will
reduce the amount of water entering the central delta while increasing the San loaquin and Mokelumne
rivers flows to the pumps. Delta smelt will be adversely affected, however, because they will be in
these waters at the times of reduced flows, and entrainment at the Tracy pumping plant might increase.
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Conservation Conflicts Between Species
93
Moreover, striped bass are probably predators of the smelt, so this action could result in increaser}
mortality of the smelt. Another provision, Provision is, advocates restoration of the striped bass
fishery, which would also have an adverse effect on the delta smelt due to increased predation (see Box
6-2~.
It is apparent that the Central Valley Improvement Act attempts to correct many problems that
the Central Valley Project causes for threatener! and endangered fish and that, in some cases, actions
will benefit all of the species involved. However, in some situations, management techniques that are
most beneficial to one threatened species adversely affect the other. In this system, the situation is
complicated by the presence of a third species, striped bass, that is being considered because of public
interest. Tradeoffs will have to be evaluated in each case to determine what measures shouIc! be
implemented. For example, aciditional flow releases without adclitional pumping after delta smelt
spawning could benefit that species by carrying eggs and larvae past the pumps to Suisun Bay where
the best rearing habitats occur cluring normal flow years.
Other actions affecting these species include the water-quality standards set by the
U.S.Environmental Protection Agency to protect the delta. Those standards (Feg. Reg. 59: 810-852)
will result in increased flows ant! decreased pumpings, which should help normalize salt levels ant!
provide larger quantities of water to facilitate migration conditions and rearing. In addition, the State
Water Resource Control Board is under federal court mandate to impose standards and regulations as
well. Such juclicial and regulatory actions have resulted in pumping restrictions at the State Water
Project and Central Valley Project to reduce losses of winter-run salmon and delta smelt.
Nevertheless, it is unclear whether these actions will be able to help both species, or if one will still
suffer at the expense of the other.
BACHMAN' S SPARROW AND RED-COCKADED WOODPECKER
Management decisions designed to improve conditions for a threatened or endangered species
may inadvertently affect dozens of nontarget species found in the same habitats. Possible effects on
nontarget species are rarely assessed before implementation of management actions. It will become
increasingly important to develop tools to assess the effect of proposed management strategies on a
wale variety of organisms as federal agencies and others put increased emphasis on management for
biodiversity.
Several research groups are (leveloping population simulation models linked to Geographical
Information System (GIS) maps that capture some of the complexity of real-worId lanclscapes and allow
simultaneous consideration of the responses of many different species to management proposals. This
approach requires, at a minimum, a good understanding of the habitat requirements of the species of
interest, and a realistic lanciscape map that shows the locations of current and future suitable habitat as
a function of management decisions. More recent versions of these models also require detailed
information on habitat-specific demography and dispersal behavior.
Liu (1992) and Liu et al. (1991) give one example of the use of such models to forecast how
management plans largely designed for one endangered species might affect a nontarget species. Liu et
al. (1991) used a mobile animal populations model (Pulliam et al., 1992) (Chapter 5) to determine how
the Bachman's sparrow (Aimophila aestivalis), a declining species of management interest in the
southeastern United States, might respond to a management strategy largely designed to favor
populations of the endangerecl red-cockaded woodpecker (Picoides borealis) (see Box 6-31.
The results of such models are useful in a variety of ways. In the particular case cliscussecl, the
motley allowed alternative cutting and thinning plans to be explored, at least some of which allowed
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larger populations of sparrows, as well as woodpeckers, to be maintained. Models of this sort can also
incorporate economic considerations (Angelstam, 1992; Liu et al., 1994) and might prove useful in
future attempts to balance ecological and economic goals. However, caution must be exercised in
using models of this sort for management decisions, because the models are not yet fully quantified or
tested against field results. A prudent use of such models would be in the context of adaptive
ecosystem management. Here, the moclels would be used to generate testable hypotheses, and forest-
management practices wouict be used as an experiment to test the mode} predictions.
MARINE MAMMALS AND SALMONIDS
The effect of predation by marine mammals on salmonids has been controversial since at least
the 19th century (Merriam, 19011. In 1899, the president of the California Board of Fish
Commissioners proposed to kill " 10,000 of the 30,000 [California sea lions, Zalophus californianus,
and Steller's sea lions, Eumatopias stelleri] that now infest our harbor entrances and contiguous
territories" to reduce their alleged depredations on salmon. Merriam pointed out that there probably
weren't even 10,000 sea lions on the coast. He described the work of L.L. Dyche, who examined the
Although formerly much more widespread, Bachman's sparrow populations have clisappeare
from much of the historic range and are now restricted mostly to the southeastern coastal plain,
where they can be fount! both in mature pine forest and in some early successional habitats. The
species is found in habitats with a dense ground cover of grasses and fortes and relatively open
understory with few shrubs (Dunning and Watts 19901. Mature pine forests (over 80 years old)
managed for the red-cockadec3 woodpecker usually provide adequate habitat for Bachman's
sparrow, particularly if the unclerstory is burned periodically. The species is also relatively
common in the young (~-5 years oIct) successional pine stancts that follow clearcutting.
Intermediate-age pine stands (approximately 6 to 80 years old) are not suitable for Bachman's
sparrow, presumably because the relatively closed canopy prevents a dense ground layer
vegetation from forming.
Liu et al. (1994) developed a MAP mode! to stucly Bachman's sparrow responses to current
and proposed forest management plans on the Savannah River Site (SRS), a large region of pine
forest in South Carolina managed by the U. S. Forest Service for timber production and wildlife
conservation. The Forest Service has developed a 50-year operations plan for the SRS that
considers the habitat requirements of over 42 plant and animal species of management concern.
However, most of the specific management practices described in the operation plan are aimed at
improving habitat for the enclangere(1 red-cockaded woodpecker. Using the operation plan, Liu
and coworkers projected future habitat conditions at SRS to determine how the proposed
management practices would impact the Bachman's sparrow, a species that is not a target of most
of the specified management strategies. According to these researchers, the forest-management
practices proposer} in the operation plan would have a strong effect on the Bachman's sparrow.
The mode} simulations suggested that, in the long run, the sparrow wouIcl benefit from the
changes because, un(ler the plan, the acreage of mature pine forest of the sort suitable for the red-
cockacled woodpecker and Bachman's sparrow would increase substantially. However, the
simulations suggest that the sparrow might decline precipitously during the first few decades of
operation of the plan because of decline in the availability of early successional habitat.
BOX 6-3 Bachman's sparrow and recI-cockadec! woodpecker.
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stomachs of 25 sea lions and found mainly octopus and squid, but no fish, and he argued against killing
sea lions. Bonnot (1928) describeci the killing of sea lions in great detail; they were hunter} in Oregon
for bounties, in California for their penises and testicles (known as "trimmings") and for various other
purposes along the coasts, including prevent them from eating fish. Adult sea lions were killed with
guns and landmines, and pups by (frowning them in weighted sacks (Bonnot, 1928~.
Fish predation by sea lions has received attention again recently, largely because of its high
visibility in one location: the Hiram M. Chittenden locks in Ballard (a section of Seattle). The
Chittenden (or Ballard) locks were completed in 1917 as part of a project of the U.S. Army Corps of
Engineers to allow ship traffic between Puget Sound and Lake Washington (Willingham, 1992~.
Previously, the lake had cirainect through the Black River, which flowed into the Cedar and Green
rivers and then into Puget Sound. The current drainage into Puget Sound is through the Lake
Washington Ship Canal, Lake Union, and the Ballard locks. Steelheac} trout (Oncorhynchus mykiss)
migrated through Lake Washington to spawn in its tributaries before 1917; they JO so today. The runs
consist of wild and hatchery fish, but the hatchery program has been discontinued recently (Fraker,
1994~. Although some people believed the current runs were derived from hatchery fish, genetic
analysis indicates that they are probably clescenciants of the original wild runs (Fraker, 1994~.
Lake Washington steelhead are winter-run fish, returning to the fresh water to spawn from
December to April. As the fish enter the ship canal below the locks, some of them are captured and
eaten by California sea lions. The first observation of such predation was macle in 1980; by the mid-
19SOs there were as many as 60 sea lions in the area arounc! the locks ant} more than 50% of the
returning steelhead were being eaten. (Between 51 % and 65 % were taken each year up to 1992,
except for 1985-1986 (15 %) and 1986-1987 (41 %), when predator-control efforts had some success.)
The number of fish in the run that escaped to spawn, which ranged from 474 to 2,575 fish from 1980-
1981 to 1985-1986, decliner! to 184 fish in 1992-1993 (Fraker, 1994) and to 70 in 1993-1994 (NMFS
and WDFW, 1995~.
It is clear that sea lions have affected the Lake Washington steelhead run, but they are not
entirely responsible for its recent decline. Cooper ant! Johnson (1992) found that steelhead had
declined generally since 1985. They considered the following items to be possible contributing factors:
competition for foot! with other salmon, in particular, ~ billion hatchery salmon released since the late
19SOs; authorized anti unauthorized drift-net fisheries (probably not currently a factor); predation by
birds and mammals; and large-scale environmental changes.
Predation by marine mammals is probably not a major factor in the current clecline of salmon
in general. Anadromous saImonids and marine mammals coexisted for thousands of years before the
current declines in salmonids, and California and Steller sea lions were much more abundant in the first
half of the 19th century a time when salmon were also abundant than later. And marine mammals
(lo not normally specialize on saImonicis; they eat a wide variety of prey items, cletermined by what is
available and how easy it is to catch (Gearin et al., 1988; Fraker, 1994; Olesiuk, 1993~. Finally, the
Ballarcl Locks area provides a local concentration of fish in space and time, and they have few refuges
there, and sea lions congregate there in large numbers (Fraker, 1994~.
However, many marine-mammal populations are increasing, at least partly because of the
protections of the Marine Mammal Protection Act (MMPA). California sea lions now number more
than 100,000 (Fraker, 1994~. Other human activities, combined with increasing marine-mammal
populations, could cause increasing problems, especially in areas where the fish congregate, as in the
case of the steelhead at Ballard. If the Lake Washington steelheacl were listed as endangered or
threatened under the En(langered Species Act, the conflict would be brought into sharper focus by the
requirements of the EncIangerect Species Act and the MMPA. Indeed, the MMPA was amended in
1994 to allow the killing of marine mammals under particular circumstances, and Washington state has
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Science and the Endangered Species Act
filed a petition to remove sea lions from the BalIarc! locks and kill them if all other methods to keep
them from eating steelhead fad! (NMFS and WDFW, 19954.
CONCLUSIONS
We have been able to document only these and a few other cases of conflicting conservation
needs resulting from management plans targeted toward individual species. It is possible that this low
number stems from several factors: lack of knowledge of the networks of which threatened and
enciangered species are part; the fact that comparatively few species are currently listed and that
recovery plans for even fewer have been formulated; anti the inadvertent protection for other listed
species uncler some current recovery plans. We expect, however, that the potential for such conflicts
will rise as ecologies of listed species become better known, more recovery plans are formulated, ant!
habitat for conserving endangered species becomes more constricted.
The greatest potential for conflicts in protecting species and for management of individual
species under current policies will arise in situations in which habitat reductions especially extreme
reductions- themselves are the causes of endangerment and the habitats of listed species are largely
overlapping. Resolution of such conflicts will have to be macle on a case by case basis. A process
should be devised that will facilitate such resolutions using analyses of risk and recovery as outlined in
Chapter 8.
The most effective way to avoid conflicts resulting from individual management plans is to
maintain large enough protected! areas for listed species to allow the existence of mosaics of habitats
and (lynamic processes of change within these areas. In a(ldition to ant! as part of this strategy,
multispecies plans should be devised that ensure the maintenance of habitat mosaics and ecological
networks. Habitat (in the broadest sense) thus plays a crucial role in protecting individual target
species and, ultimately, in reducing the need for listing additional species.
The Fish and Wilcllife Service has prepared a number of packages listing multiple species in the
same ecosystems, and it has agreed in a recent judicial settlement "to direct each region, where
biologically appropriate, to use a multi-species, ecosystem approach to their listing responsibilities
under the ESA" (settlement agreement, The Fund for Animals v. Lujan, Civ. No. 92-800, December
15, 19921. This is an important directive whose implementation and oversight warrant priority. Key
questions shouIc3 be a~iciressed as the initiative moves forward: Are listing resources best deployed to
advance the policy? To what degree have staff ant! consulting resources been arranged to optimize
cooperative work across taxa? To what extent have the FWS and National Marine Fisheries Service
macle a special effort to identify widespread species presenting great potential for conflict, but also for
conflict resolution? Finally, should the National Biological Service (NBS) be an important vehicle for
ensuring that these questions can be answered in the affirmative?
RECOMMENDATIONS
Because of the interactions of plants and animals with other organisms in their environments,
the most effective way to avoid conflicts resulting from individual management plans of co-occurring
endangered species is to maintain large enough protected areas for listed species to ensure the presence
of habitat mosaics and to allow for the dynamic processes of change that will inevitably occur within
such areas. As part of this strategy, multispecies plans (e.g., habitat conservation plans; see Chapter 4)
should be devised that ensure habitat mosaics and ecological networks are maintained.
When the available habitat is insufficient to avoid conflicts, the analysis of options will have to
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be clone separately for each situation. In most cases, long-term results are more important than short-
term ones. In the example of Bachman's sparrow and the red-cockaded woodpecker (Box 6-4), both
birds would benefit in the long term under the Forest Service's plan, despite short-term declines in the
sparrow's population. Other considerations would be which species is most likely to suffer irreversible
harm if its needs are not fully adciressed, the taxonomic level of the populations involved (e.g., a full
species is probably more important than a distinct population segment), and ecological considerations
(e.g., wouict the loss of one species have a greater effect on the ecosystem than the loss of the others.
REFERENCES
Angelstam, P. 1992. Conservation of communities -- the importance of edges, surroundings and
landscape mosaic structure. Pages 9-70 in L. Hansson, ed. Ecological principles of nature
conservation: applications in temperate and boreal environments. Elsevier Applied Science,
New York.
Bonnot, P. 1928. Report on the seals and sea lions of California. Fish Bulletin 14. California
Division of Fish ant! Game, Sacramento.
Cooper, R., and T. H. Johnson. 1992. Trencis in steelhead (Oncorhynchus mykiss) abundance in
Washington and along the coast of North America. Washington Department of Wildlife Report
92-20.
Dunning, J. B., and B. D. Watts. 1990. Regional differences in habitat occupancy by Bachman's
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FiedIer, P. L., R. A. Laidy, R. D. Laven, N. Gershenz, and L. Saul. 1993. The contemporary
paradigm in ecology and its implications for endangered species conservation. Endangered
Species Update lo: 7-12.
Fletcher, K. W. 1990. Habitats used, abundance and distribution of Mexican spotted owl (Strix
occidentalis lucida) on National Forest System Lands. USDA For. Serv., Southwest Region,
Albuquerque, NM 55 pp.
Fraker, M. 1994. California Sea Lions and Steelheac! Trout at the Chittenden Locks, Seattle,
Washington. Marine Mammal Commission, Washington, D.C.
Franklin, I. F. 1993. Preserving biocliversity: species, ecosystems, or landscapes. Ecological
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FWS (U.S. Fish ant! Wildlife Service). 1992. Measures to improve the protection of chinook salmon
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and Wildlife Service on chinook salmon technical information for State Water Resources
Control Board Water Rights Phase of the Bay/Delta Proceedings, July 6, 1992.
Ganey, J. L., and R. P. Balcia. 1989. Distribution and habitat use of Mexican spotted owls in
Arizona. Condor 91: 355-361.
Ganey, I. L., I. A. Johnson, R. P. Balcia, and R. W. Skaggs. 1988. Status report: Mexican spotted
owl. Pages 145-150 in R.L. Glinski, B.G. PencIleton, M.B. Moss, M.N. LeFranc, Ir., B.A.
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Representative terms from entire chapter:
endangered species
