The intent of this contribution is to define what is meant by
homing and straying, and to describe patterns of homing and straying
in salmon populations. I will explore what practices or other
factors in hatcheries might encourage straying, and then outline
the consequences of straying. By way of historical perspective,
it was accepted by about the 1870s that most salmon homed back
to their natal streams and rivers to spawn, although some biologists
remained unconvinced until the 1930s. A report for the U.S. Commission
of Fish and Fisheries stated that ". . . it is an established
fact that adult [salmon] will always return to the place where
they first made acquaintance with the water, passing directly
by the mouths of streams or tributaries better adapted to their
purpose, to gain their original home" (U.S. Commission of
Fish and Fisheries 1874, p. lxxxii). Biologists also recognized
that salmon could swim several hundreds of miles up a river to
their natal areas. A later report to the Commission pointed out
that a stream near Elko, Nevada "is one of the many that
form the headwaters of the Columbia River, and to this point,
eighteen hundred miles from its mouth, the salt-water salmon come
in myriads to spawn . . ." (U.S. Commission of Fish and Fisheries
1876, p. xxviii-xxix). Milner noted "[t]he generally accepted
fact in the habits of anadromous fishes that they are disposed
to return to almost the exact locality where they passed their
embryonic and earlier stages of growth . . . . Observations of
the shad brought to the large markets shows considerable difference
in the physiognomy and general contour of those from different
rivers. The suggestion is natural that they are distinct and
separate colonies of the same species, and thus slight characteristics
are perpetuated because they breed in-and-in and do not mix with
those of other rivers" (Milner 1876, p. 323).
By the 1930s, a number of biologists were aware of life-history
differences among salmon populations (Moulton 1939; e.g., Clemens
et al. 1939). In fact, this realization gave the first indication,
before tagging studies, that salmon homed to particular localities.
Salmon from various populations showed differences in morphology,
body size, egg size, fin ray counts, oil content, and so on.
In the 1950s to 1970s, knowledge of homing by Pacific salmon was
greatly enhanced by the work of Arthur Hasler and his students
(reviewed in Hasler and Scholz 1983). Their studies formed the
basis for much of what we know about salmon homing. However,
straying was not investigated as a behavior pattern in its own
right because most salmon homed, and the focus of the research
was on the sensory mechanisms of homing. Consequently, the ecological
and evolutionary importance of straying from one population to
another has received comparatively little attention until recently.
Today, we know that there is extensive variation among populations
in many traits and that this variation often has clear adaptive
value. Such local adaptations have presumably evolved because
homing leads to reduced levels of gene flow between habitats,
and because there is genetic control of the traits that adapt
the salmon for those habitats. It has been hypothesized (Quinn
1984) that adaptations evolve most rapidly in stable habitats
and that homing is likely to be positively associated with the
intricacy of adaptations for freshwater habitat, and with variation
in age at return. Homing and straying have adaptive value for
individuals; the relative advantages may depend on environmental
conditions, other life-history traits, and perhaps the relative
frequencies of homing/straying (Quinn 1984, Kaitala 1990).
Just what is meant by homing and straying? For a wild fish, home
is the natal stream where it incubated, hatched, and emerged.
Home is thus, essentially, the redd. However, when humans study
salmon homing, the definition of home is influenced by how and
where juvenile fish are collected and marked, and how they are
recaptured as adults. These factors also influence the perception
of how accurately salmon home. One might think of salmon homing
through a hierarchy of spatial scales, including first a river
basin, then a major tributary, a stream, and a particular point
in the stream. Homing will necessarily be more accurate when
measured at broader spatial scales. At the final level, the interaction
between homing and spawning site selection (Blair and Quinn 1991,
Hendry et al. 1995) or mate choice determines the final destination
of the fish. The definitions of straying or homing, therefore,
depend on the spatial scale of interest. Most research has not
been sufficiently explicit in considering the spatial definition
of home, and the transition between homing and spawning site selection.
For transplanted fish, the ancestral locality or the hatchery
where they are reared and the locality where they were released
could both be considered homes. While there is some tendency
to return to the ancestral area (McIsaac and Quinn 1988, Pascual
and Quinn 1994), salmon generally return to the site where they
were released (Ricker 1972). For salmon released from a hatchery,
the incubation, rearing, and release sites may be the same; in
this case, home is the hatchery. When planted from the hatchery
to a river, salmon tend to return to the point of release (e.g.,
Donaldson and Allen 1958, reviewed in Quinn 1993). Fish released
in the lower portion of a river tend to be caught only in the
lower portion of that river, and fish released in the middle or
upper portion of a river tend to be caught in all parts of the
river downstream from the release site (steelhead trout (Oncorhynchus
mykiss): Wagner 1969, Cramer 1981, Slaney et al. 1993; Atlantic
salmon (Salmo salar): Hvidsen et al. 1994, Potter and
The other side of the homing "coin" is straying. Adult
salmon move into non-natal streams for a variety of reasons.
We know from radio-tracking data that some fish do not home directly
to their natal streams, although these streams may be their final
destination (e.g., Berman and Quinn 1991). Upriver migration
is characterized by a certain amount of exploratory movement into
non-natal streams. If a fish makes an exploratory run up a stream,
is caught in a hatchery weir, and is spawned in the hatchery,
this constitutes straying from a functional point of view. The
fish's genes are incorporated into the hatchery gene pool regardless
of whether the fish would have left the hatchery had it been allowed
to do so. Consequently, it may be difficult to accurately estimate
straying frequencies using data from hatcheries. However, it
is clear that some salmon spawn in rivers other than their own
and so stray in the truest sense (Quinn et al. 1991).
While many studies have provided data on the proportion of salmon
that stray, almost all of these studies have been on single species,
and little information exists on comparative straying rates among
species. In one of the few such studies, Shapovalov and Taft
(1954) reported higher levels of straying by coho salmon (O.
kisutsch) than by steelhead into two small creeks in California.
It has been speculated that pink salmon (O. gorbuscha)
stray more than other species, but hard evidence is lacking.
High levels of intraspecific variability may mask interspecific
differences. The available information for coho and chinook salmon
(O. tshawytscha), for which we have the most data, indicates
large amounts of homing variability among populations, even within
a small geographical area.
Another problem with the literature on homing is that wild salmon
are tagged less frequently than hatchery-produced fish, and when
wild salmon are tagged the data are seldom analyzed to produce
estimates of straying. Consequently, little is known about straying
in wild salmon populations, and most estimates of straying come
from hatcheries. Hatchery-produced salmon may not stray with
the same frequency as wild salmon, but so few studies have been
conducted on hatchery and wild fish in the same areas that we
cannot be certain (see below). Many experiments designed to estimate
straying are also poorly controlled or are not replicated. In
many studies, measuring variability in homing was incidental to
other goals, so the data are often confounded with factors besides
straying. Most studies also fail to account for straying in and
out of a population; in many cases, only the dispersal of strays
from the marking site is documented.
As a rough estimate, 90% +/- 10% of salmon home, and this does
not include the "pathological" levels of straying that
were shown earlier in the workshop for some Snake River hatcheries
(Crateau, this volume) and have been documented for some hatcheries
on the lower Columbia River (e.g., Grays River chinook salmon:
Pascual et al. 1995). However, the overall estimate of 80-100%
homing is based largely on data from hatcheries.
It is difficult to determine from the data at hand whether straying
differs between hatchery and wild populations, because studies
of hatchery populations greatly outnumber studies of wild populations.
Comparisons between wild and hatchery-produced Pacific salmon
were conducted by McIsaac (1990) and Labelle (1992). McIsaac
(1990) studied fall-run chinook salmon in the Lewis River and
found that wild-caught juveniles homed at a higher rate than members
of the population that had been incubated and reared in the hatchery.
Moreover, short-term rearing of wild fish in a hatchery increased
their rate of straying, relative to wild fish not held in the
hatchery. On the other hand, Labelle's (1992) study of coho salmon
on the east coast of Vancouver Island did not find a significant
difference in straying rates between hatchery-produced and wild
fish. Studies of Atlantic salmon also did not find differences
between the straying rates of hatchery and wild fish (Jonsson
et al. 1991, Potter and Russell 1994).
Coded wire tagging has provided a large database which can be
used for homing studies (van der Haegen and Doty 1995). These
data show that spatial patterns of straying vary from one river
to another. The proportion of salmon that stray is not the same
in all hatcheries in a region such as the lower Columbia River.
In addition, the proportion of the total number of straying salmon
entering a given river is not simply explained by its distance
from the hatchery of origin. For example, Cowlitz River spring-run
chinook salmon strayed more often to the Lewis River than to the
Kalama River, even though the Kalama River is closer to the Cowlitz
River than is the Lewis River (Quinn and Fresh 1984).
It appears that salmon do not stray merely because they are fatigued
and cannot reach their natal spawning areas. In many cases, they
stray to localities above their river of origin. The proportions
of salmon straying into and out of a hatchery can vary considerably.
Quinn et al. (1991) found variation from 9.9-27.5% in the proportions
of fall-run chinook salmon straying from five lower Columbia River
hatcheries. More dramatic, however, was the variation in attractiveness
of rivers to strays. Virtually no salmon strayed into the Washougal
and Abernathy Hatcheries, but about 30% of the marked salmon entering
the Kalama and Lewis Rivers were strays (Quinn et al. 1991).
Expanded examination by Pascual and Quinn (1994) confirmed these
patterns of variation in straying and found that fish seemed more
likely to enter rivers or hatcheries similar to their home than
to less similar sites. For example, salmon produced in tributaries
of the Columbia River seemed to stray into other tributaries rather
than to hatcheries along the mainstream of the river.
In addition to differences in straying among rivers, straying
can also differ from year to year. Interannual variability may
be associated with catastrophic events such as the eruption of
Mount St. Helens (Leider 1989). Less dramatic environmental changes
such as variation in flow and temperature may also contribute
to temporal variability in straying, but definitive studies do
not seem to have been conducted on these subjects. There is some
evidence that temporal variation in straying is associated with
population size (Quinn and Fresh 1984). In years when many fish
returned to the Cowlitz River hatchery, homing was better than
in years when fewer fish returned. This suggests that the dynamics
of small populations may be different from those of larger populations.
This is an important issue and it needs to be evaluated with
other data sets. There is also interannual variation in straying
from a site, perhaps related to water quality, rearing conditions,
or the number of returning salmon. The tendency of hatchery-produced
salmon to enter their hatchery, as opposed to spawning in the
river, can also vary greatly from year to year (Nicholas and Downey
Age at return also contributes to variability in straying. Older
chinook salmon tend to stray more than younger fish (Quinn and
Fresh 1984, Quinn et al. 1991, Unwin and Quinn 1993, Pascual et
al. 1995). The difference in the rate of straying by chinook
jacks and by 4- or 5-year-old fish may be an order of magnitude
(Quinn and Fresh 1984). Age-specific straying rates have also
been observed for coho salmon (Labelle 1992), but not for Atlantic
salmon (Potter and Russell 1994). Perhaps, the longer a fish
is out to sea, the more it forgets the olfactory cues it needs
to return to its natal locality. The turnover of sensory epithelial
cells associated with odor recognition (Nevitt et al. 1994), changes
in the odors of river water, or some unknown evolutionary mechanism
may be responsible for this age effect. Hatchery practices can
also influence the age structure of the spawning population, which
may in turn influence straying.
Little is known about the relationship between straying and the
colonizing of unoccupied areas. Although most translocations
of salmon have been notoriously unsuccessful, some have succeeded.
For example, the inadvertent translocation of pink salmon into
the Great Lakes resulted in a rapid colonization of Lake Superior
and other Great Lakes (Kwain 1987). The translocation of chinook
salmon to one river in New Zealand quickly led to unaided colonization
of several other rivers within 15 years, but the present level
of straying among rivers is not high enough to account for the
wide-spread colonization that apparently took place after the
initial introduction (Unwin and Quinn 1993, Quinn and Unwin 1993).
In addition to translocations, some natural colonization by salmon
also occurs. For example, in Glacier Bay, Alaska, new habitat
appears as the glacier recedes, and new habitat is colonized as
it becomes suitable for spawning (Milner 1987, Milner and Bailey
1989). Straying and the ability to colonize new areas over evolutionary
time is important, but little research has been done on this topic.
It appears that soon after colonization, and coincident with
small population sizes, straying rates may be high; however, after
populations become established, only modest rates of straying
Some hatchery practices might promote straying, the most obvious
being the long-standing practice of transporting individuals from
one locality to another. Salmon are commonly displaced from hatcheries
to "seed" nearby habitat. Most fish reared at one facility
through their juvenile stages, but released at another site, return
to the site of release and not to the rearing facility (e.g.,
Donaldson and Allen 1958, Quinn et al. 1989, reviewed by Quinn
1993). Several researchers have studied the details of the timing
of imprinting and have found that fish can be imprinted not only
at the smolt stage, but also to a lesser extent at earlier stages
(Dittman et al. 1994, 1996). Therefore, if a rearing hatchery
is in one watershed and the release site is in another watershed,
fish tend to return to the release site. As the distance between
the rearing facility and the release site gets closer, larger
numbers of fish return to the rearing facility, especially if
the facility and release site are in the same watershed (Quinn
1993). However, the amount of "straying" from the release
site is only roughly correlated with geographical distance. The
release site's position within the watershed also affects homing.
Johnson et al. (1990) reported that "almost all returning
[coho salmon] released as yearlings at a site 23 km upstream from
the rearing hatchery returned to the rearing site, whereas only
7-26% of adults originally released in a tributary 11 km downstream
from the rearing hatchery returned to the rearing site" (p.
In the Columbia River system, smolts are also displaced to improve
their post-release survival. They may be taken from their hatchery
("point of origin" transportation) or captured during
their downstream migration, trucked or barged around dams, and
then released downriver. Point of origin transportation is usually
accomplished by taking the fish by truck, or by truck and then
by barge. Coho salmon trucked from the Little White Salmon Hatchery
to Youngs Bay returned to Youngs Bay, not to the hatchery (Vreeland
et al. 1975). Coho trucked 9 km downstream from Willard Hatchery
and then barged to a release point below Bonneville Dam showed
improved survival but impaired homing (McCabe et al. 1983). Releases
in salt water also tend to increase straying. Solazzi et al.
(1991) trucked coho salmon (reared at least in part at Big Creek
Hatchery) to release sites below Bonneville Dam (river km 234),
and Tongue Point (rkm 29). In addition, smolts were taken by
boat in tanks receiving ambient water to the bar of the river
(rkm 2), 19 km offshore in the river's plume, 19 km offshore outside
the river's plume, and 38 km offshore in non-plume water. These
six locations, progressively farther from the rearing site, produced
the following proportions of salmon that returned to rivers outside
the Columbia River system: <0.1%, 3.4%, 4.1%, 6.1%, 21.0%,
and 37.5%. However, salmon captured as migrants and trucked long
distances (e.g., from Ice Harbor Dam to Bonneville Dam) may return
to the rearing site (Ebel et al. 1973, Slatick et al. 1975).
Overall, the displacement studies indicate that maturing salmon
tend to reverse the sequence of their outward migration as juveniles.
This will lead them to the river or hatchery where they began
life. Displaced salmon return first to the odors of their release
site and will continue to the rearing site if its odors can be
detected. If not, they seem to seek the nearest river or hatchery.
The date of release also influences homing. Fish released too
early might be expected to stray more because they have not had
time to imprint, or because their endocrine physiology is not
synchronized with migration. Studies of Atlantic salmon (Hansen
and Jonsson 1991) and of chinook salmon in the lower Columbia
River (Pascual et al. 1995) and in New Zealand (Unwin and Quinn
1993) show that fish released after the smolt stage may also stray
more frequently than earlier releases. It appears that exposure
to site-specific water without migration is not sufficient for
imprinting and will not lead to accurate homing, hence salmon
held too long stray even though they were given a full opportunity
to imprint (Dittman et al. 1996).
Although imprinting is a large component of homing, homing is
not entirely a learned behavior. Local populations may home better
than transplanted ones (pink: Bams 1976; chinook: McIsaac and
Quinn 1988). Salmon may home better to their natal site than
to a new site (chinook: McIsaac and Quinn 1988, Pascual and Quinn
1994; coho: Labelle 1992), and transplanted populations may show
some tendency to return to their ancestral location (chinook:
McIsaac and Quinn 1988, Pascual and Quinn 1994).
If a hatchery produces a large number of salmon, straying by even
a small percentage of them has the potential to disrupt the genetic
composition of nearby wild populations. For example, the proportion
of strays from an ocean-ranching facility (Oregon Aqua-Foods)
was low, about 6%, but these strays accounted for about 74% of
the fish in nearby Yaquina Bay tributaries (Nicholas and Van Dyke
1982). In this case, not only might there be genetic interactions,
but simple stock assessment is compromised. A census of natural
spawning areas would overestimate the size of wild populations,
because the absolute number of strays--a small percentage of the
larger hatchery population--was large relative to the local population.
While there is concern that strays from hatcheries will influence
wild gene pools, wild salmon may also stray into a hatchery.
Nicholas and Van Dyke (1982) estimated that 2,022 (64.7%) of the
3,124 wild coho salmon returning to the Yaquina River watershed
in 1981 entered the Oregon Aqua-Foods hatchery. Such decoying
of wild salmon into hatcheries both reduces the number of wild
fish in the stream and contributes to genetic mixing.
Gene flow from hatchery strays may dilute beneficial genes in
populations of locally adapted wild fish, or disrupt adaptive
gene complexes. However, salmon mating is non-random. Factors
contributing to differential reproductive success include intrasexual
competition, some degree of mate choice, differences in aggressiveness
between wild and hatchery fish, size effects, different return
times, and so on. Differences between homing salmon and strays
in distribution within a river system (e.g., Atlantic salmon:
Jonsson et al. 1990) might also tend to reduce genetic interactions.
Finally, since salmon can discriminate siblings from non-relatives
(coho: Quinn and Busack 1985), and can distinguish fish in their
own population from those of other populations (sockeye: Groot
et al. 1986; coho: Quinn and Tolson 1986), the magnitude of interbreeding
may not be equivalent to the proportions of wild and hatchery-produced
fish. Wild fish may actively reject siblings and non-native hatchery
fish as mates on natural spawning grounds.
Tallman and Healey (1994) studied small chum salmon (Oncorhynchus
keta) populations on Vancouver Island and indicated that the
level of genetic exchange between strays was lower than that inferred
by the presence of strays in spawning areas. Simply counting
stray hatchery fish on spawning grounds may not provide a reliable
estimate of the genetic interaction between hatchery-produced
and wild populations. However, genetic consequences may occur
if hatchery strays spawn with locally adapted wild fish (Taylor
1991, this volume) because domestication selection and non-native
stock in the hatchery might reduce the fitness of wild fish.
If hatchery fish have experienced domestication selection or are
a non-native stock, then they may reduce the fitness of wild fish
with whom they mate (Reisenbichler and McIntyre 1977, Reisenbichler
1988, Leider et al. 1990, Hindar et al. 1991, Johnsson and Abrahams
Salmon as a group generally home to natal sites to spawn. Homing
occurs in diverse groups of salmonids with life-history patterns
differing in duration of freshwater residence, anadromy, iteroparity
or semelparity, and spawning habitat. Straying between natural
populations appears to be an integral part of the evolutionary
biology of salmonids and may be important for colonizing new habitats
or for avoiding unfavorable habitats. However, intra-specific
variation ("local adaptation") presumably results from
the scarcity of strays or their high mortality rate, or both,
relative to locally adapted salmon. This is consistent with the
generally poor survival of transplanted salmon, relative to native
populations or to the population in its home environment.
It is unclear whether some species of salmon stray more than other
species, but the amount of straying within a species varies considerably
among populations, and older salmon tend to stray more than younger
fish. It is also not clear whether hatchery-reared salmon generally
stray more than wild salmon. The degree of homing in outplanted
salmon often differs from that in locally-reared and released
salmon, and appears to be determined by complex interactions between
rearing location, release site, date, endocrine events, and migration
itself. Straying fish tend to enter nearby rivers, although there
are many exceptions. Homing, and therefore straying, may be influenced
by such factors as water temperature, flow, presence of other
salmon, habitat quality, and so on. It is not clear, however,
whether fish that stray actively identify their natal breeding
grounds, then migrate elsewhere, or whether strays are unable
to find their natal site. The propensity to stray itself may
be a genetically controlled trait, in addition to genetically
based metabolic and physiological traits that make homing possible.
To the extent that there are genetic differences between hatchery
and wild salmonids, straying of hatchery-produced salmon to interbreed
with wild fish is cause for concern if they are less fit than
wild fish. The most obvious and pressing research need is for
information linking the straying of adult salmon and the exchange
of genes between populations. Thus, data on the relative reproductive
success of homing (locally adapted) salmon and strays, whether
of wild or hatchery origin, is essential for wise management of
I gratefully acknowledge Ernest Brannon and Kees Groot, who supervised
my graduate and post-doctoral work, respectively, and with whom
I have collaborated over many years on salmon migration and homing
research. I also thank two former graduate students, Miguel Pascual
and Andy Dittman, who have also collaborated with me and given
me many insights into salmon homing.
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Question: Nils Ryman: Is it possible to select for high rates
of straying? Has this been tried?
Answer: Tom Quinn: This has not been tried to my knowledge.
However, a study of family-specific differences in several fitness
traits such as survival, growth, age composition, fecundity, and
so on, was made on Atlantic salmon in Iceland. The researchers
did find family-specific differences in homing. These family
differences in straying could simply reflect genetic differences
among families in memory, sensory ability, swimming performance,
and so on, and not differences in the direct genetic control of
Question: Audience: Would it be useful to examine physiological
changes in fish to estimate homing ability?
Answer: Tom Quinn: I think the patterns would be complex at
best. For example, at the School of Fisheries (University of
Washington), coho salmon released as zero age smolts have much
lower levels of thyroid hormones than is commonly observed in
other hatcheries, yet homing is very good (Dittman et al. 1994).
Among adults, salmon populations return at very different states
of maturity (e.g., spring- and fall-run chinook, summer- and winter-run
steelhead). There seems to be no universal relationship between
endocrine changes and homing. This is not to say that there is
no relationship, only that it may vary considerably among populations
Question: Richard Carmichael: Are you aware of information indicating
that rates of straying among natural populations may vary between
groups of salmon with different life-history patterns? For example,
the Grande Ronde Basin harbors two groups of fish. Fish in one
group stay their entire life in the area where they were spawned,
and fish in the other group move fairly long distances into main-stem
rearing areas in fall, then smolt the following year. Do these
different life-history patterns produce different levels of homing?
Answer: Tom Quinn: Yes, there is evidence that stream-type and
ocean-type sockeye salmon may stray more, or at least show less
genetic differentiation than the conventional lake-type (Wood
1995). In the Cowlitz River Hatchery, spring chinook seemed to
home more precisely than fall chinook (Quinn and Fresh 1984, Quinn
et al. 1991), but the generality of this pattern among hatcheries
and its application to wild populations is unclear.
Question: Mike Lynch: Are you saying that perhaps a straying
rate of 2-5% might be fairly normal?
Answer: Tom Quinn: Yes. Straying rates range from almost nothing
to a lot, depending on species and region. However, I must emphasize
the dearth of information on wild populations.
Question: Mike Lynch: Are these estimates of straying rates
compatible with those estimated from molecular data?
Answer: Tom Quinn: We seldom have estimates of straying in wild
salmon populations for which we also have genetic data (but see
Quinn et al. 1987 for sockeye, and Tallman and Healey 1994 for
chum). There is no reason to suspect that straying rates and
gene flow must be equivalent because poor survival of the progeny
of strays, or non-assortative mating or some other process, may
mediate the genetic interactions.
Question: Nils Ryman: Is the straying and the occurrence of jacks
related? Is migratory behavior abnormal in both cases?
Answer: Tom Quinn: I am not sure I would be willing to say that jacks display abnormal behavior; they still go to sea, return to fresh water, and spawn. They may have a different marine distribution as a consequence of their younger ages, but they still migrate far enough away so they no longer have contact with their natal rivers. To the extent that there are patterns, jacks seem to stray less often than older salmon.
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